Digital Voltmeter | How it works, Types, Advantages, Disadvantages

DIGITAL VOLTMETER –

This write-up will provide information on the digital voltmeter. After going through the write-up, you will be aware of the meaning, types, and working of a digital voltmeter.

Alongside, explore the advantages and disadvantages of a digital voltmeter.

Also, we have included the difference between analog and digital voltmeter for you to understand better.

What is a digital voltmeter?

A digital voltmeter is an electrical measuring instrument that measures the potential voltage difference between two points in a circuit.

The voltage which is being measured can be AC or DC. The acronym used for a digital voltmeter is DVM.

In a digital voltmeter, the value of AC or DC voltage being measured is displayed as a discrete numerical figure contrary to the pointer deflection on a continuous scale in case of analog voltmeters.

The DVM measures an unknown input voltage by converting the voltage to a digital value.

The digital voltmeter was invented by Andrew Kay in the year 1954.

How does a digital voltmeter work?

The given diagram will help you understand the working of a DVM better.

The terms mentioned in the diagram above are as follows:-

Input Signal: It is the signal or the voltage which is to be measured.

Pulse Generator: it is the source of the voltage and generates a rectangular impulse by using analog, digital, or both techniques. The digital circuitry inside the controller controls the frequency and width of the rectangular pulse. The analog circuitry controls the rise and fall time.

AND: It provides high output in case of both inputs being high. When a train pulse along with a rectangular pulse is introduced to it, AND gate provides an output that has train pulse. They have the duration as same as the rectangular pulses from the pulse generator.

Decimal Display: the decimal display counts the number of impulses and the duration of impulses. Then, it displays the voltage value on a display screen, which can be LCD or LED, after calibrating it.

The working of a digital voltmeter is converting an analogue signal into a train of pulses. The number of pulses is proportional to the input signal. Therefore, a digital voltmeter can be made by using any A/D conversion method.

Initially, a voltage signal is introduced to the pulse generator. It generates a pulse with a width proportional to the input signal.

Then, the output obtained from the pulse generator is fed into the AND gate through its one leg. The input signal is fed to the other leg of the AND gate which is the train of pulses.

The output obtained from the AND gate is a positive train with duration same as the width of the pulses generated by the pulse generator. The positive train is introduced to the inverter which converts it into a negative one.

The inverter output is fed to a counter. It counts the number of triggers in the duration proportional to the input signal. The counter displays the voltage in volts directly after calibrating it.

What are the various types of the digital voltmeter?

There are various types of digital voltmeters. The classification is based on the different AC and DC conversion methods.

We have discussed the various types of digital voltmeters which are as follows:-

Ramp Type DVM

The operation of the ramp type digital voltmeter primarily depends on time measurement. There is a ramp generator that generates a waveform representing a ramp.

The most important element of the circuit is the ramp generator in this type of voltmeter; therefore, it is termed as a ramp type digital voltmeter.

The basic operating principle of Ramp type digital voltmeter is based on the measurement of time that a linear ramp voltage takes to convert from the level of the input voltage.

To measure the time interval an electronic time interval counter is used. The count or measurement figure is displayed in digits as the output of the voltmeter.

Dual Slope Integrating Type DVM

In a dual-slope integrating type digital voltmeter, the input voltage is integrated with the slope of the integrator output proportional to the test input voltage.

After a fixed time, the input voltage is disconnected. The integrator input is connected to a negative voltage which results in the integrator output having a negative slope.

The negative slope is proportional to the magnitude of the input voltage and is constant.

A dual-slope integrating type digital voltmeter has the following major blocks which are as follows:-

• An op-amp employed as an integrator

• A level comparator

• Oscillator for generating time pulses

• Decimal counter

• Block of logic circuitry

Integrating Type DVM

The integrating type digital voltmeter measures the true value of input voltage over a fixed measuring time.

The integration technique employed uses the voltage to frequency conversion and the voltage to frequency converter acts as the feedback control system.

This system primary governs the pulse generation rate and is proportional to the magnitude of the applied input voltage.

