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Capacitive Displacement Sensor

Capacitive sensors are widely used in precision measurement systems. One common approach is to use a capacitor as a sensitive element, where mechanical displacement is converted into a change in capacitance. The basic principle of a parallel plate capacitor states that its capacitance is directly proportional to the area of the plates and inversely proportional to the distance between them. By using a fixed plate and a movable plate, a variable-area capacitive sensor can be created. As the overlapping area between the two plates changes, the capacitance of the sensor also changes accordingly.

The capacitive grid displacement sensor operates on this variable-area principle but uses a grid-like electrode configuration. This structure essentially functions as a parallel combination of multiple variable-area capacitors. As shown in Figure 2.2.1, the stationary plate consists of several equally spaced gates, while the moving plate has the same number of poles with consistent spacing. When the moving plate shifts relative to the fixed one, the capacitance value changes, which is then converted into an electrical signal through circuit processing.

A practical example of this technology is found in electronic digital scales used in physics experiments. These devices often employ a multi-stage chip-type capacitive grid, as illustrated in Figure 2.2.2, as their sensing element. Multiple sets of grids are connected in parallel to enhance measurement accuracy and reduce the required precision of the manufacturing process. During movement, the moving plate continuously forms a differential capacitor with different small electrodes. As the movable ruler slides relative to the fixed one, the capacitance undergoes periodic changes, generating pulse signals that are amplified, processed by the circuit, and finally converted into a digital displacement reading for display.