- Digital Voltmeter Definition: A digital voltmeter is an electronic device that measures voltage by converting the analog signal into digital data and displaying it numerically.
- Display Technology: The measured voltage is shown on a digital screen, like an LED or LCD, making it easy to read.
- Measurement Accuracy: Digital voltmeters are highly accurate, eliminating errors like parallax and approximation that are common in analog types.
- Working Principle: The core function involves converting an analog voltage into a digital signal using a pulse generator and logical circuits.
- Types of Digital Voltmeters: Various methods of analog-to-digital conversion define the types of digital voltmeters, including ramp, integrating, and successive approximation types.
What is a Digital Voltmeter?
Voltmeter is an electrical measuring instrument used to measure the potential difference between two points. The voltage to be measured may be AC or DC. Two types of voltmeters are available for the purpose of voltage measurement i.e. analog and digital.
Analog voltmeters generally contain a dial with a needle moving over it according to the measure and hence displaying the value of the same. With time analog voltmeters are replaced by digital voltmeters due to the same advantages associated with digital systems.
While digital voltmeters haven’t completely replaced analog voltmeters, the latter remain preferred in various specific applications.
Digital voltmeters provide direct numerical readings of AC or DC voltages, unlike analog voltmeters, which use a moving pointer over a scale.
Advantages Associated with Digital Voltmeters
The advantages of digital voltmeters include:
- Readout of DVMs is easy as it eliminates observational errors in measurement committed by operators.
- Error on account of parallax and approximation is entirely eliminated.
- Readings are obtained quickly, enhancing efficiency.
- Output can be fed to memory devices for storage and future computations.
- Versatile and accurate
- Compact and cheap
- Low power requirements
- Portability increased
Working Principle of Digital Voltmeter
The block diagram of a simple digital voltmeter is shown in the figure.
Explanation of various blocks
Input Signal: This is the voltage that needs to be measured.
Pulse generator: Actually it is a voltage source. It uses digital, analog or both techniques to generate a rectangular pulse. The width and frequency of the rectangular pulse is controlled by the digital circuitry inside the generator while amplitude and rise and fall time is controlled by analog circuitry.
AND Gate: This gate outputs a high signal only when both of its inputs are high. Combining a train pulse with a rectangular pulse, it outputs train pulses that match the duration of the rectangular pulses generated.
 | Train pulse |
 | Rectangular pulse |
 | Output of AND gate |
NOT gate: It inverts the output of AND gate.
 | Output of NOT gate |
Decimal Display: It counts the numbers of impulses and hence the duration and display the value of voltage on LED or LCD display after calibrating it.
Now we are in situation to understand the working of a digital voltmeter as follows:
- Unknown voltage signal is fed to the pulse generator which generates a pulse whose width is proportional to the input signal.
- Output of pulse generator is fed to one leg of the AND gate.
- The input signal to the other leg of the AND gate is a train of pulses.
- Output of AND gate is positive triggered train of duration same as the width of the pulse generated by the pulse generator.
- This positive triggered train is fed to the inverter which converts it into a negative triggered train.
- Output of the inverter is fed to a counter which counts the number of triggers in the duration which is proportional to the input signal i.e. voltage under measurement.
- Thus, counter can be calibrated to indicate voltage in volts directly.
We can see the working of digital voltmeter that it is nothing but an analog to digital converter which converts an analog signal into a train of pulses, the number of which is proportional to the input signal. So a digital voltmeter can be made by using any one of the A/D conversion methods.
On the basis of A/D conversion method used digital voltmeters can be classified as:
- Ramp type digital voltmeter
- Integrating type voltmeter
- Potentiometric type digital voltmeters
- Successive approximation type digital voltmeter
- Continuous balance type digital voltmeter
Now-a-days digital voltmeters are also replaced by digital millimeters due to its multitasking feature i.e. it can be used for measuring current, voltage and resistance. But still there are some fields where separated digital voltmeters are being used.
