WO2022033824A1 - Interface de courant pour générer un courant de sortie analogique de 4 à 20 ma, et procédé de fonctionnement d'une telle interface de courant - Google Patents

Interface de courant pour générer un courant de sortie analogique de 4 à 20 ma, et procédé de fonctionnement d'une telle interface de courant Download PDF

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Publication number
WO2022033824A1
WO2022033824A1 PCT/EP2021/070386 EP2021070386W WO2022033824A1 WO 2022033824 A1 WO2022033824 A1 WO 2022033824A1 EP 2021070386 W EP2021070386 W EP 2021070386W WO 2022033824 A1 WO2022033824 A1 WO 2022033824A1
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WO
WIPO (PCT)
Prior art keywords
current
measurement
voltage
generating
compensation
Prior art date
Application number
PCT/EP2021/070386
Other languages
German (de)
English (en)
Inventor
Werner Hoch
Original Assignee
Ifm Electronic Gmbh
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Ifm Electronic Gmbh filed Critical Ifm Electronic Gmbh
Publication of WO2022033824A1 publication Critical patent/WO2022033824A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
    • G01D3/028—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure
    • G01D3/036—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure on measuring arrangements themselves

Definitions

  • the invention relates to an interface for generating an analog current signal for transmitting a process variable to a programmable logic controller (PLC) according to DIN IEC 60381-1.
  • PLC programmable logic controller
  • the invention is suitable for measuring and classifying any burden or connected remote station.
  • a current signal has the significant advantage over a voltage signal that the voltage drop in the transmission line does not falsify the measured value.
  • a (direct current) signal is more stable against interference.
  • the current signal of 4 to 20 mA (with an offset zero point) enables wire break monitoring.
  • the current signal is impressed by the signal source, usually a measuring transducer.
  • the signal source usually a measuring transducer.
  • active current signal the transmitter is also the current source. In this case, the transmitter drives the current.
  • passive current signal an isolation amplifier or the PLC itself is the driving current source. In this case, the transmitter regulates its own power consumption according to the current measured value.
  • DE 10 2015 109 095 A1 describes a current output stage for providing a regulated output current. It has a first control device that is designed to provide a controlled output current at the output that is proportional to the input signal. Furthermore, a detection device is designed to detect whether a passive receiver or an active receiver is connected to the output. When a passive receiver (load) is connected, a second control device connected to a voltage source and the detection device provides an output voltage at the output such that an output current proportional to the input signal can flow through the passive receiver.
  • an active receiver when connected, it provides an output voltage which is greater than or equal to zero in such a way that an output current proportional to the input signal can flow through the burden and a return path, with the return path only allowing the output current to pass when an active receiver is connected whose external energy supply source provides a sufficiently high voltage to drive the output current through the burden.
  • EP 2 219 013 B1 describes a current generating device for generating and simultaneously monitoring a measuring current that corresponds to a measured value determined by a level, pressure or flow meter, the current generating device having a first current source for generating a measuring current, a second current source for generating a compensation current for Compensating for at least part of the measurement current.
  • a detection circuit for detecting deviations of the measurement current from a desired value and a current sensing resistor unit for measuring the compensation current are proposed, with the compensation current and the measurement current flowing through the current sensing resistor unit.
  • the first current source supplies a first circuit, while the second current source feeds a test current into the first circuit; and wherein the current generating device is designed in such a way that feeding in the test current generates the compensation current; where the target value is provided as the magnitude of the test current.
  • the object of the invention is to measure a load resistance (burden) in an analog current interface (current output stage) of 4 to 20 mA continuously (i.e. at specific time intervals) without the analog output signal being affected by the leakage current required for a low-impedance and therefore interference-free measurement distort.
  • the arrangement should be space-saving, inexpensive and simple.
  • Claim 6 relates to a method according to the invention.
  • the main idea behind the invention is not to monitor the current, but rather the voltage across the load.
  • the burden current is known anyway, which distinguishes the proposed arrangement from the prior art mentioned above.
