Differential pressure transmitters Calibration | DPT calibration

This Article establishes the minimum guidelines for E&I Technicians and/or Engineers to perform the calibration of Pressure Transmitter. This document also enables E&I technicians to do primary level configuration and troubleshooting.

Scope and responsibility

This document is applicable for Rosemount DP/ Level Transmitter 3051.

E&I Technicians are responsible to follow the steps as mentioned in this procedure.

E&I Manager and Instrumentation Engineers are responsible for the implementation of this procedure.

Competency Requirements

E&I Technicians must be trained and qualified to perform calibration of Pressure Transmitter.

Definition

Differential pressure transmitters are devices designed to measure fluid differential pressure and transmit that information via electrical signals such as the (4-20) mA analog standard, or in digital form such as HART or FF. These are used in a process industry for continuous monitoring/controlling. It is mandatory to calibrate them at regular intervals of time, so that there may not be any interlock failure.

References

Procedure requirement

  • Safety Precautions 

  1. Ensure that tools necessary for calibration i.e. Fluke Pressure Calibrator 718-300G and HART (375 Field Communicator) are available.
  2. If the Transmitter is an Critical instrument, take necessary precautions for maintenance of Critical instrument & follow Critical instrument procedure too.
  3. Wrong implementation of procedure/implementation without proper communication may lead to accidents or cause of plant trip.

  • Calibration Procedure

Proper procedure is necessary to ensure the satisfactory operation.

  1. Ensure the Work order (print copy after WO released) is ready to perform the calibration on Transmitter.
  2. Ensure the work permit/Maintenance request form to confirm the maintenance on transmitter.
  3. Put the Transmitter in CAL mode (i.e. in simulation mode or bypass the interlock) from DCS.
  4. Now open the equalizing valve and close isolation valve, remove the drain plug to depressurize the transmitter line.
  5. Connect HART to DP transmitter.
  6. Verify the range of transmitter using HART and also check for zero error.
  7. If accuracy is not within ±0.10% of span, zero trim using HART otherwise proceed to next step.
  8. Choose appropriate sensor for calibrator and Connect Fluke Pressure Calibrator to its HP taping.
  9. After physically isolating the transmitter, check the value of current on calibrator it should be 4mA. Check the pressure in the display of transmitter, if it is 0.0 unit (barg/mmWc/mBar), then zero setting is ok otherwise we have to adjust by pressing the zero push button for zero setting of transmitter. Cross check the configured range of the transmitter with point data base.
  10. Now Give the pressure equal to the span value of the transmitter if the display is showing correct value then it is ok; otherwise adjust the span of transmitter by pressing span button for span setting of transmitter.
  11. Give the intermediate values of pressure with Fluke Pressure calibrator, check the display on transmitter and check corresponding values of current on the calibrator display.
  12. If the values are not within 0.1% of span, the transmitter is to be repaired. Otherwise follow next step.
  13. Remove all connection from transmitter.
  14. Take the transmitter in line and remove from CAL mode.
  15. Hand back the work permit or maintenance requisition form.
  16. Now calibration is completed & Close the work order.

  • Loop Checking Procedure

Proper procedure is necessary to ensure the satisfactory operation.

  1. Ensure the work permit/Maintenance request form to confirm the maintenance on transmitter.
  2. Put the Transmitter in CAL mode (i.e. in simulation mode or bypass the interlock) from DCS.
  3. Connect HART to Pressure transmitter.
  4. Verify the range of transmitter using HART and also check for zero error.
  5. In HART goto service tools then simulate & start Loop checking.
  6. Give the 4mA current value and ensure that the reading in DCS is showing 0.0 unit (barg/mmWc/mBar), whereas in transmitter display it is showng 4mA with loop test.
  7. Give the 20mA current value and ensure that the reading in DCS is showing equal to span value (unit-barg/mmWc/mBa) whereas in transmitter display it is showng 20mA with loop test.
  8. For other values in full scale, give the various mA signal between (4 to 20)mA & ensure the respective readings in DCS (unit-barg/mmWc/mBar) & loop current value (mA) in Transmitter display.
  9. After completion of loop checking, return to process value via loop check end.
  10. Now Loop checking is completed.

Record Retention

  • Check list for calibration of DP transmitter and calibration record must be filled before & after the calibration.
  • Calibration checklist must be signed by concern authority and it should be filed in preventive maintenance record.
  • All calibration records should be kept for at least three years & after that it should be disposed off.

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