How to Use an Ohmmeter

Step-by-Step Guide

1. 1

   Step 1: Disconnect completely and/or turn off all power to the circuit you are testing.

   You must have a completely dead wire or circuit in order to ensure accuracy in measurement, as well as your own safety.
   
   Your ohmmeter will supply the voltage and current for your circuit so NO other power is necessary.
   
   As the instructions for our Blue Point volt/ohmmeter state, testing a powered circuit can "cause damage to the meter, circuit, and *you*."
2. 2

   Step 2: Select an ohmmeter suitable for your project.

   Analog ohmmeters are very basic and inexpensive, and usually range from 0-10 to 0-10,000 ohms, digital devices may have similar ranges or "auto-range"
   
   reading the resistance of your device or circuit and selecting the correct range automatically. , If you just bought an ohmmeter, the battery may have come pre-installed in your unit, or packaged separately with instructions for installing it. , For multi-functional meters, you will see a "common"
   
   or negative plug, and a "positive" plug.
   
   These may also be colored red (+) and black (-). , Notice 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.
   
   Zero resistance should be observed when your probes are connected directly to each other, and you can adjust this by holding them together and turning the "adjust" dial until the needle on the scales is at zero ohms. , For practice, you can use almost anything which conducts electricity, from a piece of aluminum foil to 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. , If you bought a 1000 ohm resistor, you can place a probe on each conductor on the resistor, and select the 1000 or 10,000 ohm range, then read the meter to see if indeed it reads 1,000 ohms. , If you are reading the ohms on a resistor in a printed circuit board, you will have to unsolder or unpin the resistor to assure you are not getting a false reading through another path in the circuit. , If you read "infinite ohms"
   
   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.
   
   Because many circuits contain "gate" devices (transistors or semiconductors), diodes, and capacitors, however, you may not read continuity even when the complete circuit is intact, which makes it difficult to test complete circuits with only an ohmmeter. , Occasionally the test leads will become shorted while the device is stored, draining the battery.
3. 3

   Step 3: Check the ohmmeter to see if it has a battery.

4. 4

   Step 4: Plug your test leads into the sockets on your meter.

5. 5

   Step 5: Zero your meter if it is equipped with a zeroing dial.

6. 6

   Step 6: Choose the circuit or electrical device you want to test.

7. 7

   Step 7: Touch one probe to one end of a circuit

8. 8

   Step 8: the other to the other end

9. 9

   Step 9: and note the reading on the instrument.

10. 10

    Step 10: Isolate components in a hard wired electrical circuit to test them individually.

11. 11

    Step 11: 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.

12. 12

    Step 12: Turn the ohmmeter off when not in use.

Detailed Guide

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