US3822482A

US3822482A - Moisture sensing control for dryer

Info

Publication number: US3822482A
Application number: US00412455A
Authority: US
Inventors: C Cotton
Original assignee: Maytag Corp
Current assignee: Maytag Corp
Priority date: 1973-11-02
Filing date: 1973-11-02
Publication date: 1974-07-09
Anticipated expiration: 1991-07-09
Also published as: CA1003530A

Abstract

In a material moisture sensing control, an integrating switch, in series circuit with a pair of moisture sensing electrodes in a fabric drying apparatus, is operable to a conductive posture for a time delay period as a function of the dryness condition of the fabrics being dried. In one embodiment an integrating switch comprises an electrolytic cell operable to the conductive posture by current flow through the wet fabrics and operable for returning to the nonconductive condition upon the fabrics achieving a predetermined dryness condition. A transistor is operable for initiating a control function responsive to the high voltage developed across the electrolytic cell in the nonconductive condition.

Description

United States Patent 1191 Co on v [4 July 9, 1974 MOISTURE SENSING CONTROL FOR plex Components, Nov. 16, 1964, Electronics, pgs.

DRYER v I 67-71. [75] Inventor: Curran D. Cotton, Newton, Iowa P h E M P l rzma xammer e er er 1n [73] Asslgnee: The Maymg Company Newton Assistd it ExaminerPail Devinsky Attorney, Agent, or Firm-William G. Landwier; Rich- [22] Filed: Nov. 2, 1973 afd Ward [21] Appl. No.: 412,455

[57] ABSTRACT [52] US. Cl 34/45, 34/48, 34/53, in a ri i e i g control, an i teg ating 318/483, 324/65 R switch, in series circuit with a pair of moisture sensing [51] Int. Cl F2611 19/00 electrodes n a a ric drying apparatus, is operable to [58] Field of Search .1. 34/45, 46, 48, 53, 55; a conductive posture for a time delay period as a func- 328/4, 293; 318/483; 324/65 R tion of the dryness condition of the fabrics being dried. in one embodiment an integrating switch com- [56] Reference Cit d prises an electrolytic cell operable to the conductive UNlTED STATES PATENTS posture by current flow through the wet fabrics and 3 301 024 1/1967 smith 34/45 operable for returning to the nonconductive condition 12/1968 Th 34/45 upon the fabrics achieving a predeterrrnned dryness 3:555:308 1/1971 Peterson .1111: IZZY isomers condinon- A transistor is Operable 3 3,647,196 3/1972 Cotton 34/45 function responsive to the high voltage developed 3,782,001 1/1972 Cotton 34/45 cro he ectrolytic cell in the nonconductive con- OTHER PUBLICATIONS Herbert Feitler, Simple Cell Competes With Comdition.

21 Claims, 2 Drawing Figures A '1 /7o v w; NM?

| J l 6/ /27 /75 A34.

ljo I f l l v {/74 F gas M4 /35 A25- i/ /3 PATENIED M 91974 SHEET 1 [1F 2 mammal mm 3.822.482

sum 2 or 2 1 MOISTURE SENSING CONTROL FOR DRYER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a dryer control system and more particularly to a control circuit for automatically initiating termination of operation of a dryer apparatus when fabrics being dried therein attain a predetermined dryness condition.

2. Description of the Prior Art One type of 'dryer control frequently used for effecting automatic termination of the drying operation of a fabric drying apparatus includes a pair of electrodes or conductors for sensing the electrical conductivity of the fabrics in the fabric tumbling chamber. The prior art patents show a number of specific control circuits for measuring fabric dryness by means of a sensing circuit including a resistance-capacitance circuit portion responsive to the resistance of the fabrics across the electrodes and operable for terminating the drying operation at a preselected dryness condition as indicated by a predetermined charge on a capacitor. The

capacitor, in at least a portion of these dryness sensing controls, has been operable for providing a time delay to insure proper drying and thus has been of relatively large capacitive value and accordingly of relatively high cost. In other systems, a timer mechanism has additionally been used to achieve all or part of the long time delay. Both of these systems have commonly included means responsive to the voltage on the capacitor, such as a neon tube, for initiating a control funcnon.

There is, however, a continuing search for improved control systems having greater reliability and accuracy as well as being more compact and of lower cost.

SUMMARY OF THE INVENTION It is an object of the instant invention to provide an improved fabric dryness sensing circuit operable for terminating the dryness sensing operation'at a desired fabric dryness condition.

It is a further object of the instant invention to provide an improved fabric dryness sensing circuit for directly integrating current flow through the wet fabrics bridging a pair of conductors.

it is a further object of the instant invention to provide an improved fabric dryness sensing circuit including an integrating switch in series connection to the fabric sensing electrodes.

it is still a further object of the instant invention to provide an improved dryness sensing circuit wherein the long time delay capacitor may be eliminated from the circuit.

It is yet a further object of the instant invention to provide an improved dryer control circuit including output means responsive to a voltage drop across an electrochemical device which is in series connection with the moisture sensing electrodes whereby an intermediate signal emitting device may be eliminated.

These objects are achieved in a fabric drying apparatus having a'dryness sensing circuit comprising an integrating switch in circuit with the moisture sensing elec trodes for directly integrating the current flow through the wet fabrics andfurther comprising accumulating circuit means and dissipating circuit means for maintaining the integrating switch means in a predetermined electrical condition during the drying operation and for operating to a second electrical condition upon the fabrics reaching a predetermined moisture condition to terminate the dryness sensing operation and to initiate termination of operation of the apparatus.

Operation of the device and further objects and advantages thereof will become evident as the description proceeds and from an examination of the accompanying two pages of drawings.

DESCRIPTION OF THE DRAWINGS The drawings illustrate a preferred embodiment of the invention with similar numerals referring to similar parts throughout the several views, wherein:

FIG. l is a view of a fabric drying apparatus partially broken away and sectioned and incorporating the control system of the instant invention; and

FIG. 2 is an electrical schematic diagram of a preferred circuit embodying the dryness sensing control of the instant invention.

