Patent EP0591926A2 successfully refreshed from Google Patents.
EP0591926A2
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EP
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Communication system and method
Assignee: Fisher Controls International LLC
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Filing: 1993-10-05
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Granted: —
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Expires: 2013-10-05
Abstract
Abstract The present invention relates to a circuit which is connected to a two-conductor control system for a variable analog DC input and that also enables bidirectional digital communication along the two conductors for diagnostic operations of a transducer. The novel circuit includes a switch circuit that has a first position that provided the ability to accept both the variable DC analog signals and the bidirectional digital communication signals by presenting a first impedance (53) for the DC signals and a second switch position for providing a second substantially higher impedance (53) while using the same two-conductor system. The novel invention also includes an auxiliary analog input signal (56) to the circuit which allows further control as a current feedback to a control algorithm in a microcontroller. An auxiliary process transmitter (58) can sense pressure, temperature, flow or some other process related variable and couple it to the circuit for control of the transducers. Finally, the novel invention includes a novel voltage regulator (55) and a capacitive voltage supply for utilizing the voltage on the two conductors from the controller to also power the device.
Inventors
- 👤 Stephen G. Seberger
- 👤 Bruce F. Grumstrup
- 👤 George W. Gassman
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-28 19:11
CPC Classifications
G; G08; G08C; G08C19/00; G08C19/02; Y; Y10; Y10T; Y10T137/00; Y10T137/7722; Y10T137/7758; Y10T137/7761
Claims Analysis
Total Claims: 41
Claim 1
Independent Claim
140 words
A system (40) for communicating between a control system (32) and a remote transducer (43), the system comprising: a single pair (33) of first and second conductors coupled between the control system (32) and the remote transducer (43) for carrying variable analog DC current signals to the transducer to cause the transducer to perform selective tasks; and an instrument (42) forming part of the transducer (43) having first and second input terminals (51, 52) coupled to the single pair of first and second conductors (33) and having an output coupled to the transducer (34) for selectively coupling the variable analog DC control signals to the transducer and simultaneously enabling bidirectional digitally encoded communication signals concerning supplemental data to be transmitted between the circuit input terminals and the control system over the same single pair of first and second conductors (35).
Claim 2
Dependent Claim
21 words
A system as in claim 1 wherein the instrument (42) is located at the site of and controls the transducer (34).
Claim 3
Dependent Claim
21 words
A system as in claim 2 wherein the instrument (42) is located on and is a part of the transducer (34).
Claim 4
Dependent Claim
35 words
A system as in claim 3 wherein: the DC control signals range from 4-20 milliamps at the transducer (34) input terminals; and the digitally encoded communication signals have a frequency band of substantially 500-5000 Hz.
Claim 5
Dependent Claim
78 words
A system as in claim 1 wherein the instrument includes: a variable impedance line interface element (53) connected in series with the first input terminal (51); and impedance control means (57) coupled to the variable impedance line interface circuit (53) for providing a first acceptable impedance for the variable analog DC control signal and a second substantially higher and relatively constant impedance for receiving and transmitting the digitally encoded communication signals from and to the control system 32.
Claim 6
Dependent Claim
34 words
A system as in claim 5 wherein: the DC control signals range from 4-20 milliamp at the transducer input terminals; and the digitally encoded communication signals have a frequency band of substantially 500-5000 Hz.
Claim 7
Dependent Claim
160 words
A system as in claim 6 wherein the instrument (42) includes: a transceiver (58) coupled to the impedance control means (57) and to the single pair of conductor terminals (51, 52) for receiving the digital communication signals from the control system (32) on the single pair of conductors (35) at the second substantially higher frequencies by decoding, filtering, buffering, demodulating, accumulating and/or converting the digital information on the single pair of conductors (35) from serial to parallel as needed; the transceiver (58) serially transmitting digital information to the control system (32) by converting, modulating and/or wave shaping as needed and coupling the digital signals to the impedance control means (57); and the impedance control means (57) controlling the impedance with a variable impedance element (53) to affect the terminal voltage and loop current of the single pair of conductors coupled to terminals (51, 52) for both the variable DC and the second substantially higher band of frequencies for digital communications.
