Author Topic: T.C. measurements on precision resistors  (Read 220461 times)

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Offline mimmus78

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Re: T.C. measurements on precision resistors
« Reply #775 on: December 19, 2017, 10:35:16 am »

humidity is the most plausible explanation that I found.
(since time constant is several days).
Of course it could also be some relaxation/creeping effect.


Actually, we've found humidity might not be all to blame here - and of course you've ruled out drift in your measurement system (we are always comparing to a known SR-104 Rref standard to help negate equipment drift):

1.  Try testing your resistors in a controlled saturated salt solution atmosphere.  I'd let them run at least a 30 days at 70% and again for another 30 days at 10% humidity.  That will give you some idea of what's going on.  Now conformal coat the resistors and see what changes.

2.  For voltage dividers, it's always better to run the divider on a test PCB in about the same physical arrangement as the final design.  It's also very important to realize the resistors need to be under typical bias condition and typical thermal flow situation as your application - in other words just testing the resistors on a DMM is not the same thermal flow characteristic you're looking at for the real divider.

Another test is to run the resistor divider set under oil, and yet another is to measure the water absorption rate of your components on a sensitive lab scale.   This usually takes a month or two (or longer) oven dry out in the oven - get a baseline weight, and then a month or two exposed to a humidity controlled atmosphere, and see what the mass change was.  The wire itself on a PWW doesn't care about humidity, but you might see some stress issues from the bobbin - but this tends to stabilize over time.   

You'll probably find that the resistance drifts a bit early on, but as the component stress-relieves itself it will become more stable over time - and not as much will be attributed to humidity as you first thought, maybe.  It all depends on how the resistor is constructed. 

What we've found is that running the divider under actual bias conditions and several thermal cycles for at least a few weeks will let you see the system stabilize.

Normally we would not see major changes over a few days time on a well-relaxed PWW divider, so you might be looking at something else.  You do see some yearly drift of course but if you spec the PWW divider resistors to have the same or similar TC you should see a relatively stable divider in RATIO TC, which is what you want normally.  You don't usually care too much about the absolute value of each resistor drifting - but be aware of this effect in balanced differential amps, since sometimes that absolute value change can sneak in to cause trouble even if the ratio TC is fairly steady.

This is also my idea: the grand part of the hysteresis after a change of more than 20°K is not due to humidity..

Unfortunately I only have limited resources of time, number of samples and my reference resistor is the 40K inside the 3458a of witch I don't know the TCR itself ... so my mileage may vary.
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Offline lars

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Re: T.C. measurements on precision resistors
« Reply #776 on: December 20, 2017, 07:31:06 am »
As far as I can see the old 8E16 (non-RoHs version of 8G16) are humidity sensitive. I enclose a graph for twelve years tests of four resistors 100 to 100k. The higher values are much worse than the lower as can be seen. I have tested many 8E16 for quite long times and the spread were large. Eg. 100kohm 8E16 are  around 0.5-2ppm/%RH. As can be seen in the graph the long term drift is low compared to the humidity sensitivity. In the graph the temperature is compensated but even if not, the humidity would be worse and much more difficult to compensate.

For the comment to use bias I don't really understand if it is necessary for the 500mW component with a power dissipation of 0.6mW in the normal LTZ1000 design I guess will be used in?

I once had two 10kohm 8E16 in a +10 to -10V amplifier (so about 10mW dissipation each) they still suffered from seasonal variations. My guess afterwards were that the two 10k 8E16 had different humidity sensitivities.

Maybe 20 years ago I also got two sets of Vishay S102 100, 1k and 10kohm to test for temperature sensitivity at work. The 1k and 10k had far to much hysteresis during test so it wasn't possible to get a temperature sensitivity from that test. This ended up that I checked them for many years at home. The 100ohm had almost no seasonal variations but both the 1 and 10kohm had about 1ppm/%RH.

Lars
 
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Offline try

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Re: T.C. measurements on precision resistors
« Reply #777 on: December 20, 2017, 08:00:15 am »
Hi Lars,

would you mind explaining the y-axis in your graph a bit?
It appears to me that it is referring to a variety of measurement units.

Humidity is expressed as relative humidity times 100.
Temperatur is expressed in Celsius.

But what about the data for all the reference dividers?
Do you plot the relative change of the ratio of the dividers?

Thank you for providing such a long time series!

