Re: [volt-nuts] Traveling Standards
I have been accumulating data on the prototype Traveling Standard. If
you follow the "pictures" link from my project page:
you can find a plot of my readings to date and a plot of the results
from a short temperature test.
I'm not sure what caused the shift around 09-20.
I still need to repackage the circuit board into a more conventional
case. If the readings settle down it will be ready to ship.
I'm not sure what caused the shift around 09-20.
Was the reference powered all the time? And your meter too? What tempco has
your meter?
Did you change orientation of the reference (20-30uV is the change that I
have with orientation).
But perhaps you have simply a bad device like my LM399#1
Attached you will find the drift of my References LM399#1 LM399#2 LTZ1000#1
LTZ1000#2
measured as average with two 24Bit ADCs ADC4 + ADC8 (with a LT1027CCN8-5
reference each).
The drift of LM399#2 LTZ1000#1 LTZ1000#2 is mainly equal. -> that what you
see is mainly the
drift of the plastic references (LT1027) of the ADCs caused by relative
humidity.
(Tempco of the LT1027 is calculated out/compensated during measurement).
Solely the LM399#1 drifts uncorrelated -> something is wrong with this guy.
By the way: it would be better for resolution to measure several devices as
absolute and difference values.
with best regards
Andreas
After way too long (boy, having to work really cuts into my hobby time) the
first Traveling Standard is on its way to the first volt-nut that signed up.
I will be reporting results as I get them.
When the unit is returned, I will send it out the next volunteer.
If you have volunteered to measure the TS, please let me have a physical mailing
address to send it to.
If you are interested in participating (I have five more volunteers at this
point) please let me know.
--
Bob Smither, PhD Circuit Concepts, Inc.
---=======
"When I despair, I remember that all through history the ways of truth
and love have always won. There have been tyrants, and murderers and
for a time they can seem invincible, but in the end they always fail.
Think of it. Always."
...Mahatma Gandhi (1869-1948)
---=======
Smither@C-C-I.Com http://www.C-C-I.Com 281-331-2744(office) -4616(fax)
Bob Smither wrote:
After way too long (boy, having to work really cuts into my hobby time)
the first Traveling Standard is on its way to the first volt-nut that
signed up.
I will be reporting results as I get them.
The first measurements are in - see http://www.c-c-i.com/node/160 .
My measurements averaged around 6.99697 for the LM199A and 5.00026 for the MAX6350.
The measurements from a fellow volt-nut with an HP 3458A are 6.997326 and
5.000541 respectively.
The TS will be on its way back to me this week. After I spend some time with
it, I will get it mailed to the next volunteer.
Thanks to all who offered to measure the TS.
If this first result holds my HP 3455A is within its 90 day spec limit after at
least 25 years of not being calibrated.
My 3455A died some years back and has been in storage. I recently got it out
and was able to repair it using the excellent HP documentation that came with it.
--
Bob Smither, PhD Circuit Concepts, Inc.
---=======
A government which robs Peter to pay Paul can always depend on the
support of Paul.
--George Bernard Shaw
---=======
Smither@C-C-I.Com http://www.C-C-I.Com 281-331-2744(office) -4616(fax)
Bob Smither wrote:
The first measurements are in - see http://www.c-c-i.com/node/160 .
Thanks to the volunteer who measured the TS with his HP 3458A. Plots of his
data are here:
MAX6350: http://c-c-i.com/node/162
LM199AH: http://c-c-i.com/node/163
Both units were well within the hoped for +/- 10PPM for the week of
observations. The LM199A was the better of the two.
The TS is in transit. After it is returned I will mail it to the next TS volunteer.
Bob Smither wrote:
Bob Smither wrote:
The TS will be on its way back to me this week. After I spend some time with
it, I will get it mailed to the next volunteer.
I put the TS in the mail today to our second volunteer. I will report his
results as I get them.
Information on the TS is available here:
including the results from Volunteer 1.
Thanks to all who are participating in this project.
--
---===============================
"There are lots of bad governments in this world.
The only bad government we have a right or obligation to change
is the one in Washington, D.C." -- Charley Reese
Bob Smither bob@smither.net
---===============================
The results from the second TS volunteer are in. Here is a summary of the
measurements so far (taking an overall average of the measurements reported to me):
5 Volt (Max6350E) results:
1st volunteer: 5.000538
2nd volunteer: 5.000520 (delta: 18 uV)
7 Volt (LM199AH) results:
1st volunteer: 6.997325
2nd volunteer: 6.997306 (delta: 19uV)
As soon as I get the unit back and test it here for a few days I will send it to
our third volunteer.
The data is available here:
Thanks to my fellow volt-nuts for helping with this project!
Best regards,
Bob Smither, PhD Circuit Concepts, Inc.
---=======
An armed society is a polite society.
-- Robert Heinlein
---=======
Smither@C-C-I.Com http://www.C-C-I.Com 281-331-2744(office) -4616(fax)
Hi Bob,
What a great job you are doing by organizing this cooperative field
comparison! It sounds like a lot of work though!
Looking at the first lab photo brought back memories of where I started
with my new (to me) 3458A three years ago! I hope it is OK to offer
suggestions that will make measuring microvolt levels on a 3458A more
accurate . Similar techniques can be used on any meter though.
