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I have a Uni-t UT210e clamp meter.

I noticed that when measuring AC current, the reading varies if I move the wire inside the clamp. The measured value displayed on the meter is higher when the wire is closer to the upper part of the clamp, and it is lower when the wire is right in the center of the clamp.

Is this happening because when moving the wire inside the clamp, the electromagnetic field around the wire is also moving, making the reading to vary?

enter image description here

Product manual: https://www.uni-trend.com/uploadfile/cloud/English%20manual/General%20Meters/UT210E%20English%20Manual.pdf

Product page: https://www.uni-trend.com/html/product/General_Meters/digitalclampmeters/UT210_Series/UT210E.html

beard999
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    It's probably related to imperfections in the closure of the clamp faces. The permeability of air is 1/1000 that of ferrous materials. Clean the faces of the clamp and try jiggling the clamp to get better face contact. Report back! – Transistor May 29 '21 at 11:00
  • I cleaned the faces of the clamp and tried jiggling the clamp, and I get the following results: https://ibb.co/S3tf7pK – beard999 May 29 '21 at 11:46
  • The information belongs in the question, not in a link in a comment. I've added it in. – Transistor May 29 '21 at 12:02
  • Please link to a product manual. – Andy aka May 29 '21 at 12:18

1 Answers1

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To measure 16 A AC you'll select the 20 A AC range. The UT210E manual say ±2.5% + 5 on the 100 A range but doesn't specify for the 20 A range. This implies that on top of the ±2.5 A accuracy on on the 100 A range that there could be an error of 5 on the least significant digit.

The fact that it is capable of measuring DC suggests that it is using a Hall effect sensor for the AC measurements rather than a current transformer. This may be sensitive to the conductor placement.

The user manual says:

Open clamp head, hook electric wire, place electric wire on geometric center indicated by clamp head, make sure the left and right clamp heads are totally closed. There is no gap between the left and right clamp heads.

enter image description here

Figure 1. The geometric center indicators?

Transistor
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  • I wonder if there are any of these out there that use a Hall sensor for DC and still have a current transformer winding for AC measurement, for the better accuracy you can get with CTs? – Hearth May 29 '21 at 18:57
  • @Hearth, I doubt it. Wouldn't the gap in the core for the Hall sensor mess up the quality of the core for a CT? I'm sure it could be compensated for but in this case I imagine that price is more important than quality. – Transistor May 29 '21 at 18:59
  • Good point, I suppose there's not too much you can do. Then again, clamp meters are already working around a gap where the clamp opens... though the best ones do make that gap as small as possible. I wonder if you could make the Hall sensor element itself out of ferromagnetic material, whether that would impact readings at all... (of course you'd need to electrically isolate it from the core still, so you'd still have a gap of insulation.) At this price point, though, you're right, none of this matters. IIRC that uni-t meter costs $30, hardly where you'd expect a high-quality meter. – Hearth May 29 '21 at 19:05