CA1314073C - Current density measurement system - Google Patents
Current density measurement systemInfo
- Publication number
- CA1314073C CA1314073C CA000590332A CA590332A CA1314073C CA 1314073 C CA1314073 C CA 1314073C CA 000590332 A CA000590332 A CA 000590332A CA 590332 A CA590332 A CA 590332A CA 1314073 C CA1314073 C CA 1314073C
- Authority
- CA
- Canada
- Prior art keywords
- current density
- transformer
- tlle
- current
- voltage
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
- G01R19/16571—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current
Abstract
CURRENT DENSITY MEASUREMENT SYSTEM
Abstract of the Disclosure A system for measuring parameters in an environment having a metallic body positioned in an electrolytic medium includes a current density sensing device positioned adjacent the metallic body in a non-invasive manner. The device is sufficiently sensitive to measure current density in the milllamp per square centimeter range. A
housing is provided for enclosing at least n portion of the current density sensing device in an electrically and thermally non-conductive manner. A computer is used for processing the data from the current density sensing device and wiring is provided for electrically interconnecting the two. The current density sensing device, which can be used separately from the apparatus, includes a toroidal transformer and a square wave magnetically coupled oscillator which drives the transformer. A pair of multi-section low pass filters are provided for monitoring the transformer. A fixed gain differential instrumentation amplifier is utilized for processing an output of the transformer. The processed transformer output is proportional to a current sensed by the transformer.
Abstract of the Disclosure A system for measuring parameters in an environment having a metallic body positioned in an electrolytic medium includes a current density sensing device positioned adjacent the metallic body in a non-invasive manner. The device is sufficiently sensitive to measure current density in the milllamp per square centimeter range. A
housing is provided for enclosing at least n portion of the current density sensing device in an electrically and thermally non-conductive manner. A computer is used for processing the data from the current density sensing device and wiring is provided for electrically interconnecting the two. The current density sensing device, which can be used separately from the apparatus, includes a toroidal transformer and a square wave magnetically coupled oscillator which drives the transformer. A pair of multi-section low pass filters are provided for monitoring the transformer. A fixed gain differential instrumentation amplifier is utilized for processing an output of the transformer. The processed transformer output is proportional to a current sensed by the transformer.
Description
~UI~ NT ~ 7S:l:TY ME2\su~ N r sYs~r~ s ~ 3 t 4 0 7 3 Background_f tlle Invent~ll lllis il-vention getlerally pertaills to meas-lril)cJ
clevices. More speeiieally, tl~e prese~-lt invtlltioll relates to a tleviee for measuring eleetrical eurrellt allcl, ol)tiollally, several otller )axameters.
l l)e :invelltioll is part Icular1y appl Leable to a current dens ity measuring device- wlliell is utili~ed i.ll an electro~epos ition system in WlliCIl a mel:~llle l~r;)dy is positiont- d i~ an elect~lyte l`lle primary ~neasuremellt environmt- nt ~or tl~e appa~atlls is an automotive electrocoatillq faeility m~ tainet;i eitller ~t all automobile pl~nt or in a laboratory. ~lowever it slloulcl be appreciatt cl by tllose 5]cillecl in tlle art t?~at tl~e inve~ lotl tlas hroadt- r applieations and may also l~e adapted Cor use i.n otlle- r envi ronlllents wl~ere a measul-t ment o~ eul-rellt an~.l, optional Ly, otller parameters is required.
Electrodeposition of aqueous noll-eollcl~letive polymer coatillrJs onto a metallie substrate l~as risen to industrial promilletlct- in reeent years. ll~is type o~ depositio E-rocess is generally eonsicleL-ed to be a type o~
electroplloresis. Tlle proeess llas mally a~vantages ineltldillfJ
relative uni~ormity ancl eompleteness of eoating, even on intrieate sllapes. Virtually any eleetrieally eonductive substrate can be coated, llowever tlle proc ess llas been primarily employed to ~rime ferro~ls metal suhstriltes.
Tlle e lectrodeposition eoating process (E-Coat) llas beeome inereasillgly important in the eoatings lndustry, beeause l~y comparison with noll-eleetroE~IIoretie COatillCJ
means, eleetrodeposition of ~ers llig)ler paillt utilizatioll outstanding corrosion proteetion al-ld low envirollme]ltal contami ~lat:ion. Initially, the worlc piece l~eing eoated servecl as tlle anode i?l the eleetrode~!ositioll proeess. lllis ~as familiarly referred to as aniollie eleetroclepositiol~.
clevices. More speeiieally, tl~e prese~-lt invtlltioll relates to a tleviee for measuring eleetrical eurrellt allcl, ol)tiollally, several otller )axameters.
l l)e :invelltioll is part Icular1y appl Leable to a current dens ity measuring device- wlliell is utili~ed i.ll an electro~epos ition system in WlliCIl a mel:~llle l~r;)dy is positiont- d i~ an elect~lyte l`lle primary ~neasuremellt environmt- nt ~or tl~e appa~atlls is an automotive electrocoatillq faeility m~ tainet;i eitller ~t all automobile pl~nt or in a laboratory. ~lowever it slloulcl be appreciatt cl by tllose 5]cillecl in tlle art t?~at tl~e inve~ lotl tlas hroadt- r applieations and may also l~e adapted Cor use i.n otlle- r envi ronlllents wl~ere a measul-t ment o~ eul-rellt an~.l, optional Ly, otller parameters is required.
Electrodeposition of aqueous noll-eollcl~letive polymer coatillrJs onto a metallie substrate l~as risen to industrial promilletlct- in reeent years. ll~is type o~ depositio E-rocess is generally eonsicleL-ed to be a type o~
electroplloresis. Tlle proeess llas mally a~vantages ineltldillfJ
relative uni~ormity ancl eompleteness of eoating, even on intrieate sllapes. Virtually any eleetrieally eonductive substrate can be coated, llowever tlle proc ess llas been primarily employed to ~rime ferro~ls metal suhstriltes.
Tlle e lectrodeposition eoating process (E-Coat) llas beeome inereasillgly important in the eoatings lndustry, beeause l~y comparison with noll-eleetroE~IIoretie COatillCJ
means, eleetrodeposition of ~ers llig)ler paillt utilizatioll outstanding corrosion proteetion al-ld low envirollme]ltal contami ~lat:ion. Initially, the worlc piece l~eing eoated servecl as tlle anode i?l the eleetrode~!ositioll proeess. lllis ~as familiarly referred to as aniollie eleetroclepositiol~.
- 2 - ~314073 11owever in tl1e early 197C7~S, CatiOIliC electrorleposi.tion~
in wi1ic11 t~1e metallie part to be eoated serves as ~1~e cat1~ode, was introdueecl commercially. Since tllat time, catio1~;c electrodeposltion l1as steadi]y yained in popl1larity a11d is today by far the most prevalent met11oc1 Or electroc1epositio11. Currently more t11a11 ~0~ oE al] motor vellieles produced around t1~e world are given a ~ase cont or a primer coat hy cationie electrodepositio11.
l1le ~roeess i1lvolves immersing tlle ear body or car parts in a eond~ctlv~ eleetrolyte batll ln a tank. Il1e E-Coat bat11 is a water thin eleetrolytie resin 1nixt:ure tllat is kept in tlle tan)c under eonstant turbulent ag~tntlo11.
11le car 1~ody becomes a eatllode an~ several anodes are attaelled to tank walls to net as tlle other eleetxoc1e in ]5 tl1e eireuit. ~ direet eurre11t voltage betwecn approximately 200 to ~oo volts is applied between tlle eatl1ode ancl tlle tank anodes. Wl1en proper eondltlons oeeur at tlle mrt:al surface i.e. eorreet pll, mlnimu1n eurrent density, ete., tlle resin precipitates onto tlle metal. ~rl~e resln Eorms a ~ilm w1~ich, after euring, ean be on the order oE between l to 2 mils (.025~ to .050~ milli111eters~ in thiekness.
Icleally, a uni~orm eoating t11ickness is c1esired 011 all l~ody surfaces. ~roblems arise whe11 ~1on-u11irorm deposition oecurs eausing widely varyi1lg thie1cnesses of resin eoatincJ on cdirCere11t parts of ~1~e body. Tl1is ean eause tlle ear body to be rejeet:ed and scrapued, at n tremendous expeose to the vehiele m~nufacturer. Even iE
tlle body is used, uneven eoatings ean lead to an early ~0 eorrosion o~ the portion oE the ~oc1y w1~iel~ was 170t eoated wlth a suEfieiently t11;ek layer of tl1e resin.
Sinee eleetroeoating is a e-]rrent drive1l process, measurement o~ the eurrent density on diEferent parts o~ a ear body would provide data on and an lnsig}1t into how tlle _ 3 1 31 4073 process could be optimized to obtain a more uniform coating layer on the car body. Collected data would aid in solving problems occurring in electrocoating systems presently installed as well as aid in the design of new electrocoating facilities.
At the moment, no suitable current measuring device exists for this type of environment. Standard current measuring devices are not sensitive enough to measure the current density in an E-Coat bath with precision.
Additionally, no standard current measuring devices are available which can be used in the harsh and corrosive E-Coat bath environment. It would be advantageous to provide such a current measuring device. It would also be advantageous to provide an apparatus which is capable of measuring several different parameters in an environment having a metallic body positioned in an electrolytic bath.
Accordingly, it has been considered desirable to develop a new and improved current measuring device, as well as an apparatus which can be used for measuring current density and other parameters, which would overcome the foregoing difficulties and others and meet the above-stated needs while pro~iding better and more advantageous overall results.
Brief summary of the Invention According to one aspect of the invention, a current measuring device is provided.
More speci~ically in accordance with this aspect of the invention, there is provided a current measuring device comprising a transformer adapted for placement within a secondary flux source; an oscillator for periodically placing said transformer in ~orward and reverse flux saturation by application of a periodic voltage to an input winding thereof, whereby a period of the fo~.rard and reverse flux satur~tion is affected by the secondary flux source; a pair of multi-section low pass filters operatively connected to an output winding -1 ~ 7l '\'~
!
_ 4 _ 1 31 ~ 0 73 of the transformer for generating an output signal including a slowly varying DC signal proportional to an on time of said transformer; and, amplifier means for processing the output signal of said pair of multi-section low pass filters, wherein said amplifier output is representative of a current sensed by said transform~r.
According to a specific embodiment of the invention, the device further comprises a means for compensating for small output offsets due to component tolerance errors.
According to a still further feature of a specific embodiment of the invention, the device further comprises a means for improving the sensitivity of the transformer. The means comprises a pair of voltage-sharing resistors.
According to a yet further feature of a specifia embodiment of the invention, the device further comprises a means for calibrating the amplifier.
According to a still yet further feature of a specific embodiment of the invention, the amplifier is monolithic precision instrumentation amplifier.
In accordance with another feature of a spe~ific embodiment o~ the present invention, a system is provided for measuring parameters in an environment having a metallic body positioned in an electrolytic medium.
More specifically in accordance with this aspact of the invention, the system comprises a current density sensing means positioned adjacent the metal body in a non-invasive manner, the current density sensing means including a transformer including an input winding and output winding, an oscillator for periodically placing the transformer in flux saturation by application of a periodic voltage to the input winding, and means for generating a slowly varying DC output level signal from .~ ~
_ 5 _ 1314073 a signal recei~ed from the output winding in accordance with a timing of the flux saturation as influenced by current in the electrolytic medium; an electrically and thermally insulative housing means for enclosing at least a portion of said current density sensing means in an electrically and thermally non-conductive manner; a computer means for processing the current level signal from said current density sensing means: and a wiring means ~or electrically interconnecting said computer means with said current density sensing means.
According to a specific embodiment of the invention, the system further comprises a temperature sensing means and a voltage sensing means each of which is located adjacent to the current density se~sing means in said housing means. The wiring means also interconnects the temperature and voltage sensing means with the computer means so that the computer means can process the data therefrom.
According to yet another feature of a specific embodiment of the invention, the system ~urther comprises a data processing means for processing an output signal from the current density sensing means before the output signal is sent to the computer means.
According to still yet another feature of a specific embodiment of the invention, the system ~urther compri~es an enclosure means for housing the computer means and the data acquisition means in an environmentally isolated manner.
According to yet still another feature of a specific embodiment of the invention, the system further comprises a trigger probe means for setting the initiation of a measuring cycle with the apparatus. The trigger probe maans is in electrical contact with the data ac~uisition means. Preferably, the trigger probe means comprises a housing, a means for securing the housing to the metallic body and at least one sensor exposed to the electrolytic medium.
,~ 1, .~
- 6 - 131~073 According to still another feature o~ a specific embodiment of the invention, the system further comprises a means for securing the housing means to the metallic body.
In accordance with still another feature of a specific embodiment of the invention, the current density sensing means comprises a toroidal transformer and a square wave magnetically coupled oscillator which drives the toroidal transformer. A pair of voltage sharing resistors are provided for improving the sensitivity of the transformer. A pair of multi-section low pass filters are also provided for monitoring the trans*ormer. A fixed gain differential instrumentation amplifier is provided for processing an output of each of the filters.
In accordance with yet another feature of a specific embodiment of the invention, a plurality of housing means are provided, each containing a current density sensing means. A plurality of wiring means are provided, each connecting a current density sensing means in one of the housing means to the computer means.
In accordance with yet another feature of a specific embodiment of the invention, the system further comprises a means for providing electrical power to the current density sensing means.
