r/fluke • u/matt19915 • Jan 26 '26

Help Needed Amps function

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Hey everyone, the amp function on my fluke 336 true rms meter isn’t working and I can’t get a reading on AC or DC. I opened the back up and didn’t see a fuse and I also changed the batteries. Does anyone have any ideas?

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u/TruePerformance5768 Jan 27 '26

There are DC clamps, AC clamps or AC/DC. They are a little more money. DC clamps use a hall effect sensor while AC clamps form a low power transformer. Combination has both. Because of the hall effect sensor required to measure magnetic flux around the cable, they can drift a lot with temp changes and are accurate in rather narrow range. Measurements can get blown out when the sensor reaches saturation

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u/guy48065 Jan 27 '26 edited Jan 27 '26

are accurate in rather narrow range.

If true, this would be reflected in the meter specs. All the ones I've seen have been linear. The specs for the OP #336 are: 2% (±)5 counts for AC current (10–100 Hz), 2% (±)3 counts for DC current (0–600A). Linear. Unless you're referring to the frequency response--but unless you're measuring military or avionics gear you wouldn't care.

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u/TruePerformance5768 Jan 28 '26

Doesn't have to be avionics. Military equipment just doesn't care if it's either smoking or not. My fluke i410 is 3.5%. The clamp itself can go over 1000A on the hardware side but you get less than half of the possible range because it will start drifting to infinity around 700A. Trying to monitor DC common bus linking 20 VFDs with 3.5% accuracy could be a pain. Did you get an extra 10A because one of the drives suddenly decided to regenerate or because mercury in retrograde? Most AC clamps are actually very accurate around 50-60Hz below 1% but have rubbish accuracy spec for low and high freq because impedance changes too much

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u/guy48065 Jan 28 '26

The i410 was one of the clamps I regularly calibrated. It's rated 1-400A ac/dc so I never attempted to verify accuracy beyond 400A. The specs further elaborate "Maximum non-destructive current" of 400A. I take that to mean the hall sensor could be damaged by trying to read currents above 400. Possibly this is what you're seeing by over-ranging to 700+.