Fluke 87-5 Multimeter AC and DC Settings

Imagine a vehicle with a no start condition and a dead battery. Measuring the amperage of a control module using a Fluke DMM (digital multimeter) in AC mode shows a reading of only 25 mA, but in DC mode, a reading of 335 mA reveals the continuous draw that would drain the battery. This type of scenario shows the importance of checking the multimeter's default settings before testing.

 

Versions 1-4 of the Fluke 87 multimeter defaults to reading DC amperage when set on the amperage or milliamp scale. The new Fluke 87-5 meter (version 5), when set on the amperage or milliamp scale, will default to reading AC current. (Fig. 8)

 

If a diagnostic test step is requesting a DC amperage reading to be taken and the meter is set on the AC amperage setting, the meter will display 0 amperage (or close to 0 amperage). This will cause an inaccurate test result that can cause the test to pass or fail when it shouldn't.

 

To avoid an incorrect test result when testing amperage, always check the multimeter's display to make sure it is either on the AC or DC setting. Use the unmarked blue or yellow button (depending on the version of multimeter being used) on the top left of the multimeter to select between the AC and DC readings.

 

- Thanks to David Nowak