CA1293550C - Transmitter for transmitting on a two-wire transmitting line - Google Patents
Transmitter for transmitting on a two-wire transmitting lineInfo
- Publication number
- CA1293550C CA1293550C CA000548222A CA548222A CA1293550C CA 1293550 C CA1293550 C CA 1293550C CA 000548222 A CA000548222 A CA 000548222A CA 548222 A CA548222 A CA 548222A CA 1293550 C CA1293550 C CA 1293550C
- Authority
- CA
- Canada
- Prior art keywords
- measured value
- transmission line
- digital
- wire transmission
- command signal
- 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 - Lifetime
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Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
- G08C19/00—Electric signal transmission systems
- G08C19/02—Electric signal transmission systems in which the signal transmitted is magnitude of current or voltage
Abstract
APPLICATION OF
DAVID L. MC GOWEN AND
STEVEN M. OXENBERG
TRANSMITTER FOR TRANSMITTING ON A
TWO-WIRE TRANSMITTING LINE
ABSTRACT
A transmitter for repeatedly transmitting a measured value in the form of a digital signal through a two-wire transmission line, includes a receiving unit for receiving a digital command signal from a communicator through the two-wire transmission line, and a processor for sending out a response signal in response to the command signal upon reception thereof. The measured value is sent using a newest measured value after repetitive transmission of the measured value is interrupted. The measured value is transmitted from the transmitter by a change in current supplied to the two-wire transmission line, and reception of the command signal is performed by a change in interline voltage of the two-wire transmission line.
DAVID L. MC GOWEN AND
STEVEN M. OXENBERG
TRANSMITTER FOR TRANSMITTING ON A
TWO-WIRE TRANSMITTING LINE
ABSTRACT
A transmitter for repeatedly transmitting a measured value in the form of a digital signal through a two-wire transmission line, includes a receiving unit for receiving a digital command signal from a communicator through the two-wire transmission line, and a processor for sending out a response signal in response to the command signal upon reception thereof. The measured value is sent using a newest measured value after repetitive transmission of the measured value is interrupted. The measured value is transmitted from the transmitter by a change in current supplied to the two-wire transmission line, and reception of the command signal is performed by a change in interline voltage of the two-wire transmission line.
Description
3~t:~
BACRGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a transmitter suitable for transmitting varivus measuxed values through a two-wire transmission line.
20 Description of the Prior Art In ord~r to transmit outputs from a differential pressure transmitter, an electromagnetic flowmeter or the like representing measured values to a remote location according to conventional industrial measurement techniques, a unique signal having a current level within a range of 4-20 mA is used. Thus, an analog signal having a current ; level selected from this range represents a measured value.
. Such differential pressure transmitters, electromagnetic ; 15 flowmeter~ and the like are normally arranged in a distributed manner to monitor industrial process states in a wide physical area. Maintenance personnel must travel ; extensively to maintain and inspect the di~tributed measuring instruments 50 as to perform adjustments and check the operating conditions thereof. In order to eliminate such time-consuming maintenance or the like, existing equipment is utilized to achieve remote control operation of the measuring instruments, as described in U.S. Patent No.
~,520,488.
~k 1~3S~- ~
As shown therein9 a transmitter is bridged to a two-wire transmission line to transmit a digital signal. After the digital signal is received by a receiver, the transmitter stops transmitting an analog measured value signal and responds to a digital signal from a communicator. The response signal is then received by the com~unicator. A
similar mode of operation is achieved for digital signal communication between the communicator and the transmitterO
Since when the transmitter communicates with the communicator by means of the digital signal, the transmitter stops transmitting the analog signal, i.e., stops transmitting the measured value, if the measured value concurrently changes, the changed measured value cannot be immediately transmitted to the receiver. Therefore, the receiver cannot perform an immediate control operation according to the changed measured value. This impairs the ability of the state of equipment to be controlled to follow changes in the measured values.
SUMMARY OF THE INVENTION
It i8, therefore, an object of the present invention to provide a transmitter capable of transmitting at least one mea~ured value within a predetermined period determined in ~ association with a system and control operation~ so that an ; operating state of equipment to be controlled can always ~ 25 follow changes in measured value, even while the transmitter 3~
communicates with a communicator to exchange digital signals representing various types of data.
In order to achieve the above object of the pre.sent invention, there is provided a transmitter for repeatedly transmitting measured values of digital signals through a two-wire transmission line, comprising means for receiving a command signal as a digital signal sent from a communicator through the transmission line, and control means for transmitting a respon.se signal responsive to the command signal upon its reception so as to transmit at least one measured value within a predetermined period.
In accordance with the present invention, there is provided a transmit~er for transmitting a measured value of a process variable in the form of a dlgital signal through a two-wire transmission line by a change in current in the two-wire ransmission line comprising means for receiving a digital command signal supplied through said two-wire transmission line and control means for adding the measured value to a digital response signal generated in response to the digital command signal and for transmitting a resultant digital signal so as to transmit on the two-wire transmission line at least one measured value within a predetermined time period.
In accordance with the present invention, there is also provided a transmitter for repeatedly transmitting a measured value of a process variable in the form of a digital signal through a two~wire transmission line by a change in a current in the two-wire transmission line comprising means for receiving a digital command signal supplied through said two-wire transmission . ~
35~
4a 641~9-965 line and control means for adding the measured value to a digital response signal generated in response to the digital commancl signal and for repeatedly transmitting a resultant digital signal so as to transmit on the two-wire transmission line at least one measured value within a predetermined time period.
In accordance with the present invention, there is also provided a transmitter for transmitting a measured value of a ~ cliS~t~
process variable in the form of a ~i~ through a two-wire transmission line by a change in a current in the two-wire 10 transmission line comprising means for receiving a digital command signal supplied through said two-wire transmission line, means for 1~ n~_ diyitally transmitting on said transmission/at least one measured value of the process variable within a predetermined time period and control means for adding the measured value to a response signal generated in response to the digital command signal and for transmitting a resultant digital signal on said transmission line.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig.1 is a block diagram showing an overall two-wire transmission system configuration, Fig. 2 is a block diagram of a transmitter suitable for use in the system shown in Fig. 1 according to a first embodiment of the present invention, Fig. 3 is a timing chart of a waveform showing changes in current for the two-wire transmission system, Fig 4 is a block diagram of a communicato~ used in the system shown in Fig. 1, Fig. 5 is a circuit diayram of a current controller used in the system shown in Fig. 2, ~2~35~0 4b 64159-965 Fig 6 is a perspec~ive pictorial view ~howin~ an outer physical appearan~e of the com~unlcator shown in Fig. 5, ~2~35~
Figs. 7(A) and 7(B) are flow charts for explaining the control operations, and - Figs. 8(A) to 8(C) are timing charts for explaining a second embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 is ~ block diagram showing an overall two-wire transmisslon system configuration utilizing the present invention. A direct current (DC) power source (re~erred to as a PS hereinafter) 2 is connected to one and of a two-wire ; 10 transmission line (referred to as a transmission line) 1 consisting of signal lines 11 and 12 to supply a current thereto. A transmitter ~referred to as a TX hereinafter) 3 such as a pressure difference transmitter and an electromagnetic flowmeter is connected to the other end of the transmission line. The TX3 3 controls a current I in the transmission line 1 to generate signal pulses. The signal pulses are sent as a digital signal representing a measured proceRs variable value onto the tranQmiscion line 1.