Regards
try
 

Offline lars

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Re: T.C. measurements on precision resistors
« Reply #778 on: December 20, 2017, 08:44:54 pm »
Hi Try,

Sorry I were sloppy. As you already figured out the temperature is °C and humidity %RH. All resistors (not dividers) are in ppm (parts per million). The resistor values are relative, that is I have applied an offset to scale it readable on the graph. So what you can for example see is that the 100kohm have about 50ppm seasonal variation for about 30%RH variation.

100, 1k, 10k and 100kohm are 8E16 wire wound resistors but the 1Mohm are standard 1% 50ppm/C 0.25W metal film through hole unknown brand. As can be seen it has higher drift per year but not so high seasonal variation. From the scale it has about +20ppm/year drift. I have tested very few MF and it is a lot of brands and types available so I have no idea what is reasonable to expect. What I have seen is that Yaego MF0207 0.1% (thick film) of 1Mohm have had up to 1000ppm/year (0.1%/year)! For lower values the Yaego MF0207 were better, down to below 100ppm/year. For Thin films I have mostly seen 5-20ppm/year for both through hole and SMD0805 I have tested. But as I said I have to little experience to say anything generic. Also remember this is tested without load on the resistors. The resistors normally have been mounted on FR4 boards. Many are in boxes as the attached picture. Between the measurements they are stored in a paper box in my lab with a room temperature of 16-32°C.

The resistors were tested with an HP3456A with 4W OC. But the results are relative to two very stable old GR1440 and series/parallel dividers as SR1010 and DIY but also checked against L&N 40xx, hermetic BMF's from Vishay and AE and old Tettex standards from 100ohm to 1Mohm. The GR1440's have a long term drift that the last 20 years have been below my measurement uncertainties.

Lars
 

Offline bopcph

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Re: T.C. measurements on precision resistors
« Reply #779 on: January 02, 2018, 03:20:55 pm »
The only way to get rid of this is to use materials that are immune to humidity such as metal, glas and ceramics which ends up in hermetic packages.

But it's not humidity only, there are a lot of materials that exibit gas in some way.

Will you care to tell my mass spectrometer that metal, glas and ceramics are immune to humidity ?!?
Yes, water doesn't penetrate any of the 3 materials (ceramics general speaking, I can find a significant number of ceramic type that does)
but you can "store" a significant and measurable amount of water in the surface of all 3 materials.

Even the super glossy polished stainless steel inner surface of my MS will suck serveral 100 ug water from my controlled lab environment
(20 degC, +/- 0.5 - 30-35%RH) if left open for just a few hours.
No, its not like a foggy mirror, you can't see it, and yes the SS is well beyond the dew point  ;)
 
For information:
You can get some epoxies that are quite immune to water - depends on how much you want to pay.


 

Online Magnificent Bastard

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Re: T.C. measurements on precision resistors
« Reply #780 on: January 02, 2018, 05:27:01 pm »
You can get some epoxies that are quite immune to water - depends on how much you want to pay.

Can you elaborate?  Manufacturer and P/N please!
 

Offline Andreas

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Re: T.C. measurements on precision resistors
« Reply #781 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 #782 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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Offline cellularmitosis

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Re: T.C. measurements on precision resistors
« Reply #783 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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Offline TiN

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Re: T.C. measurements on precision resistors
« Reply #784 on: January 16, 2018, 12:24:35 am »
Good. Details and setup? Do tell.
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Online Pipelie

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Re: T.C. measurements on precision resistors
« Reply #785 on: January 16, 2018, 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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Offline cellularmitosis

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Re: T.C. measurements on precision resistors
« Reply #786 on: January 16, 2018, 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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Offline TiN

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Re: T.C. measurements on precision resistors
« Reply #787 on: January 16, 2018, 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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Offline cellularmitosis

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Re: T.C. measurements on precision resistors
« Reply #788 on: January 16, 2018, 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 #789 on: January 16, 2018, 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
 

Offline cellularmitosis

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Re: T.C. measurements on precision resistors
« Reply #790 on: January 16, 2018, 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 #791 on: January 16, 2018, 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 #792 on: January 16, 2018, 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.
 

Online Magnificent Bastard

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Re: T.C. measurements on precision resistors
« Reply #793 on: January 17, 2018, 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 #794 on: January 17, 2018, 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
 

Offline texaspyro

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Re: T.C. measurements on precision resistors
« Reply #795 on: January 17, 2018, 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 #796 on: January 17, 2018, 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-

EDIT: Date code is 1722
« Last Edit: January 17, 2018, 07:07:50 pm by branadic »
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Offline Andreas

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Re: T.C. measurements on precision resistors
« Reply #797 on: January 17, 2018, 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 #798 on: January 17, 2018, 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 #799 on: January 17, 2018, 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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