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UNI-T UT203 Clamp Meter - Calibration?


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#1 Richard10002

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Posted 15 April 2012 - 01:02 PM

Bought this last week on eBay:

http://www.ebay.co.u...2#ht_4879wt_922

Out of the box it consistently reads just over 2 Amps when clamped around nothing but fresh air.

When clamped around the Sterling battery charger wires, it will read say, 68A around the +ve cable and -64A around the -ve cable, (can't rememeber the exact figures).

This suggests it's either reading a natural magnetic field which suggests 2 Amps, or it is calibrated to read 2 Amps when it should read zero, or it is faulty.

It was noticeably cheap, so could it be a fake? Or is this something we have to live with with cheap clamp meters?

Any suggestions? I've emailed the seller,

Thanks,

Richard
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#2 Nickhlx

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Posted 15 April 2012 - 01:53 PM

Bought this last week on eBay:

http://www.ebay.co.u...2#ht_4879wt_922

Out of the box it consistently reads just over 2 Amps when clamped around nothing but fresh air.

When clamped around the Sterling battery charger wires, it will read say, 68A around the +ve cable and -64A around the -ve cable, (can't rememeber the exact figures).

This suggests it's either reading a natural magnetic field which suggests 2 Amps, or it is calibrated to read 2 Amps when it should read zero, or it is faulty.

It was noticeably cheap, so could it be a fake? Or is this something we have to live with with cheap clamp meters?

Any suggestions? I've emailed the seller,

Thanks,



Richard





I got one of those a few months ago - seems fine and reads "zero" when not measuring anything - sounds like it is either mis-calibrated or faulty...

They may replace it if you complain as the postage, whilst it seems cheap or free, must cost them something..

Nick
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#3 by'eck

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Posted 15 April 2012 - 02:42 PM

Bought this last week on eBay:

http://www.ebay.co.u...2#ht_4879wt_922

Out of the box it consistently reads just over 2 Amps when clamped around nothing but fresh air.

When clamped around the Sterling battery charger wires, it will read say, 68A around the +ve cable and -64A around the -ve cable, (can't rememeber the exact figures).

This suggests it's either reading a natural magnetic field which suggests 2 Amps, or it is calibrated to read 2 Amps when it should read zero, or it is faulty.

It was noticeably cheap, so could it be a fake? Or is this something we have to live with with cheap clamp meters?

Any suggestions? I've emailed the seller,

Thanks,

Richard


I think for the price that sort of accuracy is not too bad. I don't think anyone would fake such a cheap one. Prices range from 14 to 33 on the net. They are never going to give the accuracy of a shunt based current measuring device.

I found best price of 78 (inc.VAT) for a Sealey MM405 which I bought.
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Regards - Richard

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There's nowt wrong wi'owt what mitherin' clutterbucks don't barley grummit!

#4 bottle

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Posted 15 April 2012 - 02:54 PM

Specification is given as + or - 2% +3

So I believe this means if the true ampearge is say 100amps then the reading displayed could be in the range of 95 to 105 amps.

So when true amperage is zero then the reading shown could be in the range of -3 to +3 amps.

Therefore yours showing +2 amps is within calibration range.

I think that is all correct, no doubt if it is wrong someone will SHOUT. :D
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Keith.

What you said, what you thought you said and what I thought you said are THREE different things.



#5 steve hayes

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Posted 15 April 2012 - 05:47 PM

Specification is given as + or - 2% +3

So I believe this means if the true ampearge is say 100amps then the reading displayed could be in the range of 95 to 105 amps.

So when true amperage is zero then the reading shown could be in the range of -3 to +3 amps.

Therefore yours showing +2 amps is within calibration range.

I think that is all correct, no doubt if it is wrong someone will SHOUT. :D


No you are right...... I have a Fluke 30Amp clamp meter and the spec for this is not a lot better than you quote +-1% +.1A
These things are effected by external magnetic fields (and lumps of steel - Boat). You do need to make sure that the jaws are properly closed (no muck keeping them open slightly). Also try turning the clamp round so the cable passes through the jaws the other way around so the reading will be negative not positive. What are the two readings? averaging them often makes a more accurate reading.

Steve
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#6 Arthur Brown

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Posted 15 April 2012 - 07:51 PM

My clamp meter has a tendency to have a reading for no current flowing BUT it has a small "CAL" button to zero the scale, does yours have a zero set or calibrate button?
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#7 Richard10002

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Posted 15 April 2012 - 08:07 PM

My clamp meter has a tendency to have a reading for no current flowing BUT it has a small "CAL" button to zero the scale, does yours have a zero set or calibrate button?


I don't think so. It's on the boat so I can't check, but I read the manual from cover to cover, looking for something relating to calibration.

Having said that, if, as seems to be the case, this isn't unusual, I'll do the mental calibration when I use it.

Thanks to all - I'll also see what the seller says.

Richard
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#8 nicknorman

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Posted 15 April 2012 - 08:48 PM

These meters are definitely fake/copies etc. I have one too, for the same sort of price and for the money it is excellent. The current range is 40 and 400A so on the 40A range the 2% would be 0.8A, but the +3 (whatever that means!) suggests that your 2A error is within spec. I don't recall my one having a +3 in the spec. On my one the zero current error is quite low, less than an amp. Perhaps these are rejects from the pukka manufacturer because they are out of spec?

Anyway, for small current measurements an ordinary ammeter that you insert into the circuit is always going to be more reliable. Even if the clamp meter itself was super accurate, as has been suggested stray magnetic fields of which there are plenty on a NB will create significant errors for low current measurement. What clamp meters are good for is measuring large currents eg the 100A or so coming out of your alternator.

Reversing the clamp is a good tip or just bearing in mind the fixed error and subtracting it from the reading. I think you have been slightly unlucky in getting a fairly inaccurate one, but it is within the spec. Reading the spec carefully on ebay purchases is always a good idea!
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