Working Principle of Capacitor Testing with an Analog Multimeter
Many analog multimeters cannot directly measure the capacitance of capacitors. The method shared here enables an analog multimeter to directly measure capacitance.
When measuring capacitance, first set the multimeter to the ohm range and perform ohm zero adjustment. Next, short-circuit the two terminals of the capacitor under test to discharge any stored charge in the capacitor. Then connect the black and red test leads of the multimeter to the two pins of the capacitor (for electrolytic capacitors, connect the red lead to the negative terminal and the black lead to the positive terminal).
At this point, the meter needle will swing to the maximum deflection position (assume this deflection corresponds to resistance R), and then gradually return to the pre-measurement position, i.e., the infinite resistance ∞ position. (If the meter needle cannot finally return to the ∞ resistance position, the capacitor under test has leakage damage.)
Measurement Observations
When measured with the same ohm range, a capacitor of fixed capacitance will yield a fixed value of R. The larger the capacitance of the capacitor under test, the smaller the value of R.
That is, R is approximately inversely proportional to the capacitance C of the capacitor, expressed as \(R=H/C\), where H is a constant with the unit ohm-farad. The value of H varies for different analog multimeters.
Based on the above principle, measure standard capacitors of known capacitance first. Specifically, use a certain ohm range to record the position of maximum needle deflection, and mark the capacitance value of the standard capacitor at that position.
Repeat this measurement for multiple standard capacitors with different capacitances and mark their corresponding capacitance values on the meter scale, so as to create a calibrated scale. With this calibrated scale, the multimeter can be used to measure the capacitance of unknown capacitors.