DESCRIFTION OF A PREFERRED EMBODIMENT Referring to FIG. l there is shown the overall construction for a clothes dryer it) including a cabinet assembly comprising a sidewall wrapper ll having generally vertical opposite side panels l3 and a rear panel 14. The sidewall wrapper 11 is supported on a base 15 which in turn is supported on ahorizontal surface through a plurality of adjustable feet 16. The cabinet assembly further comprises a front panel 19 and top cover 20 supported on the sidewall wrapper ill. The top cover 20 includes anupwardly extending housing 21 for accommodating selected controls for the dryer such as a push-to-start mechanism operated by button 22.

The front panel 19 defines a generally central access opening 23 and includes a door 24 hinged on the front panel 119 and operable between open and closed positions relative to the access opening 23. The door 24 includes an outer panel 25 substantially flush with the front panel 19 and an inner panel 26 having a portion that extends rearwardly into the access opening 23. A seal 29 supported by the inner panel 26 extends endlessly around the rearwardly extending portion of the inner panel 26 for engagement with a recessed portion 30 of the front panel 19 to effectively provide an air sea] at the access opening 23.

Disposed within the cabinet assembly is a pair of spaced apart generally

vertical bulkheads

33 and 34. The rear bulkhead 34 is fixed to the sidewall wrapper ll by a pair of brackets such as the bracket 35 that includes a front fiangeconnected to the bulkhead 34 and a rear flange connected with the rear panel 14. The front bulkhead is similarly connected to the front flanges of wrapper llllwith a pair of brackets.

A generally cylindrical peripheral sidewall 36 is disposed between the

stationary bulkheads

33 and 34. At the frontand at the rear of the peripheral sidewall 36 there are inwardly turned flanges comprising relatively

short end walls

39 and 40 juxtaposed the front and

rear bulkheads

33 and 34 and cooperable with the sidewall 36 to effectively define a fabric tumbler 4i. A plurality of baffle members 43 are fixed to the peripheral sidewall 36 and extend into the tumbling chamber for assisting in the movement of fabrics therewithin during rotation of the fabric tumbler 411.

- 3 The front and

rear bulkheads

33 and 34 include radially outwardly disposed recess portions 44 and '45 extending axially toward the front'and toward the rear, respectively, .of the dryer 10.

Seals

49 and 50 are fixed

tothe bulkheads

33 and 34 in the

recesses

44 and 45 and are engageable with the

tumbler end walls

39 and 40 to provide an air seal at the ends of the tumbler 41. The

bulkheads

33 and 34 also include generally

annular portions

51 and 53 inwardly disposed from the

recesses

44 and 45 that effectively provide extensions of the

end walls

39 and 40 of the fabric tumbler 41.

The seal member 49, for example, disposed between the stationary bulkhead 33 and the rotatable tumbler into engagement with the front wall 39 of the tumbler 41. The felt may be coated on one side with an antifric tion layer such as polytetrafluoroethylene to provide a smooth, more durable, and lower. friction running surface for engagement with the tumbler end wall 39.

The front bulkhead 33 defines an access 57 into the tumbling chamber that isosubstantially aligned with the access opening 23 in the front panel 19. The rear bulkhead34' defines an opening 58 to receive a perforate panel 59 through which airflow is directed into the tumbling chamber 60 from a duct system as will be shown.

The tumbler 41 is supported on a generally horizontal axis by a system including a pair of rollers 61 supported on brackets 62 fixed to the rear bulkhead 34 and by 'a pair of slide bearings (not shown) supported bysimilar brackets fixed to the front bulkhead 33. The tumbler 41 could be supported entirely on rollers or entirely on slides as conditions permit. a

The fabric tumbler 41 is rotated by a belt 63 encompassing the periphery of the tumbler sidewall 36 and driven by a motor 64 mounted on the'base 15.

The airflow system for the clothes dryer 10 includes 2 a heater assembly 66 supported adjacent the base 15 and into which air is drawn from the atmosphere for heating prior to movement into the fabric tumbling chamber 60. The heater assembly 66 accommodates an electric heating coil as will be considered in greater detail as related to the control circuitry of FIG. 2. The

heater assembly 66 is connected to a generally up-- wardly extending rear air duct 68 which conducts heated air from the heater assembly 66 through the 'rearwardly extending lower air duct 75 to atmosphere.

The blower 74 includes an impeller (not shown) that is drivenby the motor 64 mounted adjacent to the blower 74 on the base 15. The general airflow pattern within 4 the drying apparatus 10 is shown by the broken and solid line arrows in FIG. 1.

In order to measure the electrical conductivity or resistance of the fabrics within the chamber 60, as a measure of the condition of dryness of the fabrics, electrodes or conductors and 81 are mounted within the chamber 60. In a preferred embodiment, the electrodes are in the form of a pair of spaced-apart elongated conductor members mounted on an insulating member 82 and in turn fixed to a lower portion of bulkhead33 to provide a pair of electrically insulated contacting surfaces engageable by the fabrics tumbling within the tumbling chamber. It will be realized that different forms of electrodes or conductors may be used although the type disclosed herein is a preferred construction.

The electrical circuitry connected to the electrodes will beexplained in greater detail in the discussion of FIG. 2 hereinbelow. It is noted, however, that the cabinet and other conductive portions of the apparatus are electrically connected to each other and are in turn connected to earth ground by conductor 87.

Referring now to FIG. 2 the control circuitry includes three conductors that are connectable with a conventional three-wire 240 volt, alternating current supply. For the explanation of the circuitry of FIG. 2, it will be assumed that conductors and 101 are connected with the power lines and that the conductor 103 is connected to the earth-grounded neutral line.

The energizing circuit for'the appliance includes a door switch 104 connected to conductor 100 and also includes a manuallyactuatable momentary push-tostart switch mechanism operated by button 22 and which includes a first single-pole single-throw momentary switch 105 and a second single-pole double-throw momentary switch 106 to be described further herein. The closing of the contacts in the push-to-start switch 105 effects energization of a control relay including a coil 107 and a pair of single-pole single-

throw switches

108 and 109. The relay switch 108 is in the heater circuit while the relay switch 109 serves as a holding switch during operation of the apparatus. The relay operation in the control of the machine will be described in greater detail herein.

