What is voltmeter?
A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter.
A voltmeter in a circuit diagram is represented by the letter V in a circle.
Working Principle of Voltmeter
Voltmeter works on the principle of Ohm’s law, which states that the voltage across a resistance is directly proportional to the current passing through it. In order to implement it in real time, we form the construction of a galvanometer, such that a coil is suspended in a magnetic field.
We know that the current passing through the circuit also passes through the coil and the needle that is attached to the coil which deflects on the reading scale moves, and the movement of the needle is directly proportional to the current passing through it.
Types of voltmeter
There are many types of voltmeter :-
- PMMC Voltmeter
- MI Voltmeter
- Electro-dynamometer Voltmeter
- Rectifier voltmeter
- Analogue Voltmeter
- Digital Voltmeter
PMMC Voltmeter
It works on the principle that the current carrying conductor placed in the magnetic field and because of the current the force acting on the conductor. The current induces in the PMMC instrument because of the measurand voltage, and this current deflects the pointer of the meter.
The PMMC voltmeter uses for DC measurement.
The accuracy of the instrument is very high and having low power consumption. The only disadvantage of the instrument is that it is very costly. The range of the PMMC voltmeter increases by connecting the resistance in series with it.
MI Voltmeter
The MI instrument means moving iron instrument. This instrument uses for the measurement of both the AC and DC voltage. In this type of instrument, the deflection is directly proportional to the voltage of the coil. The moving iron instrument is classified into two types.
- Attraction Type Moving Iron Instrument
- Repulsion Type Moving Iron Instrument
Electro-dynamometer Voltmeter
The electro-dynamometer voltmeter is used for measuring the voltage of both AC and DC circuit. In this type of instruments, the calibration is same both for the AC and DC measurement.
Rectifier voltmeter
Such type of instrument is used in AC circuits for voltage measurement. The rectifier instrument converts the AC quantity into the DC quantity by the help of the rectifier. And then the DC signal is measured by the PMMC instrument.
The following are the classification of instruments regarding the displays of output reading.
Analogue Voltmeter
The analogue voltmeter uses for measuring the AC voltage. It displays the reading through the pointer which is fixed on the calibrated scale. The deflection of the pointer depends on the torque acting on it. The magnitude of the develops torque is directly proportional to the measuring voltage.
Digital Voltmeter
The voltmeter which displays the reading in the numeric form is known as the digital voltmeter The digital voltmeter gives the accurate result.
The instrument which measures the direct current is known as the DC voltmeter, and the AC voltmeter is used in the AC circuit for alternating voltage measurement.
Applications of voltmeters
Voltmeters are one of the most widely used measuring devices especially in circuitry and hardware where very precise measurement is required.
- They measure the voltage to ensure safety of the circuit and the components used.
- They are used in circuit debugging to certify that the optimal value of the required voltage is present and is available to each component
- They are used with cathode ray tubes to ensure best and accurate results.
- They are used in laboratories for experimenting and testing purposes as well.
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