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Products => Test Equipment => Topic started by: cantanko on October 10, 2014, 08:14:00 pm

Title: U1253A, resistance, shorted test leads - you'd expect a reading of...?
Post by: cantanko on October 10, 2014, 08:14:00 pm
Hello - long-time lurker, first time poster here...

I've just picked up pre-loved Agilent U1253A multimeter for just over a hundred quid and, surprisingly, it came with a brand new cal certificate from what I consider to be a reputable test house (they shall remain nameless for the time being to protect the innocent / guilty!).

I've been playing around with this thing and, when in resistance mode and shorting the supplied test leads, I get a reading of -0.04?... Now forgive my rubbish physics, but this sounds a little strange...

(https://www.cantanko.com/wp-content/uploads/2014/10/IMG_1406-1.jpg)

My 87V, with the same leads, gives a (far more plausible) reading of 0.10? - I'm assuming this probably means the cal cert is worth naff all?

Any opinions welcome  ;D

Cheers,
Harry
Title: Re: U1253A, resistance, shorted test leads - you'd expect a reading of...?
Post by: Lightages on October 10, 2014, 09:43:59 pm
You have discovered the source of dark energy! :scared:

No seriously, the calibration is off IMHO.
Title: Re: U1253A, resistance, shorted test leads - you'd expect a reading of...?
Post by: cantanko on October 10, 2014, 09:51:36 pm
Yeah - figured as much... Incidentally that was supposed to be a unicode ohm symbol after the readings - seems the act of posting just made me look like I'm a fan of the interrogative  ;D
Title: Re: U1253A, resistance, shorted test leads - you'd expect a reading of...?
Post by: ModemHead on October 10, 2014, 10:54:58 pm
I doubt it's anything to worry about.  I have a Fluke 289 here that will read -0.011 in low ohms mode with a shorting plug on the jacks.  Right or wrong, I always attributed it to software calibration (stored offsets).  Tens of milli-ohms is down in the noise for a handheld DMM using 2-wire method with low current, and you're probably going be using relative mode here anyway.
Title: Re: U1253A, resistance, shorted test leads - you'd expect a reading of...?
Post by: Wytnucls on October 11, 2014, 12:35:01 am
The meter should be reading the test leads resistance, so it is out by a significant amount. I would send it back to the calibration house, if at all possible. If they screwed that one, what else is possibly out of specs?
Title: Re: U1253A, resistance, shorted test leads - you'd expect a reading of...?
Post by: toli on October 11, 2014, 06:36:35 am
I'm not sure I understand the problem here. The manual for the U1253A states for the 500R range "0.05% + 10 counts". So the 10 counts alone are 0.1ohm for that range - meaning it can be as high as 0.14R while you read 0.04R on the screen. So even if its 0.1R as the Fluke says (and who knows if its really that accurate), its still within spec.
Title: Re: U1253A, resistance, shorted test leads - you'd expect a reading of...?
Post by: Wytnucls on October 11, 2014, 07:33:04 am
To be right on the limits of the 1-year accuracy specs, the test leads resistance should be 0.06 Ohm or less. Possible, but unlikely.
Title: Re: U1253A, resistance, shorted test leads - you'd expect a reading of...?
Post by: Neilm on October 11, 2014, 06:08:34 pm
Just check that this isn't one of those meters that allow you to null out the test leads, then helpfully keep nulling after you turn it off and on again. I have seen some like that and it is a pain until you figure it out.