Our experts provide an introduction to the origins of pressure measurement, the operation and principle of a pressure transmitter, and present the different types of industrial pressure transmitters .
- Pressure origin and measurement units
- What is pressure transmitter ?
- What is the principle of a pressure sensor?
- How does a pressure transmitter work?
- What are the different parts of a pressure transmitter?
- What is the output signal of a pressure transmitter ?
- How to choose an industrial pressure transmitter ?
- What are the different types of pressure transmitter?
- How to calibrate a pressure transmitter?
- How to install a pressure measurement system for industry?
- How to test pressure transmitter ?
- How do I configure a HART pressure transmitter?
- What are the applications of pressure transmitters ?
Pressure origin and measurement unit
The Pascal unit of measurement is named after the renowned French philosopher, physicist and mathematician. Blaise Pascal.
Blaise Pascal was born in the city of Clermont-Ferrand (France), where the production plant of Fuji Electric France SAS pressure transmitters manufacturer, is headquartered. Pascal carried out a crucial experiment by transporting a barometer to the summit of the Puy de Dôme, to prove thatatmospheric pressure decreases with altitude above sea level. However, Italian scientist Evangelista Torricelli was the pioneer in demonstrating the pressure exerted by the weight of the volume of air on the earth, and consequently designed the first mercury-based barometer.
Knowing the units of pressure and their conversion is important for making the right choice of scale for your industrial measurements.
Pressure p is expressed in units of force F per unit area A: p = F / A
Pascal (Pa): This is the International System (SI) base unit for pressure measurement. One Pascal corresponds to a force of 1 Newton per square metre (1 Pa = 1 N/m²).
Bar: This is a unit of pressure commonly used in industrial applications. One Bar corresponds to a pressure of 100,000 Pa.
Standard atmosphere (atm): used to express barometric or atmospheric pressure. One atmosphere corresponds to a pressure of 101,325 Pa.
What is pressure transmitter ?
Pressure transmitters are also known as pressure sensors, pressure probes, pressure gauges or pressure transducers. There is no significant difference between these different names. However, a distinction is made between pressure transducers and smart pressure transmitters.
If we refer to the definition of a pressure transmitter, it is, as its name indicates, a pressure-measuring device whose principle consists in converting the force applied by the pressure of a fluid on a given surface (deformation) into an electrical signal.
Manufacturers use pressure transmitters to :
- Pressure measurement
- Flow rate measurement
- Hydrostatic pressure level measurement
- Density measurement
What is the principle of a pressure sensor?
The pressure of the fluid being measured is applied to an internal measuring component via a fitting and then a mechanical interface - a measuring diaphragm made of stainless steel or another noble material. The electronic measuring element converts the pressure into a raw signal.
How does a pressure transmitter work?
There are different technologies, methods, techniques and measurement principles:
The piezoresistive pressure sensor measures the force applied to a metal diaphragm.
The stress exerted on a thin film causes it to deform, transmitting the pressure variation via an incompressible fluid (oil or water). This deforms a piezoresistive silicon element (Wheatstone bridge). This component is a variable electrical resistor that converts the deformation into an ohmic value.- The capacitive pressure sensor measures the force applied to a stainless steel or ceramic metal diaphragm.
The pressure exerted deforms the metal film, which transmits the pressure variation via an intermediary incompressible fluid (oil or water). This deforms a capacitive silicon element. This component is a variable capacitor which converts the deformation into a capacitive value.
- The frequency resonance pressure gauge
- The strain gauge or voltage gauge transducer
The signal from the measuring element is then filtered, amplified, temperature-compensated and formatted into an analog signal. The analog output signal is transmitted via an electrical connector.
- The U-tube ressure gauge pressure gauges display local pressure readings.
What are the different parts of a pressure transmitter?
The construction of a pressure transmitter comprises a mechanical connection, a metallic or ceramic diaphragm, a capacitive or piezoresistive sensing element, a filling oil integrated into pressure-measuring cells, an electronic module for signal conditioning and amplification, and an electrical connector.
