A multimeter, also called a volt-ohm meter or VOM (in Russia we call it a tester), is a device that measures resistance, voltage, and current in electronic circuits. Some of them also test diodes and conductivity. Multimeters are small, lightweight and battery operated, and can test a wide variety of electronic components in many situations, making them indispensable tools for anyone who needs to test and repair electronic circuits.
Steps
Method 1 of 5: Measuring Resistance
Step 1. Connect a multimeter to the circuit
Insert the black test lead into the common terminal and the red test lead into the connector marked for volt and ohm measurements. The terminal can also be marked for diode testing.
Step 2. Turn the knob to set the multimeter to measure resistance
This can be represented by the Greek letter omega, which stands for ohm, a unit of measure for resistance.
Step 3. Turn off power to the circuit
Step 4. Remove the resistor you want to measure
If you leave a resistor in the circuit, you may not get an accurate reading.
Step 5. Touch the leads on each side of the resistor
Step 6. Read the display, noting the units
10 can indicate 10 ohm, 10 kilo ohm, or 10 megohm.
Method 2 of 5: Measuring Voltage
Step 1. Connect a multimeter to the circuit
Insert the black test lead into the common terminal and the red test lead into the connector marked for volt and ohm measurements.
Step 2. Set the multimeter to the voltage you are measuring
You can measure DC voltage, DC millivolts, or AC volts. If your multimeter has an AutoRange function, this is not necessary.
Step 3. Measure AC voltage by connecting to components
It is not necessary to observe the polarity.
Step 4. Observe polarity when measuring DC voltage or millivolts
Connect the black test lead to the negative side of the component and the red test lead to the positive side.
Step 5. Read the display, noting the units
If you prefer, you can use the hold function on the display after removing the probes. The multimeter will beep every time it detects a different voltage
Method 3 of 5: Measuring Current
Step 1. Select either the terminal labeled for 10 amps or labeled for 300 milliamps
If you are unsure of the amperage, start at the terminal with 10 amps until you are sure the current is less than 300 mA.
Step 2. Set up a multimeter to measure current
This can be indicated by the letter A.
Step 3. Turn off power to the circuit
Step 4. Break the chain
To measure current, you must place a multimeter in series with the circuit. (Black test lead on negative pole, red test lead on positive pole) Place the test leads on either side of the break, observing the polarity.
Step 5. Turn on the power
Current will flow through the circuit, to the red probe and through the multimeter, from the black probe and into the circuit.
Step 6. Read the reading, remembering whether you are measuring amps or milliamps
You can optionally use the touch hold feature.
Method 4 of 5: Testing Diodes
Step 1. Insert the black test lead into the common jack of the terminal and the red test lead into the terminal to measure ohms, volts, or diode tests
Step 2. Use the knob to select the diode test function
This can be represented by a symbol representing a diode, an arrow pointing to a vertical line.
Step 3. Power off the circuit
Step 4. Check forward bias
Place the red test lead on the positive side of the diode and the black test lead on the negative side. If you get a measurement less than 1 but greater than 0, the forward bias is good.
Step 5. Swap the test leads to check the reverse bias
If the display shows "OL (overload)", it means that the reverse bias is good.
Step 6. A reading of "OL" or 0 for forward bias testing and 0 for reverse bias testing indicates that the diode is bad
Some multimeters will beep when the reading is less than 1. This does not necessarily indicate a good diode, because a shorted diode will also beep
Method 5 of 5: Measuring Conductivity
Step 1. Insert the black test lead into the common plug and the red test lead into the plug that is used to measure volts and ohms
Step 2. Set the multimeter to the value used for diode testing
Step 3. Power off the circuit
Step 4. Connect the wires on either side of the section of circuit you are testing
It is not necessary to observe the polarity. A reading of less than 210 ohms indicates good electrical conductivity.