The electric heating coil 102 is connected between the first and

second power conductors

100 and 101 by a circuit portion including the relay switch 108, a high limit thermostat 112, a cycling thermostat 110, and a centrifugal switch 111 in the motor .64. The centrifugal switch 111 is normally open but is operable to the closed position upon energization of the motor 64.

The drive motor 64 is initially energized by a circuit extending from the first power conductor 100 through the door switch 104, push-to-start switch 105, and through centrifugal switch 113 made to contact 114 within the motor 64.-Until the motor 64 rotates at a predetermined speed, the run and start

windings

115 and 116 are both energized through centrifugal switch 113 made to contact 114, but upon operation of the centrifugal switch 113 to the normally open contact 117 the start winding 116 is disconnected from the circuit. After initial energization of the motor 64 and operation of the centrifugal switch 113 to the normally open contact 117 and release of the push-to-start switch 105, the circuit for energizing the motor 64 and maintaining energization thereof will be completed from the first power conductor 100 through the door switch 104, the relay holding switch109 and a conductor 1 19 to the normally open contact 1 17 of the centrifugal switch 113.

A cool-down thermostat 120 is provided in the circuit to the motor 64 and is operable to a closed position at a predetermined temperature within the tumbling chamber 60 of, for example, 135 F. After the dryer apparatus has operated for a period of time with heat, the cool-down thermostat 120 will close and maintain the motor 64 energized until the temperature within the tumbling chamber 60 is reduced to 135 F. This cooldown thermostat 120 therefore provides a fabric cooldown operation following aheat On drying operation.

The lower portion of the circuit diagram of FIG. 2

comprises primarily the moisture sensing and auto matic termination circuit for the fabric drying apparatus. it is the general function of this sensing circuit to measure the moisture content of the tumbling fabrics during the drying operation and to initiate termination of operation at a particular fabric dryness condition. The circuit is operable for utilizing the resistance of momentary electrical paths completed through random samples of tumbling fabrics within the drying chamber. Generally speaking, these values of resistance are integrated and after a time delay period the control indicates the presence of fabrics having a generally predetermined or preselected condition of dryness. A- predetermined electrical condition within the circuit initiates termination of operation through an output circuit portion.

An integrating switch provides the integration of the random momentary resistance values. An electrochemical device, such as an electrolytic cell 125, is used as the integrating switch in the preferred embodiment of FIG. 2 and is operable as a timer or as an integrator. Operationally, the electrolytic cell 125 functions as a switch having a conductive posture in which the resistance through the electrolytic cell is relatively low and a nonconductive posture in which the resistance through the electrolytic cell is relatively high. The electrolytic cell 125 is operable as a bidirectional electron or current flow integrator as will become clear from the following explanation.

More specifically, the electrolytic cell 125 is a reversible micro-coulometer device designed in accordance with F aradays law of electroplating. The device operates by means of the physical transfer of atoms of metallic silver across an electrolyte. The device has a central goldelectrode, as shown schematically and desigcase. When current flows in one direction, namely,

from the silver electrode 127 to the gold electrode 126, the positive silver ions in the electrolyte are deposited on'the gold electrode 126. The effective, resistance of electrolytic cell 125 and the corresponding voltage drop across the cell are low. When'current is applied in the opposite direction, namely, from gold electrode 126 to the silver electrode 127, the silver is deplated from the gold electrode 126 but the device still exhibits a low resistance as long as there is silver remaining on the working or gold electrode 126. As soon as the silver has been depleted from this gold electrode 126, the

electrolytic device 125 changes to a nonconductive or high resistance state, usually of the order of several megohms, with a corresponding voltage rise to over 800 millivolts. a

In this specification, the convention that electrons flow by the same path as current and in the opposite direction thereto will be used. Therefore, electron flow through the electrolytic cell from the gold electrode 126 to the silver electrode 127 will effect a plating of the goldelectrode 126.

Since the flow of current through the electrolytic cell 125 is accompanied by a transfer of silver from one electrode to the other in a direct proportionality to the level and time of current flow, including periodic or random inputs of any time-current integral, the device is a true integrator of the current input over a time period. At any instant, the quantity of silver on the working or gold electrode 126 represents atrue value of the integral of the current that has passed throughthe electrolytic cell 125 during the integrating function.

As a simple timing device the electrolytic cell 125 may be given an initial charge comprising a predeten mined plating current flow, or current flow from the silver electrode 127 to the gold electrode 126, for a specific time to set or charge the device to a given level of plating. The electrolytic cell 125 may then be used to provide a time delay by connecting the electrolytic cell 125 to a circuit efiecting an opposite current flow through the device for a deplating of the silver from the gold electrode 126.

A combination of both timing and integration is utilized in the circuit of FIG. 2 as will be shown by the following detailed explanation of the circuit and operation thereof.

To set the electrolytic cell 125 for a guaranteed minimum timing function, a preplating circuit portion is connected between the first and second power lines 1110 and 1111 for effectinga plating current flow through the electrolytic cell 125 to condition the device to the conductive posture. The preplating circuit portion includes a rectifier 129 connected to the first power line 1116 through door switch 104 which permits negative charging of a capacitor 136 through the momentary start switch 106 made to the normally open contact 131. Upon the release of the momentary switch 106 foroperation to its normally closed contact 133, the accumulated negative charge on capacitor 130 is discharged through resistor 134 and through the electrolytic cell 125 and chassis 135 to ground. It is noted that the capacitor 130 is negatively charged with an accumulation of electrons on the right-hand plate 136 of the capacitor 136 so that the flow of electrons is through the electrolytic cell 125 from the gold electrode 126 to the silver electrode 127. This flow of electrons from the gold electrode 126 to the silver electrode 127 corresponds by common practice, to the flow of current from the silver electrode to the gold electrode so that silver ions are deposited on the gold electrode 126 as previously explained, to operate the electrolytic cell 125 to the conductive posture.