According to yet another aspect of the present invention, there is provided a current density sensing means for directly measuring parameters adjacent the surface of a metallic body in contact with a surrounding electrolytic medium, being sufficiently sensitive to measure current density in a range of milliamps per square centimeter comprising means for periodically placing a transformer into magnetic flux saturation by application of a periodic voltage to an input winding thereof; low pass filter means connected to an output winding of said transformer for generating a slowly varying DC signal proportional to detected alterations ' .~
- 6a -in periodicity of the magnetic flux resultant ~rom a current flow in the metallic body; amplifier means connected to said low pass filter means for detecting alterations in periodicity of the magnetic flux resultant from a current flow in the metallic body a temperature sensing means for measuring a temperature in the electrolytic medium adjacent said current density sensing means; a ~oltage sensing means for measuring a voltage in the electrolytic medium adjacent said current density sensing means, and said voltage sensing means.
Yet anDther aspect of the inven~ion resides in a current measuring device which includes trans~ormer means having a core and oscillating means for generating a square wa~e to induce forward and reverse saturation flux in the core. Means is adapted for placement of the core in an associated current field so that a flux level in the core is influenced thereby. Means is provided for generating a composite signal indicative of a flux level of the core as well as means for isolating a current level signal indicative of a portion of the composite signal attributable to the associated current field. The device has means for establishing an offset flux level in the core and means for amplifying the current level signal.
The invention also provides for a method for obtaining data concerning the deposition of a polymer resin onto a metallic substrate positioned in an electrolytic medium held in an electrocoating tank.
According to this aspect of the invention, the method comprises periodically placing a transformer into flux saturation; generating a slowly varying DC signal representative of current density in said electrolytic medium in accordance with a fluctuation of a periodicity of said flux saturation; securing said transformer to a metallic substrate; lowering said metallic substrate into an electrolytic medium held in an electrocoating tank; passing a current through said electrolytic medium .q ~i'?
_ 7 1 31 4 073 thereby depositing a polymer resin cont~ined in solution in said electrolytic medium onto said metallic substrate; detecting a current density in the electrolytic medium adjacent said transformer; and, recording information regarding current density detected by said trans~ormer.
The various aspects of the present invention have a number of advantages. One advantage of the present invention is the provision of a new and improved current measuring device which is particularly adapted for measuring current density.
In accordance with yet another feature o~ the invention, there is provided a current measuring device comprising a transformer including a core, at least one input winding, and at least one output winding;
oscillator means for generating a square wave to induce forward and reverse saturation flux in said core; means ~or communicating the square wave to an input winding of the transformer; means adapted for placement o~ said core in an associated current field, whereby a ~lux level in said core is influenced thereby; means for generating a composite signal, operatively connected to an output winding of the transformer, indicative of a flux level of the core; means for generating a slowly varying DC current level signal indicative of a portion of said composite signal attributable to the associated current field; means for establishing an offset flux level in the core; and, means for amplifying the current level signal.
In accordance with yet another feature of a specific embodiment of the invention, a means is provided for varying a characteristic of the composite signal in accordance with the current level signal.
In accordance with yet another feature o~ a specific embodiment of the invention, the current measurement device further comprises a meanc. for inducing an initial flux level in the core.
~ ~, ~,, - 7a -In accordance with yet another ~eature of a specific embodiment of the invention, the system further comprises means for generating a voltage level in accordance with the composite signal and wherein the current level signal is comprised of the voltage level.
In accordance with yet another feature of a specific embodiment o~ the invention, the means for amplifying comprises a device having a very high voltage gain, a high input impedance and a low output impedance.
Brie_ Description_of the Drawings The invention will taXe form in certain parts and arrangements of parts, a pre~erred embodiment of whi~h will `' ''Ç~' - ~ - 1 31 4073 be desc~ ed itl ~tai1 in this specification an~
illustrated in t~le accompany1ng ~rawings wllicl~ form a part llereoE al-~ wilerein:
I;'IGUI~E 1 is a block diayram of an aE~paratus for measurillg parameters itl an e1ectrocoating batll envirollmellt .lnc1uding at least one sensi~lg probe, a housLIlg contail1illg a signa1 processing mealls and a trigger probe FIG~ 2 is a perspective view of a ses~sing probe o~ F:IGUI~E I;
PlGUllE 3 i~ ~ scllematic diagram of a current dens1ty measuritlg device or SellSor of tlle sensing probe o~ FIGURE
1 ;
EIGUI~ is a scllematic diagtam oE a temperature sensor of the sensillg probe of FIGURE 1:
~IGUl~E 5 is a schematic ~iagram of a potelltia1 or vo,Ltage sensor of tlle sensing probe Or ~IGU~
EIGUl~ 6 is a side e1evationa1 view illustrating tlle use oE tl~e aE~paratus of ~IGUn~ 1 in an e1ec~:ro~epositlon coating batll envirollmellt: and, FIGUI~E 7 is a block diagram flow chart Or a me.tllocl o~ measurlng currellt density using the apparatus of FIGURE 1.
D~ 5D~9~ietion of the PreEerred Embodiment Re~errillg now to the drawings, whereiJl tlle sllowlngs are for purposes of i11ustrating a preferred etnbodimellt of tllis inventioll on1y and ilOt for ~urposes oE 1imiting same, FIGU~E 1 SIlOWS in block diagranl rorm tlle a~paratus fo1-measuring parameters such as current density, temperatllre and potential in a relatively llars~l envirollment. q'lle apparatus comprises at least one probe ~ whicl~ ig e1ectrica11y conllected to a llousi~lg U tllat contaiJls at least one signal processing and signa1 recordillg means.
Extendlnc3 rrom tl1e l~ousl11g ls a trigger probe C ~or begin11LIlg t1~e rneasuril1g process. Wl1ile the invel1tive apparatus will be described and illustrated in con1-ectlor witll tl1e measuremel1t of parameters in an ~-Coat batl1 el1vironmel1t, it sl1ould be appreciated that tlle apparatus could be used in a wide variety of e11viroome11ts an~ t1~at tl1e current density measuri11g device incorporated i11 t1te a~paratus coul~1 ~e used separately.
In otller words, t21e curre11t density measuring device l~ can be utilize~ to measure currel1t density in a wide variety oE measuril1g enviro11me11ts and not ~ust in an electrodepositiol1 bat~1. Sucl1 envirol1me1lts include, for examp]e, electroplating and catl1odic protection systems.
More gel1erally, ttle current measurlng device disclosed 11erei11 could be used Eor making var:ious types oE direct current measureme11ts wllere relatively small D.C. currents (i.e. milliamps) need to be measured, e.g. measuring a currel1t in a con~uctor. ~ccorc1il1gly, lt s11ould be appreciated tllat wl1ile tlle device will be described as being useEul particularly for making current density measuremel1ts, tlle device can also be used for makiny various otller types oE current measurements.
Tl1e curre11t density sensor of FIGU1~ l wlll be discussed first herei11below. Witl1 reEerence now to tl1e electrical circuit diagram of FIGU~F 3, the curre11t density sensor accordlng to tlle present invel1tiol1 i11cludes an apparatus whlc11 measures a current ~ensity iJl a conductive medium tllat passes ti1rough a fixed diameter bore (~ as illustrated in PIGU~I~ 2) to produce a total current Io~ In PlGU~E 3, lO represents a one tur11 winding created by a transEormer core of a transformer 12 tl1at is constructed out oE square loop magnetic material l1avi11g a moderate saturation flux density and a ~s11arply defil1ed saturatio11 state. 'I'he transformer 12 is com~rised of a core about 1 31 ~073 wl~icl~ tl~e sillyle tu~ll wisldil-g 10; ~ir.st and .second center-taE)ped wil~dings 12a 12b: and first and second fee~ack windinys 1~ 2~ are wound. All windillgs a~-e related in directloll by tl~e dot convelltion illustrated in ~IGU~F 3.
pair of associated transistors 22 2~1 fullction to illterconllect tl~e center-~apped windil-g 12a to form a maglletlcally coupled oscillator clrcuit.
~ acl~ transistor 22 2~ acts as a switcll allowiny current to alternate1y pass tl~rougll windi-lg l~alves 1~ lG
oE tlle flrst center-tapped windillg 12a", ln alternate direCti.OllS, as dictated by wl~icl~ tratlsistor is in ~lle saturatioll state. ~eedback is generated by tlle win(lillgs 1~ 20 WlliC~l a~ coupled to tlle bases oE tlle Eirst and second transistors 22 2~. Wherl tlle ~lrst trallsl~tor 22 is in tl~e saturation state, current f1Ows into tl~e windillg 1~, developirly a positive voltaye orl tl~e wil~dlng 20 wi~l~
respect to a fixed ~C blas, ancl a negative volt~ge on tlle windillg 1~ as long as tlle trallsformer is not saturated.
Tllus tlle Eirst transistor 22 is maintailled ln a saturation state wl~ile the second transistor 2~ is clamped ofE.
Tllis conditioll llolds until the transormer core enters ~Iux saturation. ~s tlle core satul:ates, lts interllal magnetic field stops cllangillg, tl~us by Faraday's Law oE In~-lctioll tlle feedback vol~ages developed by tlle 2~ feedback windings 1~ 20 become zero with respect to tlle Eixed ~C ~ias. ~t t~liS point tl~e second transistor 2~
enters s~tur~tion also allowing cur~ellt to Elow to coil 16 of tlle Eirst center-tapped windillg 12~ s a~rul-t cllarlge in llet current produces a Eeedback pulr;e oP opposite po~arity to be generated in tile willdillgs 1~, 20, causinc~
tlle first tratlsistor 22 to be c1amped oEf and tlle second transistor 2~ ~o enter saturatioll.
Tlle second ha]r oE the oscillator period operates exactly ~s described above, except that tlle roles of the - 11 - I 3 1 ~1 0 7 3 first and second translstors 22 24 are rev~3rsecl. Tl-us sustallled o~cillati.olls are producecl by the circuit. Thircl alld rourtil resistors 31 33 oE tlle circuit apply a static I~C bias to botll oE tlle transistor bases sucll that under static norl-osci11ating conditlolls bol:h trallsistors are biased s11ylltly lnto saturation. lllis ellsures that tlle circuit wil.l begin osci11ation on power up regardless vr tlle previous magtlet1zation state oE tlle transformer 12.
The amount o time requiretl Eor eacll ha1f of tl~e oscillator peri.od .is determined by tlle llumber of tota:L
volt-secollds o~ f1ux linkage supportecl by tl~e core of tlle transEormer 12. Since t}le transformer core saturates at a we:L1 defllle(l total flux determlned by tlle maglletic materia1 cllaracteristics alld the yeometry of the core, tlle transEormer suE~E~orts a well deElrled number oE vo1t-seconds oE flux 1.inkage between saturatiLon in eitller of tlle two possible directions. lhe voltage aE~p1ied ~o the first center~tapE~ed windillg ].2a is a Eullctioll oE t:lle Elxed supp1y voltage and oE tlle voltage drop across the Eirst ~nd secolld resi.stors 30, 32 alld llence tlle current draw~ y tlle tr.alls~ormer 12 during tlle trans.i.tioll Erom one saturation st:ate to tlle otller. Tllis current call be ~etermined from tlle inductioll cllaracteristics of tl~e magnetic material alld tlle core geometry. Ille time required Eor trallsitioll ~rom one saturation state to the other is equal to twice tlle total flux ~ kage oE t:lle irst center~taE)ped willdillg 12a divided by tlle voltaye applied to wind.ings 1~ 16 . Ilence tlle frequellcy oE osci11ation can l~e determ.ined.
1lle externa1 current Io generates a static flux 3û witllin tlle transFormer 12 that ad~ls to or subtracts rrolll tlle Elux due to current in the Eixst center-tapped winclillg 12a. Since tlle saturation E1ux 11nkage oE tlle core is îixed, tlle amount oE Elux 1inkage tllat the rirst and seconcl transistors 22 2 4 must apply to saturate the transEormer 12 is ~roportionally lncreased or re(l~lced depelld.illg llpOll tlle direction of lo~ Changillg tlle transitloll current drawn by tlle transformQr 12 alters tlle voltage ~rop across tlle rirst resistor 3U or the second reslstor 32 t~lus cllangillg tlle voltage appl.te~l to windings 1~ 16 ~y an amount proportional to Io~ llence windlngs 1~ lG and respective resistors 30 32 sllare tl~e voltage alplled ~y tl~e transistors provlding a lligllly sensitive an~ stable device. Since the transition time is inversely proportional to tlle voltage applied to wind3.nys 1~ lG tl~e transition time is altered in proportion -to XO. ~ecause lo acts in opposite directions wit}l re.~ect to t]le two coils 1~ 16 oE tlle Eirst center-tapped windirlg l~a one llalf oE
the oscillator perio~ is shortelled by exactly tlle a~ount 1~ tllat tlle otller hal is lengtllelle~. Tllus tlle net oscil].ator Crequency is not cllaJlged by tlle appllcation o~
Io but tlle symmetry oE the oscillator output is cllangecl almost in direct proportion to Io~
~lle circuit tllus far ~escribed is capable oE
measuring current dellsity due to tl~e presence of the rirst and second resistors 30 32. llle transitioll time is proportional to the voltage applied to the two coils 1~
16. Io causes more or less currellt to be drawn by tlle coils 1~ 16. Changillg tlle current tllrougll tlle resistors ~5 30 32 cllanges tlle volt~ye Oll tlle coils 1~ 16 - tllus also challgillg the transitioll time-. The transition time diference between the two llalves enables one to derive currellt dellsity.
First and secolld diodes 3~ 36 along witll fiftl! alld si.xth resistors 3~ ~0 in the circuit strip tlle negative llalf of tlle collector voltage o each transistor to provide clean square wave signals. ~ach signal is in a lligl~
state whell its respective transistor is in saturatioll alld in a low state when that transistor ls cut oEE. Diodes 34, 36 alol-g witll resistors 3~3, ~0 provide llearly ideally symmetric square E~ulses, allowiny higllly accurate measuremellt:s .
