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Encyclopedia of Electrical Engineering
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Encyclopedia of Electrical Engineering
HOME Q & A TABLE OF CONTENTS

Voltmeter

What is Voltmeter?

A voltmeter, also known as a voltage meter, is an instrument used for measuring the potential difference, or voltage, between two points in an electrical or electronic circuit. Some voltmeters are intended for use in direct current (DC) circuits; others are designed for alternating current (AC) circuits.
Fig.no.1: Analog Voltmeter

Symbolic Representation

The capital alphabet V represents the voltmeter in the circuit.
Fig.no.2: Voltmeter Representation.

What are different types of Voltmeter?

According to the construction principle, we have different types of voltmeters, they are mainly:
  • 1. Parmanent Magnet Moving coil (PMMC) Voltmeter.
  • 2. Moving Iron (MI) Voltmeter.
  • 3. Electro Dynamometer Type Voltmeter.
  • 4. Rectifier Type Voltmeter.
  • 5. Induction Type Voltmeter.
  • 6. Electrostatic Type Voltmeter.
  • 7. Digital Voltmeter (DVM).
Depending on the types of measurement we do, we have:
  • 1. AC Voltmeter.
  • 2. DC Voltmeter.

How does a Voltmeter work?

The main principle of a voltmeter is that it must be connected in parallel in which we want to measure the voltage. A parallel connection is used because a voltmeter is constructed in such a way that it has a very high value of resistance. So if that high resistance is connected in series than the current flow will be almost zero which means the circuit has become open.
For an ideal voltmeter, we have the resistance is to be infinity and hence the current drawn to be zero so there will be no power loss in the instrument. But this is not achievable practically as we cannot have a material that has infinite resistance.
A basic analog voltmeter consists of a sensitive galvanometer (current meter) in series with a high resistance. The internal resistance of a voltmeter must be high. Otherwise, it will draw significant current, and thereby disturb the operation of the circuit under test. The sensitivity of the galvanometer and the value of the series resistance determine the range of voltages that the meter can display.
The Digital Voltmeter is an instrument that can give the output voltage, not by a deflection but directly indicating the value.
Fig.no.3: Digital Voltmeter
It is a very good instrument to measure the voltage as it eliminates completely the error due to parallax, approximation in measurement, high-speed reading can be done and it can also be stored in memory for further analysis. The main principle is that the value is measured by the same circuit arrangement but that value is not used to deflect the pointer, but it is fed to the analog to digital converter and displayed as the digital value.
An oscilloscope can be used to measure low voltages; the vertical displacement corresponds to the instantaneous voltage. Oscilloscopes are also excellent for the measurement of peak and peak-to-peak voltages in AC and RF applications. Voltmeters for measuring high potential differences require heavy-duty probes, wiring, and insulators.
All of the voltmeters and its functions will be discussed practically in the upcoming circuit analysis topics.