EP2832071A1 - Current loop voltage modulator for communication interface - Google Patents
Current loop voltage modulator for communication interfaceInfo
- Publication number
- EP2832071A1 EP2832071A1 EP13878673.6A EP13878673A EP2832071A1 EP 2832071 A1 EP2832071 A1 EP 2832071A1 EP 13878673 A EP13878673 A EP 13878673A EP 2832071 A1 EP2832071 A1 EP 2832071A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- voltage
- circuit
- terminals
- current
- integrated circuit
- 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.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B19/00—Programme-control systems
- G05B19/02—Programme-control systems electric
- G05B19/04—Programme control other than numerical control, i.e. in sequence controllers or logic controllers
- G05B19/05—Programmable logic controllers, e.g. simulating logic interconnections of signals according to ladder diagrams or function charts
- G05B19/056—Programming the PLC
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B3/00—Line transmission systems
- H04B3/50—Systems for transmission between fixed stations via two-conductor transmission lines
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B2219/00—Program-control systems
- G05B2219/20—Pc systems
- G05B2219/25—Pc structure of the system
- G05B2219/25232—DCS, distributed control system, decentralised control unit
Definitions
- the subject matter disclosed herein relates to communication by voltage modulation and current sensing.
- HART Highway Addressable Remote Transducer
- PLCs programmable logic controllers
- DCSs distributed control systems
- BOPs balance of plant
- HART protocol is often used in asset management.
- HART is used in power plants to constantly scan devices and gather operation data.
- a receiver device communicating on the HART protocol requires the ability to modulate the terminal voltage between two terminals while monitoring the loop current flowing between the terminals.
- a HART communication device uses a transformer to impress a voltage while not altering the current.
- ASIC application specific integrated circuit
- an integrated circuit in a first embodiment, includes a circuit configured to monitor a current flowing between two terminals of the integrated circuit. Additionally, the integrated circuit includes a voltage driver configured to modulate a voltage across the two terminals of the integrated circuit while maintaining the current flowing between the two terminals of the integrated circuit. The voltage driver modulates the voltage across the two terminals according to the Highway Addressable Remote Transducer (HART) protocol.
- HART Highway Addressable Remote Transducer
- An additional embodiment includes a system including a transmitter and a receiver electrically coupled together by wires forming a current loop.
- the receiver includes an ASIC that includes a circuit designed to monitor a current flowing through the current loop, and a voltage driver designed to modulate a voltage across two terminals of the current loop while maintaining the current flowing through the current loop.
- the transmitter transfers information to the receiver by modulating the current flowing through the current loop, and the receiver transfers information to the transmitter by modulating the voltage across the two terminals of the current loop.
- an electronic circuit in an additional embodiment, includes a resistor designed to form a voltage across its terminals in relation to a current flowing through a current loop.
- the current loop is formed between the electronic circuit and a transmitting circuit.
- the electronic circuit also includes a differential amplifier designed to generate a signal in relation to the voltage formed by the resistor. The signal is passed to a modulator-demodulator (modem) and an analog-to-digital converter (ADC) for processing.
- the electronic circuit includes a voltage driving circuit that receives signals from the modem and modulates a voltage across terminals of the current loop based on the signals received from the modem.
- FIG. 1 illustrates a HART transmitter and a HART receiver electrically coupled with a current loop, in accordance with an embodiment
- FIG. 2 is a graph showing the current flowing through a current loop as well as the voltage across the terminals of the current loop, in accordance with an embodiment
- FIG. 3 illustrates an example of the HART receiver circuitry that was a voltage driver in series with a current sensing resistor, in accordance with an embodiment
- FIG. 4 illustrates a circuit-level diagram of the HART receiver circuitry illustrated in FIG. 3;
- FIG. 5 illustrates an example of the HART receiver circuitry that uses a voltage driver in parallel with a current sensing resistor, in accordance with an embodiment.
- present embodiments relate to circuitry of a receiver designed to communicate over the Highway Addressable Remote Transducer (HART) protocol.
- HART Highway Addressable Remote Transducer
- a voltage driver circuit modulates the terminal voltage of the HART receiver while a current sensing circuit monitors the loop current flowing between the terminals. In this way, the voltage driver circuit maintains the current value provided by the HART transmitter while varying the voltage value of the signal as needed. Circuits with these characteristics may also be called current followers.
- the circuitry of the HART receiver is made up of discrete components, while in other embodiments, the circuitry is part of an integrated circuit (e.g., an application specific integrated circuit (ASIC)).
