Capacitance Meter

an instrument for the measurement of the electrical capacitance of capacitors, electronic and semiconductor devices, cables, and conductors.

Several methods exist for the measurement of capacitance; the bridge method is considered to be the most accurate. The capacitance C_x to be measured is connected to the measuring bridge arm (see Figure 1). Alternating current from the builtin generator G is fed to one of the diagonals of the bridge. A balance indicator I (for example, a pointer device) is connected to the other diagonal of the bridge through an amplifier U. The bridge is balanced by selecting the reference capacitor C_P that produces the minimum deflection of the balance indicator. By changing the ratio R₁R₂, it is possible to select the required measurement range from 10 attofarads (10^-17 farad) to 1 microfarad (10⁶ farad). The measurement error usually does not exceed 1 percent.

Figure 1. Block diagram of a capacitance meter: (G) AC generator, (M) measuring bridge, (/) balance indicator, (U) amplifier, (C,) capacitance being measured. (C,) reference capacitor, (R₁,) and (R₂) resistors, (1)-(4) arms of bridge

In measuring the capacitance of electrolytic capacitors or in conducting measurements at high frequencies (up to one gigahertz), the ohmic losses within the capacitors must be taken into account. In such cases the bridge circuit is supplemented by reference resistors and compensating capacitors and is also carefully shielded. Capacitance meters with automatic balancing and a digital readout have been developed.