Claim 8
Dependent Claim
77 words
A system as in claim 7 further comprising: an actuator (16) coupled to the transducer; a current sensor element (54) coupled in series with one of the input terminals (51) and having an input and an output; and an analog circuit (56) coupled to the input of the current sensor element (54) to extract the DC analog input control signal from the single pair of conductors (35) to provide the desired output signal to the actuator (16).
Claim 9
Dependent Claim
146 words
A system as in claim 8 further comprising: electrical conductors (68) coupling actuator (16) feedback signals to the analog input circuitry (56) for monitoring physical properties of the transducer (43) and actuator (16) such as temperature, flow and pressure for digital transmission to the control system (32) on the single pair of conductors (35) at the second frequency; and a microcontroller circuit (59) coupled to the analog input circuitry (56) and the transceiver (58) to receive analog control signals on the single pair of conductors (35) at the first variable analog DC frequencies (34) and to process the digital communication signals received on the single pair of conductors (35) at the second band of substantially higher frequencies and to transmit digital communication signals on the single pair of conductors (35) to the control system (32) representing other process variables of the transducer (43) and actuator (16).
Claim 10
Dependent Claim
61 words
A system as in claim 5 wherein the variable impedance (53) comprises: at least one semiconductor element (53) having input, output and control terminals with its input and output terminals in series with the input terminals (51); and impedance control means (57) coupled to the control terminal of the at least one semiconductor element (53) to provide the desired impedance characteristic.
Claim 11
Dependent Claim
59 words
A system as in claim 10 wherein: at least one semiconductor element (53) comprises an N-channel FET having a source, drain and gate with its drain and source in series with the input terminal (51); and the impedance control element means (57) being coupled to the gate of the N-channel FET (53) to provide the desired device impedance characteristic.
Claim 12
Dependent Claim
55 words
A system as in claim 11 wherein the current sense element (54) comprises a resistor coupled in series with the source and drain terminals of the N-channel FET (53) to provide the current sensing function for both the impedance control of the variable impedance element and the sensing of the 4-20 milliamp analog DC signal.
Claim 13
Dependent Claim
65 words
A system as in claim 12 further comprising: a voltage regulator (55) coupled across the single pair of conductors coupled to the input terminal (51, 52) at the output of the current sense element (54) to provide a substantially constant regulated voltage, V N , across the single pair of conductors over the full range of loop current and with a varying input current load.
Claim 14
Dependent Claim
211 words
A system as in claim 13 wherein the impedance control means (57) comprises: a differential amplifier (80) having first (-) and second (+) and voltage inputs and a voltage output; an electrical connection (78) between the output of the differential amplifier (80) and the gate of the N-channel FET (53) to vary the impedance of the N-channel FET; a first voltage divider (102, 104) across the input terminals (51, 52) having the substantially constant regulated voltage for generating a first voltage (R₁₀₂/R₁₀₄) representing a predetermined portion of the regulated voltage, the first voltage being coupled by a first conductor (92) to the first input of the differential amplifier (80); a second voltage divider (70, 72) across the input terminals (51, 52) for generating a second voltage (R₇₀/R₇₂) representing a predetermined portion of the input voltage at the drain terminal of the N-channel FET (53), the second voltage being coupled by a second conductor (77, 90) to the second input of the differential amplifier (80); and the voltage output of the differential amplifier (80) being coupled to the gate of the N-channel FET such that a variation of the second voltage with respect to the first voltage caused by the variations of the loop current varies the impedance of the N-channel FET.
