Clamp meter unusual readings

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
107
Hello! I have a Uni-t UT202A+ clamp meter. When measuring current I found that if I move the wire inside the clamp, then the reading changes. The meter is using a current transformer for sensing the current through the measured wire.
I made some tests and I found that, if I measure the current through the wire while powering a 220V AC/1000W heater:
1. With the wire on the upper side of the clamp I=4.710A
2. With the wire on the center side of the clamp I=4.660A
3. With the wire on the lower part of the clamp (the most close to the meters body) I=4.419A
If I just close the clamp against the wire, while powering the same load as above:
1. With the upper side of the clamp I=0.022A
2. With the center side of the clamp I=0.099A
3. With the center side of the clamp I=0.134A
Tested with a UT203R, the value of the current is not varying if I move the wire inside the clamp.

I would like to know if the variations are normal ?
 
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KeithWalker

Joined Jul 10, 2017
2,099
Check the spec of the UT202A+ clamp. I think you will find that all the measurements made with the wire inside the clamp are within the specified accuracy.
 
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strantor

Joined Oct 3, 2010
5,753
Does that clamp meter measure DC? If so it's probably not a current transformer, but a hall sensor.

Try taking your measurements away from other wires and also clean the flats where the clamp meets and make sure they are making good contact.
 

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
107
I calculated the error and it seems that it isn't in the order of 1% variation. If I move the wire inside the clamp, then it shows different readings, sometimes, the difference is about 0.5A (or 500mA).
 

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
107
It is on the 6A scale...

LE: it is very weird that about a few months ago a bought another UNI-T that had the same problem. It was a AC/DC clampmeter.
 
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DickCappels

Joined Aug 21, 2008
8,177
Let me repeat this back -on the six amp scale you see the reading vary by one half amp by moving the wire around?

That sounds broken.
 

strantor

Joined Oct 3, 2010
5,753
Did you "try taking your measurements away from other wires" as I recommended?

Since this is an AC/DC clamp meter it is more susceptible to stray magnetic fields from nearby wires

https://www.fluke.com/en-us/learn/blog/clamps/inside-hall-effect-clamp-meters

Because of the dc magnetic field of the earth and the possibility of other magnetic fields near the measurement site, these clamps require the reading to be "zeroed" before taking a measurement to eliminate offsets.
Also did you read this?
Clamp meters (this one included) specify that the wire should be centered within the jaws for consistency and accuracy.
 

KeithWalker

Joined Jul 10, 2017
2,099
Please re-read post #2. The spec on the 6A range is +/- 4% +/- 10 digits.
If you don't have a user manual, it is readily available on-line.
There is not a problem with the meter.
UT202A_1.jpgUT202A.jpg
 
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Thread Starter

mike_the_begginer

Joined Dec 7, 2019
107
-on the six amp scale you see the reading vary by one half amp by moving the wire around?
Yes.
Did you "try taking your measurements away from other wires" as I recommended?
Since this is an AC/DC clamp meter it is more susceptible to stray magnetic fields from nearby wires
https://www.fluke.com/en-us/learn/blog/clamps/inside-hall-effect-clamp-meters
Also did you read this?
Yes, the measurements were took away from other wires. About 30-40cm from other wires.
This clamp meter is only AC. The previous one - which had the same problem - was an AC/DC clamp meter.
Yes, I also read that the wire needs to be centered
 

KeithWalker

Joined Jul 10, 2017
2,099
Yes.

Yes, the measurements were took away from other wires. About 30-40cm from other wires.
This clamp meter is only AC. The previous one - which had the same problem - was an AC/DC clamp meter.
Yes, I also read that the wire needs to be centered
The meter meets the published spec if it is used correctly. It does not have a problem!
 

panic mode

Joined Oct 10, 2011
2,003
"If I just close the clamp against the wire, while powering the same load as above... (readings are ~0.1A instead of ~4 Amp)"

well you are not supposed to clamp on the wire, that will prevent closing of the clamp jaw and then magnetic core is open. wire need to be inside jaw, close to center and the clamp jaw must be fully closed.
1000W load / 220V = 4.x Amps is reasonable value

if you want to get good measurement, measured value need to be significant for the selected range.
i just don't see measuring mA with clamp meter designed for 600A.

also there was a mention of different type of sensor.
note that type of sensor determines type of current one can measure.
current transformer is only good for AC.
hall sensor can be used for both AC and DC.

either of those two is still only good for relatively coarse measurement (1% at best).
any time you need precision, you need to do it in circuit, using shunt.
clamp is there for convenience, not to compete with the lab instruments.
 
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