Author Topic: T.C. measurements on precision resistors  (Read 191820 times)

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Offline Andreas

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Re: T.C. measurements on precision resistors
« Reply #825 on: January 11, 2018, 09:11:16 AM »
Hello,

and here the remaining three 70K 8G16 resistors.
following conditioning has been made:

#4   baked 4 days then 6 days room temp     (so no longer reduced hysteresis visible after 6 days room temp)
#5   baked 4 d / room temp 6 d / cycling 4 d   (this candidate has rather low hysteresis but largest T.C.)
#6   baked 4 d / room temp 6 d / cycling 4 d   (again large hysteresis)

And finally the overview of the measured 8G16 70K resistors.
Compared to other PWW resistors or metal foil resistors these have a rather large stray of the parameters T.C., hysteresis and ageing drift. Compare also here:
http://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg848965/#msg848965

with best regards

Andreas



« Last Edit: January 11, 2018, 04:55:42 PM by Andreas »
 

Offline Andreas

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Re: T.C. measurements on precision resistors
« Reply #826 on: January 13, 2018, 04:37:34 PM »
Hello,

first result of a 120 Ohms econistor 8G16. Datecode 1522

box T.C. measured 8.7 ppm/K over 30 deg C.
hysteresis: deviation up to 45 ppm from LMS approximation.
drift: 10.5 ppm over 4 days.

so around the performance of a 15ppm/K RC55Y metal film resistor. But much more hysteresis than the metal film.
See RC55Y (1K) measurements on bottom of the post here:
http://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg462301/#msg462301

with best regards

Andreas
« Last Edit: January 13, 2018, 05:36:54 PM by Andreas »
 
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Online cellularmitosis

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Re: T.C. measurements on precision resistors
« Reply #827 on: January 15, 2018, 03:47:18 PM »
Andreas, I hope to be able to contribute to this thread soon!  I spent the weekend spinning up a little rig to measure resistor tempco: http://www.eevblog.com/forum/projects/mini-tempco-characterization-rig/

Edit: fixing number of minor gridlines in chart
« Last Edit: January 15, 2018, 04:34:06 PM by cellularmitosis »
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Online TiN

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Re: T.C. measurements on precision resistors
« Reply #828 on: Yesterday at 12:24:35 AM »
Good. Details and setup? Do tell.
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Offline Pipelie

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Re: T.C. measurements on precision resistors
« Reply #829 on: Yesterday at 02:03:53 AM »
Hello,

some results of my brand new VHP101 & VHP202Z,  I'm afraid there is only 20% chance you will get an almost zero TC resistor from the batches your order or so.   |O
 
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Online cellularmitosis

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Re: T.C. measurements on precision resistors
« Reply #830 on: Yesterday at 02:30:25 AM »
Good. Details and setup? Do tell.

Sure!  I put all of the details in another thread: http://www.eevblog.com/forum/projects/mini-tempco-characterization-rig/
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Online TiN

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Re: T.C. measurements on precision resistors
« Reply #831 on: Yesterday at 02:33:29 AM »
Why would you expect zero TC from VPG H/HZ? :) They are specified at 2ppm at best, which your number confirm well with margin.  :-+
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Online cellularmitosis

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Re: T.C. measurements on precision resistors
« Reply #832 on: Yesterday at 06:33:34 PM »
Why would you expect zero TC from VPG H/HZ? :) They are specified at 2ppm at best, which your number confirm well with margin.  :-+

I just measured a 9K9850 VHP202Z at -1.3ppm/K.  What a bummer.  Now I understand what they mean by "0.2 +/- 2 ppm/C".  That means it could be as bad as 2ppm/C.

https://github.com/cellularmitosis/logs/tree/master/20180115-vhd202z

http://www.vishaypg.com/docs/63120/hzseries.pdf

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Offline Alex Nikitin

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Re: T.C. measurements on precision resistors
« Reply #833 on: Yesterday at 07:39:20 PM »
Why would you expect zero TC from VPG H/HZ? :) They are specified at 2ppm at best, which your number confirm well with margin.  :-+

I just measured a 9K9850 VHP202Z at -1.3ppm/K.  What a bummer.  Now I understand what they mean by "0.2 +/- 2 ppm/C".  That means it could be as bad as 2ppm/C.



For this particular resistor you can just add about 3.3 Ohm of copper wire in series and get very close to a zero tempco in this temperature range  ;) .

