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Pressure measurement

How to measure the pressure ?
What is the definition of a pressure sensor ?


 

Our experts explain you the operation and the principle of a pressure transmitter
and introduce the different types of pressure sensors.

How to measure the pressure What is the definition of a pressure sensor

 

  1. What is a pressure sensor ?
  2. What is the pressure measurement unit ?
  3. How does a pressure transmitter work and what is the principle of a pressure sensor ?
  4. What are the different parts of a pressure transmitter ?
  5. What is the pressure transmitter output signal  ?
  6. How to choose a pressure transmitter ?
  7. What are the different types of pressure transmitters ?
  8. How to calibrate a pressure transmitter ?
  9. How to install a pressure transmitter ?
  10. How to check a pressure transmitter ?
  11. How to set up a pressure transmitter ?
  12. What are the different industries that are using pressure transmitter ?

 

 


 

What is a pressure sensor ?Pressure transmitter brochure

The pressure sensor is also called a pressure transmitter, pressure probe or pressure transducer.

There is no notable difference between these different names. The pressure sensor is a measuring device whose principle consists of converting the force applied by the pressure of a fluid on a given surface into an electrical signal.

Air pressure, water pressure, vapor pressure, gas pressure can thus be measured.



Pressure sensors are used to :

  • Measure pressure
  • Measure flow,
  • Measure level
  • Hydrostatic measurement
  • Measure density

 

 

 

 

What is the pressure measurement unit

 

What is the pressure measurement unit ?

The pressure p is expressed in units of force F per units of area A. p = F / A
The International System of Units (SI) unit of pressure is the pascal, Pa.

It takes its name from Blaise Pascal born in Clermont-Ferrand where the headquarters of the factory of Fuji Electric France SAS, a French manufacturer of pressure sensors, is located.

Other units of measure for pressure are bar (bar), psi (pounds per square inch).

 

 



Discover the Fuji Electric France pressure transmitters range

 


 

How does a pressure transmitter work and what is the principle of a pressure sensor

pressure transmitter micro capacitive schema

The pressure of the measured fluid is applied to an internal measuring element through a fitting and then a mechanical interface - measuring membrane. The electronic measuring element converts the pressure into a raw signal.

There are different measurement technologies :

  • The piezoresistive pressure sensor measures the force applied to a metal diaphragm.

    The pressure exerted deforms the diaphragm which transmits the pressure variation via an intermediate incompressible fluid (oil or water).
    This deforms a piezoresistive silicon element (Wheatstone bridge).

    This element is a variable electrical resistance which converts the strain into an ohmic value.
  • The capacitive pressure sensor measures the force applied to a metal or ceramic membrane...

    The pressure exerted distorts the membrane, which transmits the pressure variation via an intermediate incompressible fluid (oil or water).
    This deforms a capacitive silicon element.
    This element is a variable capacitor that converts deformation into a capacitive value.
     
  • The frequency resonant pressure sensorpressure transmitter measuring cell schema
  • The voltage gauge sensor

The signal from the measuring element is then filtered, amplified, temperature compensated and then formatted into an analog signal.

The analog output signal is transmitted via an electrical connector.

 

What are the different parts of a pressure transmitter ?

Pressure transmitters consist of a mechanical fitting, a metal or ceramic membrane, a capacitive or piezoresistive sensitive element, an electronic signal conditioning and amplification module, an electrical connector.
It is packaged in a plastic or metal case (aluminium case or stainless steel case).

pressure transmitter cross section

 

What is the pressure transmitter output signal  ?

What is the pressure transmitter output signalThe output signal of a pressure sensor can be analog or digital.
The analog signal is usually 4-20mA, 0-10V or 1-5V.
A digital signal can be available with different communication protocols - HART - Fieldbus - Profibus - Modbus.
These protocols transmit the measurement value and also allow for the setting up of pressure sensors.
We call them smart electronic transmitters.
The transmitter may have a local indicator to visualize the measurement.

