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

Definitions

• the invention relates to a current loop of the 4-20 milliamperes or 0-20 milliamperes type, connecting an analog sensor to an acquisition system crossed respectively by a sensor current and an acquisition current.
• a current loop tile is widely used.
• the power supply of the sensor is carried by the same wires as the signal, which leads to a reduction in the cost on the part of the wiring compared to other types of signals requiring more wires in the cable, on the other hand the signal is very little disturbed by electromagnetic radiation, which allows transmission over long distances or in a medium with high radiation density.
• the proper functioning of the acquisition system is checked using test devices designed to simulate the operation of the sensor.
• the simulation is carried out by connecting the test device in substitution for the analog sensor.
• Disconnecting the sensor is not without drawbacks: there is a risk of incorrect recon ⁇ exio ⁇ for example by an inversion of polarity, or even a forgetting to reco ⁇ nexio ⁇ , or even insufficient tightening of the connections. In case conditions, the maintenance of the acquisition system turns out to be counter productive.
• the operation of the analog sensor is controlled by disconnecting it from the current loop. This is done in particular when the sensor is removed from its installation site. Again, the disconnection is not without drawbacks: the acquisition system generally interprets it as an open loop a ⁇ omaiie and generates an alarm. It is therefore necessary to intervene so that the anomaly is not treated as such by a control unit of the acquisition system.
• the object of the invention is to remedy the problem of controlling the operation of an acquisition system or of a sensor by disconnection - reconnection in a current loop of the 4 - 20 mA or 0 - 20 mA type.
• the idea behind the invention is to perform the control without opening the current loop.
• the subject of the invention is a current loop of the type 4 - 20 milliamperes or 0 - 20 milliamperes, connecting an analog sensor to an acquisition system crossed respectively by a sensor current and an acquisition current, characterized in that a test circuit is mounted in parallel with the current loop to inject into said loop a superposition current which is superimposed on the sensor or acquisition current.
• the superposition current injected into the current loop by the test circuit is superimposed on the current passing through the sensor to simulate its operation with respect to the acquisition system, or is superimposed on the current passing through the acquisition system to simulate its operation vis-à-vis the analog sensor.
• test circuit mounted in parallel with the current loop therefore makes it possible to inject a superposition current without opening the current loop connecting the acquisition system and the analog sensor.
• the above-mentioned drawbacks are thus remedied: on the one hand, the risk of reversing the polarity of the sensor by reconnection is eliminated, on the other hand, no open loop anomaly is detected by the acquisition system during the test of the analog sensor.
• the test circuit comprises a variable voltage generator mounted in parallel to the acquisition system for injecting the superposition current by addition to the acquisition current, which makes it possible to control a low current threshold of the acquisition system.
• test circuit comprises an ammeter connected in series with the variable DC voltage generator to determine the intensity of the superimposing current.
• test circuit comprises a diode connected in series with the variable voltage generator to protect the current loop when the variable voltage is zero.
• the test circuit comprises a diode connected in series with the acquisition system to preserve the operating independence of several current loops connecting several sensors to the same acquisition system.
• the test circuit comprises a variable current regulator mounted in parallel with the analog sensor to inject the superposition current by addition to the sensor current, which makes it possible to control a high current threshold of the system acquisition.
• the test circuit comprises a variable current regulator mounted in parallel with the analog sensor for injecting the superposition current by addition to the sensor current, the superposition current being controlled by this sensor current, which keeps the acquisition current in the current loop.
• test circuit includes an ammeter mounted in series with the variable current regulator to determine the intensity of the simulation current.
• Figure 1 shows in the form of an electrical diagram a current loop with an analog sensor and an acquisition system and a test circuit mounted in parallel to test the low current threshold of the acquisition system.
• Figure 2 shows in the form of an electrical diagram a current loop with an analog sensor and an acquisition system and a test circuit mounted in parallel to test the high current threshold of the acquisition system.
• FIG. 3 shows in the form of an electrical diagram a current loop with an analog sensor and an acquisition system and a test circuit mounted in parallel to maintain constant an acquisition current whatever a sensor current.
• a current loop of the 4-20 mA type comprises, in FIG. 1, an analog sensor 1 and an acquisition system 3.
• the analog sensor is for example a pressure sensor mounted from the outside on a casing of an electrical apparatus. at high voltage like a circuit breaker. It is clear, however, that the invention is not limited to such a pressure sensor, and applies to other analog sensors as operating in a 0-20 mA or 4-20 mA current loop. Examples of such sensors include, temperature, flow, pH, or even viscosity sensors.
• the pressure sensor 1 is traversed by a sensor current Ie which is imposed by the pressure prevailing inside the casing of the circuit breaker filled with dielectric arc extinguishing gas.
• the acquisition system 3 comprises a source 5 of direct voltage V1, for example of 24 volts (V). Voltage source flows in a series resistance R1 equal for example of 100 ohm ( ⁇ ) an acquisition current la. An ammeter A1 is temporarily mounted in parallel with a diode D1 in series with the acquisition system 3 to determine the intensity of the acquisition current la. According to the invention, a test circuit is mounted in parallel with the current loop to inject into said loop a superposition current which is superimposed on the sensor current or on the acquisition current.
• the test circuit comprises a generator 7 of DC voltage V4 variable between 0 and 24 V mounted in parallel with the acquisition system 3.
• the - generator 7 delivers a supe ⁇ osition current Is in a series resistor R4 for example equal to 100 ⁇ .
• the superposition current Is is injected via the voltage generator 7 upstream of the pressure sensor 1 relative to the direction of the acquisition current la to add to the latter, the sum la + Is being equal to the current the sensor.
• An ammeter A2 is connected in series with the generator 7 of variable direct voltage V4 to determine the intensity of the superposition current Is.
• variable voltage V4 is gradually increased to increase the superimposition current Is, and to decrease the acquisition current the taking into account the constancy of the sensor current le imposed by the constancy of the pressure inside the envelope for the duration of the test.
• the acquisition current la is thus lowered to a low threshold to verify the correct functioning of the acquisition system without opening the current loop.
• the test circuit comprises, in FIG. 1, a diode D2 connected in series with the generator 7 of variable voltage V4 for prevent the acquisition current Ia from being partially diverted in the test circuit when the variable voltage V4 is low.
• the test circuit comprises a variable direct current regulator 9 mounted in parallel with the analog sensor 1.
• the superposition current Is is injected via the current regulator 9 continuous variable downstream of the pressure sensor 1 relative to the direction of the acquisition current la to add to the sensor current le, the sum le + Is being equal to the acquisition current la.
• An ammeter A2 is connected in series with regulator 9 of variable direct current to determine the intensity of the superposition current Is.
• the superposition current Is is gradually increased to increase the acquisition current Ia taking into account the constancy of the sensor current Ie imposed by the constancy of the pressure inside the envelope during the duration of the test. .
• the acquisition current la is thus increased to a high threshold to verify the correct functioning of the acquisition system 3 without opening the current loop.
• the sensor current le is accessible from the acquisition current intensities la and superposition Is determined by the ammeters A1 and A2 mounted in the test circuit.
• the pressure of the dielectric gas contained in the envelope is monitored throughout the duration of the test of the thresholds of the acquisition system, using the test circuit mounted in parallel with the current loop.
• a leakage of the dielectric gas out of the envelope results in a drop in the sensor current Ie and consequently in a drop in the superposition current Is easily determined by the ammeter A2.
• the test circuit comprises a variable current regulator 11 mounted in parallel with the pressure sensor 1 to inject a superposition current Is by addition to the sensor current le, the current of supe ⁇ sition Is being subject to the acquisition current la.
• the intensity of the acquisition current acquired by the acquisition system at the start of the test is assigned as a setpoint to the variable direct current regulator 11 by a servo 13 connected to the ammeter A1 mounted parallel to the series diode D1 of the system. 3.
• a variation of the sensor current Ie results in a variation of the acquisition current Ia which is immediately compensated by the superposition current Is injected by the regulator 11 to keep the current constant. of acquisition. If the sensor current decreases, the superposition current Is increases to keep the constant.
• the sensor current Ic is progressively canceled by replacing it with the superposition current Is without opening said current loop.
• the pressure sensor 1 can be disconnected from the current loop to control it while preventing an open loop anomaly detected by the acquisition system. No alarm is generated by the acquisition system.
• test circuit is installed in a removable and portable casing which comprises connection pins intended to be connected to test sockets permanently mounted on the current loop.
• One of the pins 13 is connected downstream of the diode D1 connected in series with the acquisition system in a common connection with the ammeter A1 determining the intensity of the acquisition current la.
• the other 15 pin is connected downstream of the pressure sensor 1.
• the ammeter A1 is integrated into the test box which in this case comprises a third pin 17 connected upstream of the diode D1 in a common connection with the 'ammeter.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Testing Electric Properties And Detecting Electric Faults (AREA)
• Arrangements For Transmission Of Measured Signals (AREA)
• Emergency Protection Circuit Devices (AREA)
• Measurement Of Current Or Voltage (AREA)
• Continuous-Control Power Sources That Use Transistors (AREA)
• Polishing Bodies And Polishing Tools (AREA)
• Constituent Portions Of Griding Lathes, Driving, Sensing And Control (AREA)
• Interface Circuits In Exchanges (AREA)
• Internal Circuitry In Semiconductor Integrated Circuit Devices (AREA)
• Structure Of Printed Boards (AREA)
• Printing Elements For Providing Electric Connections Between Printed Circuits (AREA)
• Semiconductor Integrated Circuits (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=9528776

