How Does a Pressure Transmitter Work?

Posted on July 5, 2019 by KimGuo11

What is a pressure transmitter?

A pressure transmitter also often called a pressure transducer. A pressure transmitter is a device used to measure the pressure of liquids or gases in pipes or containers. It works by converting the pressure readings into an electrical signal that can be easily transmitted to a control system for monitoring and analysis.

These devices are commonly used in industrial settings, such as in manufacturing plants and refineries. Where it’s important to monitor the pressure of gases and liquids flowing through pipes and containers to ensure that they’re at safe levels.

Pressure transmitters can measure pressure in gases, liquids, air or oil. Widely used in various industrial processes. Such as pharmaceutical industry, chemical feed, waste water industry, food industry, farms, etc.

Overall, pressure transmitters are essential tools for measuring and monitoring pressure levels in various settings, helping to keep people and equipment safe and functioning properly.

In order to choose a suitable pressure transmitter, we must understand what types of pressure transmitters are there, what are the functions of pressure transmitters, and how do pressure transmitters work? Read on to find out the answers below.

Types of Pressure Transmitters

According to different measurement media, pressure transmitters can be divided into liquid pressure transmitters and gas pressure transmitters.
According to the measurement conditions, the pressure transmitter can have a high temperature type, a very low temperature type, and a high pressure type.
Here we divide by the type of pressure measured.

Type of Pressure Transmitter	Characteristics/Principles
Absolute Pressure Transmitter	– Measures pressure relative to atmospheric pressure – Can only measure positive pressures
Gauge Pressure Transmitter	– Measures pressure relative to atmospheric pressure – Can only measure positive pressures
Differential Pressure Transmitter	– Measures the difference between two pressures – Can measure both positive and negative pressures<br>- Used to measure flow rates
Vacuum Pressure Transmitter	– Measures pressure below atmospheric pressure – Can only measure negative pressures – Used to maintain vacuum in a process
Hydrostatic pressure transmitters	– Often called level transmitters. Because of their working principle and ability to measure level. – Hydrostatic pressure transmitters work on the basis that the amount of pressure increases with depth. – These devices are submersible and can be used for liquids and gases.

Featured Pressure Transmitters

**SI-512H High Temperature Pressure Sensor**

**SIJC-1000HSM-Silicon Pressure Sensor**

**SI-706 Combined Pressure and Temperature Sensor-Dual function**

**Diffused silicon Gauge Pressure Transmitter**

**Capacitive Gauge Pressure Transmitter**

**Explosion-proof Pressure Transmitter**

Pressure Transmitter Working Principle

A pressure transmitter is a device that measures the pressure of fluids or gases in a process and converts it into an electrical signal that can be used for monitoring or control purposes. There are several different working principles that pressure transmitters use to accomplish this:

One of the main components of piezoresistive pressure transmitters is the resistance strain gauge. It is a sensitive device that converts the strain change on the DUT into an electrical signal.

Usually, the strain gauges are closely bonded to the substrate that generates mechanical strain with a special adhesive. When the stress of the substrate changes, the resistance strain gauge also deforms together. Change the resistance value of the strain gauge, so that the voltage applied to the resistance changes. The transmitter has extremely low price and high accuracy and good linearity characteristics.

Diffused silicon pressure transmitters were introduced in the mid-1990s. It utilizes the piezoresistive effect of elastic elements. When the pressure of the measured medium directly acts on the diaphragm of the sensor, the diaphragm produces a micro-displacement proportional to the pressure of the medium, which changes the resistance value of the sensor. This change is detected electronically. And convert and output a unified standard signal.

Compared with traditional products, this transmitter has the advantages of advanced technology, reliable performance, convenient installation, high accuracy and small size.

Corrosion-resistant ceramic pressure transmitters have no liquid transfer. When the pressure acts on the ceramic diaphragm, the diaphragm will produce a slight deformation. Make the thick film resistor printed on the back of the ceramic diaphragm pass through the Wheatstone bridge (closed bridge) connected to it. Output a voltage signal proportional to the excitation voltage.

The pressure physical quantity is measured through the built-in circuit of the transmitter and converted into a unified standard signal.

The transmitter can introduce various media (corrosive and non-corrosive gases, liquids) directly to the ceramic diaphragm.

The thermal stability of the ceramic and its thick-film resistance allow it to operate over a temperature range as high as -40°C to 135°C.

Therefore, it has high measurement accuracy, good stability, strong output signal and low price.

Piezoelectric pressure transmitters work on the piezoelectric effect.

The crystal is anisotropic, and when a force is applied along a certain direction, the crystal can produce an electric effect. When the mechanical force is removed, it will return to the uncharged state again. The piezoelectric materials mainly used in sensors are quartz, sodium potassium tartrate and ammonium dihydrogen phosphate.