Claim 15
Dependent Claim
108 words
A system as in claim 14 wherein: the gate voltage of the N-channel FET (53) is varied by the output voltage of differential amplifier (80) to maintain the following relationship: V IN = V₁ x (1 + R₇₀/R₇₂) where: V IN = the input signal voltage to the circuit on the single pair of conductors connected to terminals (51, 52); V₁ = the first voltage produced by V REG and the first voltage divider network comprised of series connected resistors 102 and 104 such that V₁ = V REF x (R₁₀₄/R₁₀₂+R₁₀₄) ; and V REG = the substantially constant voltage at the output of the sense element (54).
Claim 16
Dependent Claim
78 words
A system as in claim 15 further comprising: a third voltage divider (86, 87) extending from the input of the current sense element (54) across the input terminals (51, 52) to generate a third voltage; and switch means (106, 108) coupled to the first, second and third voltages and to the differential amplifier (80) for causing the N-channel FET (53) to change the impedance characteristic of the circuit from its first impedance to its second substantially higher impedance.
Claim 17
Dependent Claim
141 words
A system as in claim 16 wherein the switch means (106, 108) comprises: first and second mechanically6 coupled switches (106, 108); the first switch (108) having a first position (96) for coupling the first voltage (92) to the first input (-) of the differential amplifier (80); the second switch (106) having a first position (77) for coupling the second voltage to the second input (+) of the differential amplifier (80) to cause the N-channel FET (53) to have its first impedance; the first switch (108) having a second position (94) for coupling the third voltage to the first input (-) of the differential amplifier (80); and the second switch (106) having a second position (92) for coupling the first voltage to the second input (+) of the differential amplifier (80) to cause the N-channel FET (53) to have its second impedance.
Claim 18
Dependent Claim
65 words
A system as in claim 17 further comprising capacitor (82) coupled from the input to the current sense element (54) to the first input (-) of the differential amplifier (80) to couple the voltage across the current sensor element (54) to the differential amplifier (80) so as to oppose changes in the input signal current and increase the impedance across the substantially higher frequency band.
Claim 19
Dependent Claim
98 words
A system as in claim 18 further comprising: a second capacitor (100) coupled between the substantially constant voltage caused by the voltage regulator (55) and the second input (+) to the differential amplifier (80); and a third capacitor (74) coupled between the source terminal of the N-channel FET (53) and the first position (77) of the second switch (106) such that only when the second switch (106) is in the first position (77), the second impedance caused by the N-channel FET (53) levels off at a relatively fixed value above a predetermined cut-off frequency for limiting signal distortion.
Claim 20
Dependent Claim
30 words
A system as in claim 1 wherein the digitally encoded communication signals produce a voltage that has an average value of zero across the single pair of conductors (51, 52).
Claim 21
Dependent Claim
70 words
A system as in claim 8 further comprising: a feedback circuit (50) coupled to the actuator (16) for generating signals for closed loop control of the actuator (16); conductor means (68) for coupling the feedback sensor circuit signals to the analog circuit (56); and microprocessor (59) coupled to the transceiver (58) and analog circuit (56) for receiving the feedback signals from the analog circuit (56) and completing the closed loop.
Claim 22
Dependent Claim
158 words
A system as in claim 8 further comprising: an auxiliary transducer (137) responsive to the operation of the actuator (16) for sensing an auxiliary function such as temperature, flow and other like process related variables and generating a corresponding output electrical current signal; a process transmitter (140) coupled (139) to the auxiliary transducer (137) for generating a variable DC output signal on a second single pair (142) of third and fourth conductors; a third input terminal on the instrument (42) coupled to the analog circuit (58); and an auxiliary current sensing device (146) having first and second inputs and an output coupled to the analog circuit (56), the first input being coupled to the first terminal (51) and the second input being coupled to the third terminal (15) for generating an output signal to the analog circuit (56) such that a second output of the analog circuit (56) is coupled to the microprocessor (59) as a feedback signal.