  • An additional benefit is that both the correctness of a connected load can be checked and the absence of one of the loads can be detected. In addition, no current sensing resistor is required in the output circuit.
  • a voltage divider reduces the voltage to be measured to the values that can be detected by the ADC (analog-to-digital converter) present in modern PCs (microcontrollers). Otherwise, an operational amplifier (OPV) would also be required here.
  • ADC analog-to-digital converter
  • FIG. 1 shows a schematic representation of a temperature sensor from process measurement technology with an analog interface according to the invention.
  • the arrangement is used to transmit a process variable, such as a temperature, as an analog current signal to a programmable logic controller (PLC) indicated on the bottom right.
  • PLC programmable logic controller
  • the current flowing through the burden 1 is proportional to a measured value of the temperature sensor 2, which represents a process variable.
  • the mode of operation of the measuring transducer shown is, on the one hand, irrelevant and, on the other hand, is known to a person skilled in the art, so that no further explanations are given.
  • the output voltage of the measuring amplifier V is supplied to a control unit 7 which, in addition to a microprocessor pP, has two A/D converters, designated 7a and 7c, and a D/A converter 7d.
  • the separately shown input resistance Ri of the A/D converter 7a is denoted by 7b.
  • the control unit 7 drives a current source 3, with at least one further control signal being transmitted in addition to the measurement signal, as will be explained in more detail below.
  • the assemblies mentioned are advantageously part of an integrated circuit.
  • the current source 3 is designed to generate both a first current, the variable measurement current 4, and a likewise variable compensation current 5.
  • the two currents mentioned are applied to burden 1 and transmitted to the PLC as an analogue current signal (loop current).
  • the load resistance R is determined with the aid of the detection circuit 6 by measuring the voltage across the load 1 with an analog/digital converter 7a, which can easily be done in the evaluation unit 7 with a known analog output signal (output current) according to Ohm's law .
  • the detection circuit 6 has a voltage divider with a series resistor 6a (Rv) and a parallel resistor 6b (Rp) and an integrating capacitor and is therefore designed as a low-pass filter.
  • a reverse polarity protection diode is not absolutely necessary.
  • the above-mentioned leakage current associated with the voltage measurement results from the quotient of the measured voltage Ui and the parallel resistance Rp 6a in the voltage divider of the detection circuit 6, taking into account the input resistance Ri, designated 7b, of the A/D converter 7a used for voltage measurement.
  • the forward voltage of the reverse polarity protection diode does not interfere with the measurement, because the leakage current is determined by the voltage drop across the resistors mentioned.
  • the voltage regulator LM is supplied with an operating voltage Ub and generates a stabilized voltage VDD for the control unit 7 and the sensor circuit.
  • the leakage current determined in the manner described above is considered to be of equal magnitude
  • the compensation current 5 is determined iteratively with the aid of a control circuit, since a changed compensation current in turn leads to a change in the leakage current.
  • the iteration is carried out in such a way that a voltage measurement is carried out first, a compensation current 5 is calculated and fed on the basis of the result of this voltage measurement, whereupon a new measurement is carried out and so on.
  • the compensation current 5 is usually between 10 pA and 1 mA.
  • the fault current at 10 V is approx. 100 pA, which should be regarded as the absolute upper limit.
  • an interruption of the signal transmission (switching off) during the measurement is advantageously not necessary because the current interface remains unaffected by this measurement.
  • the invention also includes a method for operating the current interface described, wherein the voltage drop across the burden 1 is measured, the current required for this measurement is recorded, and is fed into the burden 1 as a compensation current of the same amount, in order in this way to reduce the voltage caused by the voltage measurement to correct incorrect output current.
  • the leakage current flowing into the detection circuit 6 (compensation current 5) generates a voltage drop across the resistor Rv and a voltage Ui which can be measured by the A/D converter 7a and which is present across the parallel resistors Rp and Ri. Even if the resistance Ri, which is unknown or only imprecisely known, is neglected, an approximate value is obtained for the compensation current S, namely lli/Rp.
  • the current interface shown can be used, among other things, advantageously for detecting a process variable in process engineering production plants.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Current Or Voltage (AREA)

