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Old 05-13-2009, 18:44   #2 (permalink)
loca|host
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Quote:
Originally Posted by srikanthreddy View Post
how to check capacitor with digital multimeter?
You can use your multimeter as an ohmmeter to test the capacitor.

1) Discharge the capacitor by shortening its leads. That is - use a wire and connect the leads of the capacitor together. This will discharge it.

2) put your multimeter in the high ranges 10K-1M

3)CONNECT MULTIMETER TO CAPACITOR LEADS(OBSERVE THE POLARITY IF ELECTROLYTIC). AT SOON AS THE LEADS MAKE CONTACT, THE METER WILL SWING NEAR ZERO. IT WILL THEN MOVE SLOWLY TOWARD INFINITY. FINALLY THE METER WOULD COME TO BE INFINITE OHMS BECAUSE THE CAPACITOR IS BEING CHARGED BY THE BATTERY OF THE MULTIMETER.

4) IF THE CAPACITOR IS BAD, IT WILL GO TO ZERO OHMS AND REMAIN THERE. THIS IS CALLED A SHORTENED CAPACITOR

5) IN THE CASE OF AN OPEN CAPACITOR THERE WILL BE NO OHMMETER INDICATION.

6)SOME CAPACITORS HAVE A LOW DIELECTRIC LEAKAGE. YOU WILL KNOW THIS IF THE OHMMETER COMES TO REST AT A POINT LOWER THAN INFINITE. TEST A KNOWN GOOD CAPACITOR OF THE SAME TYPE TO BE SURE .

This method will work with sufficiently large capacitor values.
A simple way of determining the capacitance fairly accurately is to build an oscillator using a 555 timer. Substitute the cap in the circuit and then calculate the C value from the frequency. With a few resistor values, this will work over quite a wide range.

Alternatively, using a DC power supply and series resistor, capacitance can be calculated by measuring the rise time to 63% of the power supply voltage from T=RC or C=T/R.

Tiny capacitors can only be checked with a capacitance meter, or by using them in an AC circuit and checking for variation from calculated voltage drop.

Last edited by loca|host; 05-13-2009 at 18:50.
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