Circuit measures capacitance or inductance
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Engineers usually have access to signal and function generators, as well as frequency counters and oscilloscopes, but they may not have access to capacitance or inductance meters. Using the test setup in Figure 1, you can measure capacitance or inductance using a function generator, a multimeter, a frequency counter, and an oscilloscope.
Use the setup to measure the magnitude of two signals. You can then calculate the capacitance or inductance without measuring phase angles. You can express the ratio of input voltage to output voltage as:
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For best results, you can use a frequency counter to measure the frequency and a digital multimeter to measure the resistance. Most modern oscilloscopes can accurately measure the signals without loading the circuit, except for the capacitance of the probe. Capacitance is usually marked on the probe. Use the previous equation to calculate the value of the capacitor. Subtract the value of the probe capacitance from the result, and you have an accurate value for the measured capacitance.
Usually, you know the approximate value of the capacitance you want to measure, so you can pick a starting value for the resistance, R, and the frequency, f, by using the following equations:
The values for R and f are not critical; you should choose them to minimize parasitic effects. Resistance values of 300 to 3000Ω and frequencies of 100 kHz to 1 MHz should work.