Abstract

L'invention concerne une interface de courant pour générer un courant de sortie analogique de 4 à 20 mA, qui est destiné à alimenter une charge (1) et correspond à une valeur mesurée d'un capteur (2), ladite interface comportant au moins une source de courant (3) pour générer un courant de mesure (4) et un courant de compensation (5), et comportant également un circuit de détection (6) pour identifier des écarts dans le courant de mesure (4) par rapport à une valeur cible, et une unité d'évaluation (7), caractérisée en ce que l'unité d'évaluation (7) est conçue pour mesurer la chute de tension à travers la charge (1), et de plus pour détecter le courant requis pour cette mesure et pour acheminer celui-ci en tant que courant de compensation de valeur absolue égale dans la charge (1) afin de corriger ainsi le courant de sortie falsifié par la mesure de tension. L'invention concerne en outre un procédé de fonctionnement de cette interface de courant.
PCT/EP2021/070386 2020-08-11 2021-07-21 Interface de courant pour générer un courant de sortie analogique de 4 à 20 ma, et procédé de fonctionnement d'une telle interface de courant WO2022033824A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102020121076.0 2020-08-11
DE102020121076.0A DE102020121076B3 (de) 2020-08-11 2020-08-11 Stromschnittstelle zur Erzeugung eines analogen Ausgangsstroms von 4 bis 20 mA sowie Verfahren zum Betreiben einer solchen Stromschnittstelle

Publications (1)

Publication Number Publication Date
WO2022033824A1 true WO2022033824A1 (fr) 2022-02-17

Family

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PCT/EP2021/070386 WO2022033824A1 (fr) 2020-08-11 2021-07-21 Interface de courant pour générer un courant de sortie analogique de 4 à 20 ma, et procédé de fonctionnement d'une telle interface de courant

Country Status (2)

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DE (1) DE102020121076B3 (fr)
WO (1) WO2022033824A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE1030961B1 (de) * 2022-10-13 2024-05-14 Phoenix Contact Gmbh & Co Vorrichtung zur Überwachung einer Bürde

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2518422A1 (de) * 1975-04-25 1976-11-11 Philips Patentverwaltung Schaltungsanordnung zur selbsttaetigen kompensation des ohmschen widerstandes der verbindungsleitungen zwischen widerstandsgebern und messgeraeten
EP2219013A1 (fr) * 2009-02-13 2010-08-18 VEGA Grieshaber KG Dispositif de production de courant destiné à la production et la surveillance simultanée d'un courant de mesure
US20130169295A1 (en) * 2011-12-29 2013-07-04 Stmicroelectronics Asia Pacific Pte. Ltd. Leakage current compensation circuit
DE102015109095A1 (de) 2015-06-09 2016-12-15 Phoenix Contact Gmbh & Co. Kg Stromausgangsstufe zum Bereitstellen eines geregelten Ausgangsstroms

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2518422A1 (de) * 1975-04-25 1976-11-11 Philips Patentverwaltung Schaltungsanordnung zur selbsttaetigen kompensation des ohmschen widerstandes der verbindungsleitungen zwischen widerstandsgebern und messgeraeten
EP2219013A1 (fr) * 2009-02-13 2010-08-18 VEGA Grieshaber KG Dispositif de production de courant destiné à la production et la surveillance simultanée d'un courant de mesure
EP2219013B1 (fr) 2009-02-13 2019-04-10 VEGA Grieshaber KG Dispositif de production de courant destiné à la production et la surveillance simultanée d'un courant de mesure
US20130169295A1 (en) * 2011-12-29 2013-07-04 Stmicroelectronics Asia Pacific Pte. Ltd. Leakage current compensation circuit
DE102015109095A1 (de) 2015-06-09 2016-12-15 Phoenix Contact Gmbh & Co. Kg Stromausgangsstufe zum Bereitstellen eines geregelten Ausgangsstroms

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