Electronics > Metrology

Scanner/Multiplexers for voltage references

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bobAk:
What relays are there?  I have a board 7701 2 pcs.

dietert1:
The relays used in the 7706 have a red cover and are labeled "NEC Japan EC2-4.5SNJ". There is a number 389930, maybe a date code. They are single coil latch type relays, mouser have datasheet of Kemet version:
https://br.mouser.com/datasheet/2/212/1/KEM_R7002_EC2_EE2-1104574.pdf.
I mounted the multiplexer in the lower bay with the upper bay empty and with its cover on.

Regards, Dieter

bobAk:
So the relays are the same.  Thanks. I will need to take measurements with a 7701 connector and a homemade cable.  Connector contact material is phosphor bronze.

dietert1:
Meanwhile i solved the USB crashes and there is a complete 24h log now. Results are very similar to what i got before.
The day-night temperature cycle of about 2 °C causes offset variation of about 125 nV.
The third diagram shows the 8 input channel logs with continuous recalibration and stacked by 100 nV steps in order to show how well this is working. Total vertical scale is 1 uV and applies to channel 1. These curves involve a 5x running average.
With 5 second measurement time one gets about 47 nV RMS. This is 0.005 ppm of 10 V - good enough for monitoring a setup of multiple zener based references.
In this test the K2700 performs very similar to a HP 3457A + 44492A scanner plugin that tested with 45 nV RMS previously.

Regards, Dieter

aronake:
I plan to use an Agilent 34970a with a 34904a matrix switch card to have 4 3458a continuously monitor 7 voltage references where all meters measure all voltage references. This will also be a way to monitor the 3458a.

The 34970a and the 34904a are not metrology grade equipment. The 34904a is specified to have a thermal offset below 3 uV. If actual offset is close to 3 uV with much variations on the relays this would not bee good enough for my intended purpose. But usually specifications are very relaxed compared to real performance. Obviously I wanted to test this.

Test setup:
- Well warmed up 3458a, 34970a, 34904a.
- Around 1.5 meter Canare L-2B2AT cable connected to the 4 rows and 7 columns (I did not test the last column). Shield of all cables soldered to ground on the matrix switch card. Canare L-2B2AT is a tradeoff between being thin, being shielded, being flexible, but unfortunately not PTFE but PE insulation. But PE is not too far from PTFE when it comes to electrical characteristics.
- Reason for the length of the cables is that this is the length i will need once i put all in "production" so get a test of the whole system. Not too much care on keeping the cables free from electrical interference. But this will be similar to "production" environment. I do not have enough space to make this great.
- All row wires connected to 1 3458a, and from there connected to one more 3458a. The second 3458a used to validate the first.
- All column cables shorted.

The test:
- Python script to:
- Switch through all switches of the 34904a.
- For each switching of 34904a relay do 7 measurements at NPLC 100 with both 3458a. First one 3458a measure, then the second, then the first again.
- ACAL on 3458a for every third round of switching of the 34904a. The first round after each ACAL discarded in final analysis, as the 3458a take some time to settle in after ACAL.
- Total 20 runs across all switches were made.

Results:
TEMF averaged 123 nV. Max 249 nV and min 32nV.

I took average nV measurement of all measurements on all switches and mapped out as how they are located on the card.

See nV switchmap attached at end of this post.


Generally the result came out much better than expected. 249 nV will not really be much seen on 3458a at 10V. 249nV is around 1/10th of 34904a thermal offset specification. Also cables and electronic interference included here. It is also very clear that different relays have different amount of temperature gradient. The transformer of the 34970a is located close to where the highest thermal EMF can be seen.

I also wanted to check settling time of TEMF after a relay has switched. To do this, I grouped all measurements in which order it was made since relay switched and took average of each group.

Measure   nV
1           117
2           118
3           119
4           115
5           119
6           117
7           116
8           117

Conclusion here is that no settling in time can be observed. TEMF is same for first measurement since relay switched to last.

All in conclusions:
Positively good result and the 34970a / 34904a are good enough for my needs when it comes to having many 3458a monitoring each other and many voltage references.

Improvements that could be done:
Best nV measurement device i have is 3458a. It showed to be good enough to measure what I wanted to measure, so the reasonable approach would be to be satisfied with this. The more fun approach would be to get a nanovoltmeter (2182A or 34420a). That will probably be where I will go next.

Ideas in improvement on 34970a/34904a:
It is clear that the relays close to the transformer show quite a bit more TEMF. I will do some test putting copper sheets on top of the relays to have heat spread out more evenly and see if that reduce TEMF.
 

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