### Author Topic: Statistical arrays  (Read 3925 times)

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#### doktor pyta

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##### Re: Statistical arrays
« Reply #50 on: January 02, 2019, 08:43:59 am »
It would be good idea to have individual resistors; T.C. measured.
It may contribute our understanding of the problem.
I have to think how to use my gear to make 8x 4wire measurements at two temperatures easiest way.

At this point my theory of best performance of layout v.2 is that resistors R4, R2 have equal temperatures.
Same with R1, R3.

#### antintedo

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##### Re: Statistical arrays
« Reply #51 on: January 14, 2019, 11:58:05 am »
I found some time to perform TCR measurements. So far only 1 sample of 10k NOMCA was tested.
1:2 divider built out of this sample measured 0.4ppm/K which seems to agree with the results below.

Code: [Select]
No  T1     R1         T2   R2        dT     TCR1   26     10.00243   64   9.99943   38     -7.892   26     10.00286   64   9.99750   38     -14.113   26     10.00363   64   9.99877   38     -12.794   26     10.00189   64   9.99913   38     -7.265   26.5   10.00284   63   9.99927   36.5   -9.786   26     10.00264   63   9.99840   37     -11.467   26     10.00179   64   9.99839   38     -8.958   26.5   10.00230   64   9.99862   37.5   -9.81

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#### Andreas

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##### Re: Statistical arrays
« Reply #52 on: January 15, 2019, 07:25:20 am »
Thanks for the measurement,
I never had expected that the stray between neighboured resistors is that large.
I had expected more likely a rising T.C. from one side to the other or a center symmetrical behaviour.

with best regards

Andreas

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##### Re: Statistical arrays
« Reply #53 on: January 15, 2019, 07:41:18 am »
I would have expected more equal values for t.c. between single resistors as the ceramic area is comparable small so are the resistors and they are manufactured in thinfilm technology, so multiple networks are processed in parallel and films are highly uniform over small areas.

Fluke 8050A | Prema 5000 | Prema 5017 SC | Advantest R6581D | GenRad 1434-G | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work

#### Magnificent Bastard

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##### Re: Statistical arrays
« Reply #54 on: January 15, 2019, 08:34:41 am »
I found some time to perform TCR measurements. So far only 1 sample of 10k NOMCA was tested.
1:2 divider built out of this sample measured 0.4ppm/K which seems to agree with the results below.

Code: [Select]
No  T1     R1         T2   R2        dT     TCR1   26     10.00243   64   9.99943   38     -7.892   26     10.00286   64   9.99750   38     -14.113   26     10.00363   64   9.99877   38     -12.794   26     10.00189   64   9.99913   38     -7.265   26.5   10.00284   63   9.99927   36.5   -9.786   26     10.00264   63   9.99840   37     -11.467   26     10.00179   64   9.99839   38     -8.958   26.5   10.00230   64   9.99862   37.5   -9.81

These results seem suspiciously variant (not the absolute values, but the relative TCRs).  Can you describe in detail how you made these measurements?

#### antintedo

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##### Re: Statistical arrays
« Reply #55 on: January 15, 2019, 11:13:41 am »
These results seem suspiciously variant (not the absolute values, but the relative TCRs).  Can you describe in detail how you made these measurements?
The resistor was soldered on a FR-4 SOIC to DIP converter and attached to a stabilized heater with a pretty large heatspreader in between.
The whole setup was put into a lightly insulated aluminum box.

For every measurement wires were soldered to corresponding DIP holes.
I used 34401A in 4-wire mode to perform 3 measurements: first at ~25C then at ~65C then again at ~25C.
Temperature readout was done with a thermocouple placed near the middle of the package. Plenty of time was given to reach thermal equilibrium after heating/cooling cycle and soldering.

After doing all 8 resistors, I repeated the measurements in the same order as first round of measurements.
I didn't write it down, but I think repeatability of resistor values between two runs was well below 10 ppm, otherwise I would have just discarded the results.
Room temperature measurements after the experiment agreed to 7ppm with measurements taken the day before. I also used VHP101 resistor box as a sanity check.

I think the main downside of this setup was mechanical stability and the need to solder to the board between every measurement, potentially leaving flux and skin contaminants on the surface. I will try to eliminate this and re-test, but it has to wait until the weekend.

I had expected more likely a rising T.C. from one side to the other or a center symmetrical behaviour.
Andreas
I was surprised as well. Out of curiosity I tested one more more sample today and got very different results. TCR was much lower, 3.7 ppm average +/- 1 ppm spread with no obvious patterns. It is certainly possible something was wrong about my initial methodology. This time I paid more attention to handling the board when soldering and fixed the board rigidly using bolts instead of springs.

#### nfmax

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##### Re: Statistical arrays
« Reply #56 on: January 22, 2019, 08:29:08 pm »
Maybe the effect of thermally-induced strain changes from the mounting arrangement? All resistors are strain gauges!

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Smf