~ plllrality of resistors, namely sevelltll, eiglltll, rlilltl~, and terlth resistors ~2, ~ 6, and ~-3 toc~etller witl~ a plur.l1ity of capacltors namely flrst, second, tlllrd, an~ ~ourth capacitors 50, 52, 5~, and 56, apply a pi-section low pass Eilter to eacll llalE oE tlle osclllator output, to remove lliyll oscillator Erequellcy OUtptltS. Tlle resultillg slowly varying DC signals are -tllen proportional to the respective ~mounts oE "on" time that eacll llalE Or tl~e oscillator experiences.
~ n ampliLier 70, wllicll is preferably a preclsion monolitl~ic instr-lmelltation ampliEier, measures ancl ~mplifies t~le dlEEerence in voltage oE tlle two filtered oscillator outputs. The use oE an instr-lmelltatioll amplifier instead oE a simple operational ampliEier is advalltageous because it provide tlle instrument Wit]l less clrit and tiyllter calibratioll tolerances tllan a simple operational ampliEier could provide. The device has a very stable volt~ge gain, a lligll input impedallce and a low output impe~lance. It can be sllowll tl~at tlle clifferential vo1tage is, within a deEilled ran~e oL Io~ proportional to Io~ T~us, the circuit provides a cont~ uous outpllt voltage tllat varies in direct proportion to Io~
Eleventh and twelEth resistoxs 72, 7~ are in circuit witll the ampliEier 70 to set tl~e amount oE voltage gain applied by the il1strumentat~n ampliEier -to tlle dlferel1tial voltage. This provides a means for calibrating tlle instrument.
'l'lle second center-tapped winditly 12b has first an~
second halves 80, ~32. The windillg halves ~30, ~2 togetller with a tl~irteenth resistor 8~ provide a means to compensate for small O~ltpUt ofEsets due to compone~lt toLerance er~ors, providiny a mealls to set a zero ou~put value.
~ urality o~ additlotlal Eilter capacitors n5, ~n, arld 90 are advalltageously provided in the circuit as power supply coupling capacitors to provide improve~ circuit stability.
'l'he currellt sensor descrihed hereitl call ~easure DC
currellts paSsilly tllrougll the bore of tlle trallsformer.
'rilerefOre, I)C CUrrellt dellSltieS Call be measured as defined ~o by the rixed area of the bore. The device can be calibrated to measure a currellt dellsity up to 30 m~/cm~
with a precision of better thatl-l- .9 m~/cm2.
'l'he probe ~ i]lustrated in FlGU~E l also includes a temperature sensor. Measuring tlle temperature is use~ul in a probe employed for measurill~ parameters in all electrodeposition process. The temperature sensor indicates whell tllat ~robe enters the electro(leposition batll since the temperature will increase from amblellt (clrca 20~C) to batll temperature (circa 370c). The temperature of the electro]yte bath is an importallt parameter in tllat the maintellallce of proper chemlcal kinetics at tlle electrolyte - metal boun~ary is directly related to temperature.
~ecaùse di~fusioll processes occurrillg at tllis boundary are lligllly temperature dependellt, the measurement of temperature can ~e critical to tlle evaluatioll and ullderstalldil~g of tlle ~-Coat process. Thus, all increase~
local temperature could imply a ~ocalized resin depletio itl the bath from a lac~ of mixlng.
Witll referellce now more particularly to FIGUI~E ~, the temperature sensor is suitably a transducer comprising a convelltiorlal type K thermocouple lO0 and a ~lo~olithic thermocouple amplifier unit 102. These can be attaclled to tlle same circuit board as the currellt density sensor i~
desired. The tllermocouple is electrically isolated from tlle enviroll1nent in wl~icll it is sensincJ the temperature in order to preclu~e possible damage to the amplifier utllt 102 by lligll voltages appearing on the thermoco~lple leads w11ell immersed in arl electrically conductive medluln SUCII as all E-Coat batll. lhe tllermocouple amplirier provldes ~ volta~e outl)ut corresponditlg to sensed temperature. The approximate linear transEer runctioll oE the thermocouple o~
tlle preferred embodlment is 10 mlllivolts per degree Centigrade .
]0 ~lso provided :in the probe ~ is a voltage or potential sellsor. Mensuremellt of tlle voltage or electric pOtelltial i8 desirable in tllat such information can be loosely inclicative o~ tlle relative amoullt oE ~esin ~llm build on tlle metallic substrate in t:lle vicinity o the probe by virtue oE the high resistivity o~ the deposited film witll respect to tlle water-tllill resin E-Coat batl~.
Witll re~erence now more particularly to FIGUIIE 5 the voltage sensor 10~ comprises an electrically conductive sensing elemellt 110 wllich may be a conductive plate or a tube t21at is exposed to tlle measurement envirollmellt in wllicll potential is to be measured. lhe element 110 i5 conllected to a resistive voltaye divLder network comprising resistors 112 114. ~he vol~age sensor ls sultably containe~ on the same circult boar~ as tlle temperature sensor and tlle current del-sity sensor, iE that is desired. rlhe voltage divider network acts as a 20 to 1 attenuator (i.e. 20 volts in yields 1 volt out) with an input impedance oF approximately 20 megollms. ~`lle importance of this relatively higll input impedallce will be :30 discussed hereirlbelow.
llle probe ~ illustrated scllem~tic~lly in ~lGUI~ 1 ls illustrated in perspective ~orm in EIGUIIE 2. ~s shown ln FlGUII~ 2, the sensors on the probe are preferably at least partially encapsulated in a probe body 130 tllat is made from an e].ectr~ca1l~ all~ tilermally il-stllating illert materi.al sucll as sllicolle rubber to protect atld illSUlate tlle meas~ emellt electronics Erom tlle electrical and tllermal llazards of tlle measurement envlrollmellt. Tlle encapslllatioll protects tl~e sensors from corrosion and rom tlle electrolyt.ic me(lium al-d also acts as mecllanical protect.ion for tlle measurement electronics and tlle interllal mecllanical assembly. ~s mentlolle~ above, preFerably tlle current density sensor, tlle temperature sensor, and the potential sensor sllare a common circult board wllicll ls not visible .in ~IGUI~E 2.
'l'he volta~e or potentlal seosing e1ement 110 ie exposecl to tlle measurement el~virollment ~ut tlle currellt clellsity sensor is completely encapsulated. ~s melltiolled, ti~e tl~ermocouple (not visible in ~lGU1113 2) .Ls covered by a slleath 131 to electrically lsolate it Erom the measurement envirorlmellt .
PreCerably, convelltional suction cups 132, 13~1 are provided oll the body 130 as a means Eor securely fastelling tlle probe in the measurement envirollment in a readily detachable manner. Suction cups ofEer advalltages over otller mecllanical attachmerlt mealls sucll as magnets or the like due to the Eact tllat magt-ets induce a static magnetic Eield in tlle vicinlty oE the probe alld tllis could cause di.stortions in both tlle process beill~ measure~l alld tlle mecllanism by wlli.c}l tlle current densities are measurecl.
Preferably, the suctiOIl cups are made oE a suitable elastomeric material such a rubber. 'rhe suction cups ~a be provided on more tllan one surEace oE the probe body 130, if tllat is ~esired, to allow some Elexibility in tlle securing oE the probe bo~y to a work plece i~l the measuring environmellt .
Electrical power to the probe assembly ~ is provided tllrougll a conductor cable 1~0 wllich also provides a patl for electri.c~l signa1s representing tlle measured quantities to be tran~mitted. The cable l~o is preferably double sl~ ed to reduce noise plckup. Power for the probe can be provi~e~ tllrougll a su.itable convelltiollal power supply wllicll can be an 1~3 vo.l.t DC gel cell power su~ply 1~2 positioned .in tlle enclosure B as SllOWIl in ~IGUI~E 1. 'l'lle raw power is preferably regu1ated dowll to ~-15 volt DC and -15 volt ~C on tlle cixcuit board ~y mealls of convelltional mono1itllic voltage regu1ator integrated circuits. I'he regulated alld filtered power provides all the power re~uirements of the measuremellt electronics contained in tl~e probe assembly.
1'lle cal)le 1~0 o a typical probe utilizes eigllt conductors as is i.llustr~ted in FlGUI~E 2. Two of tlle conductors are for tlle plus and minlls 1~ volt UC raw power flowirlg to tlle probe. Three cond-lctors are provided, respectively, for tl~e curren~ dellsity slgnal, tlle temperature s.ignal, alld tlle potential signal. Two additional conductors are provided for thermocouple testing. Finally, olle conductor is l~rovide~ as tlle power supply/sic~llal ground lille~ e sl~ield of the cable is tled to tl-e E~ower supp1y/signal groulld at tlle power supply/siynal output end of -the cable to prevent currellts induced in tl~e shield from causiny erroneous voltage slliEts to appear between ground potent~al at tlle power supply ~nd tlle slgnal ground at tlle probe.
Witll reference now again to F:tGU~E 1, tlle measurement system can comprise a plurality oE pro~es ~
together witll tlle power supply 1~2 for them aR well as a data acquisition unit 150 and a contro1 computer 152.
Include~ in tlle central computer is a CPU 152a alld a memory 152b. Wllile three probes are illustrated in FIGU~E 1, it is contemplated that as many as nille probes would be used ill a full measurement system. Ilowever, it should be 1~ 1314073 aE~preciated tl~at more or less tlIan tllat number oE proI~e~:
could be used depencIiIlg Otl tlle number of probes requ Lred for a parl:lcular appl icatlon.
It sl~ould be notecl tl~at a divider ground is connectec~ common wll:l~ the system ground for conlIectillg all vr tIIe previously mentiolIed clrcuits into one grouncl.
1~ ~ystem groullcl 154 can be colIl~ected to tlle metallic substrate v.ia alliyator clips 1~6 or a simllar meal~s itl or~er to reEerence all potential measurements to the me ta l l ic subs tra te .
'rl~e llousing B preerably accommodates tlle power supply 1~2 t11e dal:a unit 150, ancI the computer 15~ and p~eferably comprises an envirolImelltally secure enclosure 15~ iclI C~l~ be selectively opened as necessary. In one preferred embodiment tI~e system comprises a IIew1ett Packard 3~ clata acquisition unit an~ a IIewlett: Packard IIP-75 computer. UOtlI the data acqlIisition UIIit 150 al~d the computer 152 are preEerably providecl wi th an internal power means WlIic}I carI be reclIargeable I-ickel-cadlllium batteries or tl~e like (not illustrated). ~lternatlvely, the power supply 142 for tIIe probes could also be suitably con~igured to supply power to the control computer and the data ac~uisition unit if desired.
'I'lle data acquisition UIIit 15(~ receives tl2e measured values rom the probes under control of the computer in t~le form of voltage measurements. q'he computer ls also respollsible ~or storing t21e collecte~l data until the ell~ ol~
the measurement cycle at wllicII point tlle data may be store~I
oII magnetic media or kept in tlle computer ' s contiIluous memory. '1'12e data acquisition unit and tlle computex communlcate via a suitable insl:rumeIlt loop serlal communications link 154 which in tI~e preferred embodimeIlt is a IIewlett E'ackard InstrumeIlt Loo}~ (IIP-IL) lillk.
-19- t3~073 Durillg tlle measurement proces~, only tlle co~ltrol connputer, tile data acqUiS.itioll unit, and the power supply are contaitled illside tlle envLrollmentally secure enclosure B. Tlle probes ~ are connected to the power sl~pply 1~2 alld tl~e data ac(~ui.sitioll ull.lt 150 via convellti.ol~ll waterprooE
p.last.ic collnectors ~not lllustrated) on the enclosure 15~
in order to maintaill tlle envlronmental illtegrity o~ tha ellclosure and to prevellt exposure of tlle computex 152 and the data acquisiti.on unit 150 to tlle measuremellt lo envi.ronment.
In tlle preferred embodiment, the data acqulsition Ul-lit ls capabl.e o~ ac~uirlng data from 30 c~lallnels.
Ilowever, tl~e measuremel~t system llerein envisioned utilizes only 27 cllanllels Eor data (9 pr.obes) and one c1lannel as a system tri.gc3er. It is evident tl~Qt data ac~luisitioll UllitS
llavlllg other cl~anllel capacities can also be utilized as needed. ~ter the data acquisition un.it ancl tlle comp~lter llave beell placed in the enclos-lxe and power )las been applied to tlle probes, the probes are attaclled via the suctloll cuE)s 132, 13~ to tlle metallic body which will be exposed to tl~e measuremellt envirollme]lt. Ollce the probes are attaclled, tlle data acquisition program in the computer can be started. ~ctual measurements will not be take until tlle system is trigyered via the trigger prol~e C.
Tl~e trigger prol~e can coniprise a rectangular plastic block llousillg 160 in which a pair of wires lG2, 16~ nre securely Eastened. The ends oE the wires have been stripped oE insulation and have been solder tinlled leaving approximately one half inch oE wire exposed to the measurement environmellt. The block 160 also contai31s a pair o cera1nic ma~nets 166, 16~ wllicll are used to al:tacll tlle trlgger probe to the metallic substrate. Tlle trigger probe can also be provided with a removable proteat1ve - 20 ~ 1314073 sl~eatl) 170 to protect the probe wlres ]62, 16~1 wl~en not in use, and also to prevellt accldental triggering during tl~e attacllment o~ the probes.
