How to Calibrate a Pressure Transmitter — Step-by-Step Guide

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How to Calibrate a Pressure Transmitter — Step-by-Step Guide

Pressure transmitter calibration ensures that the transmitter provides accurate readings of applied pressure by comparing it with a known reference standard. This is essential for process accuracy, safety, and reliability.

Required Equipment

  • Pressure Calibrator / Hand Pump / Dead Weight Tester – for applying known pressure.
  • Digital Reference Gauge – for precise measurement accuracy.
  • 24 V DC Power Supply – to power the transmitter.
  • Multimeter / Loop Calibrator – to measure 4–20 mA output signal.
  • HART Communicator – for SMART transmitters.
  • Tubing and Fittings – for proper connection and sealing.

Working Principle

A pressure transmitter converts the applied pressure into a proportional electrical signal (4–20 mA). Typically, 4 mA represents 0% (LRV) and 20 mA represents 100% (URV) of the calibrated pressure range.

Calibration Procedure

Step 1: Isolate & Prepare

  • Isolate the transmitter from the process.
  • Ensure it is depressurized and in safe condition/ ideal condition before starting.

Step 2: Connect Calibration Equipment

  • Connect the pressure source to the transmitter pressure port.
  • Connect 24V DC power supply to power terminals.
  • Connect multimeter/loop calibrator to read the 4–20 mA output.
  • If applicable, connect the HART communicator for SMART calibration.

Step 3: Apply Known Pressure (5-Point Test)

Apply pressure at 0%, 25%, 50%, 75%, and 100% of the transmitter range (both increasing and decreasing). Record the readings and calculate error.

Example (0–7 bar transmitter):

Applied Pressure Expected Output
0 bar (0%)4.00 mA
1 bar (25%)8.00 mA
3 bar (50%)12.00 mA
5 bar (75%)16.00 mA
7 bar (100%)20.00 mA

Step 4: Zero & Span Adjustment

Manual (Analog Transmitters):

  • Apply 0% pressure and adjust Zero to 4.00 mA.
  • Apply 100% pressure and adjust Span to 20.00 mA.
  • Repeat until both are correct.

SMART (HART Transmitters):

  • Connect HART communicator → Setup → Calibration → Trim Output / Sensor Trim.
  • Apply 0% pressure → Perform Lower Trim.
  • Apply 100% pressure → Perform Upper Trim.

Step 5: Verification

  • Repeat the 5-point test after adjustment.
  • Ensure readings are within ±0.1% tolerance or as per ISO standards.
  • Document calibration results and attach reference instrument details.

💡 Pro Tips

  • Vent air from the line before calibration (especially for liquid services).
  • For Differential Pressure (DP) transmitters, ensure correct high and low port connections.
  • Allow 5–10 minutes for signal stabilization before recording readings.
  • Perform recalibration every 6–12 months as per QA schedule.

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