Pressure transmitter calibration is what you need to do before you install the pressure transmitters. Also called pressure transducer calibration, or pressure sensor calibration.

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.

Pressure Transmitter Calibration

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 to calibrate a pressure transmitter

Calibration of conventional pressure transmitters:

First adjust the damping to zero state, first adjust the zero point.
Then add full scale pressure to adjust full scale so that the output is 20 mA.
The on-site adjustment is fast, and here we introduce the quick adjustment method of zero point and span.

There is almost no effect on the full scale when the zero point is adjusted. But the zero point is affected when the full scale is adjusted.
Without migration, its effect is about 1/5 of the span adjustment amount. That is, the span is adjusted up by 1 mA. The zero point will move up by about 0.2 mA. And vice versa.

Extended reading: Pressure Sensor Applications-Featured Industry Applications

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.

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

6. 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.

Preparing for Field Calibration of Differential Pressure Transmitters

The usual practice is to disassemble the joint of the pressure guiding tube and the differential pressure transmitter, and then connect to the pressure source for calibration. It is troublesome and labor-intensive. The most worry is that there will be leakage or the pressure guiding pipe will be broken when disassembling and assembling the joint.

No matter what type of differential pressure transmitter, the positive and negative pressure chambers have exhaust, drain valves or cocks. This provides convenience for on-site calibration of the differential pressure transmitter, so that it can be calibrated without removing the pressure guiding tube. Differential pressure transmitter.

But make a fitting with the same thread as the vent, drain valve or cock.

When the differential pressure transmitter is calibrated, first close the positive and negative valves of the three-valve group. Open the balance valve, and then loosen the exhaust and drain valves to vent.

Then use a self-made connector to replace the vent, drain valve or cock connected to the positive pressure chamber.
The negative pressure chamber is kept unscrewed, allowing it to vent to the atmosphere.

The pressure source is connected with the self-made joint through the rubber tube. Close the balance valve. And check the air circuit sealing.

Then connect the ammeter (voltmeter) and the hand-operated communicator into the differential pressure transmitter circuit, and start the calibration after power-on and preheating.

Field Calibration of Conventional Differential Pressure Transmitters

First adjust the damping to zero state, first adjust the zero point. Then add full pressure to adjust the full scale, so that the output is 20mA. The adjustment should be fast in the field. Here is a quick adjustment method for zero point and span.

When the zero point is adjusted, it has almost no effect on the full scale, but when the full scale is adjusted, it has an effect on the zero point. When there is no migration, the effect is about 1/5 of the range adjustment amount, that is, the range is adjusted upward by 1mA. The zero point will move upward by about 0.2mA ,vice versa.

E.g:
The input full scale pressure is 100kPa, the reading is 19.900mA.
The range-adjusting potentiometer makes the output 19.900+(20.000-19.900)×1.25=20.025mA, and the range increases by 0.125mA. Then the zero point increases by 1/5×0.125=0.025, and the zero-point potentiometer makes the output 20.000mA.

After the zero point and full scale adjustment are normal, check the middle scales, and make fine adjustments if they are out of tolerance. Then carry out the adjustment work of migration, linearity and damping.

Smart Differential Pressure Transmitter Field Calibration

The intelligent differential pressure transmitter is between the input pressure source and the output 4-20mA signal. In addition to machinery and circuits, there is also a microprocessor chip that operates on the input data.

Therefore, the field calibration method of intelligent differential pressure transmitter is different from that of conventional differential pressure transmitter.

The differential pressure liquid level transmitter has been calibrated according to customer requirements in terms of range, accuracy, linearity and other parameters. And mark the range, accuracy, etc. on the nameplate of the differential pressure liquid level transmitter. As long as the parameters such as the density of the measured medium meet the requirements of the nameplate, there is usually no need to adjust.

If the customer needs to adjust the span or zero position, please adjust according to the following methods. Assuming that the range of the differential pressure liquid level transmitter is 0~10 meters:

  1. Unscrew the back cover of the differential pressure liquid level transmitter, connect an external standard 24VDC power supply and an ammeter (requires an accuracy of 0.2% or higher) to adjust.
  2. When there is no liquid in the differential pressure liquid level transmitter. Adjust the zero point potentiometer so that the output current is 4mA.
  3. Pressurize the differential pressure liquid level transmitter to the full scale (10 meters). Adjust the full-scale resistor so that the output current is 20mA.
  4. Repeat the above steps two or three times until the signal is normal.
  5. Please input 25%, 50% and 75% respectively to check the deviation of the differential pressure liquid level transmitter.
  6. For non-water media, when the differential pressure liquid level transmitter is calibrated with water, it should be converted according to the pressure generated by the actual use of the medium density. For example, when the density of the medium is 1.3, the 1.3m water level should be used to calibrate the 1m range.
  7. After adjustment, tighten the back cover.
  8. The calibration cycle of the differential pressure liquid level transmitter is once a year.
  9. The HART intelligent differential pressure liquid level transmitter of Sino-Inst can be selected, which is convenient to adjust the range of the differential pressure liquid level transmitter.

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.

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.

Extended reading: Pressure Sensor Applications-Featured Industry Applications

Frequently asked questions

Yes, pressure transducers require calibration.
Pressure transducers are used in many applications to provide accurate, real-time data on how systems work. Calibration is critical to maintaining the accuracy of pressure sensors. And it’s not a one-time process.

If the sensor deviates from its specified pressure range, it may cause erroneous pressure readings. This results in degraded device performance and possible security issues.

Calibration allows users to be completely confident that their pressure transducers are performing correctly and accurately measuring the desired pressure range.

In order to prevent large errors, the use of pressure transmitters requires periodic calibration. So how often should a pressure transmitter be calibrated?

Generally speaking, there is no mandatory regulation for the calibration cycle of pressure transmitters. Generally, the company formulates the calibration cycle standard by itself, and it is usually recommended to calibrate once a year.

If there are obvious errors found. or more important. The calibration cycle can be shortened.

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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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