- ASIC application specific integrated circuit
- a HART transmitter 10 is electrically coupled to current loop wires 12 forming a current loop with a HART receiver 14.
- the HART transmitter 10 may utilize the HART communications protocol.
- the HART protocol may use the Bell 202 Frequency Shift Keying (FSK) standard, varying the frequency of the current signal in order to key digital bits into the signal.
- the current signal may be a periodic and sinusoidal low bandwidth direct current (DC) to 25 Hz signal in the 4mA to 20mA range. Since the HART protocol is half duplex, only the HART transmitter 10 may modulate the current through the current loop wires 12 or the HART receiver 14 may modulate the voltage across the current loop terminals 13 at a given time.
- FSK Bell 202 Frequency Shift Keying
- the current modulated by the HART transmitter 10 may flow through the current loop wires 12 and through a current sensing resistor Rl of the HART receiver 14.
- the current sensing resistor Rl may have a value of 250 ⁇ , but in other embodiments, the current sensing resistor may have other appropriate resistance values.
- a voltage bias may form on either side of the current sensing resistor Rl .
- a differential amplifier 16 may have two inputs electrically coupled on either side of the current sensing resistor Rl, and may be designed to generate a current signal in relation to the voltage bias across the two inputs.
- the differential amplifier 16 may be passed to an analog-to-digital converter (ADC) 18 as well as a HART modulator-demodulator (modem) 20.
- ADC 18 may convert the analog current signal produced by the differential amplifier 16 into a digital signal that may be interpreted by communication logic circuitry 22.
- the HART modem 20 may de-modulate the information carried by the current signal, and pass the information to the communication logic circuitry 22.
- a capacitor CI may filter the DC components out of the current signal before the current signal is passed to the HART modem 20.
- the circuitry of the HART receiver 14 provides galvanic isolation between the HART receiver circuitry and the communication logic circuitry 22.
- the HART receiver 14 may also modulate the terminal voltage of the current loop in order to transmit information to the HART transmitter 10.
- the communication logic circuitry 22 may send information to the HART modem 20 to be converted into voltage signals.
- a summing circuit 26 may receive the voltage signals and add them to the current flowing through the current loop to modulate the terminal voltage of the current loop. It should be noted that the summing circuit may add voltage signals to modulate the terminal voltage of the current loop, but the current flowing through the current loop may be unchanged by the HART receiver 14 circuitry.
- the summing circuit 26 may also be referred to as a voltage driver 27.
- FIG. 2 is a graph that illustrates both current signals and voltage signals that may be present in communication between a HART transmitter 10 and a HART receiver 14.
- a first waveform 40 may represent a current modulated signal and a second waveform 42 may represent a voltage modulated signal.
- the first waveform 40 may be a low bandwidth DC to 25 Hz signal in the 4 niA to 20mA range.
- Information bits may be encoded into the current modulated signal 40 by varying the frequency of the signal.
- the HART transmitter 10 may set the frequency of the current modulated signal 40 to 23 Hz, and to encode a digital "0", the HART transmitter 10 may set the frequency of the signal to 10 Hz.
- this method of encoding information bits is called Frequency Shift Keying (FSK).
- the HART receiver 14 may encode information on the voltage modulated signal using FSK.
- the voltage modulated signal is a 10 Hz periodic sinusoid modulated with much higher frequency tones (500-1000 Hz).
- the modulated frequency of the signal varies to encode digital bits into the signal.
- the frequency of the voltage modulated signal may be relatively high (1000 Hz), encoding a digital "1".
- the frequency may be relatively low (500 Hz), encoding a digital "0".
- other frequencies may be used to encode digital bits as long as they are substantially different enough to be distinguished by the circuitry of the HART transmitter 10 or the HART receiver 14.
- the HART transmitter 10 may sense the tone encoding the digital information by AC coupling the terminal voltage through a filter and a demodulator.
- FIG. 3 illustrates an alternative embodiment of the circuitry of the HART transmitter 14 shown in FIG. 1.
- the current modulated by the HART transmitter 10 may flow through the current loop wires 12 and through the current sensing resistor Rl .
- the differential amplifier 16 may have two inputs electrically coupled to either side of the current sensing resistor Rl to generate an output signal in relation to the voltage bias across the current sensing resistor Rl .
- the signal generated by the differential amplifier 16 may pass through a low pass filter 60 before being passed to the ADC 18.
- the low pass filter 60 may remove alternating current (AC) components of the signal so that the ADC 18 receives a direct current (DC) signal.
- AC alternating current
- the HART receiver 14 may include the HART modem 20 to demodulate the signals received from the HART transmitter 10 and modulate the terminal voltage of the current loop terminals 13.
