7 Steps Calibration Procedure for Pressure Transmitter

What is a pressure transmitter?

A pressure transmitter, also known as a pressure transducer or sensor, is a specialized instrument designed to gauge applied pressure. Its primary function involves the conversion of mechanical or hydraulic pressure into an electrical signal. This electrical output serves various purposes, such as displaying the pressure measurement on a screen or transmitting the signal to a controller, PLC, or data acquisition system for additional analysis and processing.

Why do we need pressure transmitter?

Pressure transmitters are essential in the process industry for monitoring and controlling the pressure of liquids, fluids, and gasses. Also known as pressure transducers, these devices go beyond just measuring pressure, contributing to safety, process optimization, and ensuring the quality of industrial processes.

7 Steps Calibration Procedure for Pressure Transmitter

This below Step by Step Pressure Transmitter calibration procedure provides a thorough explanation of how to calibrate a Pressure Transmitter using pressure calibrator.

Step 1: Prepare the Tools Required for Pressure Transmitter calibration

• Necessary hand tools.
• 24 V power supply source.
• Standard Pressure Calibrator.
• Standard Multimeter.
• Test leads and probes.
• Tubes and standard fittings 
• Soft Cloth for cleaning.
• For smart transmitters, a crucial communication tool is the Hart communicator

Step 2: Safety Precautions

1. For detailed safety guidelines, general recommendations, and calibration procedures in process industries, refer to the provided link:

Basic Safety and General Considerations for Process Industries Calibration Process

3. Request the panel operator to switch the Pressure Transmitter controller to manual mode for the control loop and MOS for the ESD loop.
4. Identify the specific Pressure Transmitter to be turned off, recording key information like Tag number, manufacturer, model number, and pressure range.
5. Before removing the Pressure Transmitter, be sure there is no pressure or fluid running through the instrument by stopping the operation.
6. Close or disconnect the pipe connecting the Pressure Transmitter to the process to isolate it from fluid flow.
7. Release any trapped pressure within the transmitter by opening bleed or vent valves.
8. Disconnect the power supply from the Pressure Transmitter and turn off nearby junction boxes or marshalling panels.
9. Plug the lines to prevent fluid seepage post-calibration.
10. Safely store the Pressure Transmitter connections in a secure location.
11. After removing tubing connections, label the Pressure Transmitter connections with relevant information (date, reason for removal) for proper storage.
12. Adhere to the manufacturer’s instructions and safety precautions during the removal process, and consult with a skilled technician or engineer if needed.
13. Follow lockout/tagout procedures to prevent unintended starts and ensure the Pressure Transmitter is isolated from the process.

Step 3 : Prepare the calibration Setup for Pressure Transmitter

1. Ensure that the calibration equipment for the Pressure Transmitter is positioned in a location free from vibrations and electromagnetic interference. The designated area should be well-ventilated and well-lit.
2. The requirements for the calibration area of the Pressure Transmitter are as follows: it needs to be level, solid, and clean.
3. Verify the Mounting of the Pressure Transmitter securely  on the field..
4. Connect one end of the tube to the pressure inlet port of the Pressure Transmitter, and attach the other end to the output of the pressure calibrator. Verify the connections for tightness and leak-free operation.
5. Establish a series connection between the Pressure Transmitter, the 24-volt power supply from the junction box, and a digital multimeter capable of measuring milliampere current.
6. Integrate the Hart communicator with the terminal of the Pressure Transmitter(for only smart type transmitter).
7. Place the Pressure Transmitter calibration setup in an environment free from vibrations and electromagnetic interference, ensuring proper ventilation and lighting.
8. As indicated in the above figure, establish a suitable and accurate calibration setup for the Pressure Transmitter by following these step-by-step instructions.
9. Ensure that the environmental conditions during calibration, such as temperature and humidity, are within the specified operating range of both the pressure transmitter and the calibration equipment.

