12 July 2021

Ohmmeter | Definition | Symbol | Types | Applications

The instrument used to measure the resistance between any two points in an electric circuit is known as an ohmmeter. It can also be used to determine the resistance of an unknown resistor. The resistance unit is ohms. The measuring instrument is a meter. So the term ohmmeter is formed by combining the words ohms and meter.

Ohmmeter Symbol:

Ohmmeter symbol

Types of Ohmmeter:

Series type ohmmeter:

The components that we want to measure can be connected in series with the metre in a series type ohmmeter. The resistance value can be calculated using the D'arsonval movement, which is connected in parallel, via the shunt resistor R2. The R2 resistance, as well as the R1 resistance, can be connected in series with the battery. The two terminals A and B are connected in series to the measuring components.


When the smearing component value is zero, a large amount of current flow through the metre. In this case, the shunt resistance can be adjusted until the metre full load current. The needle turns aside in the direction of 0 ohms for this current.

When the measuring components is removed from the circuit, the circuit resistance becomes infinite, and the current in the circuit flow. The meter needle deflects towards infinity, The meter depicts infinite resistance when there is no current flow and zero resistance when there is a large current flow through it.

Shunt type ohmmeter:

If the value of the resistor is unknown and must be measured by connecting it in parallel with the ohmmeter, the ohmmeter is referred to as a shunt ohmmeter, The circuit diagram for a shunt ohmmeter is shown in the figure below. The measuring component can be connected across terminals A and B.

When the components resistance value is zero, the current in the metre becomes zero. Similarly, as the components resistance increases, the flow of current through the battery and the needle illustrate the full-scale deflection to the left. This type of metre has no current on the scale to the left and an infinity spot to the right.

Application of ohmmeter:

  • This metre can be used to ensure circuit continuity, which means that if there is a sufficient flow of current or a large flow of current through the circuit, the circuit will be disconnected.
  • These are commonly used in engineering electronic labs to test electronic components.
  • These are used for small ICs for debugging such as PCBs and other stuff which requires to be executed in sensitive devices.

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