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How Do I Read an Analog Ohmmeter?

Before direct-reading digital multimeters became readily available, electronic technicians used analog volt-ohmmeters. These meters consisted of a d'Arsonval meter, a regulated power supply, and a network of calibrated resistors. In all settings, the meter simply indicated current flow. In the voltmeter setting the meter was series-connected with a known resistance. Placing it in the ohmmeter function connected the regulated voltage source so the user could determine the value of an unknown resistance based upon the current through the meter. Reading analog ohmmeters is simple once you become familiar with the technique.

Things You'll Need

Resistor of unknown value

Instructions

- 1
  Connect the test leads (wires with probes) to the meter. Switch the selector on the meter to the lowest ohms position. If the meter has a separate power switch, turn it on.
- 2
  Set the meter to the lowest ohms scale. Hold the two probes together and rotate the "Zero Adjust" wheel on the front of the meter until the needle indicates zero.
- 3
  Connect one of the test probes to each lead of the resistor. Polarity is unimportant in the ohms setting. The needle will be all the way to the left of the scale when the probes are not connected. This indicates infinite ohms. If the needle does not deflect to nearly the center of the scale when you connect to the resistor, advance the setting control to the next higher ohms setting. Repeat until the needle deflects to approximately the center of the scale.
- 4
  Find the scale that corresponds to the selector setting. For example, if the selector points to 200 in the ohms function, find the ohms scale on the meter face that reads from 0 to 200. Note the point the needle deflects to on that scale, and read the value to determine the resistance of the component you're testing.

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