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Home >> Electricity, capacity, piezoelectricity.  Physical principles of transformation of measureable parameters
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Physical basis of the transformation of the measured parameters

Capacity transducers
Piezoelectric
Electromagnetic transducers
Electromechanics
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Photo-electric
Capacitance-resistance transducers
Strain gauge
Transformers. Termistors
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Phototransistors
Effect of Hall. Transducers of Hall
Thermo-electric

In every transducer, a transforming element is based on certain physical principle which is related to electric descriptions of device so, that the change of measurand entails the change of these descriptions. Changes in electric descriptions are created by an electric signal, depending on a measurand.
Although there are for sale thousands of measuring transducers at the market, principles actions which they are based on, exists relatively a bit. It is therefore possible to consider these principles in detail enough. All basic principles used in transducers  can be united in categories which are described below.

Capacity transducers
Capacity transforming elements convert the changes of measurand into the changes of capacity. A condenser is formed from two plastins, divided by the layer of dielectric, and his capacity is determined from next expression:
C = εоεS/x

Where   εо - electric permanent, ε  is an inductivity  of dielectric;
S is an area of surface of every plate; х is distance between plates.

Electricity, capacity, piezoelectricity

Information about various converters and sensors of physical quantities, parameters of various physical processes is presented.
Electrophysical properties and effects in various electrical materials.
Theory, experimental results, practical application

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Fig. 1.  Capacity  measuring transducer

It ensues from this correlation, that a capacity depends on an inductivity, area of surface of plastins and distance
between them (fig. 1).
The capacity of such transducers is usually measured as follows:
1) by means of bridge chart of alternating current, in which a transducers forms one shoulder of bridge;
2) by means of multivibrator in which a condenser in a chain determines frequency of vibrations.

Thus, if some phenomenon (physical process, physical quantity) changes the permittivity between the plates, changes the area of the plates, changes the distance between the plates, then this will also change the electrical capacitance of the capacitor, measuring which it is possible to determine the size of the corresponding physical quantity associated with the physical phenomenon.

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