[volt-nuts] Some questions to zeners (1N823-1N829)

[Andreas Jahn]

Hello Tony,

I do not understand your question with thermocouples.
The temperature measurement within ADC13 is done by a NTC.
The thermocouple discussion came up because of the widely used banana plugs 
on instruments.

Most of your questions to LTZ1000 have been answered mid to late 2010 within 
this board.
Day zero of this diagram is the day when I started automatic measurement 
sequences with a relay multiplexer.
ADC13 was included around day 200. Some weeks after first powering and after 
doing all adjustments.
The whole story of ADC13 can be seen in the diagram.
First ageing around 3.4 ppm/khr (light blue) referenced to first powering.
Second ageing 2.4 ppm/khr (pink) due to loading the reference by 15mA over 
night.
After some weeks ageing slowed down suddenly. So I terminated the 15mA 
loading.

My world are the 3 references 1 LM 399 and 2 LTZ1000A.
I compare them annually to 2 Keithley 2000.
Drift is within 1 count (10uV) over 1 to 2 years. (same direction on both 
Keithleys)
LM399 seems to drift upwards. The 2 LTZ1000 seem to drift slightly 
downwards.

Out of 29 AD586LQ I found about 3-4 which have usable parameters.

With best regards

Andreas

----- Original Message ----- 
From: "Tony Holt" <vnuts at toneh.demon.co.uk>
To: <volt-nuts at febo.com>
Sent: Wednesday, January 30, 2013 10:49 AM
Subject: Re: [volt-nuts] Some questions to zeners (1N823-1N829)


> On 28/01/2013 22:47, Andreas Jahn wrote:
>> After a run in phase of nearly 1 year the ageing of ADC #13 stabilized.
>> Currently I compare ADC13 nearly every day with 3 heated references (1 
>> LM399 = LM_2 and 2 LTZ1000A = LTZ_1/2).
>> The last half year the ageing is about 0.5 to 1.5 ppm for 6 months 
>> compared to the heated references.
>> See picture ADC13_longterm:
>> X-Axis is day
>> Y-Axis left is drift in ppm with red = LM399#2, green = LTZ1000A #1, blue 
>> = LTZ1000A #2
>> Y-axis right is temperature in degree celsius of the temperature sensor 
>> near ADC13 reference.
>>
>> By the way: up to now I could not measure any effect which is related to 
>> thermocouples.
>> Ok my temperature step noise is still too high. And probably I am using 
>> the wrong connectors in my tests:
>> cheap D-Sub connectors where a metal shield is equalizing the temperature 
>> of 2 relative close neighboured contacts.
>>
>> With best regards
>>
>> Andreas
> Andreas,
>
> Very interesting results - thanks for sharing your painstaking work. Hope 
> you don't mind me asking a few questions though:
>
> How are you dealing with the issue of drift in the thermocouple 
> measurements (including the cold junction compensation)? Do you calibrate 
> it periodically? Thermocouples aren't noted for high stability - but 
> presumably at room temperature its perhaps not much of an issue.
>
> Do you know what temperature the LTZ1000 references are operating at, and 
> how long have they been operated for - ie. have they been aged prior to 
> starting the long term test? (Presumably the answer to that is the fact 
> that you are showing results from day 460 onwards?)
>
> Have you any insight into how stable the ADC's reference (AD586LJ) is? 
> I.E. Have you made any occasional or periodic measurements with other 
> calibrated instruments during the long term test or is it the long term 
> test results themselves which leads you to state: "After a run in phase of 
> nearly 1 year the ageing of ADC #13 stabilized."?
>
> Thanks, Tony H
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