[volt-nuts] Solartron 7081 NVM FAIL

[David C. Partridge]

Here are links to some photos of the two different references in the 7081s

>From serial number 180 (my working one):

<http://www.perdrix.co.uk/Solartron7081/Reference1a.jpg>
<http://www.perdrix.co.uk/Solartron7081/Reference1b.jpg>

I can't identify what this zener actually is ...

and from serial number 301 (the one with the dead NVM):

<http://www.perdrix.co.uk/Solartron7081/Reference2.jpg>

This one is a 1N829

Dave
-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On Behalf Of Fabio Eboli
Sent: 25 April 2012 20:02
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Solartron 7081 NVM FAIL

> I will try looking in monitor mode tomorrow, but suspect that I will 
> see binary zero or FF depending on HOW the EAROM has failed.

Yes, probably you are right.

>
> Do you have a scanner, it might be interesting to see how they propose 
> doing the zener calibration for the 7061?  I guess you need an 
> environmental chamber, an accurate controllable current source and a 
> logging voltmeter (at least I can provide one of the three, as my 
> other 7081 still works OK).

I had scans already done.
The instructions are very crude:
http://img842.imageshack.us/img842/8948/7061100.png
http://img6.imageshack.us/img6/5324/7061101.png
Here the schematic of the reference:
http://img843.imageshack.us/img843/2945/7061235.png
http://img402.imageshack.us/img402/8248/7061236.png

I imagine that the second order temperature compensation can be problematic in the process, maybe this is why they don't provide instructions to recalibrate the zener.

> The quote from Ametek for a FULL calibration including zener is rather 
> eye watering, and I doubt they would do a zener only calibration (or 
> if they would it would be equally expensive).

Just a question, you can also answer privately, but what is the usual price on the used market for a 7081, good or broken?
I've only seen one on ebay (other than the ones at >1k euro that never sell), and I've never seen one here on the surplus resellers.

> A question for the other 7081 owners:  The zener diodes in this 7081  
> and a 7071 are 1N829 in an orange glass DO7 (I think) case.   The  
> zener in my original 7081 is quite different as it is in a 
> hermetically sealed metal can that looks for all the world like it 
> should hold a crystal.  What is more, it is thermally connected to the 
> AD590 temperature sensor while the other two the diode is about 3/8" 
> away!
>
> What are your zeners like?
>

That's interesting! Have you some photo? :)

Fabio.

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