[volt-nuts] Cropico DO4A Digital Ohmmeter

gandalfg8 at aol.com gandalfg8 at aol.com
Mon Apr 30 05:16:56 EDT 2018

--Original Message-----

From: Dr. David Kirkby <drkirkby at kirkbymicrowave.co.uk>
To: gandalfg8 <gandalfg8 at aol.com>; Discussion of precise voltage measurement <volt-nuts at febo.com>
Sent: Sun, 29 Apr 2018 22:18
Subject: Re: [volt-nuts] Cropico DO4A Digital Ohmmeter

I see this is a low-resistance (10 u ohm resolution) ohmmeter. Have you any
idea how you are going to check the calibration? I just bought a Simpson
444, which has 1 u ohm resolution. I have not got it yet, but are wondering
how I am going to check the calibration.

0.005% resistors are available from Farnell in a fairly limited number of
values, but certainty not in the range of values needed for a milli/micro
ohm meter.



Well, the Cropico MTS2 test standard suggested in the calibration instructions actually has a specified best accuracy of 0.01%, although with a 3999 display and variable decimal point the DO4A is going to be pushed at times to display to its own spec limits anyway.
BTW the data sheet resolution chart has some errors, the manual is correct.

I certainly won't be buying an MTS2, unless as another Ebay special of course:-), and a set of 6 x 0.01% reesistors from Farnell wouldn't be exactly cheap, but still around half the cost of 0.005%.

So far I've just run it with an external PSU across the battery input and checked it against some Cropico RS3 standards. The 1K standard for example has a specified accuracy of 0.005%, albeit without a current cal certificate, and that did indicate 1.000K on the DO4A, which at least is some encouragement:-)

Nigel, GM8PZR
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