[volt-nuts] Cropico DO4A Digital Ohmmeter

Dr. David Kirkby drkirkby at kirkbymicrowave.co.uk
Sun Apr 29 17:18:13 EDT 2018

On 29 April 2018 at 21:57, Nigel Clarke via volt-nuts <volt-nuts at febo.com>

> Sorry, I realise now I could have explained better, I do know what
> transistor it is but that's not the problem, this looks to be quite a
> complex power suply/charger circuit, with at least three unmarked
> adjustment pots so if I change the device, even for the same part number,
> it's quite possible it will need readjustment and that's what I don't have
> any information on.
> Nigel, GM8PZR

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.


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