Difference Between Voltmeter and Ammeter

Voltmeter vs Ammeter

Voltmeters and ammeters are widely used tools in the fields of physics, electronic engineering, and electrical engineering. Both the ammeter and the voltmeter are used to measure properties of electronic and electrical circuits. These instruments are mainly based on a conductor coil placed in a strong magnetic field, but other forms of these devices such as digital voltmeters and ammeters, multimeters, potentiometers, current balances, and electrostatic voltmeters are also common.


The unit “Volt” is named in honor of Alessandro Volta. It is used to measure the potential of a point or potential difference between two points. Usually the voltmeter is a variation of the galvanometer. A very high resistor set up in series with the galvanometer makes the basic voltmeter. Voltmeters have ranges from a few microvolts to about a few Gigavolts. As described earlier, the basic voltmeter consists of a current carrying coil placed inside an external magnetic field. The magnetic field due to the current carrying coil repulses the permanent magnetic field. This effect causes an indicator attached to the coil to rotate; this indicator coil system is spring loaded, thereby bringing the indicator back to zero pointer when no current is present. The angle of the indicator turn is proportional to the current present in the coil. The digital voltmeter uses an analog to digital conversion (ADC) to convert the present voltage to a digital value. But the incoming signal must be amplified or reduced depending on the measuring range used in the instrument before it can be displayed as a digital value. The main problem involving voltmeters is that, they have a finite resistance value; ideally, a voltmeter should have infinite impedance, which means it must not draw any current from the circuit. However, this is not the case with real voltmeters. A real voltmeter must have to draw a current from the circuit in order to produce the repulsive magnetic field. However, this can be minimized by using amplifiers so that the disturbance to the circuit is minimal.


Ammeter is also a variation of the galvanometer. It uses the galvanometer’s principle of indicating the current variation. The current is measured in amperes (A). Thereby, ammeters, which measure in milliamperes is known as the milliammeter, and microampere ranged ammeter is known as the microammeter. Ideally, an ammeter should have a zero resistance value, but materials with zero resistivity are not present. Therefore, every ammeter has an inbuilt error. There are very accurate ammeters, such as: current balance. The ammeter also comes in the forms of moving iron ammeters, hot wire ammeters, and digital ammeters.

Difference between Voltmeter and Ammeter

- Basic ammeters and voltmeters are galvanometers. A voltmeter can be arranged by setting up a suitable resistor in series with the galvanometer.

- Ideally, ammeters should have zero resistance, and voltmeters should have infinite resistance.

- An ideal ammeter should not have voltage drop across the terminals, and an ideal voltmeter should have no current going through it.