There are various types of transducers depending upon the change in property or the energy they bring about to measure specified physical quantities. The transducers used for the measurement systems are broadly classified into following categories: mechanical and electrical. Let use see these in details.
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I) Mechanical Transducers:
The mechanical transducers are the mechanical elements that are used for converting one form of energy into other form that can be measured easily. There are number of mechanical transducers, some of the commonly used ones are described below:
1) Bellows: These are the elastic elements that convert the air pressure into displacement, and it is commonly used for the measurement of pressure.
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2) Bourdon tube: This elastic tube converts air pressure to the rotary motion of the pointer used to indicate the pressure.
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3) Spring: The spring tend to expand when force is applied to them, thus they are used for the measurement of force.
4) Proving rings: Like the springs the proving rings also convert applied force to the displacement.
5) Diaphragm: It converts applied pressure to the displacement.
6) Manometer: The manometer converts the applied pressure into variable displacement of the liquid within it enabling to measure the pressure.
7) Thermocouple: Thermocouple is the devise that produces electric current when one of its end is heated. The current produce by the devise can be measured, which can be calibrated against the temperature enabling us to measure the temperature of the body.
8) Bimetals: These are the bimetallic strips comprising of two different metals having different coefficient of thermal expansion, joint together. When the strip is heated one metal expands lesser while the other metal expands more leading to the deflection of the bimetallic strip, which is converted into the rotary motion of the pointer that indicates the temperature.
9) Hydropneumatic transducers: These include devices like orifice, venturi, pitot tube, vanes and turbines that are used for measurement of pressure, velocity, flow rate and force of water.
Apart from the mechanical transducers mentioned above there are many others like seismic mass, pendulum scale, float etc. Most of the mechanical transducers are used as the primary transducers, meaning the initial input is applied to them, while the output obtained from them can be used directly to measure the quantity or it can be given as input to the secondary transducer, which are mostly of electrical type.