Voltmeters are electronic measuring devices for measuring DC and AC voltage. The function of the voltmeter is usually also integrated in multimeters and digital multimeters. Depending on the area of use and application, voltmeters have pointer instruments on which the voltage is displayed analogously by pointer deflection. These can be field instruments with switchable voltage ranges or built-in instruments.
In addition, there are digitally indicating voltmeters with range switching for DC and AC voltage.
When measuring voltage with a voltmeter, it is connected in parallel to the component or circuit whose voltage or voltage drop is to be measured. To keep the measurement error by the voltmeter as small as possible, the internal resistance must be high. It is in parallel with the load and causes a partial current to flow through it, resulting in a measurement error.
The most sensitive voltage measuring range is available when only the internal resistance of the measuring element is connected to the circuit. Measuring ranges for higher voltage values are realized by series connection of resistors to the measuring mechanism. With some voltmeters, range switching is automatic to protect the measuring mechanism. In addition, various voltmeters are protected against overload and have reverse polarity protection, i.e. the positive and negative connection leads can be reversed without damaging the voltmeter.