How To Measure Capacitance With A Digital Multimeter | Fluke

A multimeter determines capacitance by charging a capacitor with a known current, measuring the resulting voltage, then calculating the capacitance.

A good capacitor stores an electrical charge and may remain energized after power is removed. Before touching it or taking a measurement, a) turn all power OFF, b) use your multimeter to confirm that power is OFF and c) carefully discharge the capacitor by connecting a resistor across the leads. Be sure to wear appropriate personal protective equipment. If you are troubleshooting professionally, double-check that all testing steps are listed in a work order before you begin.

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Step-by-Step Guide for Measuring Capacitance with a Digital Multimeter

To measure capacitance with a digital multimeter, follow these key steps for an accurate and safe assessment of capacitor values in electronic circuits:

Step 1. Power Off

Use your digital multimeter (DMM) to ensure all power to the circuit is OFF.

• If the capacitor is used in an AC circuit, set the multimeter to measure AC voltage.
• If the capacitor is used in a DC circuit, set the DMM to measure DC voltage.
  • Safely discharge the capacitor using a 20,000 Ω, 5-watt resistor.

Step 2. Discharge Capacitor

• After power is removed, connect a 20,000 Ω, 5-watt resistor across the capacitor terminals for five seconds.
  • Use your multimeter to confirm the capacitor is fully discharged.

Step 3. Setup Multimeter

• Turn the dial to the Capacitance Measurement mode.
  • The symbol often shares a spot on the dial with another function.
• In addition to the dial adjustment, a function button usually needs to be pressed to activate a measurement.
  • Consult your multimeter’s user manual for instructions.

Step 4. Detach Capacitor

• Detach the capacitor from the circuit to avoid measurement errors.

Step 5. Connect Leads

• Connect the test leads to the capacitor terminals.
  • Keep test leads connected for a few seconds to allow the multimeter to automatically select the proper range.

Step 6. Read Results

• Read the measurement displayed.
  • If the capacitance value is within the measurement range, the multimeter will display the capacitor’s value.
  • It will display OL if a) the capacitance value is higher than the measurement range or b) the capacitor is faulty.

Step 7. Using Relative Mode (if necessary)

• For low values, use the Relative mode to correct for the test leads' capacitance.

What to Expect from a Faulty Capacitor

Capacitors have a limited life and are often the cause of a malfunction. Faulty capacitors may have a short circuit, an open circuit or may physically deteriorate to the point of failure. When a capacitor short circuits, a fuse may blow or other components may be damaged. When a capacitor opens or deteriorates, the circuit or circuit components may not operate. Deterioration can also change the capacitance value of a capacitor, which can cause problems.

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