It is also noted at this time that the silver electrode 127 of the electrolytic cell 125 is connected to earth gound through the conductive chassis 135 of the apparatus. In the specific embodiment of FIG. 2, the chassis 135 is maintained disconnected from or electrically isolated from the neutral line 163 within the control circuit as shown in H6. 2 but is effectively connected to the earth-grounded neutral line 103 by an external ground path including the earth-grounded neutral line of a normal household supply. Such a circuit provision requires that the apparatus chassis be connected to the earth ground for operability of the circuit and apparatus. Further details and-explanation of operation 'of such a control circuit are fully shown and claimed in 'copending application Ser. No. 405,203 filed Oct. 10,

1973 by the instant inventor and assigned to the assignee of the instant application.

The control circuit also includes a plating circuit portion extending from conductor 138 and comprising rectifier 137, resistor 139 and the pair of

conductive electrodes

80 and 81 connected in series with rectifier 137, resistor 139, and junction 140. As wet fabrics contact and bridge the

electrodes

80, 81, the resistance between the electrodes will be relatively low and thus current flow therethrough will be at a high level. This current flow through the fabrics effects further plating of the electrolytic cell 125 butat a decreasing rate as the fabrics become dry and thus of higher resistance. The rectifier 137 limits the plating to half cycle operation and the variable resistance of the fabrics across the

electrodes

80, 81 as a measure of the moisture content of the fabrics provides a variable plating signal to the electrolytic cell 125.

The preplating circuit including capacitor 130 and the plating circuit including the

electrodes

80, 81 may thus be considered as accumulating circuit means operable for effecting a plating of the electrolytic cell 125.

A dissipating circuit is connected between the conductor 138 and the electrolytic cell 125 to effectively provide a deplating of the electrolytic cell 125 at a predetermined constant rate while the device remains in the conductive posture. The deplating path includes rectifier 141, resistor 143, resistor 144,-and rectifier l45..lt is noted that the relative positioning of

rectifiers

129 and 137 relative to 141 provides that electrons flowing through the electrolytic cell 125 from the conductor 100 to the chassis 135 effect plating of the electrolytic cell 125 whereas electrons flowing from ground and through the chassis 135, the electrolytic cell 125, and the deplating

circuit including rectifiers

145 and 141, effect a deplating of the electrolytic cell 125. Re,- sistance 146 functions with resistance 143 as a voltage divider for effecting the current flow required for the shutdown device as will be shown.

Also included in the circuit of FIG. 2 is an output circuit portion including a transistor 149 having a base 150, a collector 151, and an emitter 152. The

baseemitter junction

150, 152 is responsive to the voltage drop across the electrolytic cell 125 as will be shown.

The output 4 circuit further includes a siliconcontrolled rectifier, or SCR 154, in circuit with the transistor 149. A capacitor'155 and resistor '156 are connected to the conductor 138 through the rectifier 141 and function as an auxiliary'power supply for gating the SCR 154 to a conductive condition. The SCR 154 includes a path from the anode 157 to cathode 158 connected in series to the relay coil 107 and triggered to the conductive condition by the auxiliary power supply at gate 159 for maintaining the relay coil 107 energized while the drying operation proceeds. A diode 163 is shown in parallel connection to the relay coil 107 for conducting the self-induced current that is produced by the collapsing magnetic field of the inductive relay coil 107 during the half cycle of normal deenergization. A

'snubber circuit including series-connected resistor 164 and capacitor 165 is in parallel connection to the SCR anode-cathode path to protect the SCR 154 against electrical transients.

The operation of the circuit of FIG. 2 for controlling operation of the dryer apparatus will now be described. With the door switch 104 in its closed position as by the closing of the door 24, manual operation of the pushto-start button 22 will close momentary switches 105 and 106 for energizing the drive motor 64 and effectively energizing the control circuit to initiate operation of the apparatus. Initially, the circuit for energizing the motor 64 extends from the first power line 100, through door switch 104, conductor 167, switch 105, and conductor 169 to the centrifugal switch 113. The circuit continues through the run and start windings and 116 connected in parallel and through a conductor 170 to the neutral line 103.

At the same time, a circuit will be completed to the relay coil 107 and extending from the first power line 100, through door switch 104, conductor 167, the momentary switch 105, and conductor 138 to one side of the coil 107. A circuit is also completed from the conductor 138 through diode 141 and conductor 171 to one side of the capacitor 155 for positive charging thereof. The capacitor 155 with resistor 156 effectively provides a positive power supply for triggering the SCR 157 to the conductive position. This effects energization of the relay coil 107 by a circuit extending from conductor 138 and through the anode-cathode path of the SCR 157 and conductor 172 to the neutral line 103. Energization of the relay coil 107 closes relay

switches

108 and 109. I

Upon the motor 64 reaching a predetermined speed, the centrifugal switch 113 operates from the normally closed contact 114 to the normally open contact 117 for deenergizing the start winding 116 and maintaining the run winding 115 energized by a circuit which ex tends from the first power line 100 through the closed door switch 104 and relay switch 109 and conductor 119 to the normally open contact 117 of the centrifugal switch 113. The closing of the relay switch 108 also energizes the heater 102 by a circuit that extends from the first power line 100 through the relay switch 108, the high limit thermostat 112, the cycling thermostat 110, the heater 102, and the centrifugal switch 111 to the second power line 101.

For charging capacitor 130, closing of the momentary switch 133 to its nonnally open contact 131 completes a circuit between the first power line 100 and the neutral line 103. Capacitor is negatively charged by the circuit that extends from the conductor 167 through rectifier 129 and through the momentary switch 106 closed to its normally open contact 131 to the negative plate 136 of the capacitor 130. The positive plate 174 of the capacitor 130 is connected to the neutral line 103 through conductor 175.

At this stage of energization. the apparatus is operating with the motor 64 energized for tumbling fabrics in chamber 60 and the heater 102 energized to provide heat for drying the fabrics in theapparatus.

Upon manual release of the push-to-start button 22, the momentary switch 106 operates to contact 133 and completes an electrical path from the negatively charged capacitor 130 through resistance 134 and conductor 176 to the electrolytic cell 125. The electrons from the negative or right-hand plate 136 of the capacitor 130 flow through the electrolytic cell 125 to ground. This flow of electrons corresponds to the flow of current through the electrolytic cell 125 for causing a plating action to occur within the electrolytic cell and the cell 125 becomes conductive to provide a very low impedance path to ground. The charge provided by capacitor 130 provides a one-shot predetermined plating of the electrolytic cell 125 to condition it to the conductive posture and establish a minimum period of conductive operation thereof.

