Current to Pressure (I/P) Converter Calibration Procedure

What is an I to P Converter?

• In industrial control systems, a specific kind of current-to-pressure transducer known as an I/P converter is used.
• It is a compact module that converts an analogue current signal (I) into a pneumatic output (P) for usage in various applications.
• It transforms electrical impulses from a DC (direct current) signal into proportionate pneumatic pressure, to put it another way.

What is the Most Common use for an I to P Transducer?

• In order to apply pneumatic pressure to control valves, dampeners, actuators, or brakes and clutches within an industrial mechanism, I/P transducers transform electrical impulses from a controller.
• The I to P (current to pneumatic) converter is a device used in process control systems to convert a current signal, often 4-20 mA, to a pneumatic signal, typically 3-15 psi. It’s crucial to calibrate the I to P converter to make sure that it correctly converts the input signal to the desired output pressure.

How do you Calibrate an I to P Converter?

7 Steps Calibration Procedure for I to P Converter

This below Step by Step I-to-P converter calibration procedure provides a thorough explanation of how to calibrate a I-to-P converter using reference standards.

Step 1: Prepare the Tools Required for I to P Convertor Calibration

1. Necessary hand tools.
2. Instrument air supply 
3. Standard air pressure regulator.
4. Standard Multimeter.
5. Test leads and probes.
6. Tubes and standard fittings 
7. Reference standard pressure gauge for measuring pneumatic output signal 3 to 15 psi from the convertor.
8. For supplying a 4 to 20 mA signal, use a loop calibrator or multifunctional calibrator.
9. Soft Cloth for cleaning.

Step 2: Safety Precautions

1. Please follow the link given below for information on fundamental safety and general guidelines as well as details on calibrating operations in process industries – Basic Safety and General Consideration While Executing Calibration Process in process industries
2. To configure the controller in manual mode for the control loop and MOS for the ESD loop, ask the panel operator.
3. Find the I to p converter that you wish to disconnect. Verify that it is the correct converter and make a note of any relevant info Tag number (e.g., the manufacturer, model number, pressure range, etc.).
4. Turn off the I to P converter’s power source. Make sure the power supply is turned off at the source from any neighboring junction boxes or marshalling panels close to the control room.(e.g., turn off the breaker or unplug the wires).
5. Before disconnecting the I to p converter, you may need to depressurize the system, depending on the kind of system. Observe the correct steps to depressurize the system (e.g., vent the pressure or isolate the system).
6. From the I to P converter, carefully unplug the electrical connection . Be sure to adhere to any applicable safety precautions (such wearing insulated gloves or equipment) and be cautious not to damage the wires or connectors.
7. The I to P converter’s pneumatic connections should be removed. This can include removing fittings or releasing clamps, depending on the kind of connection. Be careful not to harm any fittings or tubing.
8. After disconnecting the I to P converter, mark it with any relevant info (such as the date, the explanation for removal, etc.) and keep it in a secure place. If the converter has to be fitted again, be sure to store it safely to avoid contamination or damage.
9. The individual equipment and process area may need modifying this overall technique, so keep that in mind. While working with I to p converters or other process equipment, always adhere to any manufacturer guidelines and regional safety standards.
10. To avoid an unintentional starting, adhere to all applicable lockout/tagout protocols. Make sure the I to p convertor is kept separate from the process.

Step 3 : Prepare the Setup for Calibration I to P Converter

1. The calibration equipment has to be placed in a place that is free of vibrations and electromagnetic interference. Also, the space has to be well-ventilated and bright.
2. Collect all of the essential tools and equipments.
3. A tubing system should be used to link the pressure source to the I to P converter. Make sure the tubing is clear of any twists or obstructions that can interfere with the pressure measurement.
4. A tubing system should be used to link the instrument air supply source to the I to P converter through the pressure regulator with standard fittings.  Make sure the tubing is clear of any twists or obstructions that can interfere with the pressure measurement.
5. To simulate the input signal to the I to P converter, utilize a loop calibrator. Attach the Loop calibrator to the I to P converter’s input leads.
6. To measure the output current of the loop calibrator, use a multimeter. The output leads of the loop calibrator should be connected in series with the multimeter.
7. The output of the I to P converter should be connected to the standard pressure gauge in order to measure the output pressure.

What values can be Adjusted when Calibrating an I to P Converter?

Step 4 : Calibration of I to P converter

1. Inspect the I to P converter’s input and output connections to make sure they are stable.
2. Power up the I-to-P converter by setting the input signal to 4 mA with a loop calibrator. Make sure it is stable and working correctly by measuring the mA with a multimeter.
3. Make sure that the air pressure coming into the I-P transducer is 20 PSI.
4. If it isn’t at 20 psi, appropriately adjust the pressure using the regulator.
5. Use the calibration source to provide a 4 mA current signal to the I to P converter’s input.
6. Use the connected pressure gauge to determine the I to P converter’s output pressure. The output pressure must match the minimum value required.
7. If the pressure reading is more or less than 3 psi, the I to P convertor’s zero adjustment has to be adjusted.

Zero Calibration of I to P Converter

1. To get a pressure of 3 psi, carefully move the zero adjustment screw on the I to p convertor in very tiny increments.
2. An excessive amount of turning of the zero adjustment may cause harm to the I/P converter.
3. Increase the input current signal to 20 mA, and make sure the gauge reads 15 psi on the output pressure reading.

Span Calibration of I to P Converter

1. Make sure the I to P converter’s output is at 15 psi and gently adjust the span adjustment to get the desired pressure of 15 psi. Multiple span adjustment rotation might harm the I/P converter.
2. Repeat the calibration procedure as necessary until the I to P converter is calibrated to the required tolerance.
3. The procedure for calibration might be varied based on the particular calibrator and I to P convertor that is being used. Hence, before commencing, please read the manufacturer’s instructions.

Step 5: Recording Calibration with Linearity Check

1. To ensure that the I-P converter is providing the proper output values, do linearity checks at 0%, 25%, 50%, 75%, and 100% in the upscale and downscale directions.
2. Recalibration is necessary if the output value does not fall within an acceptable range. Once again, an I to P converter has to be repaired or replaced if the output values have deviated from the allowed range.
3. If every output value (+/-%) is within accepted limits, no additional calibration is necessary.
4. The blank calibration report’s as found/as left column should be filled up with the output data.

Step 6: Completion of Calibration

1. Place the calibration label on the I to P convertor after the calibration has been successfully completed.
2. When the calibration is finished, clean the equipment, place it in a secure area, and record the calibration information for future use.
3. Disconnect the loop calibrators, pressure gauge and other setup.
4. Fix back the I to P converter in the processing area.
5. Ensure that the workplace is clean.
6. De-isolate the equipment.
7. Restore the bypassed or inhibited signal to its normal level.
8. Put the I to P convertor back into service and make sure it is functioning properly.

Step 7: Calibration Report Preparation and Validation

The next picture shows that the I to P convertor sample report of calibration was done in workshop with a loop calibrator and standard pressure gauge as the reference.

The Excel template that was used to make the I to P convertor calibration report can be downloaded from the link below. 

Calibration Standards for I to P Convertor

Follow our I to P converter calibration procedure, which has been thoroughly developed in accordance with NIST standards, to ensure accurate and reliable signal conversion for optimal performance in industrial processes.

When calibrating electropneumatic positioners, including I/P converters, refer to the industry-standard ISA-75.02.01-2005 (IEC 60534-2-1 Mod) for performance requirements, testing methods, and calibration procedures. Additionally, consult the manufacturer’s manual for model-specific instructions and recommendations.

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