- the voltage driver 27 of the embodiment of FIG. 3 may include a transistor 62 to form a common collector buffer.
- the illustrated transistor 62 is a PNP bipolar junction transistor (BJT), but other embodiments may include an NPN BJT, a p-type metal-oxide-semiconductor (PMOS) transistor, or an n-type metal-oxide-semiconductor (NMOS) transistor.
- Offset voltage from the transistor 62 may be allowed on a current return line 64, where the summing circuit 26 may provide a differential output voltage for the modulation of the terminal voltage.
- the voltage driver 27 of the embodiment of FIG. 3 may modulate the terminal voltage of the current loop to encode information intended for the HART transmitter 10.
- FIG. 4 A circuit diagram of FIG. 4 illustrates the circuitry of the embodiment of the HART receiver 14 described in FIG. 3 with additional detail.
- the circuitry includes the differential amplifier 16 designed to generate a signal in relation to the current flowing through the current sensing resistor Rl .
- the signal propagates on output line 67 to the ADC 18 and the HART modem 20 as illustrated in FIG. 3.
- Resistors R2, R3, R4, and R5 may be electrically coupled to inputs and outputs of the differential amplifier 16 to set the operation parameters of the amplifier.
- resistors R2 and R4 may have a value of 100 kQ, while resistors R3 and R5 may have a value of 400 kQ.
- current flowing from the HART transmitter 10 is modeled by a current source 66 since the current flowing through the current loop may be constant when the HART receiver 14 is modulating the terminal voltage of the current loop.
- the transistor 62 of the voltage driver 27 is a PMOS transistor, but may also be a PNP BJT transistor or any other suitable transistor such as a BJT (NPN or PNP), complementary metal-oxide- semiconductor (CMOS) transistor, or an NMOS transistor.
- the summing circuit 26 of the voltage driver may include a differential amplifier 68 that receives an offset voltage from the transistor 62 on the current return line 64 to provide a differential output voltage to the gate of the transistor 62.
- the differential amplifier may provide a differential output voltage to the base of the transistor 62. As the voltage applied to the base or the gate of the transistor 62 is varied, the impedance of the transistor may be varied as well, effectively modulating the voltage bias between the terminals 13 of the current loop.
- the differential amplifier 68 of the summing circuit 26 may receive a modulating signal from the HART modem output 70 that plays a part in determining the differential output voltage being applied to the base or the gate of the transistor 62 and, therefore, the modulation of the terminal voltage.
- a voltage source may offset the modulating signal from the HART modem output 70 to maintain correct bias on the transistor at all times. The correct bias may ensure that a voltage across the gate and source of the transistor 62 is sufficient to maintain current flow through the transistor 62.
- Resistors R6, R7, R8, R9, and R10 may be electrically coupled to the differential amplifier 68 to set the operation parameters of the amplifier.
- resistors R6, R8, R9, and R10 may have a value of 100 kD, while resistor R7 may have a value of 1000 ⁇ . In other embodiments, other resistances may be selected for resistors R6, R7, R8, R9, and R10 to permit communication using the HART receiver 14. Resistor Rl l may represent the resistance of the current loop wires 12 of the return path to the HART transmitter 10. In the illustrated embodiment, resistor Rl 1 may have a value of 50 ⁇ , but in other embodiments, resistor Rl 1 may have any other appropriate resistance that represents the resistance of the current loop wires 12.
- certain embodiments may include a grounded capacitor C2 at the gate or the base of the transistor 62 to stabilize relatively small oscillations in the signal being provided to the transistor 62 gate or base or the voltage across the differential amplifier 68.
- the capacitor C2 may have a capacitance of 80 pF or any other appropriate capacitance.
- FIG. 5 A further embodiment of the circuitry of the HART receiver 14 is illustrated in FIG. 5. The embodiment includes the same circuitry for monitoring the loop current as the embodiments described in FIG 1, FIG. 3, and FIG. 4. However, while FIGS. 1, 3, and 4 demonstrate embodiments with the voltage driver 27 in series with the current sensing resistor Rl, the embodiment of FIG. 5 illustrates the voltage driver 27 in a parallel configuration including a coupling capacitor C3.
- coupling capacitors are utilized to block a DC component of a signal while allowing the AC component to pass.
- the summing circuit 26 receives signals from the current return line 64 and the HART modem 20 and outputs a modulating signal to the coupling capacitor C3, the coupling capacitor C3 modulates the terminal voltage of the current loop without varying the current flowing through the loop.