In the technique of voltage to frequency conversion, a train of pulses is generated, the frequency of which depends on the voltage which is being measured.

These pulses appear in a definite time interval and are counted. The frequency of the pulses is a function of input voltage and the number of pulses indicates the input voltage.

Successive Approximation DVM

A successive approximation digital voltmeter is the one which compares the output of the digital to analogue converter with the unknown voltage.

This type of voltmeter has the potential of making 100 readings per second.

Initially, a start pulse is applied at the multivibrator. For this, the MSB of the control register set to high levels and all the other bits are set to low.

The final approximation of the input voltage is displayed by the output in digital format at the control register.

What are the advantages of the digital voltmeter?

There are plenty of advantages which a digital voltmeter offers. There are plenty of advantages of DVM over analogue voltmeters too.

We have compiled several advantages which are digital voltmeter offers which are as follows:-

• You do not have to figure out the readings manually to get the voltage, ohm or ampere reading unlike the analogue voltmeters

• Digital voltmeters provide a precise and computer-generated reading on the screen which eliminates the errors that might occur in case of human reading

• They provide accurate and fast readings when compared to the readings extracted from an analogue voltmeter

• Digital voltmeters do not require you to make calculations and are more stable, dependable and reliable

• Digital voltmeters provide accurate result and do not depend on the competency of the readers as in case of reading analogue voltmeter

• Digital voltmeters are cost-effective and smaller in size which makes them easy to handle and use

• Digital voltmeters have the function to measure both AC and DC voltages

• In certain latest digital voltmeters, there are microcontrollers with the use of which you can store the readings for further processing

What are the disadvantages of the digital voltmeter?

Despite the several advantages, there are certain disadvantages of digital voltmeters as well. There are certain disadvantages of DVM when compared to analogue voltmeters too.

We have provided the disadvantages which a digital voltmeter has below which are as follows:-

• Digital voltmeters work on an external battery or power source and the display depends on it

• Digital voltmeters can get heated up while measuring the voltage which might lead to wrong readings

• In case of fluctuating readings, a digital voltmeter cannot measure the fluctuations rather it would display a wrong reading or an error. However, an analogue voltmeter can measure these fluctuations

• If the voltage rises or increases beyond the limit the digital voltmeters are prone to damage

• It is very hard for digital voltmeters to spot the transient voltage spikes

• There is digitizing circuit in digital voltmeters which limits the speed of operations

The difference between analogue voltmeter and digital voltmeter

 There are two primary types of a voltmeter that are the analogue and digital voltmeter. They both differ in certain ways which we have discussed below.

The difference between the analog and digital voltmeter is given below as follows:-

Basis of Distinction	Analogue Voltmeter	Digital Voltmeter
Meaning	It is a device used to measure the voltage or voltage changes in a circuit.	Digital voltmeter is a device used to measure the voltage or the potential difference in volts in a circuit.
Representation	The reading display or representation is using a pointer or needle that is fixed on a calibrated scale.	The reading display or representation is in a digital form.
Types	The types of the analogue voltmeter are as follows: Moving Coil InstrumentsMoving Iron instrumentsElectrostatic voltmeters	The types of the digital voltmeter are as follows: Ramp Type DVMDual Slope Integrating Type DVMIntegrating Type DVMSuccessive Approximation DVM
Programming	Analogue voltmeters cannot be programmed	Digital voltmeters can be programmed
Overload indication	Analogue voltmeters do not have any overload indication	There is an overload indication in the digital voltmeters
Sensitivity	These voltmeters have less sensitivity	The sensitivity level is more in digital voltmeters
Speed	Analogue voltmeters offer less speed of operations	Digital voltmeters offer more speed of operations
Measurement range	Number of measurement range is less in these voltmeters	In digital voltmeters, the number of measurement ranges is more
Signal digitalization	Analogue voltmeters do not require digitalization of signal	These voltmeters require signal digitalization
Resolution	These voltmeters come with poor resolution	Digital voltmeters come with high resolution

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