In this simple yet accurate analogue capacitance meter circuit, the significance of a capacitor depends upon giving it exactly the same charge as a reference capacitance followed by evaluating the voltages between these.
This utilizes the method C = O/V where C is given as the capacitance in Farads, O would be the charge in Coulombs and V is the voltage in volts.
If as a result two capacitances possess identical values, their magnitudes may be determined once the voltages around these are identified. A couple of circuits guarantee that reference capacitor Cr plus the capacitor being calculated, CX, are charged evenly.
The proposed analogue capacitance meter circuit intended for Cr involves C2, D1 as well as T1 and that with regard to CX of C3, D2 and T3.
Whenever the output of gate N2 goes up, the charges of capacitors C2 and C3 tend to be shifted toCr and Cx by transistors T1 and T3 correspondingly.
While the output of N2 lowers, C2 and C3 recharge by means of diodes D1 and D22. Gate N2 is governed through astable/ multivibrator N1 that works out at a frequency of approximately 2 kHz: Cr and CX tend to be consequently charged at that frequency.
The voltage around Cr is actually investigated by C2 using a reference voltage produced by the power supply through R3/R4. As soon as the voltage around Cr surpasses the reference voltage, comparator lC2 inverts which usually prevents N2 to result in N3 to be able to illuminate LED D3. The values on Cr and CX at the moment are the same and the meter shows simply the amount of the voltage through Cx varies from that of Cf. Buffer IC3 offers a significantly high load impedance for Cx. Pushing reset button S1 leads to equally Cr and CX to discharge through T2 and T4 correspondingly, followed by the charging course of action restarts and the circuit becomes ready for another measurement procedure.
The analogue capacitance meter circuit can be calibrated by making use of a pair of exactly the same 10 nF capacitors for Cr and CX. Push the reset button and, as soon as the LED illuminates, fine-tune preset P1 to present a meter deflection of precisely 1/10th of total scale deflection (fsd).
This particular display on the meter relates to 1 x Cr. lf, for that reason, Cr = 100 nF and CX = 470 nF, the meter will probably display 0.47 of fsd.
To make certain an acceptable rate of charging periods in the course of a measurement, Cr and CX-should not possible be lower than 4.7 nF.
In order to determine smaller sized magnitudes, capacitors C2 and C3 must be minimized. As an example to make it possible for a capacitor of 470 pF being tested, C2 and C3 should be 10_ _ 20 pF. The circuit is moderately specific for magnitudes of CX around 100 pF.
More than this value the meter response will be impacted by leakage currents. To be able to determine capacitors as high as 100uF, the magnitudes of C2 and C3 needs to be raised to 1uF. Current utilization will be nominal making sure that a 9 V battery can be a suitable power source.