Family Applications (1)

Country Status (15)

Families Citing this family (9)

Family Cites Families (15)

• 1998
  • 1998-07-20 FR FR9809217A patent/FR2781301B1/fr not_active Expired - Fee Related
• 1999
  • 1999-07-19 NZ NZ503395A patent/NZ503395A/en unknown
  • 1999-07-19 AU AU46299/99A patent/AU4629999A/en not_active Abandoned
  • 1999-07-19 DE DE69938816T patent/DE69938816D1/de not_active Expired - Lifetime
  • 1999-07-19 AT AT99929506T patent/ATE397262T1/de not_active IP Right Cessation
  • 1999-07-19 CA CA002303980A patent/CA2303980A1/fr not_active Abandoned
  • 1999-07-19 US US09/508,760 patent/US6337570B1/en not_active Expired - Fee Related
  • 1999-07-19 EP EP99929506A patent/EP1036385B1/de not_active Expired - Lifetime
  • 1999-07-19 WO PCT/FR1999/001764 patent/WO2000005695A1/fr active IP Right Grant
  • 1999-07-19 KR KR1020007002925A patent/KR20010024158A/ko not_active Withdrawn
  • 1999-07-19 CN CN99801165A patent/CN1118784C/zh not_active Expired - Fee Related
  • 1999-07-19 BR BR9906610-6A patent/BR9906610A/pt not_active IP Right Cessation
  • 1999-07-19 ID IDW20000518A patent/ID24131A/id unknown
  • 1999-07-19 TR TR2000/00658T patent/TR200000658T1/xx unknown
  • 1999-08-30 TW TW088112328A patent/TW510973B/zh not_active IP Right Cessation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events