Digital Voltmeter | Electrical and Electronic Measurements - Electrical Engineering (EE) PDF Download

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.
Although digital voltmeters do not fully replace analog voltmeters, still there are many places where analog voltmeters are preferred over digital voltmeters.
Digital voltmeters display the value of AC or DC voltage being measured directly as discrete numerical instead of a pointer deflection on a continuous scale as in analog instruments.

Digital Voltmeter | Electrical and Electronic Measurements - Electrical Engineering (EE)

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.
  • Reading can be taken very fast.
  • 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

Digital Voltmeter | Electrical and Electronic Measurements - Electrical Engineering (EE)

The block diagram of a simple digital voltmeter is shown in the figure.
Explanation of various blocks
1. Input signal: It is basically the signal i.e. voltage 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.
2. AND gate: It gives high output only when both the inputs are high. When a train pulse is fed to it along with rectangular pulse, it provides us an output having train pulses with duration as same as the rectangular pulse from the pulse generator.

Digital Voltmeter | Electrical and Electronic Measurements - Electrical Engineering (EE)NOT gate: It inverts the output of AND gate.
Digital Voltmeter | Electrical and Electronic Measurements - Electrical Engineering (EE)

3. 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.
Digital Voltmeter | Electrical and Electronic Measurements - Electrical Engineering (EE)

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.

The document Digital Voltmeter | Electrical and Electronic Measurements - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Electrical and Electronic Measurements.
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FAQs on Digital Voltmeter - Electrical and Electronic Measurements - Electrical Engineering (EE)

1. What is a digital voltmeter?
Ans. A digital voltmeter is an electrical instrument used to measure the voltage of an electrical circuit or component. Unlike analog voltmeters, which use a pointer and scale, digital voltmeters display the voltage reading in numeric form on a digital display.
2. How does a digital voltmeter work?
Ans. A digital voltmeter works by converting the analog voltage signal into a digital form that can be processed and displayed. It typically uses an analog-to-digital converter (ADC) to convert the voltage into a binary code, which is then interpreted by the voltmeter's microprocessor and displayed on the digital screen.
3. What are the advantages of using a digital voltmeter over an analog voltmeter?
Ans. There are several advantages of using a digital voltmeter over an analog voltmeter. Firstly, digital voltmeters provide a more accurate and precise measurement of voltage due to their higher resolution. Secondly, they offer better readability with their digital display, making it easier to read the voltage value. Additionally, digital voltmeters can have additional features such as auto-ranging, data logging, and connectivity options, which enhance their functionality compared to analog voltmeters.
4. Can a digital voltmeter measure AC voltage?
Ans. Yes, most digital voltmeters can measure both DC (direct current) and AC (alternating current) voltage. However, it is essential to ensure that the digital voltmeter is specifically designed to measure AC voltage. Some digital voltmeters have separate AC and DC voltage measurement modes, while others have an auto-ranging feature that automatically detects the type of voltage being measured.
5. How accurate are digital voltmeters?
Ans. The accuracy of digital voltmeters can vary depending on the model and specifications. Higher-end digital voltmeters typically have better accuracy, with measurements ranging from 0.1% to 0.01% of the reading. However, it is crucial to calibrate and maintain the voltmeter regularly to ensure accurate readings. Calibration can be done using standard voltage references or by comparing the voltmeter's readings with a known accurate voltage source.
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