A resistor RL as a voltage dropping element is inserted in series with the tr~nQmissiOn line 1. A voltage across the resistor RL is supplied to a receiver ~referred to as an RX hereinafter) 4 whereby the RX ~ receives the transmitted signal. An output signal from the RX 4 is sent to a main 25 controller (referred to as an MC hereinafter) 6 such as a .~ .
12~3S~
computer through a bus S. Control operations by the MC 6 are performed on the basis of the measured value represented by the digital output signal supplied from the RX 4.
Control data i5 sent to controlled equipment (not shown) through the ~us 5, thereby controlling the equipment.
An operation unit (referred to as an OP hereinafter) 7, which can include a CRT display and a keyboard, is connected to a bus 5' through an interface treferred to as an I/F
hereinafter) 9, for displaying a controlled state of the equipment and inputting a command to the ~C 6 and the ~x 4.
A portable communicator (referred to as a CT hereinafter) 8 is bridged in the transmission line nearer to the TX 3 than the resistor RL. The CT 8 converts the current I into siqnal pulses and sends them as a digital command signal to the ~X 3. The TX 3 receives the command signal and converts the current I into signal pU18eS as a response signal which i5 sent to the CT 8 in response to the command signal.
~ ig. 3 shows a waveform of changes in current I supplied through the resistor RL as a function of time ~t~. In this ~ 20 case, the digital si~nal i8 a pulse code, the current of ; which changes in the range of Il to I2, e.g., 4-20 mA. A
~; measured process value word WPV determined by the measured value from the TX 3 comprises 4-byte data consisting of bytes BY0 to BY3 (each byte consists of eight bits). If the length of time for each of the bytes BY0 to BY3 is ~tl~, ~ ~335i~
e g., 50 msec, the length of time of the measured value word WPV is "4tln, and the disable per:iod following the word WPv : is ~tl~. The measured value word WPV is repeatedly . transmitted by changes in current ~It" suppIied across the lines of the TX 3, thereby always transmitting the newest measured value to the RX 4.
- In this state, a command signal REQ as a pulse coda is transmitted ~ithin a reception wait period ~t2 shorter than the disable period ~tl~ by changing of a current Ic supplied from the CT 8 to line terminals Tl and T2 at the end of transmission of the measured value word WP~. The change in current causes a change in voltage across the resistor RL.
The change in voltage across the resistor RL is sent as a change in voltage between the signal lines ll and 12 to the TX 3. Therefore, the command signal REQ is received by the ; TX 3.
The TX 3 stops tran mitting the measured value word WPV
in response to the command signal REQ and sends back a 2-byte response word WRE corresponding to the command signal REQ by mean of the current It. In this case, the TX 3 ~ transmits at leact one measured value word within a : predetermined period ~l which is determined in accordance with the system's control and safety requirements. If the response word WRE is long, it is divided into WRE1, WRE2, :; 25 WRE3,0..... which are then sequentially time-divisionally ~Z~33S~
sent. Referring to Fig. 3, the period T2 shorter than the predetermined period T1 is monitored. If the short period T2 exceeds the predetermined period Tl, the response word WPV is partially sent to assure the system control and safety measures, and the remaining portion of the response ~-word WPV is then sent. After transmission of the response word WPV, the period T2 is monitored. If the period T2 exceeds the period Tl, the response word WPV is transmitted. The relationship between the periods Tl and T2 is determined to transmit one WPV within Tl. Thus, the voltage between the lines 11 and 12 is changed, and this change is received by the C~ 8.
-~A start bit B0 of bits B0 to B31 in the start byte BY0 in the measured word WPV represents status ST indicating whether the TX 3 is normally operated. The bit Bl represents a proportional relation L, i.e.~ a linear relationship between the measured value and the control value according to sensor characteristics, or a squared proportlonal relationship S, i.e., a relationship representing that the measured value is a square of the control value. The bit B2 represents the number NB of continuouk bytes, i.e., that the number of continuous bytes is four or six. The bits B4 to B7 represent the type DA of the measured value transmitted by the bytes BYl to BY3. In the byte ater byte 8~1, the bits B4 to B7 represent a ~L~935~ ~
measured value DPV. The number of bytes of each word and the number of bits of each byte can be determined according to the control states. The periocls "tl~ to "t3" are also peoperly determined according to the bit rate.
Fig. 4 is a block diagram of t:he CT 8. A digital processor (referred to as a CPU hereinafter) 11 such as a microprocessor is used in the CT ~. The CPU 11 is connected to a permanent memory (referred to a~ a RQM hereinafter) 12, a programmable memory (referred to as a RAM hereinafter) 14, a display (referred to as a DP) lS such as a numerical display, a universal asynchronous reception and transmission unit (referred to as an I/F hereinafter) 17. The above components are connected to each other through a bus 18. A
program stored in the ROM 12 is used under the control of ~:~ 15 the CPU~ll, and a control operation is performed while predetermined data is accessed to the RAM 13.
If desired input data is supplied at the RB 14, the CPU
11 controls the VART 16 and sends a gate pulse "Pcgl n as an a~ ~high level) signal to the I/F 17. The AND gate 19 is turned on to gate the ~H" pulse from the U~R~ 16 to a current controller (referred to as a CC hereinafter) 20.
Therefore, a current Ic is supplied from the terminal Tl to the terminal T2.
A voltage between the line~ 11 and 12 is supplied to a filter (referred to as an FL hereinafter) 21 for filtering '~
-ln~
only a frequency component of the digital signal. The filtered signal is then supplied to one input terminal of a comparator ~referred to as a CP hereinafter3 22. The filtered signal is compared by th~ CP 22 with a reference voltage Ecs supplied to the other input terminal thereof.
The CP 22 extracts as an output a level exceeding the reference voltage Ecso For this reason, after the transmission of the command signal REQ, a gate pulse ~Pcg2~ i8 sent out as an "H~ pulse from the I/F 17 when the output representing the start bit B0 of the measured value word WPV is supplied through the I/F 17. The AND gate 23 is turned ON, and then the output representing the bit Bl and the subfiequent bits is sent to the UART 16. The resulting data is displayed on the DP 15 is response to this outpout. Even if the TX 3 repeatedly transmits the measured value word WPV, the reception is normally performed~ Therefore, the measured value can be ~; ~isplayed on ~he DP 15.