Witll rellerellCe llOW to FIGUl~E 7, the funct~o~ g oE
tl~e software routine for acquiri]lg dat:a is tl~ere il1ustrated. 'I'l~e computer waits in loop examinillg challlle zero of tlle data acquisitioll unit C11anne1 zero, previously conrigured for performing a two wire res1stance measurement, is tlle cllanlle1 usecl to trigger tlle measurement cyc1e. 'l'riggering occurs wllen the tric~ger probe i5 immersed i n the measurement enVirol7ment and "sees" a resistance betweell tlle two wires tllal: is less thall 80, 000 ollms, as sl~owll in block 172. I~fter trigyering, base line measurements can be made for each of the current density circuits in tlle several probes ~. Tllese are sZ:ored in tlle computer 152 and used to zero out any offsets that may be developed .
1~ variable software w~it routine is suitably programmed into memory 152b oE tlle computer 152 (FIGUl~E 1) so that tlle program will wait a specified number oE seconds before commencillg data collection aEter triggerillg. Sucll a wait period, as showll in block 17~1, is higll1y desiral~1e since untler certain measurement conditions tlle measurement envirollmerlt may have to stabilize . Tlle max imum number of Z5 data sets in tl~is embodimellt is firty and is determllled by tlle amount of physical memory contailled in the computer as tlle computer ' s memory is apporl:10ned lor both program and clata storage. ~ minimum samp1e intervn1 between measuremellts is 1. 5 seconds . In other words, tllis pex iod ~0 of time must elapse between each two measurements as show in block 176. The interval is constrailled by tlle data acquisition unit 150 and the finite 1ength oE time tllat is needed to make eacll measurement. In tlle preEerred embodiment, tlle minimum sample interva1 is constrailled by tlle IIE~ 3~ data unit's dual slope ,iIltegratl~g aIlalog to r3kJitctl eoIlverter. In general t1le absolute minimum measuremeIlt i.I~terva.l would be l.imited oIIly by tlle probe ' s baI~c3w idtlI . Sinee tlIe probe has a -3 db bandwidtIl oE 3-~1 IIz, tlle sampliny ~requeney would be limited to approx.imate.I.y l `5 to 2 IIz.
'l'I~e procJram qcIel.-ies wI~etIIer tlle predetermillc?d nuIlII~er Or Cl~ l S~ 19 ~c?t~ o.l.leet~,~3, as sIIowII ~ ).loek 17~3. lr IIOt, tlle pI-oc~r.llll returIls to tIle san~l-1e interval t.Lme ~lelay 1 r) t~uery. (JpoI~ eompl?t.i.oIl oE dat a eolleetioll, tlIe program .i.Il.il lates a rlueI,y wlletIIer tlle user would l.i.ke tlle )Iew.Iy c,ol].eetec3 ~Iatil to be storect oIl macJIletie metlia ag a baek-up t)reeaut.i.oIl ~s. sI~owIl .i n bloek 17~3. ~ter progrilm LerInillatiol~, l:lle c3ata .is maiIltallled in tlle eompul:eI. 's .I 5 COIltiIIUou~S memory Ullt.i.l ~3eletec3. oIlee data eolleetiolI l7as beeII eomplet:ed, tlle eompllter C;lll be tuI.l~e~I ol~ aIlcI
.isc,oIllleete(I rrom tlle clnt:a aeq~ slt;.oll uII.i t aIlcl remove~l Jlrom t,lle eIleI.osure. Wi.th tlIe t1ata c:torecl saCely iu tlle eomputer's memc)ry, or .;Il memory aIIcl OIl a ma-,3Iletie mecl.i.I.llll, 2(1 all .i.Il~Iefilli.te amouIlt oC t1me may e1.apse beCore tlle ciata ;s ret:rievecI. ~[ter tllc, ;,II~strUmeIlt lIas beeIl remove~t Lrom tlIe measuremeIlt eIlv,irollmellt, tlle eomput:?r ean ~e c,~oIllIeetecl to a su.it:a~1e eoIlvelltioua1 prlIlter (llOt illu~tl~Ited) for pri.Ilt.;l~y or pI.ottlIlcJ tlle eolleete~t data. q'Ile IlP-lI
~5 illstrument looE~ 15~ Call be usect to illter~aee tl~e t)riIlter witll tJ~e eomE~uter 152 c3ur1IIg text aIldi grapI~ia outp~t opera tiOllS .
1~ suitable ~lal:a eolleetlon prograIn reacls tlle eolleete~3 (3at~ allct priIlts tlle E~ol~e~lt;lal, eurl-eIlt dellsity aIld temperature data in a l:able fo~m Lor ea~y vi.suc-l1 eompar.isoIl. ~fter all tlIe tlata I~as bee1~ prlIlte~I, a su.itable seeollcl progt.;Im, Wllicll Ci311 be Pl t)lo~tiIlg E-rot3ram ean I~e eal.le(l ill or(ler to p10t: magIlitude~s o~ poteIlt.ia I, eurrent c]ellsity allcl teIllperature agEI.t.llst tlmce.
Wit.~l referellce now to I~GUI~I~ 6, one E;u:Ltable measuremel~t environ:nellt for t)le ~reviously clescrihed measurement i.llstrumentatloll is an automotive electrocoatilly batll. ~rl automotlve electrocoating facillty wllicll is maintailled at all automo~ile plant comprises a suitable tal)k ]90 ~or hol(lil~g tlle E-Coat bat11. ~rhe tank can ~e up to 150 ft. lon~, 12 ft. w;de, 10 ft. high, and opell on tlle top.
plurality of automobile bodies are moved througll tlle tallk ill a relatively conti~luous process. One sucll ~utomoblle lU body 192 is sl~own in ~IGU~E 6. 'l'lle body 192 acts as tlle catllode o~ tlle electro~epositioll system. Suita~le anode~.
19~ are provided on the walls o~ tlle tank. In various electrocoatillg tanks, the anodes can ~e located l diE~erent places Otl tlle tatlk alld Ca11 have varying shapes.
'~'he electrocoating enviro1lmellt is a hostile en~irollment wlllcll is q-lLte ~le~tructive. 'l`l~e E-Coat batll itself is a water tllln electrolytic resin mixture tllat is kept in t11e tank 190 under constallt turbulent agitatioll.
One such resin compositlon is a cationic resill whicll contaills blocked isocyallate curing agellts and is available from ~PG Indllstries, Inc. under the trademark UNIrl~lM~.
Tlle E-Coat process by wllicll metallic parts such as car bodles or parts of car bodies are coated wit11 a polymer resin layer involves submersion of tlle parts in the bath and tlle application of a DC voltage between the car part or body W11iCll acts as the cathode, and the anodes 19~ locatecl on the tank walls. ~hell the proper condit1OIls occur at tlle metal surface, i.e. correct pll, minimum currellt density, etc. the resin precipitates OlltO t11e Illetal.
Since the metal conductor measurillg batll ~otential can also act as a cathode, it woul~ also be prone to coating just as the other metal parts in tlle tank i~ the current flowin~ tllrough the circuit, and hence the current density on the conductor, were above the minimum required for deposition. T1le high impedance (20 megohms) of tl~e circuit en~.ures t1~at any currents flowi11g tl1roug1~ tlle measureme11t circuit wlll be below tlle thres11old require~
for such c1epositiol1 to occur.
Since the ~rocess l~ baslcally a curre~1t driven process, it is necessary to know what the curre11t del1sities are at various locatiolls 011 the c~r body in order to obtai.n t~e most ul~ orm resll1 c1epos~tiot) and to provide a ~et~er understan~ir1g o ~10W the process is working. pro~lems arise bec~use of the cl1al1ging geometries encou1~tered wl1en dealil1g Witl1 ~1;.Eferent automoblle, van, and t:ruck bodies in relatiol1 to tl1e fixed anode geometries oE the coati I~CJ
tanks. 'l~llere~ore, a u11iform conting t1~ickness along the o~1tside surface oE tlle car body is di~ficult to acllieve.
1.~ Obta.il1;.11c3 a mil1.lmum coating t11ick11ess on tl1e corrosiol1 prone inter1~al cavi.ties of tlle vellicle body suc11 as rocker panels, fender wells, door pillars, etc. i5 even more di r ficult to ac~1ieve.
Currellt density, along with pol:elltial antl ~o temperature meaSuremel1ts can provide an insight illtO
met11ods by wl1ic11 better coatings can be obtained, e.g.
t11rough a modiEicatio11 of the deposition tank geome~ry Ol^
changes in the design of t11e body parts or bodles tllemselves .
2~ T1le apparatus according to tlle present lnve1ltion will provide a better un~erstal-ldil~g of the physics o the electrocoat process by providing ~reviously unobtai1lable data co11cerni11g the currel1t densities requ.ired for the coating process. It may also ~acilitate improvements in ~0 t1~e composition of the electrocoat resin by allowlng better testing of new formulatio1ls. ~s an end result, vellicle manuacturers will obtain more evenly coated vehicles. Uy obtaining improved coating of corrosio11 prone areas, vehicle manufacturers will then be able to oEEer longer - 2~ - 1314073 corrosion warral~ties and acllieve a red~lctioll oE costs due to warrallted corrosion-related repairs.
Tl~e invelltioll llas been described wltll reEerence to a preerred embodiment. obv.iously, alterations and modiricati.olls will occur to otllers upon a reading and understalldill~ oE tllis speciEication. It is i~ltended to include all SUCIl modifications an~ alterations insoEar as they come wit~lin the scope of the appended claims or the equivalents tllereof.
in wi1ic11 t~1e metallie part to be eoated serves as ~1~e cat1~ode, was introdueecl commercially. Since tllat time, catio1~;c electrodeposltion l1as steadi]y yained in popl1larity a11d is today by far the most prevalent met11oc1 Or electroc1epositio11. Currently more t11a11 ~0~ oE al] motor vellieles produced around t1~e world are given a ~ase cont or a primer coat hy cationie electrodepositio11.
l1le ~roeess i1lvolves immersing tlle ear body or car parts in a eond~ctlv~ eleetrolyte batll ln a tank. Il1e E-Coat bat11 is a water thin eleetrolytie resin 1nixt:ure tllat is kept in tlle tan)c under eonstant turbulent ag~tntlo11.
11le car 1~ody becomes a eatllode an~ several anodes are attaelled to tank walls to net as tlle other eleetxoc1e in ]5 tl1e eireuit. ~ direet eurre11t voltage betwecn approximately 200 to ~oo volts is applied between tlle eatl1ode ancl tlle tank anodes. Wl1en proper eondltlons oeeur at tlle mrt:al surface i.e. eorreet pll, mlnimu1n eurrent density, ete., tlle resin precipitates onto tlle metal. ~rl~e resln Eorms a ~ilm w1~ich, after euring, ean be on the order oE between l to 2 mils (.025~ to .050~ milli111eters~ in thiekness.
Icleally, a uni~orm eoating t11ickness is c1esired 011 all l~ody surfaces. ~roblems arise whe11 ~1on-u11irorm deposition oecurs eausing widely varyi1lg thie1cnesses of resin eoatincJ on cdirCere11t parts of ~1~e body. Tl1is ean eause tlle ear body to be rejeet:ed and scrapued, at n tremendous expeose to the vehiele m~nufacturer. Even iE
tlle body is used, uneven eoatings ean lead to an early ~0 eorrosion o~ the portion oE the ~oc1y w1~iel~ was 170t eoated wlth a suEfieiently t11;ek layer of tl1e resin.
Sinee eleetroeoating is a e-]rrent drive1l process, measurement o~ the eurrent density on diEferent parts o~ a ear body would provide data on and an lnsig}1t into how tlle _ 3 1 31 4073 process could be optimized to obtain a more uniform coating layer on the car body. Collected data would aid in solving problems occurring in electrocoating systems presently installed as well as aid in the design of new electrocoating facilities.
At the moment, no suitable current measuring device exists for this type of environment. Standard current measuring devices are not sensitive enough to measure the current density in an E-Coat bath with precision.
Additionally, no standard current measuring devices are available which can be used in the harsh and corrosive E-Coat bath environment. It would be advantageous to provide such a current measuring device. It would also be advantageous to provide an apparatus which is capable of measuring several different parameters in an environment having a metallic body positioned in an electrolytic bath.
Accordingly, it has been considered desirable to develop a new and improved current measuring device, as well as an apparatus which can be used for measuring current density and other parameters, which would overcome the foregoing difficulties and others and meet the above-stated needs while pro~iding better and more advantageous overall results.
Brief summary of the Invention According to one aspect of the invention, a current measuring device is provided.
More speci~ically in accordance with this aspect of the invention, there is provided a current measuring device comprising a transformer adapted for placement within a secondary flux source; an oscillator for periodically placing said transformer in ~orward and reverse flux saturation by application of a periodic voltage to an input winding thereof, whereby a period of the fo~.rard and reverse flux satur~tion is affected by the secondary flux source; a pair of multi-section low pass filters operatively connected to an output winding -1 ~ 7l '\'~
!
_ 4 _ 1 31 ~ 0 73 of the transformer for generating an output signal including a slowly varying DC signal proportional to an on time of said transformer; and, amplifier means for processing the output signal of said pair of multi-section low pass filters, wherein said amplifier output is representative of a current sensed by said transform~r.
According to a specific embodiment of the invention, the device further comprises a means for compensating for small output offsets due to component tolerance errors.
According to a still further feature of a specific embodiment of the invention, the device further comprises a means for improving the sensitivity of the transformer. The means comprises a pair of voltage-sharing resistors.
According to a yet further feature of a specifia embodiment of the invention, the device further comprises a means for calibrating the amplifier.
According to a still yet further feature of a specific embodiment of the invention, the amplifier is monolithic precision instrumentation amplifier.
