How to Read an Ohmmeter

By Isaiah David

An ohmmeter is an electronic tool for reading resistance in circuits. The semiconductors and conductors in electronic circuits resist the flow of electricity as it runs through them. An ohmmeter lets an electrician, electric engineer or hobbyist precisely measure this resistance in order to fine tune the circuit. Ohmmeters can also be used to detect bad connections, burned out components and other serious circuit problems.

Step 1

Consider getting a multimeter instead of a plain ohmmeter. Multimeters can measure resistance like an ohmmeter, as well as voltage and amperage.

Step 2

Determine whether you have a digital ohmmeter or an analog one. Analog meters have a needle that swings through a series of values, while digital ohmmeters have a digital readout of the resistance. Digital ohmmeters are easier to read, but analog ohmmeters make it easier to detect certain kinds of problems, such as loose or intermittent connections. It mostly comes down to personal preference.

Step 3

Turn on the ohmmeter and set the sensitivity value to the right range. Ohmmeters usually have various settings ranging from 200 ohms (shown as 200?) to 2 million ohms (shown as 2M?). You will most likely want to set your meter to either 200 ohms or 2000 ohms (2k? ), since this is the range that most resistors and other circuit components are in.

Step 4

Turn off the circuit and unplug it. Touch one probe from the ohmmeter to each side of the circuit component you want to test and read the value. If the value it gives you is smaller than the next lowest setting, lower the setting and test the circuit again for a more accurate reading. As an example, imagine that your ohmmeter has both a 200? and a 2k? setting, and you are measuring a resistor on the 2k? setting. If it gives you a reading of 150?, you should change the setting to 200? and test it again to get a more precise reading.

Step 5

Learn what an infinite reading means. If there is no electricity getting through, an analog ohmmeter will stay all the way to the side it starts on when the probes aren't touching anything and a digital ohmmeter will generally show no value at all. Both of these readings indicate that no electricity is flowing through the component between the probes. This means that either you are not touching the component properly with the probes or something in the circuit is broken. It could be a blown component, cold solder joint, or broken circuit trace.