Fig. 5 is a circuit diagram of the CC 20. A
trans~ission pulse from the AND gate 19 through a noise reduction low-pass filter consisting of a resistor Rl and a ~ capacitor Cl i8 amplified by a differential amplifier - (referred to as an A hereinafter) 31 to turn on a transistor Ql such as a field effect transistor. The current Ic is supplied through resistors R2 and R3. A voltage across the lZ93S5~
resistor R3 is negatively fed back to the A 31 through a resistor R4 so that the current Ic is maintained at a predetermined value.
Fig. 6 is a perspective pictorial view showing the outer physical appearance of the CT 8. The DP 15 and the KB 14 are arranged on a portable case 41. At the same time, a cord 42 extends outside the case 41. Clips 43 are line terminals Tl and T2 connected at the distal end of the cord 42. Therefore, the CT 8 can be detachably connected to transmission lines 11 and 12.
B` Fig. ~ is a block diagram of the TX 3. In the same manner as in Fig. 4, a CPU 51 is connected to a ROM 52, a RAM 53, a UART 54, and an I/F 55 through a bus 56. The CPU
51 performs the control operation in the same manner as in - 15 Fig. 4. In addition, the TX 3 further includes a multiplexer (referred to as an MPX hereinafter) 59 for selecting a pressure sensor (referred to as a PSS
hereinafter) 57 for detecting a pressure difference or the like, or a temperature sensor (referred to as a TSS) 58 for detecting a temperature of the PSS 57, and an analog-to-digital converter (referred to as an ADC
hereinafter) 60 for converting an output from the MPX 59 into a digital signal.
A direct current power source circuit ~referred to as a PSC hereinafter) 61 is connected to the terminal Tl~ In ~293~C ~
this case, a current of 4 mA from the line 11 is received and stabilized as a local power source Et. The source Et is supplied to the respective components by electrical connection lines which have been omitted for the sake of clarity. The voltage between the tran~ission lines ll and 12 is filtered through a FL 62 such as a band-pass filter for filtering only the frequency component of the digital signal therethrough. The filtered outp9ut is supplied to a CP 63 in the same manner as in Fig. 4. The filtered output is compared with a reference voltage Ets and the CP 63 generates a reception output. The reception output is supplied to the UART 54 through an AND gate 64.
If the ~H" gate pulse RPtgl" is sent in the reception mode after the measured value word WPV is completely sent, the AND gate 64 is turned ON. During the ON state of the AND gate 64, the command signal REQ is sent. In response to the command signal REQ, the reception output from the CP 63 is sent to the UART 54 to receive the command signal REQ.
Thereafter, the CC 65 is turned off, and repetitive transmission of the measured value word WP~ is interrupted.
Upon reception of the command signal REQ, the CPU 51 ~ends the ~a gate pulse ~Ptg2~ through the I/F 55 and at the same time controls the UART 54. The transmission pulse i5 sent to the CC 65 through the AND gate 66. The current corresponding to the word WRE is supplied through the CC 65.
35~-~
When transmission of the words WPV and WRE representing the measured value and the response signal as described with reference to Fig. 3 is completed, the CPU 51 repeats sending out the transmission pulse in response to the measured value ; 5 word WPV, thereby repetitively sending the measured value.
The arrangement of the CC 65 is the same as that in Fig~ 5.
Th~ TX 3 includes a nonvolatile memory 52 s~ch ~s an EAROM
whereby required data is stored in the nonvolatile memory 52. Even if a power failure occurs, the data can be retained in the nonvolatile memory 52.
The CPU 51 controls the MPX 59 to alternately fetch the outputs from the PS 57 and the TS 58 at every predetermined interval. The fetched data is stored in the RAM 53. The CPU 51 then performs conversion operations of the detection output from the PS 57 and encodes the measured value. The coded measured value is sent to the UART 54 so that the measured value word WPV is sent. However~ depending on the content& of the command signal REQ, the detection outpgut from the TS 58 i sent out in the same manner as described above, or the outputs from the PS 57 and the TS 58 are sent alternately or in a combination thereof.
; Figs~ 7(A) and 7(B) are flow charts showing the operations of the CPVs for controlling the CT 8 and the TX
BACRGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a transmitter suitable for transmitting varivus measuxed values through a two-wire transmission line.
20 Description of the Prior Art In ord~r to transmit outputs from a differential pressure transmitter, an electromagnetic flowmeter or the like representing measured values to a remote location according to conventional industrial measurement techniques, a unique signal having a current level within a range of 4-20 mA is used. Thus, an analog signal having a current ; level selected from this range represents a measured value.
. Such differential pressure transmitters, electromagnetic ; 15 flowmeter~ and the like are normally arranged in a distributed manner to monitor industrial process states in a wide physical area. Maintenance personnel must travel ; extensively to maintain and inspect the di~tributed measuring instruments 50 as to perform adjustments and check the operating conditions thereof. In order to eliminate such time-consuming maintenance or the like, existing equipment is utilized to achieve remote control operation of the measuring instruments, as described in U.S. Patent No.
~,520,488.
~k 1~3S~- ~
As shown therein9 a transmitter is bridged to a two-wire transmission line to transmit a digital signal. After the digital signal is received by a receiver, the transmitter stops transmitting an analog measured value signal and responds to a digital signal from a communicator. The response signal is then received by the com~unicator. A
similar mode of operation is achieved for digital signal communication between the communicator and the transmitterO
Since when the transmitter communicates with the communicator by means of the digital signal, the transmitter stops transmitting the analog signal, i.e., stops transmitting the measured value, if the measured value concurrently changes, the changed measured value cannot be immediately transmitted to the receiver. Therefore, the receiver cannot perform an immediate control operation according to the changed measured value. This impairs the ability of the state of equipment to be controlled to follow changes in the measured values.
SUMMARY OF THE INVENTION
It i8, therefore, an object of the present invention to provide a transmitter capable of transmitting at least one mea~ured value within a predetermined period determined in ~ association with a system and control operation~ so that an ; operating state of equipment to be controlled can always ~ 25 follow changes in measured value, even while the transmitter 3~
communicates with a communicator to exchange digital signals representing various types of data.
In order to achieve the above object of the pre.sent invention, there is provided a transmitter for repeatedly transmitting measured values of digital signals through a two-wire transmission line, comprising means for receiving a command signal as a digital signal sent from a communicator through the transmission line, and control means for transmitting a respon.se signal responsive to the command signal upon its reception so as to transmit at least one measured value within a predetermined period.
In accordance with the present invention, there is provided a transmit~er for transmitting a measured value of a process variable in the form of a dlgital signal through a two-wire transmission line by a change in current in the two-wire ransmission line comprising means for receiving a digital command signal supplied through said two-wire transmission line and control means for adding the measured value to a digital response signal generated in response to the digital command signal and for transmitting a resultant digital signal so as to transmit on the two-wire transmission line at least one measured value within a predetermined time period.