Step 4 : Calibration of Pressure Transmitter

1. Ensure that the input tubing connections and output wire connections on the Pressure Transmitter are securely in place.
2. Set the power supply unit to 24 VDC to activate the Pressure Transmitter. Before powering the circuit, use a multimeter to confirm the voltage level in the power supply output.
3. Turn on the pressure calibrator.
4. Refer to the instrument datasheet for the Pressure Transmitter and ensure that the pressure calibrator’s menu is configured to the correct unit.
5. Allow sufficient time for the pressure transmitter and calibration equipment to stabilize at the calibration environment before initiating the calibration process
6. Record and document the initial conditions, including ambient temperature, pressure, and any other relevant parameters, as they may affect the calibration.
7. Set the transmitter’s 0% Lower Range Value (LRV) to match the LRV of the calibration range.
8. Adjust the upper range value (URV) of the calibration range to 100% for the Pressure Transmitter’s span.
9. Refer to the instruction manual to locate the ZERO and SPAN/RANGE adjustments in the display menu for the Pressure Transmitter.
10. Apply the LRV 0% to the pressure port of the Pressure Transmitter using the pressure calibrator.
11. While observing the 4mA reading on the multimeter, adjust the ZERO adjustment menu in the display or the zero adjustment potentiometer of the transmitter. This sets the Pressure Transmitter’s LRV output.
12. Apply pressure to the pressure port of the Pressure Transmitter to raise the reading to the calibration range’s 100% URV.
13. While focusing on the 20mA reading on the multimeter, adjust the SPAN adjustment menu in the display or the SPAN adjustment potentiometer of the Pressure Transmitter. This sets the Pressure Transmitter’s URV output.
14. For SMART Pressure Transmitters, use a HART communicator. After connecting the communicator and the transmitter, choose the lower range value trim and higher range value trim options from the HART Communicator Menu.
15. Repeat the calibration method as needed until the Pressure Transmitter is within the specified tolerance.

Note: The calibration process may vary based on the specific pressure calibrator and Pressure Transmitter used, so it is essential to follow the manufacturer’s instructions carefully.

Step 5: Recording Calibration with Linearity Checks

Conduct linearity tests in both the upscale and downscale directions at 0%, 25%, 50%, 75%, and 100% to verify the accuracy of the Pressure Transmitter’s output values.

To determine the calibration check point value for linearity checks, utilize this online calibration test points value calculator.

1. Examine the output values at each test point. If any value falls outside the acceptable range, calibration becomes necessary.
2. In case the output values deviate from the allowed range, consider either servicing the Pressure Transmitter or replacing it.
3. Confirm that, if all output values (+/- %) are within acceptable bounds, no additional calibration is required for the Pressure Transmitter.
4. Use this Instrument accuracy calculator to calculate error and accuracy for each recorded output reading.
5. Enter the obtained output data into the designated “as found/as left” columns of the blank calibration report for the Pressure Transmitter.
6. Include routine linearity tests into your calibration method, assuring systematic testing at specified times to maintain the Pressure Transmitter’s accuracy and reliability.

Note: Consistent linearity testing and dedicated collection of calibration data are required for maintaining the Pressure Transmitter’s accuracy and dependability over time.

Step 6: Completion of Calibration

1. Once the calibration is successfully finished, affix the calibration label securely to the Pressure Transmitter.
2. After completing the calibration process, clean the instrument thoroughly, store it in a secure location, and document the calibration data for future reference.
3. Disconnect the Pressure Transmitter, pressure calibrators, and any other associated setups used during calibration.
4. Reinstall the Pressure Transmitter connections back into the processing area, ensuring it is securely fixed.
5. Ensure the workplace is left in a clean and organized state.
6. De-isolate the equipment as necessary.
7. Return any bypassed or inhibited signals to their original levels.
8. Verify that the Pressure Transmitter is functioning correctly before resuming its normal operation.

Step 7: Calibration Report Preparation

Ensure that the calibration report includes information about traceability, such as the calibration standards used and their calibration certificates.

Refer to the image below for an example calibration report for the Pressure Transmitter, which was performed in the field with a loop calibrator and a standard pressure calibrator as the reference.

The Excel template used for creating the Pressure Transmitter calibration report is available for download via the link provided below for your convenience.

Calibration Procedure: Aligned with NIST and IEC 61508 Standards

To ensure accurate and reliable signal transmission for best performance in industrial operations, follow our pressure transmitter calibration method, which has been thoroughly designed in accordance with NIST standards.

IEC 61508 sets safety standards for electrical systems in critical industries. Adhering to its calibration methods is vital for safe and accurate pressure measurement. It provides a systematic approach throughout the system’s lifecycle, crucial for safety in pressure transmitters.