With the motor 64 operating, the wet fabrics within the chamber v60 are tumbling therein for random engagement with the

electrodes

80, 81. The bridging of wet fabrics between the pair of electrodes 81) and 81 completes the plating circuit between the conductor 138 and the neutral line 1113 for flow of electrons, as controlled by rectifier 137, through the electrolytic cell 125 to effect a further plating thereof. The circuit extends from the conductor 138 through rectifier 137, resistor 139, the

electrodes

80, 81 as bridged by the wet fabrics, and through the junction 140, the electrolytic cell 125, and the chassis grounding path 135 to'the earth ground potential. This current flow continues during each negative half cycle at a rate depending upon the moisture content of the fabrics and will thus decrease in rate as the fabrics become more dry. The rate of plating is directly proportional to the current flow throughthe electrolytic cell 125 from the silver electrode 127 to the gold electrode 126 and will thus also decrease as the fabrics become dry. a The'voltage divider formed by

resistances

143 and 146 establishes a resistance network to effect a predetermined current flow through the electrolytic cell 125 for deplating the electrolytic cell 125 at a generally constant rate. The deplating current flow extends through the conductive chassis grounding path 135 and the'electrolytic cell 125 to the junction 140. Thedeplating circuit then extends from the junction 146 through rectifier 145, resistor 144, resistor 143, and rectifier 141 to the conductor 138. The rate of deplating effected by the current flow is substantially constant as determined by the impedance of the deplating path.

The relative rates of charging or plating of the electrolytic cell 125 through the

electrodes

80, 81 and bridging fabrics as compared to the deplating of the electrolytic cell 125 through the dissipating or deplating circuit are thus dependent upon the fabrics attaining a predetermined dryness. It is noted thatwhile the fabrics are relatively wet at the initial portion of the cycle the rate of plating of the electrolytic cell 125 by a circuit extending through the

electrodes

80, 81 and wet fabrics exceeds the the deplating rate through the dissipating circuit. As the dryness of the fabrics approach a preselected desired dryness, the constant rate of deplating exceeds the plating achieved through the

electrodes

80, 81 and fabrics so that the remaining quantity of plated material on the gold electrode 126 decreases. Eventually the electrolytic cell 125 becomes deplated, assumes a nonconductive posture, and exhibits a high voltage drop thereacross. This plating and deplating operation of the electrolytic cell 125 provides direct integration of the current flow through the

electrodes

80, 81 as dependent upon the moisture content of the fabrics and in addition provides the time delay period deemed necessary for proper drying.

It is desirable to provide to the operator a selection of drying cycles or of degrees of dryness. To achieve this selectivity, the built-in time delay may be made variable as by providing a variable component'for capacitor 130. Alternatively, one or more of the

resistors

139, 143, 1 and 146 could be made variable. For convenience of explanation in this specification, how ever, the components are considered fixed.

When the electrolytic cell is plated, the voltage at the junction 177 is essentially the voltage drop across rectifier since the electrolytic cell 125 has a conductive posture. This same voltage is impressed across rectifier 179 and the base-emitter junction 1511, 152 of transistor 149. This voltage level, however, at the

baseemitter junction

150, 152 of transistor 149 is insufficient to cause transistor 149 to conduct across the collector-

emitter junction

151, 152. As the clothes become dry, however, the the electrolytic cell 125 be, comes deplated and changes to a relatively high impedance posture as previously shown. The electrolytic cell 125 thus becomes nonconductive in comparison to the path through rectifier 179 and base-emitter junction 151), 152 of transistor 149. Further, the increased voltage drop across the electrolytic cell 125 is effectively impressed on the base-emitter junction 1511, 152 of transistor 149 and with the resulting increased current flow through the base-

emitter junction

150, 152 causing the transistor 149 to become significantly more conductive across the collector-emitter junction 151,152. The current path to the base-emitter junction 151), 152 extends from conductor 138, through rectifier 141, resistor 143, resistor 144, and rectifier 179 to the transistor base 150.

The conductive path through the transistor 149 shunts the SCR gate signal which is provided to the SCR 154 through resistor 156. The SCR 154 then ceases conduction to deenergize the relay coil 1117 and thereby open relay switches 108 and 1119. Opening of switch 108 deenergizes the heater circuit while opening of switch 109 deenergizes the motor circuit unless the cool-down thermostat 1211 has been operated to the closed position. lf the cool-down thermostat 1211 has closed, the motor 64 will remain energized until the thermostat-reset temperature is reached. During this time, the motor 64 remains energized by a circuit extending between the first power line 101) through the door switch 104, the conductor 180, the cool-down thermostat 1211, conductor 119, and the centrifugal switch 113 made to the normally open contact 117.

During the'cool-down period, a circuit will also be completed from the first power line 1111) through the cool-down thermostat 1211, conductor 119, the centrifugal switch 113 made to the normally open contact 117, through conductor 169 and conductor 138 to one side of rectifier 141. A power supply thus remains to the capacitor and permits current flow through resistor 143, resistor 144,- rectifier 179 and the baseemitter junction 150,152 of transistor 149 to maintain the transistor 149 conductive and the SCR 154 non conductive so that the relay coil 107 remains deenergized during the cool-down operation.

Upon the temperature decreasing to the established temperature for opening the cool-down thennostat 120, the motor 64 will be deenergized and the control circuit deenergized for effectively terminating operation of the apparatus.

earth grounding of the'apparatus for operability of the apparatus. If such a ground is .not present the initial preplating charge provided by the capacitor 130 will find no path to ground through the electrolytic cell 125. Upon release of the push-to-start button22, the

transistor 149 will sense the high voltage condition and will terminate operation of the apparatus even though the fabrics remain wet within'the tumbling chamber 60. The wet fabrics in the chamber 60 will also be unable to provide a plating of the electrolytic cell 125 because of the absence of a complete circuit to ground.

