[volt-nuts] 7081 resistance accuracy issue

[m k]

Hi David,

Yes, the meter has been on for days already. It had just done a long run into a shorting plug that shows much better stability, I suspect a tempco in the opto-isolators that transfer the reference volts, but will carefully consider all possible sources first.
The other option is the input bias current that Mickle found.

Regards,

M K

> From: david.partridge at perdrix.co.uk
> To: volt-nuts at febo.com
> Date: Sun, 20 Jan 2013 11:13:00 +0000
> Subject: Re: [volt-nuts] 7081 resistance accuracy issue
> 
> How long had the meter been powered on for when you started the test?  Think days rather than hours to stabilise. 
> 
> D.
> -----Original Message-----
> From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On Behalf Of m k
> Sent: 20 January 2013 09:06
> To: volt-nuts at febo.com
> Subject: [volt-nuts] 7081 resistance accuracy issue
> 
> 
> Hi everyone, 
> 
> As part of my checking over of the behaviour of the 7081 I ran "mode,testk" and "nines=8" overnight, the result is a swing larger than I would expect!
> 
> max 166.00455
> min 166.00040
> this means a 25 ppm shift 
> 
> The circuit is meant to generate a constant current, so if that constant current can vary by 25ppm over a 20-23 degree house temperature then it is only accurate to 25ppm for resistance measurement except when used as a transfer standard.
> 
> anyone else find a similar shift?
> 
> M K 
>  		 	   		  
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