An ohmmeter is a type of electronic device mainly used to calculate the electrical resistance of a circuit and the unit of resistance in ohms.

There are various types of electronic device test gauges such as ammeters, ohmmeters, voltmeters, and multimeters to test the resistance, voltage, and current of the circuit to make sure the connections are correct.

Circuit tests can be performed using a device called an “ohmmeter” which is used to calculate the electrical resistance of a circuit. However, one cannot connect this device to the circuit to test soldering components without specifying the operating concept. 

What is an ohmmeter? 

The simple definition of ohmmeter is that these are varieties of electronic devices primarily utilized for measuring the resistance of electricity in a circuit or a type of electronic device whose resistance unit is ohms. Electrical resistance is an estimate of how much electricity flow an object resist.

Various kinds of gauges are accessible which are in great demand in the market. They have different levels of sensitivity, including micro, mega, and milli ohmmeters.

Working principle of an ohmmeter

The principle of operation of the ohmmeter is that it comprises an arrow and dual examination leads. The current of the battery regulates the deflection of the arrow.

First, the dual examination leads contained in the ohmmeter can be combined and reduced to evaluate the circuit resistance. 

When the dual gauge leads are shortened, the gauges are restored to operate properly within the specified range. The needle reaches the elevated level on the ohmmeter scale again and reaches the maximum current of the ohmmeter.  

After testing the circuit, the examination leads on the ohmmeter are removed. When the dual examination leads of the device are attached to the trail of the circuit,  discharging of the battery occurs.

Shortening the test lead adjusts the rheostat. The opposite arrow can be caught up from zero, which is the lowest point. At this position, the dual examination leads have no resistance.

Varieties of Ohmmeter

There are three varieties of ohmmeter. They are 

  • Series ohmmeter 
  • Shunt ohmmeter 
  • Multi-range ohmmeter 

Series ohmmeter 

A series resistance tester allows you to connect the component under measurement in series with the ohmmeter. 

The value of resistance is computed via a parallel-connected shunt resistor R2 with the D’Arsonval operation. The resistor R2, like the resistor R1, and the battery are computed in series. The measuring component is connected in series via two terminals A and B.  

When the value of the measured component is zero, a huge current flows through the ohmmeter. In this circumstance, the resistance of the shunt has to be corrected until the entire current load reads on the meter. This current causes the arrow to stoop in the path where ohms is 0.

 When the measurement component is disconnected, the resistance of the circuit has an unlimited current passing through the circuit. The arrow of the measuring instrument bends infinitely.

 The ohmmeter shows infinite resistance when no current is flowing and resistance of zero when a high current is flowing.

 Whenever a gauging element is attached to a circuit in sequence, and the resistance of this circuit is elevated, the measuring arrow is deflected to the left-hand side and when there is low resistance, the arrow is turned to the right-hand side.

Shunt ohmmeter

If the computing component is attached to the battery in parallel, one can connect a shunt ohmmeter. 

This circuit category is used for calculating the resistance of low values.

The circuit is set with the gauging device and battery. Gauging elements can be attached via A and B terminals.

Whenever component resistance goes to zero, the ohmmeter current goes to zero. 

Similarly, as the component resistance increases, the arrow and current in the battery will flex completely to the left. This type of ohmmeter has no current on the scale on the left and a point at infinity on the right.

Multi-Range ohmmeter

The multi-variety ohmmeter variety may be very high, and this ohmmeter consists of an adjuster. This variety of a device may be decided using an adjuster primarily based totally on the requirement.

For instance, when we make use of an ohmmeter to calculate the resistance underneath 10 ohms, initially we restore the resistance price to ten ohms. The measuring aspect is hooked up with the device in parallel. 

The resistance value may be determined via means of the deflection of the arrow.


Ohmmeters are convenient to use and they have several applications. The ohmmeters are used to measure the resistance of electrical circuits and the connection of components. Measurement resistance in ohms are classified into micro ohmmeters and mega ohmmeters. Micro ohmmeters are used to calculate low resistance. Mega ohmmeters are used to calculate high resistance.