Measurements in an electrical circuit

Measuring means comparing an unknown variable (e.g. the length of a pneumatic cylinder) with a known variable (e.g. the scale on a measuring tape). A measuring device (e.g. a steel ruler) facilitates this comparison. The result, the measured value, consists of a numerical value and a unit (e.g. 30.4 cm).

Electrical currents, voltages and resistances are usually measured using multimeters. These measuring devices can be switched between different operating modes:

• AC voltage/alternating current and DC voltage/direct current,

• current measurement, voltage measurement and resistance measurement. Correct measurements are only possible if the correct operating mode is set and the measuring device has been correctly switched into the circuit.

Procedure for measurements in an electrical circuit

Proceed in the following order when performing measurements in an electrical circuit:

• Switch off the supply voltage to the circuit.

• Set the required operating mode on the multimeter (current or voltage measurement, DC or AC voltage, resistance measurement).

• When using pointer measuring instruments, check and if necessary adjust the zero point.

• When measuring DC voltage/direct current, connect the measuring device to the correct terminal ("+" terminal of the measuring device to the positive terminal of the voltage supply).

• Choose the largest measuring range.

• Switch on the voltage supply to the circuit.

• Monitor the pointer or display and gradually switch over to a smaller measuring range.

• Read the display when the greatest pointer deflection occurs (smallest possible measuring range).

• When using pointer instruments, always read the display by looking down onto it to avoid reading errors.