In accordance with the present invention, there is also provided a transmitter for repeatedly transmitting a measured value of a process variable in the form of a digital signal through a two~wire transmission line by a change in a current in the two-wire transmission line comprising means for receiving a digital command signal supplied through said two-wire transmission . ~
35~
4a 641~9-965 line and control means for adding the measured value to a digital response signal generated in response to the digital commancl signal and for repeatedly transmitting a resultant digital signal so as to transmit on the two-wire transmission line at least one measured value within a predetermined time period.
In accordance with the present invention, there is also provided a transmitter for transmitting a measured value of a ~ cliS~t~
process variable in the form of a ~i~ through a two-wire transmission line by a change in a current in the two-wire 10 transmission line comprising means for receiving a digital command signal supplied through said two-wire transmission line, means for 1~ n~_ diyitally transmitting on said transmission/at least one measured value of the process variable within a predetermined time period and control means for adding the measured value to a response signal generated in response to the digital command signal and for transmitting a resultant digital signal on said transmission line.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig.1 is a block diagram showing an overall two-wire transmission system configuration, Fig. 2 is a block diagram of a transmitter suitable for use in the system shown in Fig. 1 according to a first embodiment of the present invention, Fig. 3 is a timing chart of a waveform showing changes in current for the two-wire transmission system, Fig 4 is a block diagram of a communicato~ used in the system shown in Fig. 1, Fig. 5 is a circuit diayram of a current controller used in the system shown in Fig. 2, ~2~35~0 4b 64159-965 Fig 6 is a perspec~ive pictorial view ~howin~ an outer physical appearan~e of the com~unlcator shown in Fig. 5, ~2~35~
Figs. 7(A) and 7(B) are flow charts for explaining the control operations, and - Figs. 8(A) to 8(C) are timing charts for explaining a second embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 is ~ block diagram showing an overall two-wire transmisslon system configuration utilizing the present invention. A direct current (DC) power source (re~erred to as a PS hereinafter) 2 is connected to one and of a two-wire ; 10 transmission line (referred to as a transmission line) 1 consisting of signal lines 11 and 12 to supply a current thereto. A transmitter ~referred to as a TX hereinafter) 3 such as a pressure difference transmitter and an electromagnetic flowmeter is connected to the other end of the transmission line. The TX3 3 controls a current I in the transmission line 1 to generate signal pulses. The signal pulses are sent as a digital signal representing a measured proceRs variable value onto the tranQmiscion line 1.
A resistor RL as a voltage dropping element is inserted in series with the tr~nQmissiOn line 1. A voltage across the resistor RL is supplied to a receiver ~referred to as an RX hereinafter) 4 whereby the RX ~ receives the transmitted signal. An output signal from the RX 4 is sent to a main 25 controller (referred to as an MC hereinafter) 6 such as a .~ .
12~3S~
computer through a bus S. Control operations by the MC 6 are performed on the basis of the measured value represented by the digital output signal supplied from the RX 4.
Control data i5 sent to controlled equipment (not shown) through the ~us 5, thereby controlling the equipment.
An operation unit (referred to as an OP hereinafter) 7, which can include a CRT display and a keyboard, is connected to a bus 5' through an interface treferred to as an I/F
hereinafter) 9, for displaying a controlled state of the equipment and inputting a command to the ~C 6 and the ~x 4.
A portable communicator (referred to as a CT hereinafter) 8 is bridged in the transmission line nearer to the TX 3 than the resistor RL. The CT 8 converts the current I into siqnal pulses and sends them as a digital command signal to the ~X 3. The TX 3 receives the command signal and converts the current I into signal pU18eS as a response signal which i5 sent to the CT 8 in response to the command signal.
~ ig. 3 shows a waveform of changes in current I supplied through the resistor RL as a function of time ~t~. In this ~ 20 case, the digital si~nal i8 a pulse code, the current of ; which changes in the range of Il to I2, e.g., 4-20 mA. A
~; measured process value word WPV determined by the measured value from the TX 3 comprises 4-byte data consisting of bytes BY0 to BY3 (each byte consists of eight bits). If the length of time for each of the bytes BY0 to BY3 is ~tl~, ~ ~335i~
e g., 50 msec, the length of time of the measured value word WPV is "4tln, and the disable per:iod following the word WPv : is ~tl~. The measured value word WPV is repeatedly . transmitted by changes in current ~It" suppIied across the lines of the TX 3, thereby always transmitting the newest measured value to the RX 4.
- In this state, a command signal REQ as a pulse coda is transmitted ~ithin a reception wait period ~t2 shorter than the disable period ~tl~ by changing of a current Ic supplied from the CT 8 to line terminals Tl and T2 at the end of transmission of the measured value word WP~. The change in current causes a change in voltage across the resistor RL.
The change in voltage across the resistor RL is sent as a change in voltage between the signal lines ll and 12 to the TX 3. Therefore, the command signal REQ is received by the ; TX 3.
The TX 3 stops tran mitting the measured value word WPV
in response to the command signal REQ and sends back a 2-byte response word WRE corresponding to the command signal REQ by mean of the current It. In this case, the TX 3 ~ transmits at leact one measured value word within a : predetermined period ~l which is determined in accordance with the system's control and safety requirements. If the response word WRE is long, it is divided into WRE1, WRE2, :; 25 WRE3,0..... which are then sequentially time-divisionally ~Z~33S~
sent. Referring to Fig. 3, the period T2 shorter than the predetermined period T1 is monitored. If the short period T2 exceeds the predetermined period Tl, the response word WPV is partially sent to assure the system control and safety measures, and the remaining portion of the response ~-word WPV is then sent. After transmission of the response word WPV, the period T2 is monitored. If the period T2 exceeds the period Tl, the response word WPV is transmitted. The relationship between the periods Tl and T2 is determined to transmit one WPV within Tl. Thus, the voltage between the lines 11 and 12 is changed, and this change is received by the C~ 8.
-~A start bit B0 of bits B0 to B31 in the start byte BY0 in the measured word WPV represents status ST indicating whether the TX 3 is normally operated. The bit Bl represents a proportional relation L, i.e.~ a linear relationship between the measured value and the control value according to sensor characteristics, or a squared proportlonal relationship S, i.e., a relationship representing that the measured value is a square of the control value. The bit B2 represents the number NB of continuouk bytes, i.e., that the number of continuous bytes is four or six. The bits B4 to B7 represent the type DA of the measured value transmitted by the bytes BYl to BY3. In the byte ater byte 8~1, the bits B4 to B7 represent a ~L~935~ ~
measured value DPV. The number of bytes of each word and the number of bits of each byte can be determined according to the control states. The periocls "tl~ to "t3" are also peoperly determined according to the bit rate.