Cheers

Alex
 

Online cellularmitosis

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Re: T.C. measurements on precision resistors
« Reply #834 on: Yesterday at 08:17:04 PM »
HMM, that’s a creative solution. At 40 AWG that’s only one meter of wire.
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Offline mimmus78

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Re: T.C. measurements on precision resistors
« Reply #835 on: Yesterday at 08:54:24 PM »
Any idea how much copper wire can be stable?

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Offline Kleinstein

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Re: T.C. measurements on precision resistors
« Reply #836 on: Yesterday at 11:06:47 PM »
If not bend too much, the resistance of copper can be relatively stable - it just has the TC as intended in this case.
 

Offline Magnificent Bastard

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Re: T.C. measurements on precision resistors
« Reply #837 on: Today at 03:08:03 AM »
Pure Nickel wire ("Ni200") with a heavy high-temperature coating is much more corrosion resistant than copper, and also has a very high TC (~0.6%/oC).  If you are looking for time stability of more than a few decades, Nickel is the way to go (and you can even consider ordering gold plating on the wire for even better stability).  If you need a lot of resistance, then you might switch to BALCO wire.
 

Offline Alex Nikitin

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Re: T.C. measurements on precision resistors
« Reply #838 on: Today at 03:40:53 AM »
Any idea how much copper wire can be stable?

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There are published designs of copper wire based temperature sensors with better than 10mK stability, so in absence of strong thermal shocks a better than 50ppm long-term stability should be possible. In the practical case of this 3.3 Ohm compensation resistor it's potential instability is reduced by 1/3000 times ratio to the main resistor value, so should not be a problem.

Cheers

Alex
 

Online texaspyro

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Re: T.C. measurements on precision resistors
« Reply #839 on: Today at 04:26:43 AM »

There are published designs of copper wire based temperature sensors with better than 10mK stability, so in absence of strong thermal shocks a better than 50ppm long-term stability should be possible.


The SR104 resistor temperature sensor uses a copper resistor for temperature compensation.
 

Offline branadic

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Re: T.C. measurements on precision resistors
« Reply #840 on: Today at 06:11:30 AM »
Hi all,

we X-rayed some PWW resistors today. Here is what the 8G16D from Rhopoint looks like. You can fairly see the strain-relief construction, but also how they try to decrease inductance, two seperate winding sets with opposite winding direction.

-branadic-
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Offline Andreas

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Re: T.C. measurements on precision resistors
« Reply #841 on: Today at 06:27:06 AM »
Hello,

thanks Branadic,

Question: which date code did you use. Same batch as my 1522 above?

From the construction there should be low influence from the housing to the resistor windings.
(The sealing is only done from one side).
So I do not understand why I have that large hysteresis.

So is it the silicone rubber sealing directly on the windings or something else.

I think its time to measure a "naked" 8G16

with best regards

Andreas
 

Offline branadic

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Re: T.C. measurements on precision resistors
« Reply #842 on: Today at 06:41:22 AM »
Will answer that question tomorrow, as the resistors are still at work for further x-ray pictures.

-branadic-
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Offline mimmus78

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Re: T.C. measurements on precision resistors
« Reply #843 on: Today at 06:55:59 AM »
Any idea how much copper wire can be stable?

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There are published designs of copper wire based temperature sensors with better than 10mK stability, so in absence of strong thermal shocks a better than 50ppm long-term stability should be possible. In the practical case of this 3.3 Ohm compensation resistor it's potential instability is reduced by 1/3000 times ratio to the main resistor value, so should not be a problem.

Cheers

Alex
Copper is ok also from a EMF point of view as resistors leads are also of copper if I'm not wrong. Or not?

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Offline Dr. Frank

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Re: T.C. measurements on precision resistors
« Reply #844 on: Today at 08:51:10 AM »
Hi all,

we X-rayed some PWW resistors today. Here is what the 8G16D from Rhopoint looks like. You can fairly see the strain-relief construction, but also how they try to decrease inductance, two seperate winding sets with opposite winding direction.

-branadic-

Great!!!
I assumed, that the 120 Ohm type would be wound extremely tight to the outer case, but that seems not to be the case.
I've seen the same big hysteresis (and apparent T.C.) like Andreas on this value; the rest of the set was ok.
So there are other explanations to be found.
What about x-ray of a 12k econistor, in comparison?

