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тензометрическое преобразование
мост Уитстона
потенциометрическое устройство
резистивное преобразование
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General principles of transducers (sensors) 
    In the strict sense of the word transducer is a device that converts a change in one quantity changes in the other. In terms of electronic transmitter ... >>>
The principles of the transformation of the measured physical parameters 
    In each converter, which converts the element is based on certain physical principle, which is associated with the electrical characteristics of the device so that a change in the quantity being measured   >>>


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See also:
Temperature sensors, thermocouple             Sensors of mechanical stress
Force, pressure, flow                                    Phototransducers
Ionization transducers                                    Hall sensors
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Capacitance-resistance transducers

      The very large class of measuring transducers are capacitance-resistance transducers, principle of action of which is based on transformation of value of measurand to the change of resistance. The last can be caused by different effects in a transforming element, for example heating or cooling, mechanical tension, influence of light stream (as in photo conducting transducers ), moistening, drainage, mechanical moving of pin brush of rheostat.
      If through resistance material the fixed current flows during the change of measurand, then a result will be a change of tension along material, which reflects the change of measurand.
      One of variants of capacitance-resistance transducer is a potentiometer transformer, in which the change of measurand will be transformed in the change of relation of tensions because of change of position of pin brush on capacitance-resistance material, fed from outsourcing (fig. 10). A certain mechanical element will transduce the change of measurand in moving of brush.

Fig. 10. Capacitance-resistance transformation, which a potentiometer device is used for, defiant the change of output tension

Fig. 11. Equivalent chart of potentiometer device,   represented on a fig. 10

      Potentiometer, represented on a fig. 10, it is possible to present as an equivalent electric chart, as it is done on a fig. 11. His output tension is determined by expression


                                                                                   Vo = V1R2 /( R1 + R2)


where V1 is tension on an entrance.
      When the tension put on the entrance of device is permanent and a measureable value is determined by position of brush of potentiometer, then output tension is directly function of measurand.
      In transducers potentiometer devices (with one or a few resistances in a chart) can be used or they are a potentiometer. In last case a potentiometer element will be variable. Some transducers have unwire resistances, such, as ceramet substrate or conducting plastic tape. There are potentiometers in which complete range changes of position of brush 270°is equal, while other constructions have a range in 10 or even 20 complete turns (3600 or 7200°),

Bridge of Uitstona
      The bridge of Uitstona appears by parallel connection of two potentiometer devices (fig. 12). He can be used for the high-fidelity measuring of resistance. Output tension of bridge of Uitstona


                                                                   Vo = V1(R3/(R3 + R4)  -  R1/(R1 + R2).
Fig. 12. Combination of two potentiometer divizors,  formative the bridge of  Uitstona          

Fig. 13.Tenzometrical  transducer


      During the exact setting output tension of bridge of Uitstona  must be equal to the zero, where it is necessary from, that

                                                         R3/R4            =              R1/R2   
                                                        1+ R3/R4                      1+ R1/R2
then get

                                                              R1/R2        =      R3/R4

Датчики, преобразователи. Sensors, transducers
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Датчики, преобразователи, sensors, gauge