where: = dielectric constant of the insulating medium, for air =1 εr εr =permittivity of air or free space = 8.854 x 10-12 F/m. εo A = the area of the plate, (m2). d = the plate spacing, (m). Since C is inversely proportional to d, any change in d will cause a change in C. A change in capacitance can be done by varying any of the following parameters: Changing the distance between the two parallel electrodes (d). Changing the dielectric constant, permittivity, of the dielectric medium. Changing the area of the electrode (A). Some transducers work by making one of the capacitor plate’s movable, either in such a way as to vary the overlapping area or the distance between the plates. Other transducers work by moving a dielectric material in and out between two fixed plates to detect and transmit the physical position of mechanical parts via electrical signals as shown in figure 4. Figure 4: Capacitive Transducers. Example 1: An electrode-diaphragm pressure transducer has plates whose area is 5 × 10-3 m2 and whose distance between plates is 1 × 10-3 m. Calculate its capacitance if it measures air pressure. The dielectric constant of air is =1. Solution:-
where: εr = dielectric constant of the insulating medium, for air εr =1 εo =permittivity of air or free space = 8.854 x 10-12 F/m. A = the area of the plate, (m2). d = the plate spacing, (m). Since C is inversely proportional to d, any change in d will cause a change in C. A change in capacitance can be done by varying any of the following parameters: Changing the distance between the two parallel electrodes (d). Changing the dielectric constant, permittivity, of the dielectric medium. Changing the area of the electrode (A). Some transducers work by making one of the capacitor plate’s movable, either in such a way as to vary the overlapping area or the distance between the plates. Other transducers work by moving a dielectric material in and out between two fixed plates to detect and transmit the physical position of mechanical parts via electrical signals as shown in figure 4. Figure 4: Capacitive Transducers. Example 1: An electrode-diaphragm pressure transducer has plates whose area is 5 × 10-3 m2 and whose distance between plates is 1 × 10-3 m. Calculate its capacitance if it measures air pressure. The dielectric constant of air is =1. Solution:-