Note also in FIG. 2 that

rectifiers

145 and 179 are placed in a back-to-back relationship to prevent damage to the circuit components in case a two-wire connector is'utilized,-such as in a l20-volt gasappliance, where the user could inadvertently interchange the neutral and hot power lines at the appliance input connections. 1n the circuit of P16. 2, the neutralline 103 is connected to the emitter terminal 152 of the transistor 149 and a ground line is connected to the electrolytic cell 125. Should a two-wire connection be used and should the plug be reversed, the line to the emitter 152 of transistor 149 would become the hot lineand there would be l20-volt difierential between the emitter of transistor 149 and ground. This differential could cause damaging current to flowboth through the transistor 149 and the electrolytic cell 125 were it not blocked by the back-to-back relationship of

rectifiers

145 and 179.

' The circuit for.preplating the electrolytic cell 125 is provided to insure proper operation of the, device and in particular .to provide the ability to dry small loads. This preplating provides a guaranteed heat time so that regardless of the amount of plating or deplating the time delay provides an insured drying operation.

' For the purposes of a particular reduction to practice of this circuit the following values of components were utilized? capacitor 130 30 MFD capacitors 155,165 0.1 MFD I resistor 134 200 K ohms resistor 139 variable from 360 K ohms to 1.45

megohms resistor 143 820 K ohms resistor [46 33 K ohms resistor I44 285 K ohms transistor 149 transistor 2N 4123 SCR 154 GB; C1038 electrolytic cell 125 Bisset Berman E Cell 560-0002 In the drawings and specification there has been set contemplated as circumstances may suggest or render expedient without departing from the spirit or scope of the invention as further defined in the following claims.

I claim:

l. A moisture sensing control for use with a drying apparatus and operative to control said apparatus in accordance with the moisture content of material being dried therein, the combination comprising: electrode means including a pair of spaced conductors engageable with the material being dried for completing a current path through said pair of conductors and wet material therebetween; electrical supply means for applying power across said pair of conductors; integrating switch means in series with said pair of conductors and operable for effectively integrating the current flow through the material bridging said pair of conductors as a measure of the moisture content thereof; accumulating circuit means operable for initially conditioning said integrating switch means to a conductive posture and establishing a time delay period of conductive operation thereof and also operable for effectively extending said time delay period at a rate dependent upon the moisture content of said material; dissipating circuit means connected to said integrating switch means for decreasing the time delay period of conductive operation thereof at a rate less than the extending rate ture after a period of conductive operation which is a function of said material attaining a predetermined degree of dryness; and output means responsive to the nonconductive posture of said integrating switch means indicative of the material attaining said predetermined degree of dryness for initiating a control function.

2. A moisture sensing control as defined in claim 1 wherein said integrating switch means includes an electrochemical integrating device responsive to current flow therethrough in a first direction for operation to said conductive posture and responsive to current flow therethrough in the opposite direction over a time delay period for operating to said nonconductive posture from said conductive posture.

3. A moisture sensing control as defined by claim 1 wherein said accumulating circuit means includes a first circuit portion for initially conditioning said integrating switch means to saidconductive posture and establishing a minimum time delay period of conductive'operation thereof and further includes a second circuit portion for extending the effective time period of conductive operation thereof at a rate dependent upon the moisture content of said material.

4. A moisture sensing control as defined in claim 1 wherein said integrating switch means includes an electrolytic cell operable to said nonconductive posture for exhibiting a substantially increased voltage concurrent with the material attaining a predetermined degree of dryness and wherein said output means includes a transistor responsive to said substantially increased voltage for initiating said control function.

' 5. A moisture sensing control for use with a drying apparatus and operative to control said apparatus in accordance with the moisture content of material being dried therein, the combination comprising: electrode means including a pair of spaced conductors engageable with the material being dried for completing a current path through said pair of conductors and wet ma terial therebetween; electrical supply means for applying power across said pair of conductors; integrating switch means in series circuit with said pair of conductors and operable for effectively integrating the current flow through thematerial bridging said pair of conductors as a measure of the moisture content thereof; first means for initially conditioning said integrating switch means to a conductive posture and establishing a minimum time delayperiod of conductive operation thereof; second means including the current path through said pair of conductors and wet material therebetween and operable for effectively maintaining said integrating switch means in said conductive posture by extending the effective time delay period at a rate dependent upon the moisture content of said material; third means connected to said integrating switch means for decreasing the time delay period of conductive operation thereof at a rate less than the extending rate of said second means when said materials are relatively wet and at a rate greater than the extending rate of said second means when said materials are relatively dry whereby said integrating switch means is operated to said nonconductive posture after a time period of conductive operation which is a function of said material attaining a predetermined degree of dryness; and output means responsive to the nonconductive posture of said integrating switch means indicative of the material attaining said predetermined degree of dryness for initiating a control function. y

6. A moisture sensing control as defined in claim wherein said first means includes a resistancecapacitance circuit and a momentary switch for supplying a one-time pulse of current to said integrating switch means to effect the initial conditioning of said integrating switch means to said conductive posture.

7. A moisture sensing control as defined in claim 5 wherein said integrating switch means includes an electrolytic cell and wherein said first means is operable for' effecting a predetermined quantity of charging thereof, said second means is operable for effecting an additional quantity of charging dependent upon the moisture content of the material bridging said electrodes andwherein said third means is operable for clearing the electrolytic cell at a generally constant rate.

8. A moisture sensing control as defined in claim 7 wherein said output means includes a transistor responsive to a substantial increase in voltage drop across said electrolytic cell.