Claim 23
Dependent Claim
105 words
A system as in claim 22 further comprising: a first comparator means (116) in the microprocessor (59) for comparing the input control signal (112) as a setpoint (114) from transceiver (110) on the first single pair of first and second conductors (111) with the second output (118) of the analog circuit (56) to establish a first corrected control signal (122); and a second comparator means (124) in the microprocessor (59) for comparing the first corrected control signal (122) with the first output (119) of the analog circuit (56) to establish a second corrected control signal (125) that is coupled to and controls the instrument (34).
Claim 24
Dependent Claim
25 words
A system as in claim 23 wherein: the first comparator means (116) is a process algorithm; and the second comparator means (124) is a servo-algorithm.
Claim 25
Dependent Claim
28 words
A system as in claim 23 wherein: the first comparator means (116) is a first analog comparator; and the second comparator means (124) is a second analog comparator.
Claim 26
Dependent Claim
50 words
A system as in claim 13 wherein the voltage regulator (53) further includes a current shunting element (171) across the single pair of conductors (51, 52) for shunting any excess current flowing in the pair of conductors, and not required for powering the circuit, from one conductor to the other.
Claim 27
Dependent Claim
210 words
A system as in claim 26 wherein the current shunting element comprises: a common node (174) and a substantially constant voltage node (172) having a voltage V N formed at the output of the current sensor element (54) on the first of the pair of conductors with respect to the second conductor; an operational amplifier (164) having first and second inputs (162, 170) and an output (165); a circuit (156, 158) having a output (160) coupled to the first input (+) of the amplifier (164) for providing a reference voltage, V REF ; first and second (R₂) series coupled resistors, R₁ and R₂ (166 and 168), respectively, coupled across the common node (174) and the constant voltage node (172) and coupling the voltage (170) across the second resistor (161) to the second input (-) of the operational amplifier 164; a transistor (170) having a base, emitter and collector with the emitter and collector coupled across the common node (174) and the constant voltage node (172); and the output (165) of the operational amplifier (164) being coupled to the base of the transistor (170) such that the voltage, V N , at the substantially constant voltage node (172) is regulated according to the equation: V N = V REF x (1+R₁/R₂).
Claim 28
Dependent Claim
67 words
A circuit as in claim 27 wherein the circuit for providing a reference voltage, V REF , comprises: a resistor (156) and zener diode (158) coupled in series across the common node (174) and the constant voltage node (172); and the voltage (160) developed across the zener diode (158) being coupled to the first input of the operational amplifier (164) as the reference voltage, V REF .
Claim 29
Dependent Claim
59 words
A circuit as in claim 13 further including: a voltage converter (150) coupled to the voltage regulator (55) for receiving the substantially constant voltage, V N , on the first conductor and developing an output voltage of substantially V N /2 at a first terminal and a second output voltage of substantially -V N /2 at a second terminal.
Claim 30
Dependent Claim
154 words
A transducer (43) for communicating with a control system (32) through only a single pair (35) of first and second conductors from a remote location with both digital and variable analog DC control signals so as to drive an actuator (16), the instrument comprising: first and second input terminals (51 and 52) for receiving both 4-20 milliamp variable DC analog control signals and bidirectional digital communication control signals on the same two input terminals (51 and 52); circuit means (42) for converting the input control signals to actuator drive signals; actuator responsive signals coupled to the circuit means (42) for acknowledging actuator responses to the drive signals; and digital signal generating means (59) coupled to the first and second terminals for transmission of digital information signals relating to the transducer (43) and the actuator (16) to the control system on the single two-conductor line and further receiving digital command signals from the control system.
Claim 31
Dependent Claim
57 words
A transducer as in claim 30 further including: a variable impedance element (53) coupled to the first and second input terminals (51, 52); and an impedance controller (57) coupled to the variable impedance element (53) to vary the input impedance of the transducer according to the analog control signals and the digital signals being received or transmitted.
Claim 32
Dependent Claim
53 words
A transducer as in claim 31 wherein the digital signal generating means includes a microprocessor (59) coupled to the transceiver for processing received digital or DC signals, interrogating the actuator according to the received signals to obtain a desired actuator condition and generating corresponding digital signals for transmission to the control system (32).
