[volt-nuts] Traveling Standards
warrensjmail-one at yahoo.com
Fri Aug 26 18:25:41 UTC 2011
>I appreciate the offer of a 1n825, but the TC is too large for
>this purpose. I also suspect it will be noisier than the LM199a.
"ZERO TC" means that over some temperature range there is NO significant
change in the output.
This family of zeners have a reasonable wide and flat room temperature True
"ZERO TC" current point that can easily be found and set.
Parts can be selected with noise and stability under 1 PPM, better than any
399's that I've tested.
Also they are hermetically sealed and have few of the problems others have
My experience with 399's after months of long term test is,
they are great for having a very wide temp range low TC,
but they are not so good for noise and long turn stability at the sub PPM
Holding a part at 90 degC is how you burn them in to age them 64 times
not how to hold good long term stability
from Bob Smither smither at c-c-i.com
Thank you so much for the great responses! You have all given me a lot
to think about.
Andreas mentioned the lm339. One candidate I am considering is the
lm119ah. Of the references I have at hand (lm119a, lt1027bcn, and
max6350cpa) the lm119a looks the most promising. Andreas mentioned that
humidity and stress can cause several ppm errors. The lm119a is in a
hermetic to-46 package in a thermal shield - so hopefully those effects
will be minimized. The idea that the orientation matters is a new one
for me. I will be sure to mark "TOP" on the final package.
Fred advised against the use of pots. I agree. I was thinking of just
using the raw reference output. For my purposes, I don't really care
what the voltage is as long as it is stable and can withstand shipping.
Warren - I appreciate the offer of a 1n825, but the TC is too large for
this purpose. I also suspect it will be noisier than the lm119a.
Dick and Charles M. - thanks for offering help with this project! I
will contact you off list for your address when I have a traveling unit
prepared and will welcome your measurements of it.
Charles S. - your understanding is correct - I would ship the unit to
anyone that is willing to measure it for me. You idea of shipping it
powered up deserves some more thought. One concern I had about this was
the added weight of the batteries for shipping. It may be an even trade
against having a transformer / rectifier / capacitor to make the
required power supply level.
Thanks all! Now to do some serious design and construction.
If you want something Kiss simple that will more than do what you're asking
Take an AGED & SELECTED 1n825 type zener. (or 1n827, 1n829)
Select a stable resistor that will apply it's measured "Zero TC current"
(which is generally between 4 and 9 ma),
at say 15.000 volts or whatever stable PS voltage you care to use.
Measure the zener's voltage and with only two parts Plus a PS and some fun
Volt nut time you have a 6.2xxx volt reference.
If you're interested, I'll send you the zener, because I got a lot of them
on EBay a long time ago when they where only 1 cent each.
[volt-nuts] Traveling Standards
Bob Smither smither at c-c-i.com
Fellow voltage aficionados ,
If this has already been discussed - my apologies. I could not find
this topic in the past several months of list archives.
Like many of us, I have an ever growing collection of voltmeters and
related instruments. Like the man with two clocks who is never sure of
the time, I now have enough volt meters to have doubts about all of them.
So - I was wondering if those on this list with really good voltage
measurement capabilities would be willing to help those of us without.
What I have in mind is creating a small voltage reference circuit based
on one of the many available IC references that is stable enough in both
time and temperature to use as a transfer standard. I am thinking that
the actual voltage is not important, just the stability. Using the ICs
that I am familiar with the actual reference voltage would be around 5,
7, or 10 volts. Said reference would be mailed to a willing list member
who would record his reading of the reference and mail it back.
I don't have such a reference yet, but have breadboarded a couple and
the idea seems like it might work.
My first objective would be to obtain a reference that I could use to
get all my meters to agree. Since the best meters I have are an HP3455A
(best accuracy about 20 - 40 ppm, and only for 24 hours) and an ancient
(but very usable) Fluke 883AB (best accuracy is 100ppm), I would be very
happy to have a reference that I could trust to 10ppm.
So - two questions for the list:
1. Does this sound feasible? Am I overlooking anything that would keep
me from being able to transfer a 10ppm known reference?
2. Any list members that would be willing to help with this? I
envision mailing a small package with the reference in it along with an
enclosed, postage paid, return box. I am asking for a member that would
take the reference, apply power, let it warm up, record the room
temperature and the reference voltage to within 10ppm, and return it to
me. If you prefer to respond off-list - smither at c-c-i.com.
BTW - I live in Friendswood, Texas (near Houston). Any fellow nutters
close enough that I could hand deliver the reference?
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