In accordance with another feature of a spe~ific embodiment o~ the present invention, a system is provided for measuring parameters in an environment having a metallic body positioned in an electrolytic medium.
More specifically in accordance with this aspact of the invention, the system comprises a current density sensing means positioned adjacent the metal body in a non-invasive manner, the current density sensing means including a transformer including an input winding and output winding, an oscillator for periodically placing the transformer in flux saturation by application of a periodic voltage to the input winding, and means for generating a slowly varying DC output level signal from .~ ~
_ 5 _ 1314073 a signal recei~ed from the output winding in accordance with a timing of the flux saturation as influenced by current in the electrolytic medium; an electrically and thermally insulative housing means for enclosing at least a portion of said current density sensing means in an electrically and thermally non-conductive manner; a computer means for processing the current level signal from said current density sensing means: and a wiring means ~or electrically interconnecting said computer means with said current density sensing means.
According to a specific embodiment of the invention, the system further comprises a temperature sensing means and a voltage sensing means each of which is located adjacent to the current density se~sing means in said housing means. The wiring means also interconnects the temperature and voltage sensing means with the computer means so that the computer means can process the data therefrom.
According to yet another feature of a specific embodiment of the invention, the system ~urther comprises a data processing means for processing an output signal from the current density sensing means before the output signal is sent to the computer means.
According to still yet another feature of a specific embodiment of the invention, the system ~urther compri~es an enclosure means for housing the computer means and the data acquisition means in an environmentally isolated manner.
According to yet still another feature of a specific embodiment of the invention, the system further comprises a trigger probe means for setting the initiation of a measuring cycle with the apparatus. The trigger probe maans is in electrical contact with the data ac~uisition means. Preferably, the trigger probe means comprises a housing, a means for securing the housing to the metallic body and at least one sensor exposed to the electrolytic medium.
,~ 1, .~
- 6 - 131~073 According to still another feature o~ a specific embodiment of the invention, the system further comprises a means for securing the housing means to the metallic body.
In accordance with still another feature of a specific embodiment of the invention, the current density sensing means comprises a toroidal transformer and a square wave magnetically coupled oscillator which drives the toroidal transformer. A pair of voltage sharing resistors are provided for improving the sensitivity of the transformer. A pair of multi-section low pass filters are also provided for monitoring the trans*ormer. A fixed gain differential instrumentation amplifier is provided for processing an output of each of the filters.
In accordance with yet another feature of a specific embodiment of the invention, a plurality of housing means are provided, each containing a current density sensing means. A plurality of wiring means are provided, each connecting a current density sensing means in one of the housing means to the computer means.
In accordance with yet another feature of a specific embodiment of the invention, the system further comprises a means for providing electrical power to the current density sensing means.
According to yet another aspect of the present invention, there is provided a current density sensing means for directly measuring parameters adjacent the surface of a metallic body in contact with a surrounding electrolytic medium, being sufficiently sensitive to measure current density in a range of milliamps per square centimeter comprising means for periodically placing a transformer into magnetic flux saturation by application of a periodic voltage to an input winding thereof; low pass filter means connected to an output winding of said transformer for generating a slowly varying DC signal proportional to detected alterations ' .~
- 6a -in periodicity of the magnetic flux resultant ~rom a current flow in the metallic body; amplifier means connected to said low pass filter means for detecting alterations in periodicity of the magnetic flux resultant from a current flow in the metallic body a temperature sensing means for measuring a temperature in the electrolytic medium adjacent said current density sensing means; a ~oltage sensing means for measuring a voltage in the electrolytic medium adjacent said current density sensing means, and said voltage sensing means.
Yet anDther aspect of the inven~ion resides in a current measuring device which includes trans~ormer means having a core and oscillating means for generating a square wa~e to induce forward and reverse saturation flux in the core. Means is adapted for placement of the core in an associated current field so that a flux level in the core is influenced thereby. Means is provided for generating a composite signal indicative of a flux level of the core as well as means for isolating a current level signal indicative of a portion of the composite signal attributable to the associated current field. The device has means for establishing an offset flux level in the core and means for amplifying the current level signal.
The invention also provides for a method for obtaining data concerning the deposition of a polymer resin onto a metallic substrate positioned in an electrolytic medium held in an electrocoating tank.
According to this aspect of the invention, the method comprises periodically placing a transformer into flux saturation; generating a slowly varying DC signal representative of current density in said electrolytic medium in accordance with a fluctuation of a periodicity of said flux saturation; securing said transformer to a metallic substrate; lowering said metallic substrate into an electrolytic medium held in an electrocoating tank; passing a current through said electrolytic medium .q ~i'?
_ 7 1 31 4 073 thereby depositing a polymer resin cont~ined in solution in said electrolytic medium onto said metallic substrate; detecting a current density in the electrolytic medium adjacent said transformer; and, recording information regarding current density detected by said trans~ormer.
The various aspects of the present invention have a number of advantages. One advantage of the present invention is the provision of a new and improved current measuring device which is particularly adapted for measuring current density.
In accordance with yet another feature o~ the invention, there is provided a current measuring device comprising a transformer including a core, at least one input winding, and at least one output winding;
oscillator means for generating a square wave to induce forward and reverse saturation flux in said core; means ~or communicating the square wave to an input winding of the transformer; means adapted for placement o~ said core in an associated current field, whereby a ~lux level in said core is influenced thereby; means for generating a composite signal, operatively connected to an output winding of the transformer, indicative of a flux level of the core; means for generating a slowly varying DC current level signal indicative of a portion of said composite signal attributable to the associated current field; means for establishing an offset flux level in the core; and, means for amplifying the current level signal.
In accordance with yet another feature of a specific embodiment of the invention, a means is provided for varying a characteristic of the composite signal in accordance with the current level signal.
In accordance with yet another feature o~ a specific embodiment of the invention, the current measurement device further comprises a meanc. for inducing an initial flux level in the core.
~ ~, ~,, - 7a -In accordance with yet another ~eature of a specific embodiment of the invention, the system further comprises means for generating a voltage level in accordance with the composite signal and wherein the current level signal is comprised of the voltage level.
In accordance with yet another feature of a specific embodiment o~ the invention, the means for amplifying comprises a device having a very high voltage gain, a high input impedance and a low output impedance.
Brie_ Description_of the Drawings The invention will taXe form in certain parts and arrangements of parts, a pre~erred embodiment of whi~h will `' ''Ç~' - ~ - 1 31 4073 be desc~ ed itl ~tai1 in this specification an~
illustrated in t~le accompany1ng ~rawings wllicl~ form a part llereoE al-~ wilerein:
I;'IGUI~E 1 is a block diayram of an aE~paratus for measurillg parameters itl an e1ectrocoating batll envirollmellt .lnc1uding at least one sensi~lg probe, a housLIlg contail1illg a signa1 processing mealls and a trigger probe FIG~ 2 is a perspective view of a ses~sing probe o~ F:IGUI~E I;
PlGUllE 3 i~ ~ scllematic diagram of a current dens1ty measuritlg device or SellSor of tlle sensing probe o~ FIGURE
1 ;
EIGUI~ is a scllematic diagtam oE a temperature sensor of the sensillg probe of FIGURE 1:
~IGUl~E 5 is a schematic ~iagram of a potelltia1 or vo,Ltage sensor of tlle sensing probe Or ~IGU~
EIGUl~ 6 is a side e1evationa1 view illustrating tlle use oE tl~e aE~paratus of ~IGUn~ 1 in an e1ec~:ro~epositlon coating batll envirollmellt: and, FIGUI~E 7 is a block diagram flow chart Or a me.tllocl o~ measurlng currellt density using the apparatus of FIGURE 1.
D~ 5D~9~ietion of the PreEerred Embodiment Re~errillg now to the drawings, whereiJl tlle sllowlngs are for purposes of i11ustrating a preferred etnbodimellt of tllis inventioll on1y and ilOt for ~urposes oE 1imiting same, FIGU~E 1 SIlOWS in block diagranl rorm tlle a~paratus fo1-measuring parameters such as current density, temperatllre and potential in a relatively llars~l envirollment. q'lle apparatus comprises at least one probe ~ whicl~ ig e1ectrica11y conllected to a llousi~lg U tllat contaiJls at least one signal processing and signa1 recordillg means.
Extendlnc3 rrom tl1e l~ousl11g ls a trigger probe C ~or begin11LIlg t1~e rneasuril1g process. Wl1ile the invel1tive apparatus will be described and illustrated in con1-ectlor witll tl1e measuremel1t of parameters in an ~-Coat batl1 el1vironmel1t, it sl1ould be appreciated that tlle apparatus could be used in a wide variety of e11viroome11ts an~ t1~at tl1e current density measuri11g device incorporated i11 t1te a~paratus coul~1 ~e used separately.
In otller words, t21e curre11t density measuring device l~ can be utilize~ to measure currel1t density in a wide variety oE measuril1g enviro11me11ts and not ~ust in an electrodepositiol1 bat~1. Sucl1 envirol1me1lts include, for examp]e, electroplating and catl1odic protection systems.
More gel1erally, ttle current measurlng device disclosed 11erei11 could be used Eor making var:ious types oE direct current measureme11ts wllere relatively small D.C. currents (i.e. milliamps) need to be measured, e.g. measuring a currel1t in a con~uctor. ~ccorc1il1gly, lt s11ould be appreciated tllat wl1ile tlle device will be described as being useEul particularly for making current density measuremel1ts, tlle device can also be used for makiny various otller types oE current measurements.
Tl1e curre11t density sensor of FIGU1~ l wlll be discussed first herei11below. Witl1 reEerence now to tl1e electrical circuit diagram of FIGU~F 3, the curre11t density sensor accordlng to tlle present invel1tiol1 i11cludes an apparatus whlc11 measures a current ~ensity iJl a conductive medium tllat passes ti1rough a fixed diameter bore (~ as illustrated in PIGU~I~ 2) to produce a total current Io~ In PlGU~E 3, lO represents a one tur11 winding created by a transEormer core of a transformer 12 tl1at is constructed out oE square loop magnetic material l1avi11g a moderate saturation flux density and a ~s11arply defil1ed saturatio11 state. 'I'he transformer 12 is com~rised of a core about 1 31 ~073 wl~icl~ tl~e sillyle tu~ll wisldil-g 10; ~ir.st and .second center-taE)ped wil~dings 12a 12b: and first and second fee~ack windinys 1~ 2~ are wound. All windillgs a~-e related in directloll by tl~e dot convelltion illustrated in ~IGU~F 3.
pair of associated transistors 22 2~1 fullction to illterconllect tl~e center-~apped windil-g 12a to form a maglletlcally coupled oscillator clrcuit.
~ acl~ transistor 22 2~ acts as a switcll allowiny current to alternate1y pass tl~rougll windi-lg l~alves 1~ lG
oE tlle flrst center-tapped windillg 12a", ln alternate direCti.OllS, as dictated by wl~icl~ tratlsistor is in ~lle saturatioll state. ~eedback is generated by tlle win(lillgs 1~ 20 WlliC~l a~ coupled to tlle bases oE tlle Eirst and second transistors 22 2~. Wherl tlle ~lrst trallsl~tor 22 is in tl~e saturation state, current f1Ows into tl~e windillg 1~, developirly a positive voltaye orl tl~e wil~dlng 20 wi~l~
respect to a fixed ~C blas, ancl a negative volt~ge on tlle windillg 1~ as long as tlle trallsformer is not saturated.
Tllus tlle Eirst transistor 22 is maintailled ln a saturation state wl~ile the second transistor 2~ is clamped ofE.
Tllis conditioll llolds until the transormer core enters ~Iux saturation. ~s tlle core satul:ates, lts interllal magnetic field stops cllangillg, tl~us by Faraday's Law oE In~-lctioll tlle feedback vol~ages developed by tlle 2~ feedback windings 1~ 20 become zero with respect to tlle Eixed ~C ~ias. ~t t~liS point tl~e second transistor 2~
enters s~tur~tion also allowing cur~ellt to Elow to coil 16 of tlle Eirst center-tapped windillg 12~ s a~rul-t cllarlge in llet current produces a Eeedback pulr;e oP opposite po~arity to be generated in tile willdillgs 1~, 20, causinc~
tlle first tratlsistor 22 to be c1amped oEf and tlle second transistor 2~ ~o enter saturatioll.
Tlle second ha]r oE the oscillator period operates exactly ~s described above, except that tlle roles of the - 11 - I 3 1 ~1 0 7 3 first and second translstors 22 24 are rev~3rsecl. Tl-us sustallled o~cillati.olls are producecl by the circuit. Thircl alld rourtil resistors 31 33 oE tlle circuit apply a static I~C bias to botll oE tlle transistor bases sucll that under static norl-osci11ating conditlolls bol:h trallsistors are biased s11ylltly lnto saturation. lllis ellsures that tlle circuit wil.l begin osci11ation on power up regardless vr tlle previous magtlet1zation state oE tlle transformer 12.
The amount o time requiretl Eor eacll ha1f of tl~e oscillator peri.od .is determined by tlle llumber of tota:L
volt-secollds o~ f1ux linkage supportecl by tl~e core of tlle transEormer 12. Since t}le transformer core saturates at a we:L1 defllle(l total flux determlned by tlle maglletic materia1 cllaracteristics alld the yeometry of the core, tlle transEormer suE~E~orts a well deElrled number oE vo1t-seconds oE flux 1.inkage between saturatiLon in eitller of tlle two possible directions. lhe voltage aE~p1ied ~o the first center~tapE~ed windillg ].2a is a Eullctioll oE t:lle Elxed supp1y voltage and oE tlle voltage drop across the Eirst ~nd secolld resi.stors 30, 32 alld llence tlle current draw~ y tlle tr.alls~ormer 12 during tlle trans.i.tioll Erom one saturation st:ate to tlle otller. Tllis current call be ~etermined from tlle inductioll cllaracteristics of tl~e magnetic material alld tlle core geometry. Ille time required Eor trallsitioll ~rom one saturation state to the other is equal to twice tlle total flux ~ kage oE t:lle irst center~taE)ped willdillg 12a divided by tlle voltaye applied to wind.ings 1~ 16 . Ilence tlle frequellcy oE osci11ation can l~e determ.ined.