9. A moisture sensing control for use with a drying apparatus and operative to control said apparatus in accordance with the moisture content of material being dried therein, the combination comprising: electrode means including a pair of spaced conductors engageable with the material being dried for completing a current path through said pair of conductors and wet material therebetween; electrical supply means for applying power across said pair of conductors; integrating switch means in series circuit with said pair of conductors and operable for effectively integrating the current flow through the material bridging said pair of conductors as a measure of the moisture content thereof; accumulating circuit means for initially conditioning said integrating switch means to a conductive posture and also operable for effectively extending a time delay period of conductive operation thereof at a rate dependent upon the moisture content of said material; dissipating circuit means connected to said integrating switch means for decreasing the time delay period of conductive operation thereof at-a rate less than the extending rate of said accumulating circuit means when said materials are relatively wet and at a'rate greater than the extending rate of said accumulating circuit means when said materials are relatively dry whereby said integrating switch means is operated to said nonconductive posture after a period of conductive operation which is a function of said material attaining a predetermined degree of dryness; output circuit means including a transistor having a base-emitter junction in parallel connection to said integrating switch means; and voltage divider circuit means connected to said integrating switch means and said base-emitter junction, said transistor being responsive to the substantially increased voltage drop across said integrating switch means in the nonconductive condition upon the material attaining said predetermined degree of dryness for becoming conductive to initiate a control function.

10. A moisture sensing control as defined in claim 9 wherein said accumulating circuit means and said dissipating circuit means are in parallel connection to each other and wherein said accumulating circuit means establishes a minimum time delay period and extends the time delay period dependent upon the moisture content of said material and wherein said dissipating circuit means decreases the effective time delay period at a generally constant rate.

11. A moisture sensing control as defined in claim 9 whereinsaid integrating switch means includes a bidirectional current integrating device responsive to current flow in one direction therethrough for operation to said conductive posture and responsive to current flow in the opposite direction therethrough for operation to said nonconductive posture after a time period controlled by the amount of current in the first direction.

. apparatus and operative to control said apparatus in accordance with the moisture content of material being dried therein, the combination comprising: electrode means including a pair of spaced conductors engageable with the material being dried for completing an electrical path through said pair of conductors and wet material therebetween; electrical supply means for applying power across said pair of conductors; a bidirectional current integrating device in circuit with said tors and wet material therebetween and operable for effecting current flow through said integrating device in said first direction to extend the effective time delay period of conductive operation at a rate'dependent upon the moisture content of said material; third circuit means connected to said integrating device for effecting current flow through said integrating device in a second direction to decrease the time delay period at a rate less than the extending rate of said second circuit means when said materials are relatively wet and at a rate greater than the extending rate of said second circuit means when said materials are relatively dry and thus return said integrating device to said nonconductive posture after a period of conductive operation which is a function of said material attaining a predetermined degree of dryness; and output means responsive to the nonconductive posture of said integrating device indicative of the material attaining said predetermined degree of dryness for initiating a control function.

14. A moisture sensing control as defined in claim 13 wherein said bidirectional current integrating device includes an electrolytic cell responsive to current flow in said first direction for becoming plated to assume said conductive posture and responsive to current flow in said second direction for becoming deplated over a period of time controlled by the relative rates of plating and deplating to return to said nonconductive posture.

15. A moisture sensing control as defined in claim 14 wherein said second circuit means is operable for effecting a plating of said electrolytic cell at a rate dependent upon the moisture content of the material between said electrodes and wherein said third circuit means is operable for effecting a generally constant deplating of said electrolytic cell.

16. A moisture sensing control for use with a drying apparatus and operative to control said apparatus in accordance with the moisture content of material being dried therein, the combination comprising: electrode means including a pair of spaced conductors engageable with the material being dried for completing an electrical path through said pair of conductors and wet material therebetween; electrical supply means for applying power across said pair of conductors; an electrolytic device in circuit with said pair of conductors and operable between a nonconductive deplated condition and a conductive plated condition; first circuit means for effecting an initial plating of said electrolytic device; second circuit means including the electrical path through said pair of conductors and wet material therebetween and operable for effecting additional plating of said electrolytic device at a rate comprising a function of the conductivity condition of the material between said conductors; third circuit means connected to said electrolytic device for effecting a deplating thereof at a rate less than the plating rate effected by said second circuit means when said material is relatively wet and at rate exceeding the plating rate of said second circuit means when said material is relatively dry whereby said electrolytic device effectively integrates the conductivity condition of said material as a measure of the moisture content thereof during a drying operation of said apparatus and is operated to the nonconductive condition upon the material attaining a predetermined degree of dryness; and output circuit means responsive to the nonconductive deplated condition of said electrolytic device for initiating a control function.

17. A moisture sensing control as defined in claim 16 wherein said first circuit means is operable for effecting an initial predetermined quantity of plating of said electrolytic device, wherein said second circuit means is operable for effecting a plating of said electrolytic device at a rate proportional to the moisture content of the material between said conductors and wherein said third circuit means is operable for effecting a deplating of said electrolytic device at a generally constant rate.

18. A moisture sensing control as defined in claim 16 wherein said output circuit means includes a transistor having a base-emitter junction responsive to an increased voltage drop across the electrolytic device in said nonconductive condition for initiating said control function.

19. A moisture sensing control as defined in claim 16 wherein said first circuit means includes a resistancecapacitance circuit and a manually operable momentary switch for effecting a predetermined plating of said electrolytic device to initiate conductive operation of said electrolytic device for a predetermined period of time.

20. A moisture sensing control as defined in claim 16 wherein said second circuit means provides a variable half cycle current for plating said electrolytic device at a rate dependent upon the moisture of the material bridging said conductors.

21. A moisture sensing control as defined in claim 20 wherein said third circuit means includes a resistive network for providing a predetermined deplating current flow through said electrolytic device to achieve a deplating thereof at a generally constant rate.

Claims

1. A moisture sensing control for use with a drying apparatus and operative to control said apparatus in accordance with the moisture content of material being dried therein, the combination comprising: electrode means including a pair of spaced conductors engageable with the material being dried for completing a current path through said pair of conductors and wet material therebetween; electrical supply means for applying power across said pair of conductors; integrating switch means in series with said pair of conductors and operable for effectively integrating the current flow through the material bridging said pair of conductors as a measure of the moisture content thereof; accumulating circuit means operable for initially conditioning said integrating switch means to a conductive posture and establishing a time delay period of conductive operation thereof and also operable for effectively extendinG said time delay period at a rate dependent upon the moisture content of said material; dissipating circuit means connected to said integrating switch means for decreasing the time delay period of conductive operation thereof at a rate less than the extending rate of said accumulating circuit means when said materials are relatively wet and at a rate greater than the extending rate of said accumulating circuit means when said materials are relatively dry, said integrating switch means being thereby operated to a nonconductive posture after a period of conductive operation which is a function of said material attaining a predetermined degree of dryness; and output means responsive to the nonconductive posture of said integrating switch means indicative of the material attaining said predetermined degree of dryness for initiating a control function.

