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How to Use an Ohmmeter

An ohmmeter is an electronic device used to measure resistance in an electronic component or circuit.

Analog vs Digital

An ohmmeter is composed of a ruled scale with an indicator needle (analog) or digital display (digital), a range selector, and two probes.
Analog ohmmeters (left) are very basic and inexpensive, and usually range from 0-10 to 0-10,000 ohms.

Digital ohmmeters (right) may have similar ranges, or "auto-ranges," reading the resistance of your device or circuit and selecting the correct range automatically.

How to Use Your Ohmmeter in Steps:

1)

Select an ohmmeter suitable for your project.

2)

Check the ohmmeter to see if it has a battery and if it has been pre-installed.

3)

Plug your test leads into the sockets on your meter. For multi-functional meters, you will see a negative plug (-) and a positive plug (+).

4)

Zero your meter if it is equipped with a zeroing dial. Notice that the scale reads in the reverse direction of most conventional measuring scales - less resistance is to the right and more resistance is to the left. Zero resistance is when probes are connected directly to each other. You can adjust this by holding them together and turning the "adjust" dial until the needle on the scales is at zero ohms.

5)

Choose the circuit or electrical device you want to test. For practice, you can use almost anything which conducts electricity, including a piece of aluminum foil or a pencil mark on a sheet of paper. To get an idea of the accuracy of your readings, buy a few different resistors from an electronics supplier, or some other device with a known resistance value.

6)

Touch one probe to one end of a circuit, the other to the other end. Note the reading on the instrument. If you bought a 1000 ohm resistor, you can place a probe on each conductor of the resistor, and select the 1000 or 10,000 ohm range, then read the meter.

7)

Isolate components in a hard wired electrical circuit to test them individually. If you are reading the ohms on a resistor in a printed circuit board, you will have to unsolder or unpin the resistor to ensure you are not getting a false reading.

8)

Read the resistance of a run of wire or a branch of a circuit to see if there is a short or open break in the circuit. If you read "infinite ohms," then there is no path for the electrical current to follow, and in simple terms, this suggests a burned out component somewhere in the circuit, or a broken conductor.

9)

Turn the ohmmeter off when not in use. Occasionally the test leads will become shorted while the device is stored, draining the battery.