capacitive pressure sensor

First let us look capacitors. Capacity of the capacitor with a capacitance formed between the plates and relative dielectric effective area is proportional to the distance between the two plates is inversely proportional to C = ε A / d, where ε is the dielectric constant of the dielectric , A is both of the metal relative to the effective area between the electrode plates , d is the distance between the two metal electrode plates . From this relationship can be seen, when the two parameters constant , and the other parameter as a variable , capacitance will vary with changes in parameters . Capacitive pressure Coolant Temperature Sensor is placed in the cavity by the two movable piece ( flexible metal diaphragm ) , two fixed pieces ( elastic diaphragm concave metal coating on the glass ) , the output terminal and the housing and other components. The movable piece is formed between the two fixed pieces of two capacitors in series . When the intake pressure force is applied to the elastic diaphragm , a flexible diaphragm is displaced , it is bound with a fixed slice distance decreases , while increasing the distance with another set piece ( can be a piece of paper to demonstrate ) . We can see from the formula , the distance between the two metal electrode plates is an important factor affecting the capacity of power , the distance increases , the capacitance is decreased , the distance is reduced, the capacity increases. This is measured by the amount of a sensing component parameters cause two equal , opposite changes in structure called a differential configuration . If the elastic membrane is placed between the side of the pressure and the atmospheric pressure ( the upper chamber through flexible diaphragm
Atmosphere) , a gauge pressure measured ; if the elastic membrane is placed between the vacuum pressure and by the side ( the upper chamber through the elastic diaphragm vacuum) , the measured absolute pressure . Used in conjunction with the capacitive Camshaft Sensors measuring circuit there are many, here we come to the bridge circuit as an example the differential capacitive Sensor Camshaft circuit works , as shown , since the capacitor is AC parameter, so the bridge through a transformer with AC motivation. Two coils of the transformer and two capacitors bridge, when there is no inlet pressure , the bridge is in equilibrium , the two values ​​are equal and the capacitance C0, when a pressure is applied , one of the capacitance value C0 + △ C, other a capacitance value C0-△ C, (△ C as an external pressure caused when the amount of change in capacitance value ) , then the bridge out of balance , where the high voltage capacitance is high , the two capacitors of the voltage difference between , whereby the bridge representative of the intake pressure generated output voltage U.