Fig. 4 is a block diagram of t:he CT 8. A digital processor (referred to as a CPU hereinafter) 11 such as a microprocessor is used in the CT ~. The CPU 11 is connected to a permanent memory (referred to a~ a RQM hereinafter) 12, a programmable memory (referred to as a RAM hereinafter) 14, a display (referred to as a DP) lS such as a numerical display, a universal asynchronous reception and transmission unit (referred to as an I/F hereinafter) 17. The above components are connected to each other through a bus 18. A
program stored in the ROM 12 is used under the control of ~:~ 15 the CPU~ll, and a control operation is performed while predetermined data is accessed to the RAM 13.
If desired input data is supplied at the RB 14, the CPU
11 controls the VART 16 and sends a gate pulse "Pcgl n as an a~ ~high level) signal to the I/F 17. The AND gate 19 is turned on to gate the ~H" pulse from the U~R~ 16 to a current controller (referred to as a CC hereinafter) 20.
Therefore, a current Ic is supplied from the terminal Tl to the terminal T2.
A voltage between the line~ 11 and 12 is supplied to a filter (referred to as an FL hereinafter) 21 for filtering '~
-ln~
only a frequency component of the digital signal. The filtered signal is then supplied to one input terminal of a comparator ~referred to as a CP hereinafter3 22. The filtered signal is compared by th~ CP 22 with a reference voltage Ecs supplied to the other input terminal thereof.
The CP 22 extracts as an output a level exceeding the reference voltage Ecso For this reason, after the transmission of the command signal REQ, a gate pulse ~Pcg2~ i8 sent out as an "H~ pulse from the I/F 17 when the output representing the start bit B0 of the measured value word WPV is supplied through the I/F 17. The AND gate 23 is turned ON, and then the output representing the bit Bl and the subfiequent bits is sent to the UART 16. The resulting data is displayed on the DP 15 is response to this outpout. Even if the TX 3 repeatedly transmits the measured value word WPV, the reception is normally performed~ Therefore, the measured value can be ~; ~isplayed on ~he DP 15.
Fig. 5 is a circuit diagram of the CC 20. A
trans~ission pulse from the AND gate 19 through a noise reduction low-pass filter consisting of a resistor Rl and a ~ capacitor Cl i8 amplified by a differential amplifier - (referred to as an A hereinafter) 31 to turn on a transistor Ql such as a field effect transistor. The current Ic is supplied through resistors R2 and R3. A voltage across the lZ93S5~
resistor R3 is negatively fed back to the A 31 through a resistor R4 so that the current Ic is maintained at a predetermined value.
Fig. 6 is a perspective pictorial view showing the outer physical appearance of the CT 8. The DP 15 and the KB 14 are arranged on a portable case 41. At the same time, a cord 42 extends outside the case 41. Clips 43 are line terminals Tl and T2 connected at the distal end of the cord 42. Therefore, the CT 8 can be detachably connected to transmission lines 11 and 12.
B` Fig. ~ is a block diagram of the TX 3. In the same manner as in Fig. 4, a CPU 51 is connected to a ROM 52, a RAM 53, a UART 54, and an I/F 55 through a bus 56. The CPU
51 performs the control operation in the same manner as in - 15 Fig. 4. In addition, the TX 3 further includes a multiplexer (referred to as an MPX hereinafter) 59 for selecting a pressure sensor (referred to as a PSS
hereinafter) 57 for detecting a pressure difference or the like, or a temperature sensor (referred to as a TSS) 58 for detecting a temperature of the PSS 57, and an analog-to-digital converter (referred to as an ADC
hereinafter) 60 for converting an output from the MPX 59 into a digital signal.
A direct current power source circuit ~referred to as a PSC hereinafter) 61 is connected to the terminal Tl~ In ~293~C ~
this case, a current of 4 mA from the line 11 is received and stabilized as a local power source Et. The source Et is supplied to the respective components by electrical connection lines which have been omitted for the sake of clarity. The voltage between the tran~ission lines ll and 12 is filtered through a FL 62 such as a band-pass filter for filtering only the frequency component of the digital signal therethrough. The filtered outp9ut is supplied to a CP 63 in the same manner as in Fig. 4. The filtered output is compared with a reference voltage Ets and the CP 63 generates a reception output. The reception output is supplied to the UART 54 through an AND gate 64.
If the ~H" gate pulse RPtgl" is sent in the reception mode after the measured value word WPV is completely sent, the AND gate 64 is turned ON. During the ON state of the AND gate 64, the command signal REQ is sent. In response to the command signal REQ, the reception output from the CP 63 is sent to the UART 54 to receive the command signal REQ.
Thereafter, the CC 65 is turned off, and repetitive transmission of the measured value word WP~ is interrupted.
Upon reception of the command signal REQ, the CPU 51 ~ends the ~a gate pulse ~Ptg2~ through the I/F 55 and at the same time controls the UART 54. The transmission pulse i5 sent to the CC 65 through the AND gate 66. The current corresponding to the word WRE is supplied through the CC 65.
35~-~
When transmission of the words WPV and WRE representing the measured value and the response signal as described with reference to Fig. 3 is completed, the CPU 51 repeats sending out the transmission pulse in response to the measured value ; 5 word WPV, thereby repetitively sending the measured value.
The arrangement of the CC 65 is the same as that in Fig~ 5.
Th~ TX 3 includes a nonvolatile memory 52 s~ch ~s an EAROM
whereby required data is stored in the nonvolatile memory 52. Even if a power failure occurs, the data can be retained in the nonvolatile memory 52.
The CPU 51 controls the MPX 59 to alternately fetch the outputs from the PS 57 and the TS 58 at every predetermined interval. The fetched data is stored in the RAM 53. The CPU 51 then performs conversion operations of the detection output from the PS 57 and encodes the measured value. The coded measured value is sent to the UART 54 so that the measured value word WPV is sent. However~ depending on the content& of the command signal REQ, the detection outpgut from the TS 58 i sent out in the same manner as described above, or the outputs from the PS 57 and the TS 58 are sent alternately or in a combination thereof.
; Figs~ 7(A) and 7(B) are flow charts showing the operations of the CPVs for controlling the CT 8 and the TX
3, respectively. More pecifically, Fig. 7(A~ shows the control operation of the CPU 11 in the CT 8, and Fig. 7(B) ;
1~9 3 ~ ~3 : shows the control operation of the CPU 51 in the TX 3.
Referring to Fig. 7(A), the CPU 11 determines in step 101 : whether a transmission request is presen~. If YES in step 101, the CPU 11 determines in step 102 whether WPV is received. If YES in step 102, a counter incorporated in the ~: CPU 11 for defining the transmission timing is restarted toperform ~Setting of Synchronous State with WPV~. ~he CPU 11 determines whether the next WPV has been received. If YES
in lll according to the transmission timing on the basis of a frequency-divided output of the clock pulse by means of this counter, the command signal REQ is sent out in step : 112. The program flo~ advances to ~Exit" and other routinesand then returns to step 101. The command signal REQ is transmitted as soon as the measured value word WPV is completely transmitted, as shown in Fig. 3.