1lle externa1 current Io generates a static flux 3û witllin tlle transFormer 12 that ad~ls to or subtracts rrolll tlle Elux due to current in the Eixst center-tapped winclillg 12a. Since tlle saturation E1ux 11nkage oE tlle core is îixed, tlle amount oE Elux 1inkage tllat the rirst and seconcl transistors 22 2 4 must apply to saturate the transEormer 12 is ~roportionally lncreased or re(l~lced depelld.illg llpOll tlle direction of lo~ Changillg tlle transitloll current drawn by tlle transformQr 12 alters tlle voltage ~rop across tlle rirst resistor 3U or the second reslstor 32 t~lus cllangillg tlle voltage appl.te~l to windings 1~ 16 ~y an amount proportional to Io~ llence windlngs 1~ lG and respective resistors 30 32 sllare tl~e voltage alplled ~y tl~e transistors provlding a lligllly sensitive an~ stable device. Since the transition time is inversely proportional to tlle voltage applied to wind3.nys 1~ lG tl~e transition time is altered in proportion -to XO. ~ecause lo acts in opposite directions wit}l re.~ect to t]le two coils 1~ 16 oE tlle Eirst center-tapped windirlg l~a one llalf oE
the oscillator perio~ is shortelled by exactly tlle a~ount 1~ tllat tlle otller hal is lengtllelle~. Tllus tlle net oscil].ator Crequency is not cllaJlged by tlle appllcation o~
Io but tlle symmetry oE the oscillator output is cllangecl almost in direct proportion to Io~
~lle circuit tllus far ~escribed is capable oE
measuring current dellsity due to tl~e presence of the rirst and second resistors 30 32. llle transitioll time is proportional to the voltage applied to the two coils 1~
16. Io causes more or less currellt to be drawn by tlle coils 1~ 16. Changillg tlle current tllrougll tlle resistors ~5 30 32 cllanges tlle volt~ye Oll tlle coils 1~ 16 - tllus also challgillg the transitioll time-. The transition time diference between the two llalves enables one to derive currellt dellsity.
First and secolld diodes 3~ 36 along witll fiftl! alld si.xth resistors 3~ ~0 in the circuit strip tlle negative llalf of tlle collector voltage o each transistor to provide clean square wave signals. ~ach signal is in a lligl~
state whell its respective transistor is in saturatioll alld in a low state when that transistor ls cut oEE. Diodes 34, 36 alol-g witll resistors 3~3, ~0 provide llearly ideally symmetric square E~ulses, allowiny higllly accurate measuremellt:s .
~ plllrality of resistors, namely sevelltll, eiglltll, rlilltl~, and terlth resistors ~2, ~ 6, and ~-3 toc~etller witl~ a plur.l1ity of capacltors namely flrst, second, tlllrd, an~ ~ourth capacitors 50, 52, 5~, and 56, apply a pi-section low pass Eilter to eacll llalE oE tlle osclllator output, to remove lliyll oscillator Erequellcy OUtptltS. Tlle resultillg slowly varying DC signals are -tllen proportional to the respective ~mounts oE "on" time that eacll llalE Or tl~e oscillator experiences.
~ n ampliLier 70, wllicll is preferably a preclsion monolitl~ic instr-lmelltation ampliEier, measures ancl ~mplifies t~le dlEEerence in voltage oE tlle two filtered oscillator outputs. The use oE an instr-lmelltatioll amplifier instead oE a simple operational ampliEier is advalltageous because it provide tlle instrument Wit]l less clrit and tiyllter calibratioll tolerances tllan a simple operational ampliEier could provide. The device has a very stable volt~ge gain, a lligll input impedallce and a low output impe~lance. It can be sllowll tl~at tlle clifferential vo1tage is, within a deEilled ran~e oL Io~ proportional to Io~ T~us, the circuit provides a cont~ uous outpllt voltage tllat varies in direct proportion to Io~
Eleventh and twelEth resistoxs 72, 7~ are in circuit witll the ampliEier 70 to set tl~e amount oE voltage gain applied by the il1strumentat~n ampliEier -to tlle dlferel1tial voltage. This provides a means for calibrating tlle instrument.
'l'lle second center-tapped winditly 12b has first an~
second halves 80, ~32. The windillg halves ~30, ~2 togetller with a tl~irteenth resistor 8~ provide a means to compensate for small O~ltpUt ofEsets due to compone~lt toLerance er~ors, providiny a mealls to set a zero ou~put value.
~ urality o~ additlotlal Eilter capacitors n5, ~n, arld 90 are advalltageously provided in the circuit as power supply coupling capacitors to provide improve~ circuit stability.
'l'he currellt sensor descrihed hereitl call ~easure DC
currellts paSsilly tllrougll the bore of tlle trallsformer.
'rilerefOre, I)C CUrrellt dellSltieS Call be measured as defined ~o by the rixed area of the bore. The device can be calibrated to measure a currellt dellsity up to 30 m~/cm~
with a precision of better thatl-l- .9 m~/cm2.
'l'he probe ~ i]lustrated in FlGU~E l also includes a temperature sensor. Measuring tlle temperature is use~ul in a probe employed for measurill~ parameters in all electrodeposition process. The temperature sensor indicates whell tllat ~robe enters the electro(leposition batll since the temperature will increase from amblellt (clrca 20~C) to batll temperature (circa 370c). The temperature of the electro]yte bath is an importallt parameter in tllat the maintellallce of proper chemlcal kinetics at tlle electrolyte - metal boun~ary is directly related to temperature.
~ecaùse di~fusioll processes occurrillg at tllis boundary are lligllly temperature dependellt, the measurement of temperature can ~e critical to tlle evaluatioll and ullderstalldil~g of tlle ~-Coat process. Thus, all increase~
local temperature could imply a ~ocalized resin depletio itl the bath from a lac~ of mixlng.
Witll referellce now more particularly to FIGUI~E ~, the temperature sensor is suitably a transducer comprising a convelltiorlal type K thermocouple lO0 and a ~lo~olithic thermocouple amplifier unit 102. These can be attaclled to tlle same circuit board as the currellt density sensor i~
desired. The tllermocouple is electrically isolated from tlle enviroll1nent in wl~icll it is sensincJ the temperature in order to preclu~e possible damage to the amplifier utllt 102 by lligll voltages appearing on the thermoco~lple leads w11ell immersed in arl electrically conductive medluln SUCII as all E-Coat batll. lhe tllermocouple amplirier provldes ~ volta~e outl)ut corresponditlg to sensed temperature. The approximate linear transEer runctioll oE the thermocouple o~
tlle preferred embodlment is 10 mlllivolts per degree Centigrade .
]0 ~lso provided :in the probe ~ is a voltage or potential sellsor. Mensuremellt of tlle voltage or electric pOtelltial i8 desirable in tllat such information can be loosely inclicative o~ tlle relative amoullt oE ~esin ~llm build on tlle metallic substrate in t:lle vicinity o the probe by virtue oE the high resistivity o~ the deposited film witll respect to tlle water-tllill resin E-Coat batl~.
Witll re~erence now more particularly to FIGUIIE 5 the voltage sensor 10~ comprises an electrically conductive sensing elemellt 110 wllich may be a conductive plate or a tube t21at is exposed to tlle measurement envirollmellt in wllicll potential is to be measured. lhe element 110 i5 conllected to a resistive voltaye divLder network comprising resistors 112 114. ~he vol~age sensor ls sultably containe~ on the same circult boar~ as tlle temperature sensor and tlle current del-sity sensor, iE that is desired. rlhe voltage divider network acts as a 20 to 1 attenuator (i.e. 20 volts in yields 1 volt out) with an input impedance oF approximately 20 megollms. ~`lle importance of this relatively higll input impedallce will be :30 discussed hereirlbelow.
llle probe ~ illustrated scllem~tic~lly in ~lGUI~ 1 ls illustrated in perspective ~orm in EIGUIIE 2. ~s shown ln FlGUII~ 2, the sensors on the probe are preferably at least partially encapsulated in a probe body 130 tllat is made from an e].ectr~ca1l~ all~ tilermally il-stllating illert materi.al sucll as sllicolle rubber to protect atld illSUlate tlle meas~ emellt electronics Erom tlle electrical and tllermal llazards of tlle measurement envlrollmellt. Tlle encapslllatioll protects tl~e sensors from corrosion and rom tlle electrolyt.ic me(lium al-d also acts as mecllanical protect.ion for tlle measurement electronics and tlle interllal mecllanical assembly. ~s mentlolle~ above, preFerably tlle current density sensor, tlle temperature sensor, and the potential sensor sllare a common circult board wllicll ls not visible .in ~IGUI~E 2.
'l'he volta~e or potentlal seosing e1ement 110 ie exposecl to tlle measurement el~virollment ~ut tlle currellt clellsity sensor is completely encapsulated. ~s melltiolled, ti~e tl~ermocouple (not visible in ~lGU1113 2) .Ls covered by a slleath 131 to electrically lsolate it Erom the measurement envirorlmellt .
PreCerably, convelltional suction cups 132, 13~1 are provided oll the body 130 as a means Eor securely fastelling tlle probe in the measurement envirollment in a readily detachable manner. Suction cups ofEer advalltages over otller mecllanical attachmerlt mealls sucll as magnets or the like due to the Eact tllat magt-ets induce a static magnetic Eield in tlle vicinlty oE the probe alld tllis could cause di.stortions in both tlle process beill~ measure~l alld tlle mecllanism by wlli.c}l tlle current densities are measurecl.
Preferably, the suctiOIl cups are made oE a suitable elastomeric material such a rubber. 'rhe suction cups ~a be provided on more tllan one surEace oE the probe body 130, if tllat is ~esired, to allow some Elexibility in tlle securing oE the probe bo~y to a work plece i~l the measuring environmellt .
Electrical power to the probe assembly ~ is provided tllrougll a conductor cable 1~0 wllich also provides a patl for electri.c~l signa1s representing tlle measured quantities to be tran~mitted. The cable l~o is preferably double sl~ ed to reduce noise plckup. Power for the probe can be provi~e~ tllrougll a su.itable convelltiollal power supply wllicll can be an 1~3 vo.l.t DC gel cell power su~ply 1~2 positioned .in tlle enclosure B as SllOWIl in ~IGUI~E 1. 'l'lle raw power is preferably regu1ated dowll to ~-15 volt DC and -15 volt ~C on tlle cixcuit board ~y mealls of convelltional mono1itllic voltage regu1ator integrated circuits. I'he regulated alld filtered power provides all the power re~uirements of the measuremellt electronics contained in tl~e probe assembly.
1'lle cal)le 1~0 o a typical probe utilizes eigllt conductors as is i.llustr~ted in FlGUI~E 2. Two of tlle conductors are for tlle plus and minlls 1~ volt UC raw power flowirlg to tlle probe. Three cond-lctors are provided, respectively, for tl~e curren~ dellsity slgnal, tlle temperature s.ignal, alld tlle potential signal. Two additional conductors are provided for thermocouple testing. Finally, olle conductor is l~rovide~ as tlle power supply/sic~llal ground lille~ e sl~ield of the cable is tled to tl-e E~ower supp1y/signal groulld at tlle power supply/siynal output end of -the cable to prevent currellts induced in tl~e shield from causiny erroneous voltage slliEts to appear between ground potent~al at tlle power supply ~nd tlle slgnal ground at tlle probe.
Witll reference now again to F:tGU~E 1, tlle measurement system can comprise a plurality oE pro~es ~
together witll tlle power supply 1~2 for them aR well as a data acquisition unit 150 and a contro1 computer 152.
Include~ in tlle central computer is a CPU 152a alld a memory 152b. Wllile three probes are illustrated in FIGU~E 1, it is contemplated that as many as nille probes would be used ill a full measurement system. Ilowever, it should be 1~ 1314073 aE~preciated tl~at more or less tlIan tllat number oE proI~e~:
could be used depencIiIlg Otl tlle number of probes requ Lred for a parl:lcular appl icatlon.
It sl~ould be notecl tl~at a divider ground is connectec~ common wll:l~ the system ground for conlIectillg all vr tIIe previously mentiolIed clrcuits into one grouncl.
1~ ~ystem groullcl 154 can be colIl~ected to tlle metallic substrate v.ia alliyator clips 1~6 or a simllar meal~s itl or~er to reEerence all potential measurements to the me ta l l ic subs tra te .
'rl~e llousing B preerably accommodates tlle power supply 1~2 t11e dal:a unit 150, ancI the computer 15~ and p~eferably comprises an envirolImelltally secure enclosure 15~ iclI C~l~ be selectively opened as necessary. In one preferred embodiment tI~e system comprises a IIew1ett Packard 3~ clata acquisition unit an~ a IIewlett: Packard IIP-75 computer. UOtlI the data acqlIisition UIIit 150 al~d the computer 152 are preEerably providecl wi th an internal power means WlIic}I carI be reclIargeable I-ickel-cadlllium batteries or tl~e like (not illustrated). ~lternatlvely, the power supply 142 for tIIe probes could also be suitably con~igured to supply power to the control computer and the data ac~uisition unit if desired.
