EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: dexters_lab on May 06, 2015, 07:45:53 am
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I saw something strange happen the other day, i was measuring he resistance of some of the windings on a transformer and it makes my Keysight U3401A DMM go all wonky after the measurement.
I made a short video of it here;
I would welcome any comments about it, is this something than can be expected to happen or does it indicate some poor design or a fault with my DMM?
I have contacted Keysight, who have not responded yet.
Keysight U3401A Bench DMM Resistance Strangeness (https://www.youtube.com/watch?v=YsoWTwYSoBw#ws)
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I would second your thoughts on the inductive voltage spike. Though i would have figured that some relays would latch/ unlatch for the diode measurement. Then again it still sends a constant current through the diode and measures the voltage, most likely a few mA. Though for the voltage meaeurement probably starts at the high end and drops down in scale.
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Just tried a quick test using my Fluke 89-IV and Keysight 34465A to measure the resistance of a toroidal mains transformer's windings. The transformer is a Noratel TA050/12, which has 2x 115V primaries and 2x 12V secondaries.
Across one primary, the Fluke reads 24.41 Ohms, which seems entirely reasonable to me. It reads the same in auto-ranging mode as in manual (500R range).
If I set the Fluke to the 500k range, it reads -0.05k.
On the 5M range, it reads -0.0009M, and on the higher ranges it reads zero as expected.
The Keysight doesn't fare quite so well on auto-range. I get a reading that's not stable, but hovers around -0.0014M.
In manual ranging modes, it works fine, and I read 24.4643 Ohms or thereabouts. I've no doubt the reading would be stable if I bothered to make a good, clean connection rather than just holding the probes against the transformer leads.
Seems that auto-ranging might be confused by inductance?
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Just tried a quick test using my Fluke 89-IV and Keysight 34465A to measure the resistance of a toroidal mains transformer's windings. The transformer is a Noratel TA050/12, which has 2x 115V primaries and 2x 12V secondaries.
Across one primary, the Fluke reads 24.41 Ohms, which seems entirely reasonable to me. It reads the same in auto-ranging mode as in manual (500R range).
If I set the Fluke to the 500k range, it reads -0.05k.
On the 5M range, it reads -0.0009M, and on the higher ranges it reads zero as expected.
The Keysight doesn't fare quite so well on auto-range. I get a reading that's not stable, but hovers around -0.0014M.
In manual ranging modes, it works fine, and I read 24.4643 Ohms or thereabouts. I've no doubt the reading would be stable if I bothered to make a good, clean connection rather than just holding the probes against the transformer leads.
Seems that auto-ranging might be confused by inductance?
i didn't show in the video as i wanted to keep it short but i get the same effect in manual ranging too, where after measuring i get a permanent offset until i change to volts and then back again
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just had a call from Keysight:
basically, it's a known problem with this particular model
they did suggest i upgrade to a better model, lol... well i guess they would!