Some solutions of this project are based on a very simple idea, which is demonstrated by the figure below.
Under the impact of pulses from the rectangular pulse generator G transistor T1 is provided in one of two modes. The first mode - T1 is open and capacitor is charged to the value of the test voltage. The second mode - T1 is closed and goes into deep cut-off. When transistor T1 is closed capacitor is discharged through the measured resistance Rx and through emitter-base p-n transition of transistor T1. When the transistor T1 opens amplitude of capacitor Ccalib charge impulse depends on the value of the measured resistance Rx, duration of discharge and the value of leakage current i2. In deep cutoff mode emitter-base leakage current is much less than the collector-base leakage current (i2<<i1). This allows you to use this circuit for measuring very high resistances (10000000000 ohms).
Various modifications of this circuit can be used to measure capacitance, resistance, inductance, the insulation resistance of various objects including capacitors, pulse duration, frequency, and others.
For more information.
Sergey Leontyevich Panasyuk
Marinesko str. 19A r.12
Mob phone: +79787642060