'I'lle data acquisition UIIit 15(~ receives tl2e measured values rom the probes under control of the computer in t~le form of voltage measurements. q'he computer ls also respollsible ~or storing t21e collecte~l data until the ell~ ol~
the measurement cycle at wllicII point tlle data may be store~I
oII magnetic media or kept in tlle computer ' s contiIluous memory. '1'12e data acquisition unit and tlle computex communlcate via a suitable insl:rumeIlt loop serlal communications link 154 which in tI~e preferred embodimeIlt is a IIewlett E'ackard InstrumeIlt Loo}~ (IIP-IL) lillk.
-19- t3~073 Durillg tlle measurement proces~, only tlle co~ltrol connputer, tile data acqUiS.itioll unit, and the power supply are contaitled illside tlle envLrollmentally secure enclosure B. Tlle probes ~ are connected to the power sl~pply 1~2 alld tl~e data ac(~ui.sitioll ull.lt 150 via convellti.ol~ll waterprooE
p.last.ic collnectors ~not lllustrated) on the enclosure 15~
in order to maintaill tlle envlronmental illtegrity o~ tha ellclosure and to prevellt exposure of tlle computex 152 and the data acquisiti.on unit 150 to tlle measuremellt lo envi.ronment.
In tlle preferred embodiment, the data acqulsition Ul-lit ls capabl.e o~ ac~uirlng data from 30 c~lallnels.
Ilowever, tl~e measuremel~t system llerein envisioned utilizes only 27 cllanllels Eor data (9 pr.obes) and one c1lannel as a system tri.gc3er. It is evident tl~Qt data ac~luisitioll UllitS
llavlllg other cl~anllel capacities can also be utilized as needed. ~ter the data acquisition un.it ancl tlle comp~lter llave beell placed in the enclos-lxe and power )las been applied to tlle probes, the probes are attaclled via the suctloll cuE)s 132, 13~ to tlle metallic body which will be exposed to tl~e measuremellt envirollme]lt. Ollce the probes are attaclled, tlle data acquisition program in the computer can be started. ~ctual measurements will not be take until tlle system is trigyered via the trigger prol~e C.
Tl~e trigger prol~e can coniprise a rectangular plastic block llousillg 160 in which a pair of wires lG2, 16~ nre securely Eastened. The ends oE the wires have been stripped oE insulation and have been solder tinlled leaving approximately one half inch oE wire exposed to the measurement environmellt. The block 160 also contai31s a pair o cera1nic ma~nets 166, 16~ wllicll are used to al:tacll tlle trlgger probe to the metallic substrate. Tlle trigger probe can also be provided with a removable proteat1ve - 20 ~ 1314073 sl~eatl) 170 to protect the probe wlres ]62, 16~1 wl~en not in use, and also to prevellt accldental triggering during tl~e attacllment o~ the probes.
Witll rellerellCe llOW to FIGUl~E 7, the funct~o~ g oE
tl~e software routine for acquiri]lg dat:a is tl~ere il1ustrated. 'I'l~e computer waits in loop examinillg challlle zero of tlle data acquisitioll unit C11anne1 zero, previously conrigured for performing a two wire res1stance measurement, is tlle cllanlle1 usecl to trigger tlle measurement cyc1e. 'l'riggering occurs wllen the tric~ger probe i5 immersed i n the measurement enVirol7ment and "sees" a resistance betweell tlle two wires tllal: is less thall 80, 000 ollms, as sl~owll in block 172. I~fter trigyering, base line measurements can be made for each of the current density circuits in tlle several probes ~. Tllese are sZ:ored in tlle computer 152 and used to zero out any offsets that may be developed .
1~ variable software w~it routine is suitably programmed into memory 152b oE tlle computer 152 (FIGUl~E 1) so that tlle program will wait a specified number oE seconds before commencillg data collection aEter triggerillg. Sucll a wait period, as showll in block 17~1, is higll1y desiral~1e since untler certain measurement conditions tlle measurement envirollmerlt may have to stabilize . Tlle max imum number of Z5 data sets in tl~is embodimellt is firty and is determllled by tlle amount of physical memory contailled in the computer as tlle computer ' s memory is apporl:10ned lor both program and clata storage. ~ minimum samp1e intervn1 between measuremellts is 1. 5 seconds . In other words, tllis pex iod ~0 of time must elapse between each two measurements as show in block 176. The interval is constrailled by tlle data acquisition unit 150 and the finite 1ength oE time tllat is needed to make eacll measurement. In tlle preEerred embodiment, tlle minimum sample interva1 is constrailled by tlle IIE~ 3~ data unit's dual slope ,iIltegratl~g aIlalog to r3kJitctl eoIlverter. In general t1le absolute minimum measuremeIlt i.I~terva.l would be l.imited oIIly by tlle probe ' s baI~c3w idtlI . Sinee tlIe probe has a -3 db bandwidtIl oE 3-~1 IIz, tlle sampliny ~requeney would be limited to approx.imate.I.y l `5 to 2 IIz.
'l'I~e procJram qcIel.-ies wI~etIIer tlle predetermillc?d nuIlII~er Or Cl~ l S~ 19 ~c?t~ o.l.leet~,~3, as sIIowII ~ ).loek 17~3. lr IIOt, tlle pI-oc~r.llll returIls to tIle san~l-1e interval t.Lme ~lelay 1 r) t~uery. (JpoI~ eompl?t.i.oIl oE dat a eolleetioll, tlIe program .i.Il.il lates a rlueI,y wlletIIer tlle user would l.i.ke tlle )Iew.Iy c,ol].eetec3 ~Iatil to be storect oIl macJIletie metlia ag a baek-up t)reeaut.i.oIl ~s. sI~owIl .i n bloek 17~3. ~ter progrilm LerInillatiol~, l:lle c3ata .is maiIltallled in tlle eompul:eI. 's .I 5 COIltiIIUou~S memory Ullt.i.l ~3eletec3. oIlee data eolleetiolI l7as beeII eomplet:ed, tlle eompllter C;lll be tuI.l~e~I ol~ aIlcI
.isc,oIllleete(I rrom tlle clnt:a aeq~ slt;.oll uII.i t aIlcl remove~l Jlrom t,lle eIleI.osure. Wi.th tlIe t1ata c:torecl saCely iu tlle eomputer's memc)ry, or .;Il memory aIIcl OIl a ma-,3Iletie mecl.i.I.llll, 2(1 all .i.Il~Iefilli.te amouIlt oC t1me may e1.apse beCore tlle ciata ;s ret:rievecI. ~[ter tllc, ;,II~strUmeIlt lIas beeIl remove~t Lrom tlIe measuremeIlt eIlv,irollmellt, tlle eomput:?r ean ~e c,~oIllIeetecl to a su.it:a~1e eoIlvelltioua1 prlIlter (llOt illu~tl~Ited) for pri.Ilt.;l~y or pI.ottlIlcJ tlle eolleete~t data. q'Ile IlP-lI
~5 illstrument looE~ 15~ Call be usect to illter~aee tl~e t)riIlter witll tJ~e eomE~uter 152 c3ur1IIg text aIldi grapI~ia outp~t opera tiOllS .
1~ suitable ~lal:a eolleetlon prograIn reacls tlle eolleete~3 (3at~ allct priIlts tlle E~ol~e~lt;lal, eurl-eIlt dellsity aIld temperature data in a l:able fo~m Lor ea~y vi.suc-l1 eompar.isoIl. ~fter all tlIe tlata I~as bee1~ prlIlte~I, a su.itable seeollcl progt.;Im, Wllicll Ci311 be Pl t)lo~tiIlg E-rot3ram ean I~e eal.le(l ill or(ler to p10t: magIlitude~s o~ poteIlt.ia I, eurrent c]ellsity allcl teIllperature agEI.t.llst tlmce.
Wit.~l referellce now to I~GUI~I~ 6, one E;u:Ltable measuremel~t environ:nellt for t)le ~reviously clescrihed measurement i.llstrumentatloll is an automotive electrocoatilly batll. ~rl automotlve electrocoating facillty wllicll is maintailled at all automo~ile plant comprises a suitable tal)k ]90 ~or hol(lil~g tlle E-Coat bat11. ~rhe tank can ~e up to 150 ft. lon~, 12 ft. w;de, 10 ft. high, and opell on tlle top.
plurality of automobile bodies are moved througll tlle tallk ill a relatively conti~luous process. One sucll ~utomoblle lU body 192 is sl~own in ~IGU~E 6. 'l'lle body 192 acts as tlle catllode o~ tlle electro~epositioll system. Suita~le anode~.
19~ are provided on the walls o~ tlle tank. In various electrocoatillg tanks, the anodes can ~e located l diE~erent places Otl tlle tatlk alld Ca11 have varying shapes.
'~'he electrocoating enviro1lmellt is a hostile en~irollment wlllcll is q-lLte ~le~tructive. 'l`l~e E-Coat batll itself is a water tllln electrolytic resin mixture tllat is kept in t11e tank 190 under constallt turbulent agitatioll.
One such resin compositlon is a cationic resill whicll contaills blocked isocyallate curing agellts and is available from ~PG Indllstries, Inc. under the trademark UNIrl~lM~.
Tlle E-Coat process by wllicll metallic parts such as car bodles or parts of car bodies are coated wit11 a polymer resin layer involves submersion of tlle parts in the bath and tlle application of a DC voltage between the car part or body W11iCll acts as the cathode, and the anodes 19~ locatecl on the tank walls. ~hell the proper condit1OIls occur at tlle metal surface, i.e. correct pll, minimum currellt density, etc. the resin precipitates OlltO t11e Illetal.
Since the metal conductor measurillg batll ~otential can also act as a cathode, it woul~ also be prone to coating just as the other metal parts in tlle tank i~ the current flowin~ tllrough the circuit, and hence the current density on the conductor, were above the minimum required for deposition. T1le high impedance (20 megohms) of tl~e circuit en~.ures t1~at any currents flowi11g tl1roug1~ tlle measureme11t circuit wlll be below tlle thres11old require~
for such c1epositiol1 to occur.
Since the ~rocess l~ baslcally a curre~1t driven process, it is necessary to know what the curre11t del1sities are at various locatiolls 011 the c~r body in order to obtai.n t~e most ul~ orm resll1 c1epos~tiot) and to provide a ~et~er understan~ir1g o ~10W the process is working. pro~lems arise bec~use of the cl1al1ging geometries encou1~tered wl1en dealil1g Witl1 ~1;.Eferent automoblle, van, and t:ruck bodies in relatiol1 to tl1e fixed anode geometries oE the coati I~CJ
tanks. 'l~llere~ore, a u11iform conting t1~ickness along the o~1tside surface oE tlle car body is di~ficult to acllieve.
1.~ Obta.il1;.11c3 a mil1.lmum coating t11ick11ess on tl1e corrosiol1 prone inter1~al cavi.ties of tlle vellicle body suc11 as rocker panels, fender wells, door pillars, etc. i5 even more di r ficult to ac~1ieve.
Currellt density, along with pol:elltial antl ~o temperature meaSuremel1ts can provide an insight illtO
met11ods by wl1ic11 better coatings can be obtained, e.g.
t11rough a modiEicatio11 of the deposition tank geome~ry Ol^
changes in the design of t11e body parts or bodles tllemselves .
2~ T1le apparatus according to tlle present lnve1ltion will provide a better un~erstal-ldil~g of the physics o the electrocoat process by providing ~reviously unobtai1lable data co11cerni11g the currel1t densities requ.ired for the coating process. It may also ~acilitate improvements in ~0 t1~e composition of the electrocoat resin by allowlng better testing of new formulatio1ls. ~s an end result, vellicle manuacturers will obtain more evenly coated vehicles. Uy obtaining improved coating of corrosio11 prone areas, vehicle manufacturers will then be able to oEEer longer - 2~ - 1314073 corrosion warral~ties and acllieve a red~lctioll oE costs due to warrallted corrosion-related repairs.
Tl~e invelltioll llas been described wltll reEerence to a preerred embodiment. obv.iously, alterations and modiricati.olls will occur to otllers upon a reading and understalldill~ oE tllis speciEication. It is i~ltended to include all SUCIl modifications an~ alterations insoEar as they come wit~lin the scope of the appended claims or the equivalents tllereof.
Claims (34)
1. A current measuring device comprising:
a transformer adapted for placement within a secondary flux source;
an oscillator for periodically placing said transformer in forward and reverse flux saturation by application of a periodic voltage to an input winding thereof, whereby a period of the forward and reverse flux saturation is affected by the secondary flux source;
a pair of multi-section low pass filters operatively connected to an output winding of the transformer for generating an output signal including a slowly varying DC signal proportional to an on time of said transformer; and, amplifier means for processing the output signal of said pair of multi-section low pass filters, wherein said amplifier output is representative of a current sensed by said transformer.
a transformer adapted for placement within a secondary flux source;
an oscillator for periodically placing said transformer in forward and reverse flux saturation by application of a periodic voltage to an input winding thereof, whereby a period of the forward and reverse flux saturation is affected by the secondary flux source;
a pair of multi-section low pass filters operatively connected to an output winding of the transformer for generating an output signal including a slowly varying DC signal proportional to an on time of said transformer; and, amplifier means for processing the output signal of said pair of multi-section low pass filters, wherein said amplifier output is representative of a current sensed by said transformer.
2. The device of claim 1 further comprising a means for compensating for small output offsets due to component tolerance errors.
3. The device of claim 1 further comprising a means for improving the sensitivity of the transformer, said means for improving comprising a pair of voltage-sharing resistors.
4. The device of claim 1 further comprising a means for calibrating said amplifier.
5. The device of claim 1 further comprising a means for providing improved circuit stability for said oscillator and said amplifier.