3. A moisture sensing control as defined by claim 1 wherein said accumulating circuit means includes a first circuit portion for initially conditioning said integrating switch means to said conductive posture and establishing a minimum time delay period of conductive operation thereof and further includes a second circuit portion for extending the effective time period of conductive operation thereof at a rate dependent upon the moisture content of said material.

5. A moisture sensing control for use with a drying apparatus and operative to control said apparatus in accordance with the moisture content of material being dried therein, the combination comprising: electrode means including a pair of spaced conductors engageable with the material being dried for completing a current path through said pair of conductors and wet material therebetween; electrical supply means for applying power across said pair of conductors; integrating switch means in series circuit with said pair of conductors and operable for effectively integrating the current flow through the material bridging said pair of conductors as a measure of the moisture content thereof; first means for initially conditioning said integrating switch means to a conductive posture and establishing a minimum time delay period of conductive operation thereof; second means including the current path through said pair of conductors and wet material therebetween and operable for effectively maintaining said integrating switch means in said conductive posture by extending the effective time delay period at a rate dependent upon the moisture content of said material; third means connected to said integrating switch means for decreasing the time delay period of conductive operation thereof at a rate less than the extending rate of said second means when said materials are relatively wet and at a rate greater than the extending rate of said second means when said materials are relatively dry whereby said integrating switch means is operated to said nonconductive posture after a time period of conductive operation which is a function of said material attaining a predetermined degree of dryness; and output means responsive to the nonconductive posture of said integrating switch means indicative of the material attaining said predetermined degree of dryness for initiaTing a control function.

6. A moisture sensing control as defined in claim 5 wherein said first means includes a resistance-capacitance circuit and a momentary switch for supplying a one-time pulse of current to said integrating switch means to effect the initial conditioning of said integrating switch means to said conductive posture.

7. A moisture sensing control as defined in claim 5 wherein said integrating switch means includes an electrolytic cell and wherein said first means is operable for effecting a predetermined quantity of charging thereof, said second means is operable for effecting an additional quantity of charging dependent upon the moisture content of the material bridging said electrodes and wherein said third means is operable for clearing the electrolytic cell at a generally constant rate.

9. A moisture sensing control for use with a drying apparatus and operative to control said apparatus in accordance with the moisture content of material being dried therein, the combination comprising: electrode means including a pair of spaced conductors engageable with the material being dried for completing a current path through said pair of conductors and wet material therebetween; electrical supply means for applying power across said pair of conductors; integrating switch means in series circuit with said pair of conductors and operable for effectively integrating the current flow through the material bridging said pair of conductors as a measure of the moisture content thereof; accumulating circuit means for initially conditioning said integrating switch means to a conductive posture and also operable for effectively extending a time delay period of conductive operation thereof at a rate dependent upon the moisture content of said material; dissipating circuit means connected to said integrating switch means for decreasing the time delay period of conductive operation thereof at a rate less than the extending rate of said accumulating circuit means when said materials are relatively wet and at a rate greater than the extending rate of said accumulating circuit means when said materials are relatively dry whereby said integrating switch means is operated to said nonconductive posture after a period of conductive operation which is a function of said material attaining a predetermined degree of dryness; output circuit means including a transistor having a base-emitter junction in parallel connection to said integrating switch means; and voltage divider circuit means connected to said integrating switch means and said base-emitter junction, said transistor being responsive to the substantially increased voltage drop across said integrating switch means in the nonconductive condition upon the material attaining said predetermined degree of dryness for becoming conductive to initiate a control function.

11. A moisture sensing control as defined in claim 9 wherein said integrating switch means includes a bidirectional current integrating device responsive to current flow in one direction therethrough for operation to said conductive posture and responsive to current flow in the opposite direction therethrough for operation to said nonconductive posture after a time period controlled by the amount of current in the first direction.

12. A moisture sensing control as defined in claim 9 wherein said integrating switch means includEs an electrolytic cell responsive to current flow in one direction through said accumulating circuit means for operation to said conductive posture and responsive to a generally equal quantity of current flow in the opposite direction through said dissipating circuit means for operation to said nonconductive posture.

13. A moisture sensing control for use with a drying apparatus and operative to control said apparatus in accordance with the moisture content of material being dried therein, the combination comprising: electrode means including a pair of spaced conductors engageable with the material being dried for completing an electrical path through said pair of conductors and wet material therebetween; electrical supply means for applying power across said pair of conductors; a bidirectional current integrating device in circuit with said pair of conductors and operable between a conductive posture and a nonconductive posture for effectively integrating the current flow through the material bridging said pair of conductors as a measure of the moisture content thereof; first circuit means for effecting current flow through said integrating device in a first direction to condition said integrating device to said conductive posture and establish a minimum time delay period of conductive operation thereof; second circuit means including the electrical path through said pair of conductors and wet material therebetween and operable for effecting current flow through said integrating device in said first direction to extend the effective time delay period of conductive operation at a rate dependent upon the moisture content of said material; third circuit means connected to said integrating device for effecting current flow through said integrating device in a second direction to decrease the time delay period at a rate less than the extending rate of said second circuit means when said materials are relatively wet and at a rate greater than the extending rate of said second circuit means when said materials are relatively dry and thus return said integrating device to said nonconductive posture after a period of conductive operation which is a function of said material attaining a predetermined degree of dryness; and output means responsive to the nonconductive posture of said integrating device indicative of the material attaining said predetermined degree of dryness for initiating a control function.

19. A moisture sensing control as defined in claim 16 wherein said first circuit means includes a resistance-capacitance circuit and a manually operable momentary switch for effecting a predetermined plating of said electrolytic device to initiate conductive operation of said electrolytic device for a predetermined period of time.