:;
: Referring to Fig7 7~B), the CPU 51 performs ~Timer Clear : (t)~ for clearing the timer for monitoring a predetermined period and for causing the timer to ætart counting in step 201. The CPU 51 then sends the measured value word ~PV in step 202 and sets the reception mode in step 211. The CPU
51 then determines in step 212 whether the reception wait period ~tl~ (Fig. 3) has elapsed after the end of step 201.
If NO in step 212, the CPU 51 determines in step 222 whether the command signal REW is received. If NO in step 222, the operations in step 212 and the subsequent ~teps are 1~3~
repeated. ~owever, if YES in step 222 while NO in step 212, the program flow advances to step 231. The CPU 51 deter~ines in step 231 whether the reception is completed.
If YES in step 231, the CPU 51 performs ~n = 1" in step 241. The CPU 51 then sends the response signal word WREn in step 242, as described with reference to Fig. 3. The CPU 51 performs "n = n + 1~ in step 251. The CPU 51 determines in step 252 whether the response is completed. While NO in step 252, the CPU 51 determines in step 252 whether the timer time "t~ exceeds ~T2~. If N0 in step 261, the flow returns to step 242. However, if YES in step 261, the word WPV is sent in step 262 so as to completely send the word WPV within the predetermined period Tl. After the word WPV
is sent, the timer is cleared in step ~71. The CPU 51 then monitors the period T2, and the flow returns to step 242.
If YES in step 212 while N0 in step 222, the program flow advances to step 322. If the CP~ determines that the disable period tl has elapsed, i.e., if YES in step 232, the operations in step 201 and the subsequent steps are repeated.
The start of reception of the command signal REQ is allowed for a short reception wait period ~t2" after the end of transmission of the measured value word WPV. During this period, if the command signal REQ is received, the gate pulse "Ptgl" is continuously sent out until the recep~ion is 3SS~
completed. However, if reception is not performed within the reception wait period ~t2", the gate pulse "ptgln is disabled after the lapse of the pleriod "t2~. The reception mode is cancelled to prevént an o~peration failure caused by reception of noise or the like.
The insertion of the disable period ~tlR allows the RX 4 to detect the start of each word Eollowing the reception ; wait period ~t2N upon detection of the disable period "tla.
The number NB of bytes in Fig. 3 counted from this timing are fetched as significant bytes. Therefore, only the measured value word WPV can be accurately received.
An address code or the like for designating a destination need not be added to each word and each signal, and communication between the TX 3 and the RX 4 can be accurately performed while system disturbance is properly eliminated during measured value transmission between the TX
3 and the RX 4. At the same time, the RX 4 causes a simple means such as timer to selectively receive the measured value word WPV.
Figs. 8(A) to 8(C) are timing charts showing another embodiment of the present invention. Fig. 8(A) shows a case wherein a mea~ured value word WPV and a response word WRE
are sent together as 14-byte data within a time period "14tln. Fig. 8(B) shows a case wherein the measured value word WPV based on the newest measured value is transmitted ~35r 33 twice after reception of the oommand signal REQ, and then the measured value word WPV and the response signal word WRE
are sent as 14-byte data in the same manner as in Fig. 8(A).
If the measured value word TPV based on the ne~est measured value is always sent to the RX 4, it is suitable to allow the TX 4 to perform a control function. Howeverl for allowable variations in measured values, the immediately preceding value may be repeatedly sent. If a variation exceeding the allowable range occurs, the newest measured value may be sent.
Referring to Fig. 8(C), the TX 3 interrupts transmission of the measured value word WPV in response to tbe command signal REQ. When a predetermined period "t3 n has elapsed after the end of the command signal REQ, 4-byte measured value word WPV and 2-byte response word WRE in response to the command signal REQ are sent together by means of a current It. This transmission for a period "6tl~ ~rom a ~tart word WREtS) to an end word WRE(E) is repeatedly performed throu~h the disable period "tl~. The measured value word WPV is repeatedly sent again.
Transmission of data including the measured value word WPV ~uarantees transmission of the meaaured value while the CT 8 communicates with the TX 3. The control state in the RX 4 can always follow the changes in measured value and the response time of the control state is improved. The :;
~IL293~
measured value word WPV and the response signal word WRB are sent together when the predetermined period t3 has elapsed, thereby easily discriminating the measured value word WPV
and preventing control disturbance in the RX 4.
The predetermined period ~t3~ can be defined not only by a timer but also by various time defining means. For example, a transmission timing defi~ition pulse may be generated by freque~cy-dividing a clock pulse~ and the timer time may be defined by a transmission timing pulse after reception of the control signal REQ.
In the above embodiment, the CPU 51 is used as a control means. However, the control means may be a control circuit constitued by a combination of various logic circuits.
Referring to Fig. 3, a parity check bit may be added to each byte or an identification code or the like of the TX 3 may be added. The period ~tl~ may be equal to the period t3 according to given conditions.
According to the present invention as is apparent from the above description, there has been provided, a transmitter whereby the transmi~sion of the measured value can be performed during communication between the T% and the C~. The control state in the RX can follow changes in the measured value. At the same tlme, the reception of the measured value can be discriminated in the RX since the predetermined period is set.
1~9 3 ~ ~3 : shows the control operation of the CPU 51 in the TX 3.
Referring to Fig. 7(A), the CPU 11 determines in step 101 : whether a transmission request is presen~. If YES in step 101, the CPU 11 determines in step 102 whether WPV is received. If YES in step 102, a counter incorporated in the ~: CPU 11 for defining the transmission timing is restarted toperform ~Setting of Synchronous State with WPV~. ~he CPU 11 determines whether the next WPV has been received. If YES
in lll according to the transmission timing on the basis of a frequency-divided output of the clock pulse by means of this counter, the command signal REQ is sent out in step : 112. The program flo~ advances to ~Exit" and other routinesand then returns to step 101. The command signal REQ is transmitted as soon as the measured value word WPV is completely transmitted, as shown in Fig. 3.
:;
: Referring to Fig7 7~B), the CPU 51 performs ~Timer Clear : (t)~ for clearing the timer for monitoring a predetermined period and for causing the timer to ætart counting in step 201. The CPU 51 then sends the measured value word ~PV in step 202 and sets the reception mode in step 211. The CPU
51 then determines in step 212 whether the reception wait period ~tl~ (Fig. 3) has elapsed after the end of step 201.
If NO in step 212, the CPU 51 determines in step 222 whether the command signal REW is received. If NO in step 222, the operations in step 212 and the subsequent ~teps are 1~3~
repeated. ~owever, if YES in step 222 while NO in step 212, the program flow advances to step 231. The CPU 51 deter~ines in step 231 whether the reception is completed.
