Calibrating a pressure transmitter using a hand-held calibrator involves comparing the transmitter’s output signal with the known pressure applied to the system. The goal is to ensure that the transmitter’s readings are accurate across its full range of operation. Below is a step-by-step guide on how to perform this calibration:

Equipment Needed:

• Hand-held calibrator (e.g., digital pressure calibrator)

• Pressure source (e.g., a hand pump, pneumatic or hydraulic pump)

• Pressure transmitter (the device under calibration)

• Pressure reference device (e.g., a precision manometer or a calibrated pressure gauge, if required)

Steps for Calibration:

1. Prepare the Equipment

• Check the Calibration of Your Hand-Held Calibrator: Ensure that your hand-held calibrator is properly calibrated and within its calibration interval. It should be able to measure pressure accurately in the range you’ll be testing.

• Ensure Proper Connection: Connect the pressure transmitter to the pressure source. You’ll be applying pressure to the transmitter and reading the output using the hand-held calibrator.

• If the hand-held calibrator has an input for a pressure transmitter signal (e.g., 4-20 mA, 0-10 V), connect the transmitter’s output signal to the input of the calibrator.

2. Zero the Pressure Transmitter

• Zero the Transmitter: Before applying any pressure, make sure the transmitter’s output is zeroed. This ensures that the transmitter is correctly reading zero pressure at the baseline (e.g., 4 mA for a 4-20 mA transmitter).

• Use your hand-held calibrator to verify the signal at zero pressure (e.g., a pressure of 0 bar or 0 psi) and adjust the transmitter’s zero if needed.

3. Apply Pressure

• Generate Test Pressures: Gradually increase the pressure using the pressure source (e.g., hand pump or pneumatic pump) in increments. Start at the low end of the transmitter’s measurement range and work towards the high end.

• For example, if you are calibrating a transmitter with a range of 0-100 psi, you may start at 0 psi, then apply 25 psi, 50 psi, 75 psi, and finally 100 psi.

• Ensure that the hand-held calibrator is connected to the pressure source and is measuring the actual applied pressure.

4. Verify the Transmitter Output

• Read the Output Signal: As you apply each pressure increment, check the corresponding output signal from the pressure transmitter (e.g., 4 mA at 0 psi, 12 mA at 50 psi, 20 mA at 100 psi for a 4-20 mA transmitter).

• Use the hand-held calibrator to compare the output signal of the transmitter with the expected signal at each pressure value. You should see a linear relationship between pressure and output signal for most transmitters.

• The hand-held calibrator should display the measured signal, and you should note any discrepancies between the applied pressure and the transmitter’s output.

5. Adjust the Transmitter (if needed)

• If the transmitter's output is not matching the expected values (e.g., 4 mA at 0 psi, 20 mA at full-scale pressure), you will need to make adjustments.

• Many transmitters allow for zero adjustment and span adjustment (i.e., adjustment for the low end and high end of the measurement range).

• Adjust the zero setting to match the expected signal at 0 pressure (typically 4 mA for a 4-20 mA signal).

• Adjust the span setting to match the expected signal at the full-scale pressure (e.g., 20 mA at 100 psi).

• Make small adjustments and then verify the calibration at each pressure point.

6. Test Intermediate Points

• Once the zero and span are set correctly, check intermediate pressure values (e.g., 25 psi, 50 psi, 75 psi) to verify the transmitter’s accuracy across the full range.

• For a 4-20 mA output, check that the output signal corresponds to the pressure:

• 0 psi = 4 mA

• 25 psi = 8 mA

• 50 psi = 12 mA

• 75 psi = 16 mA

• 100 psi = 20 mA

7. Final Calibration Check

• After adjusting and confirming the accuracy at all pressure points, perform a final check of the calibration. Re-verify the output signal at zero pressure and full-scale pressure.

• Ensure that all intermediate points still fall within acceptable tolerances.

8. Document the Calibration

• Once calibration is complete, document the results. Most hand-held calibrators will store calibration data, but you should also record the date, pressure points tested, and any adjustments made for reference.

Summary Checklist:

1. Verify calibrator and set it up for pressure measurement.

2. Zero the transmitter before applying pressure.

3. Apply pressure in increments (e.g., 0%, 25%, 50%, 75%, 100% of range).

4. Measure output signal at each increment using the calibrator.

5. Adjust transmitter as needed (zero and span adjustments).

6. Check intermediate points to ensure linearity.

7. Verify accuracy at zero and full-scale pressure.

8. Document results for future reference and compliance.

Conclusion:

Using a hand-held calibrator to calibrate a pressure transmitter ensures that the instrument provides accurate, reliable readings across its full range. This process involves applying known pressures, comparing the transmitter's output to expected values, making adjustments, and verifying calibration at various points. Regular calibration helps maintain the accuracy and functionality of the transmitter, ensuring optimal performance in industrial applications.