This device is packaged in a plastic or metal housing (aluminum housing, stainless steel housing or stainless steel housing).
A digital display can be added as an option.
What is the output signal of an industrial pressure transmitter ?
The signal from a pressure sensor can be either analog or digital. The analog signal is usually of the 4-20mA current, 0-10V voltage or 1-5V voltage type. The output signal is sent to the control unit to influence the manufacturing process.
The 4-20mA signal is commonly used by these devices because of its many advantages.
Firstly, it is resistant to signal loss due to the transmission line, guaranteeing accurate measurement. In addition, it extends the distance between the sensor and the system concerned. In addition, the absence of current makes it possible to detect line faults, facilitating troubleshooting. The 4-20mA signal is also less sensitive to electromagnetic interference, guaranteeing reliability. Last but not least, it can be used in a loop to supply several items of equipment, such as displays, controllers and recorders.
A digital signal can be available with different communication protocols - HART - Fieldbus - Profibus - Modbus. These protocols not only transmit the measured value, but also enable pressure measurement devices to be configured. These are known as SMART electronic pressure transmitters.
The field instruments can be fitted with digital display for pressure measurement visualization.
How to choose an industrial pressure transmitter ?
The industrial pressure transmitter must be selected according to the fluid to be measured, the pressure range and the operating conditions of the application and process.
When measuring pressure, a number of questions need to be asked in order to choose the right pressure transmitter :
- The fluid to be measured such as: air, gas, hydrogen, steam, water or other liquid and its characteristics (density, viscosity, corrosiveness...).
- Process operating conditions: pressure to be measured, static pressure, process temperature, risk of corrosion
- The type of measurement: pressure measurement, Differential Pressure (DP) flow measurement, hydrostatic level measurement, density measurement
- The type of pressure to be measured :
- Relative and gauge pressure
- Atmospheric pressure
- Absolute pressure
- Differential pressure
- Barometric pressure
- The pressure range or measuring span
- The turndown ratio or rangeability
- The accuracy of pressure measurement
- The response time
- The mechanical interface or the process connection fitting: screw connection, flange connection
- The output signal : analog and/or digital output signal, wired or wireless
- The climatic environment and associated constraints:
- Industrial environment, associated constraints, current regulations:
What are the different types of pressure transmitter?
The gauge pressure transmitters allow measurement of gauge pressure of the process in relation to atmospheric pressure. Atmospheric pressure is measured using a reference cavity inside the transmitter. This pressure decreases as altitude increases.
Differential pressure transmitters use two separate chambers connected by a flexible diaphragm. Pressure is measured on either side of the diaphragm of the DP cell. The differential pressure (DP) is the pressure difference between these two pressures - a reference pressure on the low pressure side (BP or LP) and a pressure on the high pressure side (HP). These differential pressure meters are used to measure fluid flow rate in piping systems, and to monitor filter clogging.
The pressure transmitters absolute compares gauge pressure with absolute vacuum. Absolute pressure is always positive.
The advantage of this device is that, thanks to a vacuum reference chamber, it is unaffected by variations in atmospheric pressure, thus providing greater precision.
Absolute pressure can be expressed from gauge pressure by adding 1.013 bar, i.e. p. absolute (bar abs.) = p. relative (bar) + 1.013.
A diaphragm seals pressure transmitter separates the process fluid being measured from the pressure cell. The diaphragm and wetted parts are made of a material resistant to the fluid being measured, and are welded to the base of the pressure cell.
A capillary tube or connecting sleeve provides the link between the separating diaphragm and the pressure cell. This space must be degassed under vacuum, then filled with oil and sealed. The measured pressure exerts a force on the outer surface of the diaphragm. As the diaphragm flexes inwards, it attempts to compress the filling fluid inside the instrument.
This filling liquid is designed to resist compression, so the force is channeled directly to the pressure-measuring cell. The entire operation of a pressure transmitter with diaphragm seal membrane is based on Blaise Pascal's principle.
