RESISTIVE TRANSDUCERS

In such a transducer,resistance between the output terminals of a transducer gets varied according to the measurand. Resistive transducers are preferred over other transducers because dc and ac both are suitable for resistance measurement.

Resistance of any metal conductor is given by the equation 

R=ρ l/a

Where ρ  is the resistivity of the material of conductor in Ω-m,l is the length of conductor in meters,and a is the cross-sectional area of conductor in m^2.

Physical phenomenon i.e., input signal to the transducer causes variation in resistance by changing any one of the quantities,ρ ,l,and a,.For measurement of displacement length of conductor is varied in potentiometer thereby resulting in change in resistance.For measurement of force and pressure resistance of a conductor or semiconductor is varied in strain gauges.Variation in temperature causes change in the resistivity of the conductor material and so change in resistance  takes place which is noted for measurement of temperature.with some devices resistance varies with the change in light intensity because of photoconductive effect,while with others resistance varies on exposure to magnetic field due to magnetoresistive effect.Thus resistive transducer have a wide field of application.

Though every wire is associated with self inductance and capacitance across its ends but these are important only at low and high values of R respectively while the resistance of most of the resistive transducer lies in the mid-range 100 Ω-100k Ω.