Claim 33
Dependent Claim
67 words
A transducer as in claim 32 further including: a current sense element (54) coupled in series with one of the single pair of conductors and having an input and an output; and an analog circuit coupled to the input of the current sense element to extract the DC analog control signal from the single pair of conductors to provide the desired output signal to the actuator (16).
Claim 34
Dependent Claim
45 words
A transducer as in claim 33 further including: a voltage regulator (55) for maintaining a substantially constant voltage; and an auxiliary current sensing element (146) for generating condition signals from the actuator (16) and coupling them to the microprocessor (59) as a feedback control signal.
Claim 35
Dependent Claim
70 words
A transducer as in claim 34 further including: a third input terminal (15); a two-conductor processor transmitter (140) generating signals that are coupled to the first and third input terminals; the auxiliary current sensor (146) sensing the signals from the two-conductor process transmitter and coupling the signals to the microprocessor (59); and the microprocessor (59) being used to process and store the signals received from the auxiliary current sensor (146).
Claim 36
Dependent Claim
176 words
A voltage regulator for developing a substantially constant voltage between first and second conductors (172, 174) and comprising: the first and second conductors receiving an input current; an operational amplifier (164) having first (-) and second (+) inputs and an output (165); a circuit (156, 158) coupled between the first and second conductors and generating an output to the first input (-) of the amplifier (164) as a reference voltage, V REF ; first and second series coupled resistors, R₁ (166) and R₂ (168), connected across the first and second conductors and coupling the voltage across the second resistor, R₂, to the second input (+) of the amplifier (164); a transistor (170) having a base, emitter and collector with the emitter and collector coupled across the first and second conductors; and the output (165) of the operational amplifier (164) being coupled to the base of the transistor (170) such that a voltage, V N , on the first conductor is a substantially constant voltage regulated according to the equation: V N = V REF x (1+R₁/R₂).
Claim 37
Dependent Claim
61 words
A voltage regulator as in claim 36 wherein the circuit for providing a reference voltage, V REF , comprises: a resistor (156) and a zener diode (158) coupled in series across the single pair of first and second conductors; and the voltage developed across the zener diode being coupled to the first input of the operational amplifier as the reference voltage.
Claim 38
Dependent Claim
39 words
A system as in claim 13 further comprising a switched capacitor voltage converter coupled to the voltage regulator (55) for receiving the regulated voltage, V N , and providing an output voltage, V N /2 and -V N /2.
Claim 39
Dependent Claim
157 words
An impedance transformation circuit coupled to a single pair of first and second input conductors carrying either a variable DC analog signal or a digital signal for changing its impedance as presented to the single pair of conductors from a first impedance for the DC analog signal and the digital signal to a second substantially higher impedance, the circuit comprising: a variable impedance element coupled between the first and second input conductors; impedance control means coupled to the variable impedance element for causing the variable impedance element to present a first acceptable impedance to the single pair of conductors when the DC analog and the digital signal; and switch means coupled to the first input conductor and the impedance control means and having first and second positions such that in the first position the variable impedance presents the first impedance and in the second position presents a second substantially higher impedance to the single pair of conductors.
Claim 40
Dependent Claim
76 words
A circuit as in claim 39 wherein the variable impedance comprises: at least one semiconductor element having input, output and control terminals with its input and output terminals in series with one of the single pair of conductors; and the impedance control means having an input coupled to the switch means and having an output coupled to the control terminal of the at least one semiconductor element to provide the desired first and second impedance characteristics.
Claim 41
Dependent Claim
62 words
A circuit as in claim 40 wherein: the at least one semiconductor element comprises an N-channel FET having a source, drain and gate with its drain and source in series with one of the single pair of conductors; and the impedance control element means having its output coupled to the gate of the N-channel FET to provide the desired device impedance characteristic.
References Cited (Backward Citations)
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