If YES in step 231, the CPU 51 performs ~n = 1" in step 241. The CPU 51 then sends the response signal word WREn in step 242, as described with reference to Fig. 3. The CPU 51 performs "n = n + 1~ in step 251. The CPU 51 determines in step 252 whether the response is completed. While NO in step 252, the CPU 51 determines in step 252 whether the timer time "t~ exceeds ~T2~. If N0 in step 261, the flow returns to step 242. However, if YES in step 261, the word WPV is sent in step 262 so as to completely send the word WPV within the predetermined period Tl. After the word WPV
is sent, the timer is cleared in step ~71. The CPU 51 then monitors the period T2, and the flow returns to step 242.
If YES in step 212 while N0 in step 222, the program flow advances to step 322. If the CP~ determines that the disable period tl has elapsed, i.e., if YES in step 232, the operations in step 201 and the subsequent steps are repeated.
The start of reception of the command signal REQ is allowed for a short reception wait period ~t2" after the end of transmission of the measured value word WPV. During this period, if the command signal REQ is received, the gate pulse "Ptgl" is continuously sent out until the recep~ion is 3SS~
completed. However, if reception is not performed within the reception wait period ~t2", the gate pulse "ptgln is disabled after the lapse of the pleriod "t2~. The reception mode is cancelled to prevént an o~peration failure caused by reception of noise or the like.
The insertion of the disable period ~tlR allows the RX 4 to detect the start of each word Eollowing the reception ; wait period ~t2N upon detection of the disable period "tla.
The number NB of bytes in Fig. 3 counted from this timing are fetched as significant bytes. Therefore, only the measured value word WPV can be accurately received.
An address code or the like for designating a destination need not be added to each word and each signal, and communication between the TX 3 and the RX 4 can be accurately performed while system disturbance is properly eliminated during measured value transmission between the TX
3 and the RX 4. At the same time, the RX 4 causes a simple means such as timer to selectively receive the measured value word WPV.
Figs. 8(A) to 8(C) are timing charts showing another embodiment of the present invention. Fig. 8(A) shows a case wherein a mea~ured value word WPV and a response word WRE
are sent together as 14-byte data within a time period "14tln. Fig. 8(B) shows a case wherein the measured value word WPV based on the newest measured value is transmitted ~35r 33 twice after reception of the oommand signal REQ, and then the measured value word WPV and the response signal word WRE
are sent as 14-byte data in the same manner as in Fig. 8(A).
If the measured value word TPV based on the ne~est measured value is always sent to the RX 4, it is suitable to allow the TX 4 to perform a control function. Howeverl for allowable variations in measured values, the immediately preceding value may be repeatedly sent. If a variation exceeding the allowable range occurs, the newest measured value may be sent.
Referring to Fig. 8(C), the TX 3 interrupts transmission of the measured value word WPV in response to tbe command signal REQ. When a predetermined period "t3 n has elapsed after the end of the command signal REQ, 4-byte measured value word WPV and 2-byte response word WRE in response to the command signal REQ are sent together by means of a current It. This transmission for a period "6tl~ ~rom a ~tart word WREtS) to an end word WRE(E) is repeatedly performed throu~h the disable period "tl~. The measured value word WPV is repeatedly sent again.
Transmission of data including the measured value word WPV ~uarantees transmission of the meaaured value while the CT 8 communicates with the TX 3. The control state in the RX 4 can always follow the changes in measured value and the response time of the control state is improved. The :;
~IL293~
measured value word WPV and the response signal word WRB are sent together when the predetermined period t3 has elapsed, thereby easily discriminating the measured value word WPV
and preventing control disturbance in the RX 4.
The predetermined period ~t3~ can be defined not only by a timer but also by various time defining means. For example, a transmission timing defi~ition pulse may be generated by freque~cy-dividing a clock pulse~ and the timer time may be defined by a transmission timing pulse after reception of the control signal REQ.
In the above embodiment, the CPU 51 is used as a control means. However, the control means may be a control circuit constitued by a combination of various logic circuits.
Referring to Fig. 3, a parity check bit may be added to each byte or an identification code or the like of the TX 3 may be added. The period ~tl~ may be equal to the period t3 according to given conditions.
According to the present invention as is apparent from the above description, there has been provided, a transmitter whereby the transmi~sion of the measured value can be performed during communication between the T% and the C~. The control state in the RX can follow changes in the measured value. At the same tlme, the reception of the measured value can be discriminated in the RX since the predetermined period is set.
Claims (15)
1. A transmitter for transmitting a measured value of a process variable in the form of a digital signal through a two-wire transmission line by a change in current in the two-wire transmission line comprising means for receiving a digital command signal supplied through said two-wire transmission line and control means for adding the measured value to a digital response signal generated in response to the digital command signal and for transmitting a resultant digital signal so as to transmit on the two-wire transmission line at least one measured value within a predetermined time period.
2. A transmitter according to claim 1 wherein the measured value is sent as a newest measured value is interrupted for said predetermined time period.
3. A transmitter according to claim 1 wherein the reception of the command signal utilizes a change in an interline voltage of said two-wire transmission line.
4. A transmitter according to claim 1 and including means for monitoring said predetermined period comprising a timer.
5. A transmitter according to claim 1 wherein said control means comprises a digital processor.
6. A transmitter for repeatedly transmitting a measured value of a process variable in the form of a digital signal through a two-wire transmission line by a change in a current in the two-wire transmission line comprising means for receiving a digital command signal supplied through said two-wire transmission line and control means for adding the measured value to a digital response signal generated in response to the digital command signal and for repeatedly transmitting a resultant digital signal so as to transmit on the two-wire transmission line at least one measured value within a predetermined time period.
7. A transmitter according to claim 6 wherein the measured value is sent as a newest measured value after the repetitive transmission of the measured value is interrupted for said predetermined time period.
8. A transmitter according to claim 6 wherein the reception of the command signal utilize a change in an interline voltage of said two-wire transmission line.
9. A transmitter according to claim 6 and including means for monitoring said predetermined period comprising a timer.
10. A transmitter according to claim 6 wherein said control means comprises a digital processor.
11. A transmitter for transmitting a measured value of a process variable in the form of a digital signal through a two-wire transmission line by a change in a current in the two-wire transmission line comprising means for receiving a digital command signal supplied through said two-wire transmission line, means for digitally transmitting on said transmission line at least one measured value of the process variable within a predetermined time period and control means for adding the measured value to a response signal generated in response to the digital command signal and for transmitting a resultant digital signal on said transmission line.
12. A transmitter according to claim 11 wherein the measured value is sent as a newest measured value after the transmission of the measured value is interrupted for said predetermined time period,
13. A transmitter according to claim 11 wherein the reception of the command signal utilizes a change in an interline voltage of said two-wire transmission line.