 

How to choose a pressure transmitter ?

The pressure sensor should be chosen based on the fluid to be measured and the conditions of service of the application.
It is necessary to define:

  • The fluid to be measured such as air, gas, steam, water or other liquid and its characteristics (density, viscosity,...)
     
  • The fluid process operating conditions :
    • the pressure,
    • the temperature,
    • the corrosion ;
  • The measurement type :
    • Pressure measurement,
    • Flow measurement,
    • Level measurement,
    • Density measurement,
  • The type of pressure to be measured (relative pressure, absolute pressure, differential pressure) ;
     
  • the pressure measurement range ;
     
  • the measurement dynamic (rangeability) : the difference between the smallest measured value and the highest measured value ;
     
  • the measurement accuracy ;
     
  • the measurement response time ;
     
  • the mechanical interface or the process connection (screwed, flanged) ;
     
  • the output signal : analog and/or digital ;
     
  • Climate environment and associated constraints :
    • the ambient temperature,
    • the relative ambient humidity,
    • the dust content,
    • the corrosive gas content,
    • the waterproofness and IP tightness level ;
  • The industrial environment, associated constraints existing regulations   :
    • The use in explosive atmosphere and areas ;
      • the dust,
      • the explosiveness,
    • the electromagnetic waves (CEM),
    • the vibrations,
    • the radiations ;
  • The functional Safety and Security Integrity Level (SIL); CEI 61508 and 61511.

 

What are the different types of pressure transmitters ?

The gauge pressure transmitter

Relative pressure sensors measure pressure relative to atmospheric pressure.

The differential pressure transmitter

The ABSOLUTE pressure transmitter

Pressure sensors compare relative pressure to absolute vacuum. Absolute pressure is always positive.
The absolute pressure sensor has the advantage of freeing from changes in atmospheric pressure thanks to a reference chamber to the vacuum.
Absolute pressure can be expressed from relative pressure by adding 1,013 bar or absolute bar (bar abs.) - relative (bar) - 1,013

The remote seal pressure transmitter

The MULTIVARIABLE PRESSURE transmitter

Multivariable pressure sensors combine differential pressure measurement, absolute pressure measurement and temperature measurement in the same sensor.
They are used in particular for the measurement of mass flow.


The SUBMERSIBLE PRESSURE transmitter

These pressure sensors can be immersed in a liquid and can be used to measure the level of a tank or tank.

 

How to calibrate a pressure transmitter ?

Industrial pressure transmitters require periodic calibration to ensure accurate pressure measurement.
The calibration period is defined by the manufacturer. Zero (Zero) and full-scale sensor (Span) should be calibrated.
Calibration involves applying a reference pressure to the sensor's mechanical interface, checking the output signal and then applying a compensation.
The sensor can be calibrated using an external adjustment screw, a local digital indicator, a programming interface or programming software.
In order to perform the various manipulations, it may be necessary to have an isolated faucet or manifold on the pressure transmitter.

 

How to install a pressure transmitter ?

The pressure sensor can be fixed with a mechanical connection to the measuring organ or to the piping where the pressure is to be measured.
Special precautions should be taken depending on pressure and temperature conditions.
The sensor output signal can be connected to a display system (display, recorder or supervision) or an PLC to drive a control device.

 

How to check a pressure transmitter ?

A pressure sensor can be tested by applying a reference pressure to the process connection and by checking the signal of the measured analog output or the value displayed on the indicator.

 

How to set up a pressure transmitter ?

There are different ways to set up pressure sensors.
Pressure sensors can have a local digital indicator that can be adjusted to adjust the parameters.
They can also be configured remotely with a programming interface (hand held communicator) or a configuration software via the digital signal and HART protocol.

 

What are the different industries that are using pressure transmitter ?

Pressure transmitters are used in all industrial areas.
The right model should be chosen based on the application and constraints of the industrial environment.