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irina irina
wrote...
Posts: 919
11 years ago
How to measure the value of capacitor with multi meter which doesn't have capacitor range?
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wrote...
11 years ago
It depends on whether or not you are talking about a flux capacitor.
wrote...
11 years ago
You will have to build a circuit. If the meter is very high impedance and the capacitor is very large, you could use a precision voltage source, a suitably chosen resistor, and a stopwatch to time the charge. At the time constant RC, voltage is equal to 0.63 of the charging voltage.

But this involves you watching for a meter to reach a particular value, not very accurate as digital meters are slow to respond and hard to reach changing values, and involves a stopwatch.

If the meter has a frequency counter on it, you could wire up the capacitor as part of an LC or RC oscillator and measure the frequency.

Or you can build something more permanent. I use a 555 timer as a reference clock, then a 555 timer wired as a monostable with the unknown capacitor as the C portion of the monostable timer. The output is then filtered by an RC lowpass filter to get a DC output proportional to the unknown capacitor. The meter connects to this output, with the negative lead to a trimpot that provides a zero set calibration.

If you use 1% or 2% capacitors in the monostable timing resistors, you can calibrate it as good or better than the accuracy of your meter using only one reference capacitor. See the link below.

I've been using this circuit for many, many years. Cheap to build, I built mine with parts from my junkbox. I strongly suggest making the zero set potentiometer a front panel control. It can be used with a digital or analog multimeter.
wrote...
11 years ago
I had a very old moving coil type multimeter that marked with a capacitance measurement scale under the AC volt scale. To do that, it requires an external AC power source 10V rms in series with AC  10V voltmeter.Using this setup can measure capacitor range between 0.1uF till 1000uF. By increasing the AC into 250V rms and set voltmeter into 250V ac scale,it can measure between 100pF to 0.1uF.
You can do the same way, however you need to mark your own capacitance scale since your meter did not have this scale. By compare the result of some known capacitors value showing on AC volt scale,you can estimate the unknown capacitor value.
This principle is quite simple. Capacitance causing AC voltage drops,the less capacitance it was, the more voltage drops it shown.
wrote...
11 years ago
Apply a sine wave across a resistor and capacitor in series.

Measure the RMS voltage across each.

Adjust the frequency until the two voltages are equal.  Then, you know the resistance is equal to the reactance, and you can solve the equation:

R = Xc = 1 / ( 2 pi f C )
irina Author
wrote...
10 years ago
Thx!
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