# EEVblog Electronics Community Forum

## Electronics => Metrology => Topic started by: MasterTech on February 22, 2018, 07:49:20 am

Title: 10k precision resistor project
Post by: MasterTech on February 22, 2018, 07:49:20 am
I'm in the mood of experimenting with the build of a 10k precision resistor. After reading the posts here about standard resistors I've decided to try my own design given the constraint that I'll rely on commercial items only.

This is the design, it will be inside a small metallic box filled with oil (except for the potentiomenter) with pomona 3770 binding posts.
The composite adjusting resistors vary between 9.1 and 10.7 ohm, so each degree of turn of the potentiometer (26 turns) accounts for around 0.2mOhms of change (given a linear curve which is not)

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=397332;image)

Let me know what you think or even if it is an idea worth trying or not
Title: Re: 10k precision resistor project
Post by: The Soulman on February 22, 2018, 08:45:48 am
The trim range is to big, it will be a pain to adjust to read 10.000.xx? on your favorite meter, assuming that is the plan.
After that you're depending heavily on the stability of the trimmer and its accompanying resistors.

The stability of the main 10K resistor is the most important, others can be lower tolerance/higher tempco depending on how much the attribute to the end value, you can calculate what their influence would be.  :)

I'd probably go for a low value r in series with the main 10K and use a high value r in series with a trim pot parallel to the main 10K.
Calculate for a minimum (leave some margin..) trim range.

Edit: It would be helpful to know it's intended purpose and how you are going to adjust it.
Title: Re: 10k precision resistor project
Post by: MasterTech on February 22, 2018, 10:14:38 am
Reducing the trim range is something I still have to look. However note my comment about "given the constraint that I'll rely on commercial items only". Once you come up with a topology, like the one you suggested which is fine, and start crunching numbers you'll realize you need exotic values like 0.33 or 9.9 which are not readily available, and I do not plan to select among a purchase of 50 expensive resistors.

I plan to adjust it with a 3458A and later probably send it to someone to have it checked/retrimmed
Title: Re: 10k precision resistor project
Post by: RandallMcRee on February 23, 2018, 05:33:37 am

I have been measuring a lot of 10K Z-foil resistors lately (VAR and S102K, not the Y series but same technology, similar datasheet). 6.5 digit measurements only, but tcr and hysteresis are readily visible.

So, yeah, 0.2ppm TCR typical is not that typical. Temperature hysteresis is real.

Personally, I would investigate PWWs like Ultrohm. For the same price you can buy several and pick a winner.

See Andreas' thread for measurements which, I believe, confirm my observations.
Title: Re: 10k precision resistor project
Post by: cellularmitosis on February 23, 2018, 05:51:49 am
I am just about to post my own results in Andreas thread.  The summary is that yes, 0.2ppm/C is not what I would call "typical"  :(

Title: Re: 10k precision resistor project
Post by: MasterTech on February 23, 2018, 05:57:57 am
So, yeah, 0.2ppm TCR typical is not that typical. Temperature hysteresis is real
hmm, because of this I was thinking of ovenizing the whole thing to 40C. It is something not common in standard resistors, but I prefer short term stability and would be interesting to see the 1-year drift for this kind of setup
Title: Re: 10k precision resistor project
Post by: cellularmitosis on February 23, 2018, 07:02:30 am
Drift may be higher if you ovenize at a higher temperature.  I'm planning to ovenize my resistance transfer standard as well, but at 25C.
Title: Re: 10k precision resistor project
Post by: MasterTech on February 23, 2018, 07:13:31 am
Drift may be higher if you ovenize at a higher temperature.  I'm planning to ovenize my resistance transfer standard as well, but at 25C.
40C is just a bit higher than the max temperatures I expect where I live, thats why.
Title: Re: 10k precision resistor project
Post by: MasterTech on February 23, 2018, 10:26:09 am
I'll think I'll change the circuit for this one. This way the whole 26 turns of the 10ohm pot will create a change of 0.416 ohms, or 35mOhms per turn (considering its linear which is not)

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=397756;image)

Besides that I'll think i'll put the potentiomenter also inside the oil box with means to be adjusted from the outside

Edit: the schematic had a mistake
Title: Re: 10k precision resistor project
Post by: Conrad Hoffman on February 23, 2018, 01:31:10 pm
That just seems way too complicated when you consider all the internal terminations and whatever problems get added by the physical construction. I'd probably buy as many good 10k parts as I could reasonably afford, then select one that's just a tiny bit high, and apply a pad to that.
Title: Re: 10k precision resistor project
Post by: MasterTech on February 23, 2018, 01:56:08 pm
I'd probably buy as many good 10k parts as I could reasonably afford, then select one that's just a tiny bit high, and apply a pad to that.
That’s boring and same ol same ol, where’s all the fun of building something new then, you and Tin are no fun
Title: Re: 10k precision resistor project
Post by: eurofox on February 23, 2018, 02:28:46 pm
That just seems way too complicated when you consider all the internal terminations and whatever problems get added by the physical construction. I'd probably buy as many good 10k parts as I could reasonably afford, then select one that's just a tiny bit high, and apply a pad to that.