The transmitter is mainly used in the measurement of acceleration and pressure. It has the characteristics of simple structure, small size, light weight and long service life. But it can only be used to measure dynamic stress.

The capacitive pressure transmitter is composed of a measuring diaphragm and electrodes on both sides of the insulating sheet to form a capacitance.

When the pressure on both sides is inconsistent, the displacement of the measuring diaphragm is proportional to the pressure difference. Therefore, the capacitance on both sides is not equal.

Through the oscillation and demodulation link, it is converted into a signal proportional to the pressure. Then the pressure physical quantity is measured and converted into a unified standard signal through the transmission circuit.

It has high precision, corrosion resistance, pollution resistance and good stability. It is recognized as an ideal instrument for detecting low vacuum pressure at home and abroad. It is mainly used in various fields of civil industry, and plays a unique role in military industries such as aerospace industry and nuclear industry.

Extended Reading: Smart pressure transmitter

Video source: https://www.youtube.com/embed/QrT8VWxdxwk?rel=0

Flange Mounted Differential Pressure Transmitter

Extended Diaphragm Seal DP Level Transmitter

Remote Seal Differential Pressure Transmitter

Differential pressure(DP) level transmitter

Pressure transmitter signal output

There are three common signal outputs that pressure transmitters provide: millivolt, amplified voltage, and 4-20mA.

Below is a summary of the outputs and when they are best used.

Millivolt Output:

This type of output signal is a low-level voltage signal that is proportional to the pressure being measured. The signal typically ranges from 0-50mV or 0-100mV, depending on the specific pressure range being measured.

This type of output signal is usually used in applications where the signal needs to be amplified or converted to a different format before it can be used by the control system.

Amplified Voltage Output:

This type of output signal is a higher-level voltage signal that has been amplified to a specific range, such as 0-5V or 0-10V.

The voltage signal is proportional to the pressure being measured and can be used directly by the control system without the need for additional signal conditioning.

Amplified voltage output signals are commonly used in applications where the control system requires a voltage input signal.

4-20mA Output:

This type of output signal is a current signal that ranges from 4mA at zero pressure to 20mA at the maximum pressure being measured.

This type of signal output is popular because it is immune to electrical noise and can be transmitted over long distances without signal degradation.

4-20mA output signals are commonly used in industrial applications where the control system requires a current input signal.

The choice of signal output will depend on the specific requirements of the application, such as the distance between the pressure transmitter and the control system, the required accuracy and resolution, and the environmental conditions.

Extended reading: Pressure indicator transmitters

How to Choose Pressure Transducer

There are multiple types of pressure transducers for a variety of applications.

Each pressure transducer has different aspects, that will impact how it works and the applications the pressure transducer works best for.

When selecting a pressure transducer, keep these 6 criteria in mind:

Application and measurement type
Pressure range
Process media
Temperature range and installation environment
Accuracy
Output

If you still don’t know how to choose the pressure transmitter, please contact our sales engineers.

how to use a pressure transducer?

Once you receive the pressure transmitter you ordered, you are ready to use it. First, please check the instruction manual configured by the manufacturer. Based on our many years of experience at Sino-Inst, you can start using a pressure transmitter by following these steps:

Confirm parameters: Before use, please confirm whether the model, range, output type (generally 4-20 mA current output or 0-10 V voltage output) and working voltage of the pressure transmitter meet your application requirements.
Check the appearance: Carefully check whether the transmitter is physically damaged and whether the interface is clean.
Installation location: Install the pressure transmitter on the pipe or container that needs to be measured, ensuring that it is installed securely. Usually the pressure interface should be vertical to the ground.
Connect the power supply and output: According to the instructions of the pressure transmitter, connect the power cord and output cord. Current-type transmitters need to be connected in series in the control loop, and voltage-type transmitters need to be connected in parallel on the measuring equipment.
Zero point calibration: Perform zero point calibration in a no-pressure state to ensure that the output of the transmitter is 4 mA or 0 V when there is no load.
Testing and debugging: Turn on the power and gradually increase the pressure. Observe whether the output signal changes linearly with pressure. Adjust settings until the transmitter’s output meets operating requirements.
Record data: Record the output current or voltage value under different pressures. To ensure that the pressure transmitter can accurately reflect pressure changes throughout the entire working range.
Periodic calibration: Check and calibrate the pressure transmitter regularly to ensure its accuracy and stability in long-term operation.

Can a pressure transducer be used to measure volume?

Pressure transducer cannot be used to directly measure volume. Pressure transmitters are used to measure medium pressure.

However, we can also calculate the volume indirectly through measurements from a pressure transmitter. But this requires other parameters.

