A digital multimeter, or DMM, is an essential tool for testing and troubleshooting electronic circuit boards. DMMs vary widely in measurement functionality and accuracy, but they all can measure current, voltage and resistance. The measurement values are reported on the DMM's numeric display, providing greatly improved readability and precision compared to analog multimeters. The simple procedures associated with measuring voltage, current and resistance help to ensure that you obtain an accurate and reliable measurement.
Instructions
Measuring Voltage
1 Insert the red probe of the DMM into the socket labeled for voltage measurements, and ensure that the black probe is inserted into the ground (or common) socket.
2 Touch the red probe to a conductive surface on your circuit board, and touch the black probe to the ground plane. This will measure the voltage of the conductive surface relative to the circuit's ground potential. You can touch the black probe to any other part of the circuit if you want to measure a voltage that is not referenced to ground (such as the voltage dropped across a resistor).
3 Look at the DMM's numeric display and note the voltage after the reading has become steady. If your DMM does not automatically change the measurement range, you must manually adjust the range (usually by turning the dial) until the measurement provides sufficient precision.
Measuring Current
4 Insert the red probe of the DMM into the socket labeled for current measurements, and ensure that the black probe is inserted into the ground (or common) socket.
5 Make an open circuit at the place where you want to measure the current. This usually involves removing a component from the board in order to interrupt the current path.
6 Touch the red probe to one terminal where you interrupted the current path, and touch the black probe to the other terminal. The red probe should touch the terminal that you expect to be at a higher potential. The probes of the DMM must be in series with the current path you are measuring.
7 Look at the DMM's numeric display and note the current after the reading has become steady. If your DMM does not automatically change the measurement range, you must manually adjust the range until the measurement provides sufficient precision.
Measuring Resistance
8 Insert the red probe of the DMM into the socket labeled for resistance measurements, and ensure that the black probe is inserted into the ground (or common) socket. The resistance socket is usually the same as the voltage socket.
9 Remove the component from the circuit. In general, the component must be removed from the circuit to allow for an accurate resistance measurement.
10 Touch the red probe to one lead of the component and the black probe to the other lead.
11 Look at the DMM's numeric display and note the resistance after the reading has become steady. If your DMM does not automatically change the measurement range, you must manually adjust the range until the measurement provides sufficient precision.