I have been periodically monitoring my Datron 4910 and 4912 10V
standards for about 3 years looking at measurement drifts mainly
caused by temperature. I have many hours of recorded data looking at
0.1 PPM resolution drifts in my system. In order to improve data
stability I had to change my measuring technique from a BNC cable with
dual banana adapters (what is shown in the photo) to twisted pair
copper wires or shielded twisted pair wires (22 or 24 gauge) to
minimize input thermal offsets and settling time. Tin plating on the
wires measures about the same offset voltage as copper so it hasn't
been a problem to use it so far. If I put a huge thermal mass on my
input terminals (plastic dual banana plug) it can take many minutes to
stabilize and even then air currents will keep my meter from
stabilizing as completely as it can. Today my meter has about -240nv
offset voltage from a copper wire short but I see -1.2 microvolt with a
shorted dual banana plug, even a gold plated one. I have a shielded
dual banana to BNC adapter that's even worse.
My 3458A is very temperature sensitive so I constantly monitor the
temperature right in front of the input jacks to 0.1 degree C. I try to
keep mine at 23 degrees and do frequent ACAL's and repeat the ACAL if
more the terminal temperature varies much over a degree from 23C. The
TEMP? is also very important to watch and could be used to predict
temperature offset error. The TEMP? creeps up over a few months due to
dust in the filter but it is easy to clean with a little tap water.
The 3458A has a variable resolution feature that can be a problem at
high resolutions. Full DC resolution is acheived at NPLC = 1000. Lower
NPLC levels can be used to speed up measurements if loss of accuracy is
not a concern.
My shop has distinct thermal stratification so I try to keep the test
unit I am measuring at the same height as the meter and close to the
meter when doing accurate work.
As far as the portable standard goes - it would be great if it had gold
plated dual banana spaced terminal posts similar to the 3458A posts for
best repeatability and flexibility but, of course, any jacks will work
if they have enough time to stabilize.
Charlie
On 1/8/2012 8:59 PM, Bob Smither wrote:
Bob Smither wrote:
After way too long (boy, having to work really cuts into my hobby time)
the first Traveling Standard is on its way to the first volt-nut that
signed up.
I will be reporting results as I get them.
The first measurements are in - see [1]http://www.c-c-i.com/node/160 .
My measurements averaged around 6.99697 for the LM199A and 5.00026 for the MAX63
50.
The measurements from a fellow volt-nut with an HP 3458A are 6.997326 and
5.000541 respectively.
The TS will be on its way back to me this week. After I spend some time with
it, I will get it mailed to the next volunteer.
Thanks to all who offered to measure the TS.
If this first result holds my HP 3455A is within its 90 day spec limit after at
least 25 years of not being calibrated.
My 3455A died some years back and has been in storage. I recently got it out
and was able to repair it using the excellent HP documentation that came with it
.
volt-nuts mailing list -- [2]volt-nuts@febo.com
To unsubscribe, go to [3]https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
References
Charlie,
That's very interesting information. A couple of things that I'm curious about:
-
What is your typical TEMP? reading when your external sensor reads 23C?
-
Do you see any difference between averaging 10 readings w/ NPLC=100
versus 1 reading w/ NPLC=1000? That is, if I want to spend a given amount of
time taking a measurement, does it make any difference to let the 3458A do the
averaging over a longer integration time or can I just average multiple readings
with a shorter integration time? -
Have you see any unusual change in output immediately following
ACAL? I haven't
investigated it thoroughly, but I'm seeing a slight increase in DCV
readings immediately
following an ACAL. The offset goes away after a few minutes . See
the attached plot
(with ACAL DC every 24 hours, measurements every 30 minutes, spikes are clearly
seen).
Thanks.
Randy.
Hi Randy,
On 5/8/2012 2:19 PM, Randy Scott wrote:
Charlie,
That's very interesting information. A couple of things that I'm curious about:
-
What is your typical TEMP? reading when your external sensor reads 23C?
It was 36.67 last time I did a DC CAL at 23.0 +/- 0.2C. That was
several weeks ago so it would be higher now. The sun has warmed the
room to 26C and TEMP? is 41.3 now. When I got the unit the last CAL was
done at 39.77C so I guess that the cal lab didn't bother cleaning the
filter or maybe the room was warmer than 23C. -
Do you see any difference between averaging 10 readings w/ NPLC=100
versus 1 reading w/ NPLC=1000? That is, if I want to spend a given amount of
time taking a measurement, does it make any difference to let the 3458A do the
averaging over a longer integration time or can I just average multiple readings
with a shorter integration time?I haven't tryed averaging since just using NPLC = 1000 is simpler and a
bit faster and thoroughly checked out. It takes about 33 seconds per
reading. The end result would mathematically be the same though. -
Have you see any unusual change in output immediately following
ACAL? I haven't
investigated it thoroughly, but I'm seeing a slight increase in DCV
readings immediately
following an ACAL. The offset goes away after a few minutes . See
the attached plot
(with ACAL DC every 24 hours, measurements every 30 minutes, spikes are clearly
seen).Settling errors for DC volts are specified for the 3458A as 0.0001% of
the input voltage step and HP wrote that it's due to source impedance
and dielectric absorption. I don't use early data after ACAL or range
changes since it takes some time for my 3458a to reach equilibrium. The
Agilent 3499 switch requires a delay each time a new input is made to
allow for settling especially for 4-wire ohms.
Thanks.
Randy.
volt-nuts mailing list -- [1]volt-nuts@febo.com
To unsubscribe, go to [2]https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
Charlie
References