Diaphragm seals pressure transmitters are manufactured from a variety of materials, including Stainless Steel, Titanium, Inconel, Hastelloy, Monel, Tantalum and Nickel. The materials used depend on the type of application and temperature for which the industrial pressure transmitter is designed.
Pressure transmitters with diaphragm seals are used to measure fluid pressure at high temperatures.
- Multivariable pressure transmitters
The multivariable pressure transmitters combine differential pressure measurement, absolute pressure measurement and temperature measurement in a single sensor.
These field instruments are used in particular for mass flow measurement.
Hydrostatic level sensors are measuring devices used to determine the liquids level in tanks or vessels. The measurement principle is based on hydrostatic pressure, which is the weight exerted by a liquid as a function of the height of the filling column.
Submersible pressure transducer
These submersible pressure sensors can be immersed in a liquid to measure the level in a tank or reservoir. They are generally fitted with a stainless steel diaphragm.
How to calibrate a pressure transmitter?
Industrial pressure transmitters require periodic calibration to ensure accurate metrology throughout their lifecycle, and to ensure that their performance is maintained and avoid factors that influence precision. The calibration period is defined by the pressure transmitter manufacturer. Zero and span calibration is required.
At the factory or at the laboratory, the accuracy is verified at several points in the pressure range to check the linearity of the output signal over the entiere range.
Calibration involves applying a defined reference pressure to the sensor's mechanical interface, checking the output signal and then applying compensation. The sensor can be calibrated using an external adjustment screw, a local digital indicator, a programming interface or programming software.
In order to carry out the various manipulations, it may be necessary to have an isolating valve or manifold mounted on the pressure transmitter to isolate it from the process.
For your annual calibrations, you can call on a company specializing in pressure transmitters calibration.
Regular calibration ensures accurate pressure measurement for consistent results.
How to install a pressure measurement system for industry ?
Pressure transmitters can be attached to the Primary Elements for DP Flow or to the pipe where the pressure is to be measured, by means of a mechanical process connection.
Special precautions must be taken depending on process pressure and temperature conditions.
The signal from this device can be connected to a display system (industrial digital displayIt can also be connected to a PLC (automation system for pressure measurement) to control a control device and regulate process pressure.
If you need help, we recommend that you call in a professional company to install and commission your measuring instrument.
How to test pressure transmitter ?
A pressure transmitter can be tested by applying a defined known pressure (reference pressure) to the mechanical interface of the pressure sensor and checking the measured analog output signal or the value displayed on the local digital display.
If your device is faulty, you can ask a specialist of one of the pressure transmitter manufacturer to repair your field instrument.
How do I configure a HART pressure transmitter?
SMART pressure transmitters with HART protocol can be configured :
What are the applications of pressure transmitters ?
Understanding why measure pressure in the process industries is important to guarantee safety, optimize process control, improve energy efficiency and maintain the quality of finished products.
Pressure transmitters are used in many industrial applications.
This device can detect pressures of up to several thousand millibars. It is therefore essential in a wide range of industries. Air pressure, water pressure, steam pressure and gas pressure can all be measured.
For example, applications include measuring the flow of liquids in a pipe, the flow of gases or steam, filter monitoring, level measurement with a flush diaphragm sensor of a fluid in a tank, measuring the density of a fluid or measuring gauge pressure.
Depending on your industry, you need to choose the right measuring instrument for your application according to the constraints of your industrial environment.
How to select the right pressure measuring instrument?
To ensure that your processes and systems operate as expected in terms of performance and results and to avoid pressure measurement errors, the experts from Fuji Electric, made-in-France pressure transmitters manufacturer will guide you. They will offer you a pressure measurement solution designed for your most demanding application.
Measuring pressure can't be improvised!
Pressure measurement requires the services of instrumentation manufacturer.
Fuji Electric pressure transmitters are renowned for their high technology, pressure measurement accuracy, wide measurement range, long-term stability, build quality, reliability, durability, technical support, easy return policy and fast delivery service for customers.
ref : FKE
