Table of Contents
Purpose and Scope:
This procedure provides a thorough explanation of how to calibrate a motorized control valve in the process area using standards.
Tools Required for Motorized Control Valve Calibration:
- Necessary hand tools.
- Standard Multimeter with mA option.
- Test leads and probes.
- For supplying a 4 to 20 mA signal, use a loop calibrator or multifunction calibrator.
- Soft Cloth for cleaning.
Safety
- Please follow the link provided below for information on fundamental safety and general principles, as well as specifics on calibrating activities in process industries.
Basic Safety and General Consideration While Executing Calibration Process in process industries
- Always perform a LOTO procedure to isolate and de-energize the control valve, ensuring it cannot be inadvertently operated during calibration.
- Turn off the motorized control valve’s power source. Make sure the power supply is turned off at the source from any neighboring junction boxes.(e.g., turn off the breaker or unplug the wires).
- Make sure the control valve is properly isolated from the process line to prevent unintended product release during calibration.
- In some cases, use a bypass line to allow the process to continue while the valve is being calibrated. Follow established procedures for creating and using a bypass line.
- During calibration, ensure that the process control system is aware of the calibration, and alarms are set to notify operators of any anomalies.
- Understand the impact of valve calibration on the overall process and monitor parameters like pressure, temperature, and flow closely.
- Check that the Maintenance Override Switch (MOS) is working correctly and can be used to manually control the valve during maintenance activities.
- Ensure that the MOS system has appropriate safety interlocks to prevent unintended or unsafe valve operation.
- Ensure personnel involved in calibration wear the appropriate PPE, including safety glasses, gloves, and hearing protection as needed.
- Identify potential hazards, such as hazardous process materials, electrical hazards, and confined spaces, and take appropriate precautions.
- Ensure that personnel are well-trained in control valve handling and calibration, and that they fully understand the calibration procedure.
Calibration Setup
- Ensure you have the necessary tools and equipment, including a multimeter and a loop calibrator.
- Verify that the multimeter is functioning correctly and calibrated.
- Double-check that the loop calibrator is in good working condition.
- Disconnect the wires from the analog input and feedback terminals of the motorized control valve. Ensure that they are properly tagged for reconnection.
- Connect the multimeter with mA mode in series with the analog input feedback wires. This allows you to measure the analog input 4- 20 mA signal output from the motorized valve position feedback. Alway refer the instrument loop diagram for connections.
- Connect the loop calibrator to the analog output terminals of the motorized control valve in the junction box or motorized control valve, where you previously disconnected the wires. Ensure proper polarity.
- Set the loop calibrator to the desired output range, typically 4-20mA, which matches the valve’s control signal range from the control system.
- Re-energize the motorized control valve by normalizing the main power supply to the valve. Ensure that this is done safely and according to your facility’s procedures.
- Now the above setup is ready for the calibration of the motorized control valve.
How to Calibrate Motorized Operated Valve?
Calibration Procedure
- Examine the input and output connections of the motorized control valve to ensure their stability and integrity.
- Before calibration, confirm that the motorized control valve can be manually operated using the hand wheel or manual override feature.
- Verify that manual operation is functioning correctly.
- If equipped, check the local control of the motorized control valve.
- Ensure that local control settings are operational, and the motorized control valve responds as expected.
- Set the loop calibrator to output 4mA, representing the fully closed position.
- Check the initial mechanical position or stroke angle of the motorized control valve.
- Compare the “as found” reading of the motorized control valve with the feedback measured from the motorized control valve’s 4mA signal using a multimeter.
- If there is a significant deviation, proceed with necessary adjustments to align with the 4mA position feedback.
- Set the loop calibrator to output 20mA, representing the fully open position.
- Check the mechanical position or stroke angle of the motorized control valve.
- Compare the “as found” reading of the motorized control valve with the feedback measured from the motorized control valve’s 20mA signal using a multimeter.
- If there is a significant deviation, proceed with necessary adjustments to align with the 20mA position feedback.
- Make necessary mechanical adjustments to bring the motorized control valve into alignment with the simulated 4mA and 20mA positions.
- Fine-tune the motorized control valve’s position to ensure it precisely matches the simulated 4mA and 20mA output signals.
- Repeat the adjustment and fine-tuning steps as needed until the mechanical position accurately aligns with the simulated 4mA and 20mA output signals.
- Change the loop calibrator’s output to 12mA, simulating the mid-range position.
- Adjust the motorized control valve to match this mid-range position mechanically and ensure stability.
- Cycle through the 4mA, 12mA, and 20mA output signals on the loop calibrator.
- Check if the mechanical position of the motorized control valve corresponds correctly at each signal level
- You will need to perform the method of calibration as many times as necessary until the motorized control valve is calibrated to the appropriate tolerance.
- Depending on the specific motorized control valve, power supply system and kind of control valve body being utilized, the calibration process may change. Please read the manufacturer’s instructions before starting, then.
Recording Calibration
- Perform linearity tests in both the upscale and downscale directions.
- Test at the following positions: 0%, 25%, 50%, 75%, and 100% open.
- Check if the motorized control valve’s output values are within an acceptable range at each position.
- If the output values are within the acceptable range, no further calibration is needed.
- If any output values deviate from the accepted limits, calibration is required.
- If calibration cannot correct the deviation, the motorized control valve may need servicing or replacement.
- Record the output data obtained during the tests in the “as found/as left” columns of the calibration report for the motorized control valve.
Completion of Calibration
- Attach the calibration label to the motorized control valve to indicate that calibration has been successfully completed.
- After calibration, clean the calibration apparatus and store it in a safe location.
- Record the calibration information for future reference and documentation.
- Disconnect any loop calibrator ,multimeter, and other equipment that were used during the calibration process.
- Re- Connect the wiring of the motorized control valve in the processing area.
- Ensure the workplace is tidy and free from any debris or hazards.
- De-isolate the equipment if any isolation measures were applied during calibration.
- Restore the signal to its usual level if it had been bypassed or inhibited for the calibration.
- Put the motorized control valve back into active use and carefully monitor its operation to ensure it is functioning normally.
Sample Calibration Report
The following picture displays how the motorized control valve calibration sample report was completed in the field using a standard loop calibrator and a multimeter as the reference.
The Excel template that was used to make the motorized control valve calibration report can be downloaded from the link below.
Click here for Loop checking of Motor operated valve(MOV)