This is my option as well, I got Vishay 10K 0.005% 2PPM for 7 Euros per unit.  :-+
Title: Re: 10k precision resistor project
Post by: quarks on February 24, 2018, 11:40:00 am
It is always good to experiment with new designs, but why tell a good meant suggestion boring?
Title: Re: 10k precision resistor project
Post by: MasterTech on February 24, 2018, 11:59:19 am
It is always good to experiment with new designs, but why tell a good meant suggestion boring?

Because that approach lacks my interest and greatly deviates from the objective of this project?  :-//
Title: Re: 10k precision resistor project
Post by: Vtile on February 24, 2018, 02:01:06 pm
May I ask why you use series pot?

At parallel configuration:
If your fixed value is A and the pot value is 100*A your drop area stays inside 2.5% of the fixed value in aprox. 65% of the control window (pot turns). You might want to calculate which one is better for your application series or parallel pot?
Title: Re: 10k precision resistor project
Post by: MasterTech on February 24, 2018, 03:05:50 pm
I've simplified the circuit to eliminate a few resistors:

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=398344;image)

May I ask why you use series pot?

It mainly has to do with the availability of low TCR good quality precision trimmers, they are made for low Rs, like the Accutrim series from Vishay (attached PDF). Maybe there are others but with Mouser being my preferred distributor this is what they have.
Besides that the series configuration in this case seems ok, the series adjustment varies from 0.5 to 0.916:

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=398347;image)

The area of interest for adjustment of the composite series part is at 0.6667 ohm approximately (ie when the total resistance amounts exactly to 10k). That is not very convenient because by the way because the slope there is high. Still a 15ppm increase in resistance of the 26 turn trim at that point creates an overall change of 1.7uohms at the output terminals. So the sensitivity to its TCR is quite good.
Anyway I'll look If I can shift the area of interest to a place with a lower slope

EDIT: just noticed that lowering the 50M resistor to 20M, the adjusting point moves to 0.833 which is better.
Title: Re: 10k precision resistor project
Post by: Vtile on February 24, 2018, 03:24:18 pm
Have you noticed this piece of information from accutrim datasheet: "through the wiper ± 50 ppm/°C"
Title: Re: 10k precision resistor project
Post by: MasterTech on February 24, 2018, 03:33:54 pm
Have you noticed this piece of information from accutrim datasheet: "through the wiper ± 50 ppm/°C"
Yep, I'm still taking the 15ppm because those TCRs are stated for -55 to +125 and I expect them to be much better around 25º and also I've decided to place the trim inside the oil box (trimmable from the outside)
And still, this is the best trim I have right now
Title: Re: 10k precision resistor project
Post by: Svgeesus on February 24, 2018, 04:07:45 pm
That just seems way too complicated when you consider all the internal terminations and whatever problems get added by the physical construction. I'd probably buy as many good 10k parts as I could reasonably afford, then select one that's just a tiny bit high, and apply a pad to that.

I understand the point I believe you are making about minimizing the effect of all those copper to solder to copper connections in the circuit.

Title: Re: 10k precision resistor project
Post by: cellularmitosis on February 24, 2018, 05:06:13 pm
Your simplified design is similar to the SRX-10k.

https://www.eevblog.com/forum/metrology/teardown-standard-resistors/msg891673/#msg891673 (https://www.eevblog.com/forum/metrology/teardown-standard-resistors/msg891673/#msg891673)

Title: Re: 10k precision resistor project
Post by: MasterTech on February 24, 2018, 05:21:45 pm
Your simplified design is similar to the SRX-10k.

Its seems so, and if I had a custom made 9999.x resistor I could eliminate the parallel with 120Mohms, but commercial resistors are my constraint
Title: Re: 10k precision resistor project
Post by: TiN on February 24, 2018, 05:42:14 pm
TiN is boring? :D
Try to build 5700A from bits and pieces, then you call me boring  :-DD

I'll just leave this here:

(https://xdevs.com/doc/Guildline/9330/g9330_100k.png).
Title: Re: 10k precision resistor project
Post by: cellularmitosis on February 24, 2018, 05:42:36 pm
MasterTech, I'm not sure I understand.  Your 10k Vishay resistors are the same as 9.999k Vishay resistors ordered from Texas Components (which can deliver in 2-3 weeks).  They are both "commercial".  They are both custom laser-trimmed to meet a spec.  The only difference is that with the 10k, they decided what value to laser-trim to, instead of asking which value you wanted.