14. A transmitter according to claim 11 and including means for monitoring a predetermined period comprising said time.
15. A transmitter according to claim 11 wherein said control means comprises a digital processor.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/914,031 US4806905A (en) | 1986-10-01 | 1986-10-01 | Transmitter for transmitting on a two-wire transmitting line |
| US914,031 | 1986-10-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1293550C true CA1293550C (en) | 1991-12-24 |
Family
ID=25433833
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000548222A Expired - Lifetime CA1293550C (en) | 1986-10-01 | 1987-09-30 | Transmitter for transmitting on a two-wire transmitting line |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4806905A (en) |
| JP (1) | JPH0824392B2 (en) |
| CA (1) | CA1293550C (en) |
Families Citing this family (36)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5896418A (en) * | 1983-06-16 | 1999-04-20 | Hitachi, Ltd. | Data transmission system having a communication control computer for controlling communication between a communication interface module and terminal devices |
| FR2629609B1 (en) * | 1988-03-31 | 1990-12-28 | Jacques Lewiner | IMPROVEMENTS TO ELECTRONIC INTERROGATION CIRCUITS |
| NO303200B1 (en) * | 1988-11-04 | 1998-06-08 | Merlin Gerin | Building engineering control unit with two-wire data and power supply line |
| JPH0650557B2 (en) * | 1989-07-04 | 1994-06-29 | 株式会社日立製作所 | Field instrument communication method |
| EP0495001B1 (en) * | 1989-10-02 | 1999-02-17 | Rosemount Inc. | Field-mounted control unit |
| FR2668846B1 (en) * | 1990-11-07 | 1993-02-12 | Rasec Communication Sa | ELECTRONIC DATA DISPLAY DEVICE. |
| CA2049618A1 (en) * | 1991-07-18 | 1993-01-19 | Christopher J. O'brien | Integrated transmitter and controller |
| CA2107519C (en) * | 1992-10-05 | 2002-04-09 | Stephen George Seberger | Communication system and method |
| US5469746A (en) * | 1993-03-30 | 1995-11-28 | Hitachi, Ltd. | Electromagnetic flow meter |
| US5652755A (en) * | 1994-02-03 | 1997-07-29 | Boehringer Mannheim Corporation | Printer interface system |
| DE4405037A1 (en) * | 1994-02-17 | 1995-08-24 | Sel Alcatel Ag | Network and apron termination device of a telecommunications network |
| AU692201B2 (en) * | 1994-02-17 | 1998-06-04 | Alcatel N.V. | Network termination unit |
| US5710552A (en) * | 1994-09-30 | 1998-01-20 | Rosemount Inc. | Barrier device |
| NO951291L (en) * | 1995-04-04 | 1996-10-07 | Einar Gotaas | Method and system for two-way data communication between a central unit and a number of stations |
| US5610552A (en) * | 1995-07-28 | 1997-03-11 | Rosemount, Inc. | Isolation circuitry for transmitter electronics in process control system |
| JP2882316B2 (en) * | 1995-08-29 | 1999-04-12 | 株式会社デンソー | Data communication device |
| EP0825506B1 (en) * | 1996-08-20 | 2013-03-06 | Invensys Systems, Inc. | Methods and apparatus for remote process control |
| US5694109A (en) * | 1996-09-04 | 1997-12-02 | International Controls And Measurement Corp. | Two-wire dc communication system and transceiver |
| DE19723645B4 (en) * | 1997-06-05 | 2006-04-13 | Endress + Hauser Gmbh + Co. Kg | Arrangement for signal transmission between a donor site and a receiving site |
| US6480510B1 (en) * | 1998-07-28 | 2002-11-12 | Serconet Ltd. | Local area network of serial intelligent cells |
| US6640308B1 (en) | 1999-04-16 | 2003-10-28 | Invensys Systems, Inc. | System and method of powering and communicating field ethernet device for an instrumentation and control using a single pair of powered ethernet wire |
| WO2000070417A1 (en) * | 1999-05-17 | 2000-11-23 | The Foxboro Company | Process control configuration system with parameterized objects |
| US7089530B1 (en) * | 1999-05-17 | 2006-08-08 | Invensys Systems, Inc. | Process control configuration system with connection validation and configuration |
| US6788980B1 (en) * | 1999-06-11 | 2004-09-07 | Invensys Systems, Inc. | Methods and apparatus for control using control devices that provide a virtual machine environment and that communicate via an IP network |
| US6956826B1 (en) | 1999-07-07 | 2005-10-18 | Serconet Ltd. | Local area network for distributing data communication, sensing and control signals |
| US6549616B1 (en) | 2000-03-20 | 2003-04-15 | Serconet Ltd. | Telephone outlet for implementing a local area network over telephone lines and a local area network using such outlets |
| US6961303B1 (en) | 2000-09-21 | 2005-11-01 | Serconet Ltd. | Telephone communication system and method over local area network wiring |
| IL152824A (en) | 2002-11-13 | 2012-05-31 | Mosaid Technologies Inc | Addressable outlet and a network using same |
| IL159838A0 (en) | 2004-01-13 | 2004-06-20 | Yehuda Binder | Information device |
| US7761923B2 (en) * | 2004-03-01 | 2010-07-20 | Invensys Systems, Inc. | Process control methods and apparatus for intrusion detection, protection and network hardening |
| WO2006055948A1 (en) * | 2004-11-18 | 2006-05-26 | Panduit Corp. | Ethernet-to-analog controller |
| US7860857B2 (en) | 2006-03-30 | 2010-12-28 | Invensys Systems, Inc. | Digital data processing apparatus and methods for improving plant performance |
| RU2495476C2 (en) | 2008-06-20 | 2013-10-10 | Инвенсис Системз, Инк. | Systems and methods for immersive interaction with actual and/or simulated facilities for process, environmental and industrial control |
| US7779702B2 (en) * | 2008-11-03 | 2010-08-24 | Rosemount Inc. | Flow disturbance compensation for magnetic flowmeter |
| US8127060B2 (en) * | 2009-05-29 | 2012-02-28 | Invensys Systems, Inc | Methods and apparatus for control configuration with control objects that are fieldbus protocol-aware |
| US8463964B2 (en) * | 2009-05-29 | 2013-06-11 | Invensys Systems, Inc. | Methods and apparatus for control configuration with enhanced change-tracking |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1087266A (en) * | 1976-01-16 | 1980-10-07 | Reed H. Johnston | Method and apparatus for communication over electric power lines |
| US4520488A (en) * | 1981-03-02 | 1985-05-28 | Honeywell, Inc. | Communication system and method |
| JPS5925536A (en) * | 1982-07-30 | 1984-02-09 | シャープ株式会社 | Power line data transmission system |
-
1986
- 1986-10-01 US US06/914,031 patent/US4806905A/en not_active Expired - Lifetime
-
1987
- 1987-09-30 CA CA000548222A patent/CA1293550C/en not_active Expired - Lifetime
- 1987-09-30 JP JP62247759A patent/JPH0824392B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0824392B2 (en) | 1996-03-06 |
| JPS63121395A (en) | 1988-05-25 |
| US4806905A (en) | 1989-02-21 |
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| MKEX | Expiry |