General calibration procedure for differential pressure transmitters

pressure

#1

Calibrating a differential pressure transmitter is much more difficult than calibrating a pressure transmitter. This is because the pressures are very small. So low-pressure gauges are used to calibrate the differential pressure gauge.

In industries, calibration is done using devices like Wallace & Tiernan calibrator. Understand the port connections of the Wallace & Tiernan calibrator.

##Calibration steps for pneumatic differential pressure transmitter:

  • Connect the calibrated pressure supply to the HIGH inlet pressure. Leave the LOW pressure inlet connection open.

  • Connect the air supply port to the 20 psi (1.4 bar) supply.

  • Use a pressure gauge to cover the range 0 - 20 psi (0 - 1.4bar). Connect it to the output port.

  • Using the manufacturer’s manual set up the differential pressure transmitter to values given by the instructor.

  • Use the results to draw a calibration curve in the same way as for a pressure gauge. Ensure the device gives a linear output of 3-15 psi (0.2-1 bar). Check its accuracy is within specification. Remember: 3-15 psi is not equivalent to 0.2-1bar. Calibrate using either 3-15 psi or 0.2-1 bar.

##Calibration steps for electrical differential pressure transmitter:

  • Connect the “HIGH” inlet pressure connection to the calibrated pressure supply. Leave the “LOW” pressure connection open.

  • Connect up the 24V D.C. supply to the transmitter output terminals using the manufacturer’s calibration manual.

  • The calibration method depends on the manufacturer. You may or may not need a series load resistor. The device may be current or voltage calibrated. The manual must be used.

  • Set up the differential pressure transmitter to values given by the instructor.

  • From results obtained in the same way as for a pressure gauge, draw a calibration curve. Ensure the device gives a linear output (4 - 20 mA) and check its accuracy is within specification.