6. A system for measuring parameters in an environment having a metallic body positioned in an electrolytic medium, comprising:
a current density sensing means positioned adjacent the metal body in an non-invasive manner, the current density sensing means including, a transformer including an input winding and output winding, an oscillator for periodically placing the transformer in flux saturation by application of a periodic voltage to the input winding, and means for generating a slowly varying DC output level signal from a signal received from the output winding in accordance with a timing of the flux saturation as influenced by current in the electrolytic medium;
an electrically and thermally insulative housing means for enclosing at least a portion of said current density sensing means in an electrically and thermally non-conductive manner;
a computer means for processing the current level signal from said current density sensing means; and a wiring means for electrically interconnecting said computer means with said current density sensing means.
a current density sensing means positioned adjacent the metal body in an non-invasive manner, the current density sensing means including, a transformer including an input winding and output winding, an oscillator for periodically placing the transformer in flux saturation by application of a periodic voltage to the input winding, and means for generating a slowly varying DC output level signal from a signal received from the output winding in accordance with a timing of the flux saturation as influenced by current in the electrolytic medium;
an electrically and thermally insulative housing means for enclosing at least a portion of said current density sensing means in an electrically and thermally non-conductive manner;
a computer means for processing the current level signal from said current density sensing means; and a wiring means for electrically interconnecting said computer means with said current density sensing means.
7. The system of claim 6 further comprising a temperature sensing means and a voltage sensing means each of which is located adjacent said current density sensing means in said housing means, wherein said wiring means also interconnects said temperature and voltage sensing means with said computer means so that said computer means can process the data therefrom.
8. The system of claim 6 further comprising a data acquisition means for processing an output signal from said current density sensing means before said output signal is sent to said computer means.
9. The system of claim 8 further comprising an enclosure means for housing said computer means and said data acquisition means in an environmentally isolated manner.
10. The system of claim 8 further comprising a trigger probe means for setting the initiation of a measuring cycle in the apparatus, said trigger probe means being in electrical contact with said data acquisition means.
11. The system of claim 10 wherein said trigger probe means comprises a housing, a means for securing said housing to the metallic body, and at least one sensor exposed to the electrolytic medium.
12. The system of claim 6 further comprising a means for securing said housing means to said metallic body.
13. The system of claim 6 wherein said current density sensing means comprises:
a toroidal transformer;
a square wave magnetically coupled oscillator which drives said toroidal transformer;
a pair of voltage sharing resistors to improve the sensitivity of said transformer;
a pair of multi-section low pass filters which monitor said transformer; and a fixed gain differential instrumentation amplifier for processing an output of each of said filters.
a toroidal transformer;
a square wave magnetically coupled oscillator which drives said toroidal transformer;
a pair of voltage sharing resistors to improve the sensitivity of said transformer;
a pair of multi-section low pass filters which monitor said transformer; and a fixed gain differential instrumentation amplifier for processing an output of each of said filters.
14. The system of claim 6 wherein a plurality of current density sensing means are provided and further comprising:
a plurality of housing means, each enclosing at least a portion of one of said current density sensing means; and a plurality of wiring means, each connecting a current density sensing means in one of said housing means to said computer means.
a plurality of housing means, each enclosing at least a portion of one of said current density sensing means; and a plurality of wiring means, each connecting a current density sensing means in one of said housing means to said computer means.
15. The system of claim 6 further comprising a means for providing electrical power to said current density sensing means.
16. A current density sensing means for directly measuring parameters adjacent the surface of a metallic body in contact with a surrounding electrolytic medium, being sufficiently sensitive to measure current density in a range of milliamps per square centimeter comprising:
means for periodically placing a transformer into magnetic flux saturation by application of a periodic voltage to an input winding thereof;
low pass filter means connected to an output winding of said transformer for generating a slowly varying DC signal proportional to detected alterations in periodicity of the magnetic flux resultant from a current flow in the metallic body;
amplifier means connected to said low pass filter means for detecting alterations in periodicity of the magnetic flux resultant from a current flow in the metallic body;
a temperature sensing means for measuring a temperature in the electrolytic medium adjacent said current density sensing means;
a voltage sensing means for measuring a voltage in the electrolytic medium adjacent said current density sensing means, and said voltage sensing means.
means for periodically placing a transformer into magnetic flux saturation by application of a periodic voltage to an input winding thereof;
low pass filter means connected to an output winding of said transformer for generating a slowly varying DC signal proportional to detected alterations in periodicity of the magnetic flux resultant from a current flow in the metallic body;
amplifier means connected to said low pass filter means for detecting alterations in periodicity of the magnetic flux resultant from a current flow in the metallic body;
a temperature sensing means for measuring a temperature in the electrolytic medium adjacent said current density sensing means;
a voltage sensing means for measuring a voltage in the electrolytic medium adjacent said current density sensing means, and said voltage sensing means.
17. The apparatus of claim 16 further comprising a securing means for affixing said housing means to the metal structure.
18. The apparatus of claim 17 wherein said securing means comprises at least one suction cup.
19. The apparatus of claim 16 wherein said current density sensing means comprises:
a toroidal transformer;
a square wave magnetically coupled oscillator which drives said transformer;
a pair of voltage-sharing resistors to improve the sensitivity of said transformer;
a pair of multi-section low pass filters which monitor said transformer; and, a fixed gain differential instrumentation amplifier for processing an output of each of said filters.
a toroidal transformer;
a square wave magnetically coupled oscillator which drives said transformer;
a pair of voltage-sharing resistors to improve the sensitivity of said transformer;
a pair of multi-section low pass filters which monitor said transformer; and, a fixed gain differential instrumentation amplifier for processing an output of each of said filters.
20. The apparatus of claim is wherein said current density sensing means further comprises:
a means for compensating for small output offsets due to tolerance errors;
a means for providing improved circuit stability for said oscillator and said amplifier; and, a means for calibrating said amplifier.
a means for compensating for small output offsets due to tolerance errors;
a means for providing improved circuit stability for said oscillator and said amplifier; and, a means for calibrating said amplifier.
21. The apparatus of claim 15 further comprising a means for providing electrical power to said current density sensing means and said temperature sensing means.
22. A method of obtaining data concerning the deposition of a polymer resin onto a metallic substrate positioned in an electrolytic medium held in an electrocoating tank, comprising:
periodically placing a transformer into flux saturation:
generating a slowly varying DC signal representative of current density in said electrolytic medium in accordance with a fluctuation of a periodicity of said flux saturation;
securing said transformer to a metallic substrate;
lowering said metallic substrate into an electrolytic medium held in an electrocoating tank;
passing a current through said electrolytic medium thereby depositing a polymer resin contained in solution in said electrolytic medium onto said metallic substrate;
detecting a current density in the electrolytic medium adjacent said transformer; and, recording information regarding current density detected by said transformer.
periodically placing a transformer into flux saturation:
generating a slowly varying DC signal representative of current density in said electrolytic medium in accordance with a fluctuation of a periodicity of said flux saturation;
securing said transformer to a metallic substrate;
lowering said metallic substrate into an electrolytic medium held in an electrocoating tank;
passing a current through said electrolytic medium thereby depositing a polymer resin contained in solution in said electrolytic medium onto said metallic substrate;
detecting a current density in the electrolytic medium adjacent said transformer; and, recording information regarding current density detected by said transformer.
23. The method of claim 22 wherein a plurality of current density sensors are provided, each being secured, in a spaced manner, to said metallic substrate and further comprising the step of activating each sensor to perform said step of detecting current density.
24. The method of claim 23 wherein said step of activating each sensor is repeated a set number of times.
25. The method of claim 22 further comprising the steps of:
providing a trigger probe securing said trigger probe to said metallic substrate;
sensing a resistance less than a preselected maximum with said trigger probe; and, subsequently triggering said step of detecting current density.
providing a trigger probe securing said trigger probe to said metallic substrate;
sensing a resistance less than a preselected maximum with said trigger probe; and, subsequently triggering said step of detecting current density.
26. The method of claim 22 further comprising the step of reading out information obtained during said step of recording information.
27. The method of claim 22 further comprising the steps of;
sensing a temperature in said electrolytic medium simultaneously with said step of detecting current density; and, recording information regarding temperature.
sensing a temperature in said electrolytic medium simultaneously with said step of detecting current density; and, recording information regarding temperature.
28. The method of claim 22 further comprising the steps of:
sensing a voltage in said electrolytic medium simultaneously with said step of detecting current density: and, recording information regarding voltage.
sensing a voltage in said electrolytic medium simultaneously with said step of detecting current density: and, recording information regarding voltage.
29 23. The method of claim 22 further comprising the step of making a base line current density measurement before said step of detecting a current density.
30. A current measurement device comprising:
a transformer including a core, at least one input winding, and at least one output winding;
oscillator means for generating a square wave to induce forward and reverse saturation flux in said core;
means for communicating the square wave to an input winding of the transformer:
means adapted for placement of said core in an associated current field, whereby a flux level in said core is influenced thereby;
means for generating a composite signal, operatively connected to an output winding of the transformer, indicative of a flux level of the core;
means for generating a slowly varying DC current level signal indicative of a portion of said composite signal attributable to the associated current field;
means for establishing an offset flux level in the core;
and, means for amplifying the current level signal.
a transformer including a core, at least one input winding, and at least one output winding;
oscillator means for generating a square wave to induce forward and reverse saturation flux in said core;
means for communicating the square wave to an input winding of the transformer:
means adapted for placement of said core in an associated current field, whereby a flux level in said core is influenced thereby;
means for generating a composite signal, operatively connected to an output winding of the transformer, indicative of a flux level of the core;
means for generating a slowly varying DC current level signal indicative of a portion of said composite signal attributable to the associated current field;
means for establishing an offset flux level in the core;
and, means for amplifying the current level signal.
31. The current measurement device of claim 30 further comprising a means for varying a characteristic of the composite signal in accordance with said current level signal.
32. The current measurement device of claim 31 further comprising a means for inducing an initial flux level in the core.
33. The current measurement device of claim 32 further comprising a means for generating a voltage level in accordance with said composite signal, and wherein said current level signal is comprised of said voltage level.
34. The current measurement device of claim 30 wherein said means for amplifying comprises a device having a very high voltage gain, a high input impedance and a low output impedance.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US155,205 | 1988-02-12 | ||
| US07/155,205 US4956610A (en) | 1988-02-12 | 1988-02-12 | Current density measurement system by self-sustaining magnetic oscillation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1314073C true CA1314073C (en) | 1993-03-02 |
Family
ID=22554488
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000590332A Expired - Fee Related CA1314073C (en) | 1988-02-12 | 1989-02-07 | Current density measurement system |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4956610A (en) |
| CA (1) | CA1314073C (en) |
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| US3748899A (en) * | 1972-06-12 | 1973-07-31 | Us Navy | Conductivity and temperature sensing probe |
| US4004989A (en) * | 1974-04-18 | 1977-01-25 | Olin Corporation | Method for automatic adjustment of anodes based upon current density and current |
| AT337829B (en) * | 1974-10-28 | 1977-07-25 | Vianova Kunstharz Ag | MEASURING ARRANGEMENT FOR DETERMINING THE HANDLING PARAMETERS OF ELECTRO-DIPPING LAMPS |
| US4037194A (en) * | 1975-12-17 | 1977-07-19 | Boyden Willis G | Current sensing alarm circuit for a motor vehicle |
| JPS5459199A (en) * | 1977-10-20 | 1979-05-12 | Olympus Optical Co Ltd | Ion concentration measuring apparatus |
| US4207566A (en) * | 1978-05-05 | 1980-06-10 | American Aerospace Controls, Inc. | DC Current level detector for monitoring a pitot tube heater and associated method |
| EP0010921B1 (en) * | 1978-10-30 | 1983-02-09 | Hitachi, Ltd. | Direct current detecting device using saturable reactors |
| US4278938A (en) * | 1979-07-27 | 1981-07-14 | Bell Telephone Laboratories, Incorporated | Electromagnetic arrangement for measuring electrical current |
| DE3030664C2 (en) * | 1980-08-13 | 1982-10-21 | Siemens AG, 1000 Berlin und 8000 München | Method for determining the current yield in electroplating baths |
| US4639677A (en) * | 1982-01-04 | 1987-01-27 | Shell Oil Company | Cathodic protection monitoring system |
| US4489277A (en) * | 1982-01-04 | 1984-12-18 | Shell Oil Company | Cathodic protection monitoring system |
| DE3404720A1 (en) * | 1984-02-10 | 1985-08-14 | Karl Deutsch Prüf- und Meßgerätebau GmbH + Co KG, 5600 Wuppertal | METHOD AND DEVICE FOR MEASURING THICKNESS |
| US4627905A (en) * | 1984-10-05 | 1986-12-09 | Pulp And Paper Research Institute Of Canada | Monitor assembly for monitoring anodic corrosion protection of carbon steel vessels |
| US4644285A (en) * | 1984-10-09 | 1987-02-17 | Wayne Graham & Associates International, Inc. | Method and apparatus for direct measurement of current density |
| US4713347A (en) * | 1985-01-14 | 1987-12-15 | Sensor Diagnostics, Inc. | Measurement of ligand/anti-ligand interactions using bulk conductance |
-
1988
- 1988-02-12 US US07/155,205 patent/US4956610A/en not_active Expired - Lifetime
-
1989
- 1989-02-07 CA CA000590332A patent/CA1314073C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016183654A1 (en) * | 2015-05-19 | 2016-11-24 | Tractebel Energia S.A. | System and method for identifying the characteristics of an electric machine |
Also Published As
| Publication number | Publication date |
|---|---|
| US4956610A (en) | 1990-09-11 |
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