Frank
 

Offline branadic

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Re: T.C. measurements on precision resistors
« Reply #845 on: Today at 09:07:30 AM »
Be patient, further images of 1k, 12k and 70k (complete resistor set) will follow. I also need to think about possible reasons for that large hysteresis.

-branadic-
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Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #846 on: Today at 11:45:38 AM »
Let's start with the questions about the G.R. resistor first, the rubber silicone filling in theory was put there to help absorb stress between the windings and the bobbin/shell, the problem I found was if the shell is overfilled with the silicone (i.e. no gap between it and the shell) it does just the opposite.  After quite a bit of digging I found that silicone rubber has an COE of 900 microinches/°C, somewhat higher than I thought it would.  So as the resistor gets hotter, everything is expanding and within a certain range, the silicone does absorb some of the stress but after that point it begins 'spreading' the stress around from the expansion against the outer shell and actually increases stress on the windings (even if you've cooked the resistor silly).  I found through actual measurements that this stress takes quite a bit of time to relax and even over a period of days just sitting, the resistors did not return to the original starting points, albeit the differences became smaller with time, almost none of the test resistors went back to the starting resistance.  I also had these tests confirmed by another independent tester.  So that becomes another variable in the stability equation.

Next, the question of how snug the windings are, as indicated in the X-ray, if you look closely at the X-ray, particularly the lower winding, you will see rater uneven, even sloppy turns of wire, not the even turns one would expect, that indicates that the tension of the wire was essentially uncontrolled during winding and during calibration the turns in the upper pi was likely loosened by the calibrator when searching for the correct resistance point.  I noticed that the wire size used in this resistor was unusually small for a 120R0 resistor, not the best idea.  To some degree, loose turns are good except when they are too loose and sloppy, this can cause problems (not so much in low ohms), the wire must be wound with a certain minimum tension, without that the resistors become inconsistent, this tension is taken care of later on.  In the resistor X-rayed, the less than great winding may be because of an inexperienced winder.

Also a problem is kinks or loops in the wire (often caused by insufficient tension while winding or by jerky feed of the wire from the spool), there appears to be a rather sharp bend in the wire at the top weld joint, these can affect the TCR, another point is that G.R. uses alloy 180 ribbon to connect the resistance wire to the lead, this is used by multiple manufacturers as an intermediary since Evanohm cannot be directly welded to a copper lead.  While it is a relatively small resistance, it is also of a higher TCR than Evanohm and is in series with the resistor at both ends, this will cause a slight hyperbolic curve in the TCR line particularly with lower resistances.  The main reason for using the ribbon is the attachment between the lead and Evanohm, as far as 'relieving' stress on the weld, yes and no, while molding the lead/ribbon into the bobbin does substantially prevent external applied stress on the lead from getting to the weld joint, it doesn't protect the weld joint from stress applied inside the resistor and like all welds of this tiny physical size, various factors come into play that can affect the weld joint, in turn affecting the overall apparent TCR of the resistor.

Not to throw bricks at the competition, but I'm trying to illustrate the complexity of the interaction of all the materials that can go into the making of a precision wire wound resistor and also applies to the film/foil resistors as well, there are no absolute solutions to completely fix any of the various causes of stress on the resistor/element.  Each set of materials has its own characteristics and interactions and when you're working in the lower PPM range, everything becomes important and more difficult to adjust for.

Finally, variables change with wire size used, larger wire sizes must be handled differently than smaller wire and the techniques used for winding varies with the size, how the wire is wound onto the bobbin can also affect the resistance.  One other 'myth' I'll pop while I'm at it, the misbelief that reverse winding the pi has a significant effect on overall inductance, it doesn't, measurements indicate that while there is a small reduction in overall inductance, it is not really that significant when it comes to AC signals.  The coupling between pi is quite loose and therefore has little cancelling effect because they are next to each other in series so the flux lines do not cancel significantly, not to mention that the Q of resistors is exceedingly low.

« Last Edit: Today at 12:38:57 PM by Edwin G. Pettis »
 
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Offline hwj-d

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Re: T.C. measurements on precision resistors
« Reply #847 on: Today at 12:25:32 PM »
May I ask here, what the cost is for two kx sets of Mr. Edwin G. Pettis resistors to germany incl. tax, customs fees, sending, packing, approximately to germany?
Sorry, have absolutely no plan for that :-[
  Thanks.
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