Pressure transmitter calibration is what you need to do before you install the pressure transmitters.

In this article, we will share pressure transmitter calibration using hart communicator.

Pressure transmitters used in the process industries are very durable and reliable instruments.

Even so, they still require periodic maintenance and calibration to ensure optimal performance.

Before we start to calibrate the pressure transmitter, we should know:

What is span in pressure transmitter?

Pressure Transmitter Calibration

Fig. showing span and zero adjustment

Span value:
The difference between two minimum value and maximum value of readings is known as a span value.

As shown in fig. below span = 20mA – 4mA

Zero Value:
The value of readings at zero lines (Y-axis) is known as zero value as shown in the figure.

How do you calibrate a smart pressure transmitter?

Once you have established the calibration interval and MPE, you are ready to perform the actual calibration procedure on your pressure transmitter.

The best-practice recommendation is:

  1. Mount the transmitter in a stable fixture free from vibration or movement.

2. Exercise the sensor or membrane before performing the calibration.

This means applying pressure and raising the level to approximately 90 percent of the maximum range.

For a 150 psi cell that means pressurizing it to 130–135 psig.

Hold this pressure for 30 seconds, and then vent.

Your overall results will be much better than if you calibrate “cold.”

cent of the maximum range.

For a 150 psi cell that means pressurizing it to 130–135 psig.

Hold this pressure for 30 seconds, and then vent.

Your overall results will be much better than if you calibrate “cold.”

3. Perform a position zero adjustment (zero the transmitter).

This is important because the orientation of the fixture used for calibration may be different than the way the transmitter is mounted in the process.

Failing to correct for this by skipping this step can result in nonconformance.

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4. Begin the Pressure Transmitter Calibration procedure.

Typically this means three points up (0 percent/50 percent/100 percent) and then three points down.

The 4–20 mA output should be 4 mA, 12 mA, and 20 mA at the three points (or the correct digital values for a smart transmitter).

Each test point should be held and allowed to stabilize before proceeding to the next.

Normally that should take no more than 30 seconds.

You can use more points if you require higher confidence in the performance of the instrument.

4. Compare the results of your pressure transmitter to your reference device.

5. Document the results for your records.

Pressure transmitter calibration formula

There is a formula that we can easily use to convert most (or all) units utilizing 4 to 20 mA signal to mA units.

There are others out there but this is the simplest I know.

Below is a simple formula for pressure to current conversion. 

For example:

the range is :  0 to 10 Bar

Full range = 10 Bar

Displayed or measured value:  7 Bar

15.2 mA is the equivalent current value of a 7 Bar pressure.

For Value or range which is not starting with zero ( with a vacuum range),

use below linear interpolation formula. 

You can also encode this to excel for easier conversion.

If you want to know and calculate the error,

Just subtract the True value with your computed value.

Error = Measured Value – True Value.

If the Pressure Transmitter has an accuracy of 0.5% of the range,

then 0.005 x 7= +/-0.035 Bar,

you can use this as the tolerance to determine a pass or fail result.

Or you can ask the user for their respective tolerances.

How to calibrate pressure transmitter with hart communicator

Equipment required for Pressure Transmitter Calibration

Pressure transmitter, multimeter, HART communicator

The basic procedure for Pressure Transmitter Calibration

  1. Isolate the Pressure Transmitter from the Process.
  2. Slowly open the vent plug and the vent valve to release the pressure.
  3. Connect the multimeter with the transmitter and ensure that output is 4ma when 0 pressures are applied.
  4. Connect the handheld test pump (pressure source) to the transmitter.
  5. Ensure there is no leak.
  6. Apply pressure range at 0%, 25%, 50%, 75%, 100% and check there is any error.
  7. If there is any error calibration should be done.

Read more about HART Pressure Transmitter

If the transmitter is the analog transmitter

  1. Apply 0% pressure as per LRV with handheld test pump and check multimeter if it is not 4ma adjust the zero pot in the transmitter and correct transmitter output to 4ma
  2. Apply 100%pressure as per the URV and correct 20ma in multimeter by adjusting span pot in the transmitter
  3. Repeat these steps to rectify the error.

In case of SMART Transmitter

  1. We have to use HART communicator, connect the communicator with the transmitter select the HART Communicator Menu for lower range value trim and upper range value trim.
  2. Basic Set up – Calibration – Zero Trim/Sensor Trim —Lower/Upper range value trims.
  3. HART communicator will automatically calibrate the transmitter.
  4. Restore the process connection
  5. Take the transmitter on line. Ensure there is no leak  

a small example of five-point calibration is given below

Low range value=0psi

upper range value=200psi

This calibration can work for Rosemount 3051 calibration.

What is the calibration span?

When you buy a pressure transmitter, for example, you have the instrument range, which is the pressure range the device can support.

This range covers the overpressure that might occur in the device.

The measuring range covers the values where the transmitter works properly, omitting the overpressure zone.

The lower range limit (LRL) and upper range limit (URL) define this range.

calibration span

What is the calibration span?

Inside the measuring range,

you’ll find the calibration span,

the range in which your device will be working,

depending on your application.

The calibration span covers the difference between your upper range value (URV),

the maximum value your transmitter can read,

and the lower range value (LRV), the minimum value the device can read.

So there you go!

You should also know that each instrument has a minimum and maximum calibration span it can support.

If you go below or over these limits, you’ll lose accuracy in your readings.

Make sense? Let me give you an example, just to make it clearer.

Let’s say you want a pressure transmitter with a measurement range of -100 to 200 kilopascals (kPa).

This device can measure pressures as low as -100 and as high as 200 kPa.

If your application just requires pressure between -20 to 50 kpa,

then this will be your calibration range.

Your calibration span is the URV-LRV.

By the numbers: 50 – (-20) = 70 kPa.

Therefore, you get a calibration span of 70 kPa,

which falls inside the span range (10 to 200 kPa).

What does a pressure transmitter do?

A pressure transmitter or pressure sensor is a device

that measures pressure in a liquid, fluid, or gas. 

Pressure transmitters are commonly used to measure the pressure inside of industrial machinery,

in order to alert the user before a catastrophe occurs.

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Sino-Instrument is pressure transmitters manufacturer in China.

We offer all types of pressure transmitters.

Like Direct Mounted seal, flange-mounted, single flange, double flange, Remote Diaphragm Seals, High Static, Digital Remote.

Most of our pressure transmitters are used in oil, liquids,

DP transmitterflow measurementlevel measurement (like the ultrasonic level measurement), density, and other process variables.

Pressure transducers are generally available with three types of electrical output; millivolt, amplified voltage, and 4-20mA.

You can ensure product safety by selecting from certified suppliers, with ISO9001, ISO14001 certification.

We will share more about instrument calibration, like the flow transmitter calibration.

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