Pressure transducer and types of electric pressure transducer

What is a Transducer

A transducer is a device which can convert a non-electrical physical quantity into an electrical signal, in other words, it can convert the energy of one to another. Energy forms can be mechanical, visual, aural, electrical, chemical… it can be used to change information into a form that can be easily transferred, stored, processed… a pressure transducer is a device which can be used to measure the pressure.

What are the types of electric pressure Transducer

  • Capacitive pressure transducers
  • Strain gauge pressure transducers
  • Potentiometer pressure transducers
  • Electro-magnetic pressure transducer
  • Piezoelectric pressure transducer

Capacitive pressure transducers

Electrical capacitors are used in this transducer, like the parallel plate capacitor it uses the diaphragm and a pressure cavity to create a variable capacitor to detect strain due to applied pressure. Mostly the diaphragm is ceramic and silicon. Two metal plates are used in an electrical capacitor and a dielectric material is sandwiched between them in capacitive pressure transducer one of these metal plates are allowed to move in and out so that the capacitance between them changes due to the varying distance between the plates. The diaphragm is connected to the movable plate and the diaphragm senses the pressure and then expands or compresses accordingly this movement of the diaphragm would affect the attached metal plates position and capacitance would vary


Advantages of capacitive pressure transducer

  • It only needs small force for operation and has a high input impedance
  • Measuring low pressure
  • Good frequency response and it is less affected by stray magnetic fields

Disadvantages of capacitive pressure transducer

  • Complex circuit arrangement
  • Dust and temperature could affect its performance

Strain gauge pressure transducer

This is a passive type of resistance pressure transducer and its electrical resistance will change when it is stretched or compressed. A strain gauge is a wire which will change its resistance when mechanically strained, due to physical effects. Strain gauge is connected to the diaphragm and when the diaphragm flexes due to the applied pressure, the strain gauge will stretch or compress and because of this variation in its cross-sectional areas and its resistance will change due to this and this change is converted into voltage by linking two or four similar gauges similar to Wheatstone bridge so that the output can be maximized and reduces sensitivity to errors.

Advantages of strain gauge pressure transducer

  • Simple to maintain and easy to install
  • Good accuracy and stability
  • Fast speed of response
  • Wide range of measurements
  • No moving parts and high output signal strength over range capacity

Disadvantages of strain gauge pressure transducer

  • Temperature compensation and constant voltage supply is needed
  • Electrical readout is necessary

Potentiometer pressure transducer

A potentiometer is made by winding resistance wire around an insulated cylinder. A movable electrical contact called a wiper slides along the cylinder, the motion of the wiper along with the resistive mechanism is used to detect the strain caused by applied pressure and the position of the wiper determines the resistance of the potentiometer which in turn determines the pressure.

Advantages of potentiometer pressure transducer

  • Strong output and no need for additional amplifier
  • Low cost, high range, ruggedness, and electrical efficiency

Disadvantages of potentiometer pressure transducer

  • Limited life and large size
  • Poor frequency to response and it could develop noise

Electromagnetic pressure transducer

Electromagnetic pressure transducer are of two types they are linear variable differential transformer and servo pressure transducers, these transducer measures the displacement of a diaphragm by means of changes in inductance

Advantages of electromagnetic pressure transducer

  • Stability, ruggedness, and high sensitivity
  • Infinite resolution
  • Low hysteresis

Disadvantages of electromagnetic pressure transducer

  • Temperature affects the performance of a transducer
  • Sensitivity to stray magnetic fields but shielding is possible

Piezoelectric pressure transducer

Piezoelectricity is the ability of some materials mostly crystals to generate an electric potential in response to applied mechanical stress. In this transducer, the piezoelectric effect is used in certain materials such as quartz to generate rapid electrical signals and measuring the strain upon the sensing mechanism due to pressure. Common types of piezoelectric pressure transducers are charge mode type and low impedance voltage-mode type

Advantages of piezoelectric pressure transducer

It has good frequency response and no need for external power

Disadvantages of piezoelectric pressure transducer

Changes in temperature will affect the output and it cannot measure static pressure