Analog ohmmeters are very basic and inexpensive and usually range from 0-10 to 0-10,000 ohms. Digital ohmmeters may have similar ranges or “auto-range,” where the device will read a circuit’s resistance and automatically select the best measuring range.
Ohmmeters are typically sold along with these test leads. If your meter was recently purchased, you should not have to buy your leads separately. Be sure to plug the short ends of the leads into the sockets. The longer ends, with the grips and probes, are the ends you’ll use to actually test a circuit’s resistance.
Note that the scale reads in the reverse direction of most conventional measuring scales: that is, less resistance is to the right and more resistance is to the left. If yours is a digital ohmmeter, the screen should read “0” when you touch the 2 probes together.
You can technically use anything that conducts electricity, from a piece of aluminum foil to a pencil mark on a sheet of paper, to test your ohmmeter, as long as you know that object’s resistance value ahead of time. Place the meter’s probes on opposite ends of the conductor and look to see if the correct resistance reading shows up on the meter’s screen.
Another source of power isn’t necessary since your ohmmeter will supply all of the voltage and current for your circuit. Trying to use an ohmmeter on a powered circuit can cause damage to the meter, the circuit, and you.
For example, if you expect the circuit you’re measuring to have a resistance of 1100 ohms, then your ohmmeter should be set to X100. This means, a reading of “11” on your ohmmeter would be equal to 1100 ohms. Note that you can only do this if you have an idea of what the resistance of what you’re measuring ought to be.
Because you’re measuring the resistance in the circuit and resistance doesn’t change with the direction of current flow, the positive probe and the negative probe can be on either end of the circuit to get an accurate resistance reading.
For example, if a circuit has 0 ohms, current would be able to flow through the circuit completely unimpeded.
In other words, by testing a resistor while it’s still in a circuit board, you can’t be sure that the resistance you’re measuring is only coming from that particular resistor.
