How to Use a 3-Function Multimeter
- 1). Measure volts by selecting volts with the control knob. You can measure either AC or DC by selecting the appropriate setting of the control knob. To measure voltage, place the meter probes at two different points in the circuit. The meter will measure the difference in potential between the two test points. If you have a needle-type multimeter and the needle does not move, try reversing the leads -- you might be trying to read in the reverse direction. For digital readout meters, the meter readout will have a negative sign in the same situation.
- 2). Set the control knob to amps to measure current. Measuring current is more difficult than measuring voltage, because the meter must be in the circuit to measure amps. This usually means cutting a wire so that you can temporarily put the meter in the circuit. Because of this, people often use Ohm's law to calculate the current instead of measuring it. Ohm's law says that volts = amps x ohms. So, if you know the resistance of a component, you can measure the voltage and compute the amps.
- 3). Select one of the ohm settings on the control knob to measure resistance. You should not try to measure the resistance of a component that has power supplied to it. The multimeter has a battery in it. When measuring resistance, the multimeter sends electricity with a known voltage through the component being measured, and then uses Ohm's law to compute the resistance. If there is any current flowing through the component, the reading will be inaccurate. It is also necessary to isolate the component from the circuit to measure its resistance.
If the component is connected to anything, the current from the multimeter battery will split up into two paths which will make the reading incorrect.
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