Pressure Transmitter Calibration | Step-by-Step Calibration Process

Brian Craig

April 20, 2017

Transmitter calibration requires meticulous preparation. In the preceding post, we have discussed basic setups for calibrating a pressure transmitter. Here we will discuss how to proceed with pressure transmitter calibration.

What Is Pressure Transmitter Calibration?

Pressure transmitter calibration is the process of verifying and adjusting a transmitter so that its output signal accurately represents the applied pressure. The calibration ensures that the transmitter’s 4–20 mA output corresponds correctly to the configured lower range value (LRV) and upper range value (URV).

Regular pressure transmitter calibration is essential to maintain measurement accuracy, process reliability, and safe operation in industrial systems where precise pressure readings are required.

Tools Required for Pressure Transmitter Calibration

Before starting pressure transmitter calibration, ensure that the required tools and reference equipment are available. Using properly calibrated instruments is critical for achieving accurate results.

Commonly required tools include:

Pressure calibration source such as a hand pump or pressure calibrator
Certified pressure reference or test gauge
Loop calibrator or digital multimeter
Stable power supply (typically 24 VDC)
Manufacturer’s instruction manual

Preparing these tools in advance helps avoid interruptions during the calibration process.

How to Calibrate a Pressure Transmitter

Step-by-Step Pressure Transmitter Calibration Procedure

After completing all the preliminary requirements, you can proceed in the following ways:

Calibrate the 0%, Lower Range Value (LRV) of the transmitter to the LRV of the calibration range. Calibrate the transmitters span to 100%, Upper Range Value (URV) of the calibration range. For example: If you are using Differential Pressure transmitter with power output 4-20mA to measure pressure in the range 0-300 PSIG, then the transmitter’s 0% LRV is 4mA, and is calibrated to 0PSIG. Similarly, the 100% URV is 20mA, and will be calibrated to 20 mA.
Locate the ZERO and SPAN/RANGE screws of the transmitter by referring the instruction manual. These screws are each connected to the potentiometer and can be turned easily.
The potentiometer allows up to 20 turns between the maximum and minimum resistance. This means 20 clockwise or anticlockwise turns of ZERO and SPAN screw will cause the potentiometer to be at maximum or minimum. In many brands of DP transmitters, the ZERO and RANGE adjustments are interconnected. This means adjusting one screw may affect the other.
Turn the RANGE and ZERO screws clockwise 20 times. Next, turn the screws 10 times in the counter clockwise direction to adjust the potentiometer between the maximum and minimum resistance. This step is performed to set the mid resistance point at 50%.
Apply the LRV 0% on the high side of the transmitter, and low vented side. This helps diminish the differential pressure across the DP cell of the transmitter.
Adjust the ZERO screw on the transmitter by observing the 4mA indication in the current meter. This is the LRV output of your transmitter. At times, this value may not be 4 mA, but you should get a value closer to that.
Next, apply pressure on the high side of the transmitter to increase the value to the 100% higher value (URV) of the calibration range.
Adjust the RANGE Screw by observing the meter’s current indication, which should show 20 mA, which is the 100% URV output of the transmitter.
In ideal situation, 100% of the transmitters input should correspond to the set standard readings of transmitters 100% output (4-20 mA). Accurately calibrated pressure is the one, where the values of input equals to the output for all values between 0-100percent.

The pressure transmitter calibration is complete if you find that input and output values are same as expected. If you are not satisfied with the results, you should continue fine tuning the calibration process, until acceptable levels of accuracy is achieved.

The steps mentioned above may differ from the actual steps mentioned in the manufacturer’s guide, however they will help you understand the procedure.

Verification and Acceptance Criteria

After completing pressure transmitter calibration, verification should be performed by applying pressure at multiple points across the operating range. The transmitter output should match the expected 4–20 mA values within acceptable tolerance limits.

An accurately calibrated pressure transmitter produces output values that correspond consistently to input pressure values across the entire range. If deviations are observed, additional fine adjustments should be made until stable and repeatable readings are achieved.

Pressure Transmitter Calibration in Industrial Practice

Pressure transmitter calibration is a routine maintenance activity in industries such as oil and gas, power generation, chemical processing, and manufacturing. The procedure outlined in this article reflects commonly followed calibration practices used by instrumentation technicians and engineers in industrial environments.

Proper calibration supports process accuracy, reduces measurement errors, and helps maintain operational reliability.

FAQ's

How often should pressure transmitter calibration be performed?

Calibration frequency depends on process conditions and criticality. Many industrial applications require calibration during scheduled maintenance or annually.

What is zero and span adjustment in pressure transmitter calibration?

Zero adjustment aligns the transmitter output at the lower range value, while span adjustment ensures correct output at the upper range value.

Can pressure transmitter calibration be performed in the field?

Yes. Many pressure transmitters are designed for field calibration using portable pressure sources and loop calibrators.

Why is pressure transmitter calibration important?

Calibration ensures accurate pressure measurement, improves process efficiency, and reduces the risk of operational or safety issues caused by incorrect readings.