Electronics > Metrology

ADR1001 - Ovenized Voltage Reference System

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Dr. Frank:
iMo,
I think your measurements using the 3458A will be done quickly. Have fun!

Here's a recent stability measurement on the ADR1000, and its Allan Deviation.
That indicates, that a sampling interval of about 20..40sec will give best StD performance for the 3458A.
I.e. NPLC 100, 10..16 samples is sufficient

I will have a closer look on the 3458A stability directly after an ACAL..
Thanks again for the hint to the latest 3458A manual from March 2023, page 77, that 15min. of waiting time after an ACAL DCV should be obeyed.

Frank

iMo:
Hi Frank!
Thanks for the hints on the 3458A measurements, unfortunately the 3458A is in a permanent action during working hours this summer, thus I've made measurements with the Fluke 8508A only.. 3458A in October/November this year most probably. There is still LAB1 with the Fluke 8588A and with a planned measurement in August this year.
Anyhow, I incorporated your hints into below measurements, at least I hope so  :D

BTW - I've got an info from ADI the ADR1001 will most probably be released in FEB 2024..

####

A new LAB measurement today - this time in LAB2 and with Fluke 8508A.

The previous measurement with the same 8508A in the LAB2 (April 18th):

Vref =  9.9998697
Vref = -9.9998745  at T_amb=21.1C, T_board=35.49C, AC powered.

This time aprox 5.5uV higher at T_amb=23.0C, T_board=35.52C, battery powered.

Below the results - the measurements were performed in a sequence from "A" to "O".
The green 10xFast measurements - the math has been performed inside the Fluke.

The shot as usual for demo purposes, during the measurements the myADR box was placed about 50cm off the meter.

Dr. Frank:
Hello iMo,
many thanks for your measurements.
The Fluke 8508A should have very similar noise figures compared to the 3458A.
I don't quite understand, which NPLC number you have used, or what means "SLOW" and "FAST", so to compare your measurement with the NPLC 100 on the 3458A. A NPLC 100 measurement takes 2sec sampling and 2 sec Auto Zero, so about 4.1 sec in total.
20sec each measurement on the FLUKE 8508A, does that indicate NPLC 500 or even NPLC 1000?

The StD values seem to be much too high, I always achieve around StD = 120nV or less on the ADR1000.
On the usual LTZ1000 references, I see slightly higher noise.
Therefore, I suggest that you do an absolute noise measurement.

Btw: I have to build an ADR1001 board as well, as I got one sample here.

Frank

iMo:
Yep, the 0.6-0.7uV STDEV is in range I get with my 34401A measurements at 100NPLC and over 100 samples (in quiet periods).
There are some results with around 0.3uV - that is definitely off my 34401A capabilities, indeed.
It could be the opamp (OPA189) in my wiring is causing that? Cables and the air drafts caused by the air-condition?

Has to be measured by the experienced voltnuts here who are having those nice LNAs :)

The NPLC number of the Fluke5808A in "slow" and "fast" settings - hmm, I have to investigate :)

Slow - ~20secs per sample
Fast - ~6secs per sample - I did it with NRDGS=10, performing 10 samples in series, then it printed out the Mean and STDEV, thus the "measurement" was 60secs in total.

Dr. Frank:

--- Quote from: iMo on July 19, 2023, 01:46:49 pm ---Yep, the 0.6-0.7uV STDEV is in range I get with my 34401A measurements at 100NPLC and over 100 samples (in quiet periods).
There are some results with around 0.3uV - that is definitely off my 34401A capabilities, indeed.
It could be the opamp (OPA189) in my wiring is causing that? Cables and the air drafts caused by the air-condition?

...

Slow - ~20secs per sample
Fast - ~6secs per sample - I did it with NRDGS=10, performing 10 samples in series, then it printed out the Mean and STDEV, thus the "measurement" was 60secs in total.

--- End quote ---

So the FAST measurement is comparable to the NPLC 100 measurements with the 3458A.
You'll always see a convolution of noise from the ADR1001, the OpAmp and the 8508A noise.
Your OpAmp will presumably not contribute that much, as well not the FLUKE 8508A.
I think that the ADR1001 itself is more on par with the LM399, than with the ADR1000.. don't know why.

I'll have to build my sample asap, to find out.
Frank

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