For example, in a closed tank, if the temperature of the gas can be kept constant. Then measuring the pressure of the gas can be used to calculate the volume of the gas. This is based on Boyle’s law, which states that the pressure of a gas is inversely proportional to its volume.

Or, in some liquid tanks, if the tank is regular, then we can calculate the cross-sectional area of the tank. Then by measuring the pressure at the bottom of the container, we can calculate the volume of the liquid. Our volumetric recorders also enable this conversion.

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Pressure Transducer Price

There are a number of factors, that will impact the price of a pressure transducer.

The biggest differentiator is whether you can use a standard, off-the-shelf pressure transducer or if you need a custom pressure transducer.

For an off-the shelf pressure transducer, pressure transducer prices will be most affected, by the level of accuracy required for your application.

The more accurate, typically the more expensive the pressure transducer.

Extended reading: What is a pressure sensor?

Choose the right pressure transducer for your application

Sino-Inst offers over 20 Pressure Transmitters. A wide variety of Pressure sensors options are available to you. Such as free samples, paid samples. Sino-Inst is a globally recognized manufacturer of Pressure sensors, located in China.

Sino-Inst sells through a mature distribution network that reaches all 30 countries worldwide. Pressure sensors products are most popular in Europe, Southeast Asia, and Mid East. You can ensure product safety by selecting from certified suppliers. With ISO9001, ISO14001 certification.

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KimGuo11

Wu Peng, born in 1980, is a highly respected and accomplished male engineer with extensive experience in the field of automation. With over 20 years of industry experience, Wu has made significant contributions to both academia and engineering projects.

Throughout his career, Wu Peng has participated in numerous national and international engineering projects. Some of his most notable projects include the development of an intelligent control system for oil refineries, the design of a cutting-edge distributed control system for petrochemical plants, and the optimization of control algorithms for natural gas pipelines.

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Pressure Transmitter Calibration

Posted on July 3, 2019 by KimGuo11

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.

RFQ Pressure Transmitter

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

What is span in pressure transmitter?

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 Often Should You Calibrate a Pressure Transmitter?

Pressure transmitters require regular maintenance and calibration to ensure optimum performance.

There are no specific rules for the calibration of pressure transmitters. However, this depends on the regulations the company must comply with and the purpose of the calibration. Examples include safety specifications, application requirements, process conditions or as part of standard maintenance.

General industry practice is to calibrate pressure transmitters every 1 to 3 years based on the above conditions.

If it is found that there are obvious errors, or it is more important, the calibration cycle can be shortened.

Extended reading: Pressure Sensor Applications-Featured Industry Applications

how to calibrate a 4-20mA 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:

Mount the transmitter in a stable fixture free from vibration or movement.
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.”
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.
You may like:
Magnetostrictive level transmitters
Magnetostrictive level sensor
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.
Compare the results of your pressure transmitter to your reference device.
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.

（Read more about: Common Units Of 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.

Read more about: What Is 0-10V Signal Output?

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

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

Read more about HART Pressure Transmitter

If the transmitter is the analog transmitter

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
Apply 100%pressure as per the URV and correct 20ma in multimeter by adjusting span pot in the transmitter
Repeat these steps to rectify the error.

In case of SMART Transmitter

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.
Basic Set up – Calibration – Zero Trim/Sensor Trim —Lower/Upper range value trims.
HART communicator will automatically calibrate the transmitter.
Restore the process connection
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:

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.
When there is no liquid in the differential pressure liquid level transmitter. Adjust the zero point potentiometer so that the output current is 4mA.
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.
Repeat the above steps two or three times until the signal is normal.
Please input 25%, 50% and 75% respectively to check the deviation of the differential pressure liquid level transmitter.
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.
After adjustment, tighten the back cover.
The calibration cycle of the differential pressure liquid level transmitter is once a year.
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.

Learn more about Pressure Transmitter Calibration

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.

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).

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

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.

If you cannot find an answer to your question in our Pressure Transmitter Calibration you can always contact us and we will be with you shortly.

Contact Support

Conclusion:

It is normal for the pressure transmitter to have a certain error. But if the error is too large, it needs to be calibrated. There are two types of Pressure Transmitter Calibrations: conventional method and intelligent calibration. no matter where
Kinds of preparations must be done before calibration, and then calibrate and debug through the handheld operator.

There are no mandatory fixed requirements for Pressure Transmitter Calibration. Generally, enterprises can formulate them by themselves. Normally, they can be calibrated once a year. Crucially, the calibration cycle can be shortened.

About how to calibrate the pressure transmitter, and what needs to be paid attention to during the process of Pressure Transmitter Calibration. If you still have questions, please feel free to contact our engineers.