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Measuring voltage with a multimeter

- an overview or tutorial about how to measure voltage with a digitial multimeter (DMM) or an analogue multimeter.

One the important measurements that it is possible to make with a multimeter (either and analog / analogue multimeter) or a digital multimeter is that of voltage. Voltage measurements look at the potential difference between two points. In other words they look at the difference in electric pressure at the two points. In most cases the voltage is measured between a particular point and the ground or zero volt line on a circuit. However this does not mean that the voltage cannot be measured between any two points.

When making a voltage measurement with a multimeter, the first step is to switch the multimeter to the voltage ranges. It is best to select a range higher than the expected voltage so that there is no chance of the meter being overloaded and damaged. In addition to this check that the test leads are plugged into the correct sockets. Many multimeters have different sockets for different types of measurement so it is worth checking the correct ones have been chosen before making the measurement. Usually a meter will be provided with two leads, one black, and the other red. The black one is normally taken as the negative one. It is connected to the negative or "common" socket on the meter. The red one is connected to the positive socket.

When making the measurement, the positive lead should be connected to terminal which is expected to have the more positive voltage. If the leads are connected the wrong way round a negative voltage will be displayed. This is acceptable for a digital multimeter (DMM) because it will just display a negative sign. However for an analogue multimeter, the meter needle will move backwards and hit a stop. If at all possible it is best not to allow this to happen.

With the multimeter connected, power can be applied to the circuit. The multimeter switches can then be changed to reduce the value of the range. This is done until the largest deflection is seen on the meter without it going over the top of the range. In this way the most accurate reading is obtained.