Digital Voltmeter (DVM) is used to measure voltage between two points. It displays DC or AC voltage as discrete numerals. It is a very useful laboratory instrument for several applications. It is also a useful building block of digital instrumentation systems. The utility of a DVM can be easily extended for multiple functions, such as a Digital Multimeter (DMM), by the addition of simple auxiliary hardware. The DVM is often used in data processing systems. An ideal voltmeter has an infinitely high input resistance so that it doesn’t draw any current from the circuit.
Consider a meter that has a low input resistance of 1000 ohms. It can’t give an accurate value of the voltage across a resistance of the same magnitude because the meter shunts the resistance. Therefore it is important to measure the loading effect of a voltmeter in terms of ohms per volt. The block diagram of a digital voltmeter is shown below figure:
It has mainly three stages:
i. Signal Preparation
ii. Analog to digital conversion
iii. Display unit