It's a Fluke 77 meter. I've notice when its set to ohms and something with a voltage is measured, it spits out a negative reading, usually around -3 megohms. However, I was measuring a some FETs on a board that was unpowered to make sure there were no shorts, and I was getting a negative resistance reading. Why? Is there some current flow from a cap discharge causing the false reading?
2007-06-07 07:38:30 · 5 answers · asked by nipsy3 2 in Science & Mathematics ➔ Engineering
I have a Fluke 77III right here. The only time I've ever gotten a negative reading was when there was a potential across it.
You must have had a charge built up somewhere. You know those things aren't very accurate at that low of a resistance.
2007-06-07 07:45:14 · answer #1 · answered by ? 5 · 0⤊ 0⤋
Obviously there are some caps. that have a charge leaking through your leads as you take the measurment.
My Fluke 75 will only show 'negative' Ohms when there is a potential present (other than that caused by the current source in the meter).
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2007-06-07 15:34:32 · answer #2 · answered by tlbs101 7 · 0⤊ 0⤋
I have a Fluke 233/A and when the red lead is on a conductor that is hotter than the one that the black lead is on, I get a negative resistance. Likewise switching the leads shows an increased positive resistance. If you've done recent soldering, be sure to let everything normalize for the most accurate readings.
2013-12-30 10:48:05 · answer #3 · answered by Anonymous · 0⤊ 0⤋
"Is there some current flow from a cap discharge causing the false reading?"
That would be my guess,
2007-06-08 07:03:28 · answer #4 · answered by tinkertailorcandlestickmaker 7 · 0⤊ 0⤋
Does it show negative if you reverse the leads? A diode will show positive or negative depending on the direction.
2007-06-07 14:46:27 · answer #5 · answered by stuart b 2 · 0⤊ 1⤋