capacitance meter

elektor july/august 1983 capacitance meter In this capacitance m eter, the value of a capacitor is determined by giving it the same charge as a refer- ence capacitance and then comparing the voltages across them. This relies on the formula C = Q/V where C is the capacitance in Farads, 0 is the charge in Coulombs and V is the voltage in volts. If therefore two capacitances have equal charges, their values can be calculated when the voltages across them are known. Two circuits ensure that reference capacitor C r and the capacitor to be measured, Cx, are charged equally. The circuit for C r consists of C2, Dl and T1 and that for Cx of C3, D2 and T3. Each time the output of gate N2 rises, the charges of capacitors C2 and C3 are transferred to C r and C x by transistors T1 and T3 respectively. When the output of N2 drops, C2 and C3 recharge via diodes Dl and D2. Gate N2 is controlled by astable multivibrator N 1 which operates at a frequency of about 2 kHz: C r and Cx are therefore cha...