[volt-nuts] 1N825 selection, was Traveling Standards ...

WarrenS warrensjmail-one at yahoo.com
Thu Sep 8 20:23:56 UTC 2011


John asked:

>Do you have a feel for how these golden 1N825 tend to be distributed?

The Simple (and useless) answer is:
All depends on just which Golden thing you mean.
As far as the likely spread, Ten to 0ne is a good guess.

Much depends on their burn-in. After burn-in the most important thing is the
manufacture followed by the batch lot.
For any given batch they will generally be very consistent, and get from
near zero to 100% yield.

I don't know which manufactures made the good ones and which where bad.
What I did in the past was sample a few from a batch and if they looked real
good I got more.

There are three different and mostly unrelated basic things that need to be
considered and graded for.
The importance of each will depend on the application.

1) Most important to me is the "PopCorn Noise".
This is small random voltage steps and what limits their usable accuracy as
transfer standards over shorter periods of time of minutes to days.
Values I've seen are under 0.1 ppm to 1ppm  with 1/2 PPM (3uv PP) typical.

2) Second is the TC.  Voltage changes with temperature
It is easy enough to get zero voltage difference at two different
temperatures with most any 1N825 (or better) that I've ever tried by
changing their operating current.
Just how flat the voltage is and how wide the temperature range is and at
what current all depend on the part.
I've seen total voltage changes from under 0.1 ppm to 1/2 ppm over normal
room temperatures of + - 10 DegF

3) And third is the long term ageing rate which causes a slow and mostly
constant voltage change with time.
Until the part is run in at 50ma for a while, their initial drift rate is so
much that you can not do much testing of noise or TC.
One day is the minimum needed for burn-in if you're in a big hurry, A year
if you want to get the best from them.

>From past experience, I'd expect about 25% of the "good brand" to have a
long term stability of under 10 PPM / year after 90 days of burn-in.
One that I've had mostly continuous on for 30 + years is still within 10 PPM
or so.

After finding the best 10% or so, the next step would be to torture them by
cycling their power and temperature, etc, to see how repeatable they are.
That is something that I've not willing done in the past, but I'm now
grading some new ones so I can run those kind of test.


>And, what is the stability of an unselected part?
I think they're guaranteed to be with-in 3%
If you start with a non burned-in part and run it at it's rated current.
The stability will be more in the mV range instead of the uV range.

ws

*******************
******************
[volt-nuts] Traveling Standards - Measuring Protocol
John Devereux john at devereux.me.uk wrote:

Hi Warren,

Do you have a feel for how these golden 1N825 tend to be distributed?
For example. are ~10% of them ~10 times better than the rest in terms of
stability? More like 1%?

And, what is the stability of an unselected part?

Thanks,
John
********************

"WarrenS" <warrensjmail-one at yahoo.com> writes:

> A good thing to include in the "Measuring Protocol"
> The type of filtering used  and a 24 hr plot would be a great thing to
> show.
>
> In the LM399 data reported below, Its noise starts at 10-30 uv PP  (3 PPM)
> Once per minute averaged readings gave 2 uv PP (0.3 PPM)
> 21 min moving average data is below 0.5 uv PP  (under 0.1 PP)
> The PP variation over a couple hours time where the temperature is not
> changing is about 0.5 PPM
>
> What I've seen is that the LM399 has good TC over a wide temperature
> but they
> can be pretty noisy PP short and medium term when measured at the sub
> PPM level.
>
> The total PP noise on the plot I posted of the selected 1N825#2,
> running at its 'Zero-TC' current
> shows about 0.1 PPM variation over the couple hours where the
> temperature is not changing.
> The plot is once per second samples taken from with a 15 sec analog RC
> filter time constant.
> http://www.febo.com/pipermail/volt-nuts/attachments/20110904/15d2a3ab/attachment-0001.jpg
>
> All 1N825 are not the same. Starting with a selected low noise one,
> it must then be aged and run in at 50 ma for a long time before it is
> fully stabilize.
>
> ws
>
> ***********************




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