- the size of the coupling capacitor C3 may be much larger than what is practical for an integrated circuit.
- the large capacitance may be used to drive the relatively low impedance of the current loop.
- the coupling capacitor C3 may be external to the rest of the integrated circuit and may consume two additional package pins for connecting the integrated circuit to a larger circuit.
- HART receiver circuitry designed to monitor a current flowing in a current loop while modulating the terminal voltage of the current loop.
- a voltage driver circuit is in series with a current sensing resistor.
- a differential amplifier may amplify the voltage difference across the current sensing resistor and pass a signal to a HART modem and an analog-to-digital converter to decode the information sent by a HART transmitter.
- the HART modem and a feedback signal from a transistor are summed by a summing circuit and applied to the gate or base of the transistor to modulate the voltage between the terminals of the current loop, effectively transmitting information to the HART transmitter.
- HART receiver circuitry dispose the voltage driver circuit in parallel with the current sensing resistor.
- a coupling capacitor is used with a feedback driven summing circuit and a HART modem to modulate the terminal voltage of the current loop in order to transmit information to the HART transmitter.
- the circuitry may be implemented without the use of a transformer, enabling the HART circuitry to be placed on an integrated circuit.
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Arrangements For Transmission Of Measured Signals (AREA)
- Dc Digital Transmission (AREA)
Abstract
Description
Claims
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PCT/CN2013/072847 WO2014146243A1 (en) | 2013-03-19 | 2013-03-19 | Current loop voltage modulator for communication interface |
Publications (2)
Publication Number | Publication Date |
---|---|
EP2832071A1 true EP2832071A1 (en) | 2015-02-04 |
EP2832071A4 EP2832071A4 (en) | 2015-11-18 |
Family
ID=51579267
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP13878673.6A Withdrawn EP2832071A4 (en) | 2013-03-19 | 2013-03-19 | Current loop voltage modulator for communication interface |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP2832071A4 (en) |
CN (1) | CN104221348B (en) |
WO (1) | WO2014146243A1 (en) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2016082840A1 (en) * | 2014-11-28 | 2016-06-02 | Pr Electronics A/S | Low-power hart transmitter |
JP7113677B2 (en) * | 2018-06-19 | 2022-08-05 | 三菱重工業株式会社 | Signal processor and signal processing module |
US20200162076A1 (en) * | 2018-11-16 | 2020-05-21 | Analog Devices Global Unlimited Company | Communication transmitter interface for current-loop circuit |
Family Cites Families (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6850973B1 (en) * | 1999-09-29 | 2005-02-01 | Fisher-Rosemount Systems, Inc. | Downloadable code in a distributed process control system |
US7280048B2 (en) * | 2003-08-07 | 2007-10-09 | Rosemount Inc. | Process control loop current verification |
US7262693B2 (en) * | 2004-06-28 | 2007-08-28 | Rosemount Inc. | Process field device with radio frequency communication |
CN103380556B (en) * | 2010-03-24 | 2016-02-03 | 马克·辛莱希 | For Wireless Telecom Equipment electric power management circuit and use its process control system |
US8786128B2 (en) * | 2010-05-11 | 2014-07-22 | Rosemount Inc. | Two-wire industrial process field device with power scavenging |
CN102538904A (en) * | 2010-12-08 | 2012-07-04 | 上海自动化仪表股份有限公司 | HART (Highway Addressable Remote Transducer)-communication-based capacitive level transmitter and working method thereof |
US20120253481A1 (en) * | 2011-03-29 | 2012-10-04 | General Electric Company | Hart channel interface component including redundancy |
-
2013
- 2013-03-19 CN CN201380019336.6A patent/CN104221348B/en not_active Expired - Fee Related
- 2013-03-19 WO PCT/CN2013/072847 patent/WO2014146243A1/en active Application Filing
- 2013-03-19 EP EP13878673.6A patent/EP2832071A4/en not_active Withdrawn
Also Published As
Publication number | Publication date |
---|---|
CN104221348B (en) | 2017-07-18 |
WO2014146243A1 (en) | 2014-09-25 |
CN104221348A (en) | 2014-12-17 |
EP2832071A4 (en) | 2015-11-18 |
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RA4 | Supplementary search report drawn up and despatched (corrected) |
Effective date: 20151015 |
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RIC1 | Information provided on ipc code assigned before grant |
Ipc: H04L 29/06 20060101AFI20151009BHEP Ipc: G05B 23/02 20060101ALI20151009BHEP |
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DAX | Request for extension of the european patent (deleted) | ||
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18D | Application deemed to be withdrawn |
Effective date: 20181002 |