Calibrating a Differential Pressure Transmitter (DPT) level transmitter in the field involves verifying and adjusting its output signal to accurately measure the level of a liquid or gas in a tank or vessel. Here's a step-by-step guide on how to calibrate a DPT level transmitter in the field:

1. Prepare Equipment:

   • Gather the necessary equipment, including a pressure calibrator, multimeter, reference pressure source (e.g., hand pump), and calibration certificate.
   • Ensure that all equipment is properly calibrated and in good working condition.

2. Isolate Transmitter:

   • Isolate the DPT level transmitter from the process by closing any isolation valves and ensuring that the process conditions are stable.

3. Verify Zero Point:

   • Zero the DPT level transmitter by venting both pressure ports to atmospheric pressure or a known reference pressure.
   • Use a pressure calibrator to measure the output signal of the transmitter and verify that it reads zero.
   • If necessary, adjust the zero trim potentiometer on the transmitter to ensure that the output signal reads zero.

4. Apply Span Pressure:

   • Apply a known span pressure to the high-pressure side of the DPT level transmitter using a pressure calibrator or hand pump.
   • Measure the output signal of the transmitter using a multimeter or loop calibrator and compare it to the expected output for the applied pressure.
   • Adjust the span trim potentiometer on the transmitter to ensure that the output signal corresponds accurately to the applied pressure.

5. Check Linearity:

   • Apply additional pressure points across the measurement range of the DPT level transmitter to verify its linearity.
   • Measure the output signal of the transmitter at each pressure point and compare it to the expected output.
   • Adjust the span trim potentiometer as necessary to correct any deviations from linearity.

6. Perform Hysteresis Test:

   • Apply pressure to the DPT level transmitter in both increasing and decreasing directions to check for hysteresis.
   • Measure the output signal of the transmitter at each pressure point and compare it to the expected output.
   • Adjust the zero and span trim potentiometers as necessary to minimize hysteresis effects.

7. Finalize Calibration:

   • Once satisfied with the calibration results, finalize the process by documenting the calibration procedure, including the applied pressures, measured output signals, adjustments made, and any observed errors or deviations.
   • Complete the calibration certificate and sign it to provide evidence of the DPT level transmitter's calibration.
   • Restore the DPT level transmitter to normal operation and ensure that it is properly integrated into the process.

8. Post-Calibration Checks:

   • Conduct post-calibration checks periodically to verify the performance and accuracy of the DPT level transmitter under normal operating conditions.
   • Review and update the calibration records as necessary to maintain traceability and compliance with regulatory requirements.

By following these steps, you can effectively calibrate a Differential Pressure Transmitter (DPT) level transmitter in the field to ensure accurate and reliable level measurement in your process or application. It's essential to follow manufacturer guidelines, industry best practices, and organizational procedures to perform effective transmitter calibration and maintain the integrity of level measurement systems.