To calibrate a HART pressure transmitter, the procedure is quite similar to calibrating a standard pressure transmitter, but with the added benefit of using HART (Highway Addressable Remote Transducer) communication to monitor and adjust parameters via a handheld communicator or software. Here’s a step-by-step guide:
1. Preparation:
Disconnect the pressure transmitter from the process and ensure it is powered off.
Gather the necessary equipment: a precision pressure source (e.g., a pressure calibrator or calibration pump), a digital multimeter (DMM) or calibrator, a HART communicator (handheld or software), and any required fittings or adapters.
2. Connect the Pressure Transmitter:
Connect the pressure transmitter to the calibration equipment. Ensure the pressure transmitter’s output is connected to a digital multimeter or calibrator to measure its output signal.
If using a handheld HART communicator, connect it to the transmitter’s HART output (usually via a HART interface cable or a communicator with an appropriate connection).
3. Check the Current Calibration Settings via HART Communicator:
Power up the pressure transmitter and the HART communicator.
Using the HART communicator, establish communication with the transmitter by accessing its unique address or device identifier.
Check the transmitter’s current configuration and calibration data (e.g., the zero and span values). This will allow you to verify the settings before calibration.
4. Zero Calibration (Pressure Transmitter Zero Adjustment):
Apply 0 pressure (atmospheric pressure) to the transmitter.
On the HART communicator, select the Zero Adjustment option. This may vary depending on the manufacturer, but typically, the HART communicator will allow you to input or confirm the zero setting.
The output signal should correspond to the transmitter’s zero value (e.g., 4 mA for a 4-20 mA output transmitter).
If necessary, adjust the zero setting via the HART communicator or via the transmitter's internal settings.
5. Span Calibration (Full-Scale Pressure):
Apply the full-scale pressure (e.g., the highest pressure value the transmitter is designed to measure).
Using the HART communicator, select the Span Adjustment option. This should allow you to verify and adjust the full-scale output of the transmitter (e.g., 20 mA for a 4-20 mA output transmitter).
Ensure the output signal at full-scale pressure is accurate and matches the expected value.
6. Check Intermediate Points:
Apply intermediate pressure values (e.g., 25%, 50%, 75% of full scale) to the transmitter and check the corresponding output values using the HART communicator.
Use the communicator to confirm that the transmitter is responding linearly across the pressure range.
If necessary, adjust the span or zero settings further to achieve linearity across the entire range.
7. Fine-Tuning and Adjustments:
If any readings are off, fine-tune the transmitter’s zero and span settings using the HART communicator.
Make any adjustments to compensate for errors and improve linearity between the pressure values and output signals.
8. Verify the Calibration:
After making adjustments, reapply the range of pressures to the transmitter (zero, intermediate, and full-scale pressures) and verify that the output signals are correct.
Use the HART communicator to check that the calibration is consistent with the expected values.
9. Document Calibration Results:
Record the calibration data (applied pressures and corresponding output signals).
Document any changes or adjustments made during the process and keep a calibration certificate for your records.
Most HART communicators allow you to save the calibration data and export it for documentation purposes.
10. Reinstall and Test in Process:
After calibration, reinstall the pressure transmitter into the process and connect it to the system.
Use the HART communicator to perform a final test in the field and ensure that the transmitter provides accurate readings in actual process conditions.
11. Post-Calibration Validation:
Key Notes:
HART Calibration Tools: The HART communicator can provide real-time data and diagnostics, making it easier to monitor the calibration process and make adjustments remotely. Some HART systems can even display error codes or provide diagnostic information if calibration fails.
Device-Specific Software: Some advanced transmitters might require specific software (e.g., Emerson’s Rosemount or Yokogawa’s proprietary tools) for calibration. Always refer to the manufacturer’s manual for detailed instructions on using the HART communicator for calibration.
This approach takes full advantage of the HART protocol’s capabilities, allowing you to calibrate more efficiently and accurately. Let me know if you need more details about any particular part of the process!