In other words, they are all "custom".
Title: Re: 10k precision resistor project
Post by: MasterTech on February 24, 2018, 05:57:25 pm
MasterTech, I'm not sure I understand.  Your 10k Vishay resistors are the same as 9.999k Vishay resistors ordered from Texas Components (which can deliver in 2-3 weeks).  They are both "commercial".  They are both custom laser-trimmed to meet a spec.  The only difference is that with the 10k, they decided what value to laser-trim to, instead of asking which value you wanted.

In other words, they are all "custom".
U are right, what I meant is that although all are custom manufactured some are stocked and sold thru distributors and others needs to be backordered. Basically I need a 9999.2, 0.2ppm resistor. For a production unit it may be worth it to order one, but for a one-time project I'm not sure....
Title: Re: 10k precision resistor project
Post by: MasterTech on February 24, 2018, 05:58:34 pm
TiN is boring? :D
Try to build 5700A from bits and pieces, then you call me boring  :-DD
I knew you'd bite  :-*
Title: Re: 10k precision resistor project
Post by: MisterDiodes on February 24, 2018, 07:44:45 pm
Have you noticed this piece of information from accutrim datasheet: "through the wiper ± 50 ppm/°C"
Yep, I'm still taking the 15ppm because those TCRs are stated for -55 to +125 and I expect them to be much better around 25º and also I've decided to place the trim inside the oil box (trimmable from the outside)
And still, this is the best trim I have right now

Not quite.

The Vishay's will tend to have around 50+ppm TC any time you use the wiper - which is "always" (Otherwise why do you have a pot?).  Their datasheet is somewhat fantasy when you actually measure the pot's TC and long term stability.  If you're at DC, we stick with Bourns WW pots if possible - at least their datasheets are more realistic.  You get a little more stepped adjustment effect on the lower values, but on 1k and up values it's really not that noticeable.

On the upside if you use the pots correctly they contribute very little TC as long as the precision resistor they are trimming has a very overwhelming TC effect on the final trimmed value.
Title: Re: 10k precision resistor project
Post by: MisterDiodes on February 24, 2018, 09:16:57 pm
...Remember that a "Standard" reference resistor doesn't necessarily mean "Low TC".  That's why SR-104's have a temperature compensation curve right on the cover.  L & N standard resistors are actually pretty good thermometers too.  It's up to you to maintain the proper lab temperature for best performance.

What you're talking about in a "standard" resistor is -low- long term drift @ a certain fixed temperature.  Normally you want that close to around 20 ~ 25C, 40C is going to probably cause accelerated drift depending on what resistor material you're using.  Devices with very low long term drift aren't that common in the commercial market.

A "Precision" resistor might be something that you could trim up and null out on a resistance bridge to match a good resistor (like an SR-104) for a short term transfer;  the word "short" might be up to interpretation - depending on what you really need and at what uncertainty, since this is the metrology section.

A 3458a isn't really the best resistance transfer device - (or for voltage transfer, despite the claims of the HFL version) - for really accurate measures a resistance bridge + good reference resistor + good null meter are your best friends... Even when you're building you're own "precision" resistor, you'll want to know how well it really works, and how fast is it drifting (it will, guaranteed).

Or at least have some buddies with good Ohms-nut equipment :D

Title: Re: 10k precision resistor project
Post by: Vtile on February 24, 2018, 09:52:45 pm
Have you noticed this piece of information from accutrim datasheet: "through the wiper ± 50 ppm/°C"
Yep, I'm still taking the 15ppm because those TCRs are stated for -55 to +125 and I expect them to be much better around 25º and also I've decided to place the trim inside the oil box (trimmable from the outside)
And still, this is the best trim I have right now

Not quite.

The Vishay's will tend to have around 50+ppm TC any time you use the wiper - which is "always" (Otherwise why do you have a pot?).  Their datasheet is somewhat fantasy when you actually measure the pot's TC and long term stability.  If you're at DC, we stick with Bourns WW pots if possible - at least their datasheets are more realistic.  You get a little more stepped adjustment effect on the lower values, but on 1k and up values it's really not that noticeable.

On the upside if you use the pots correctly they contribute very little TC as long as the precision resistor they are trimming has a very overwhelming TC effect on the final trimmed value.
It is nice when someone who knows backs up ones amateur free thinking.  ;D I think the TC of those Vishay resistors are more for "biasing" use case, not as much as trim resistor. Ie. in case you put one of those to output of voltage reference and the current consumption needs to be in 15 ppm and the output voltage of the wiper is buffered.   ... or something on those lines.

Title: Re: 10k precision resistor project
Post by: Inverted18650 on February 25, 2018, 01:11:29 am
I recently scored these and will donate a set to any/all of you for testing. If interested, just send an offer for \$1 (eBay min) and I will accept( or PM me to set it up). I am currently working on getting my K2000 DMM's to work with LabView and then I plan on trying a few experiments of my own based on forum suggestions. I quickly tested a handful and they seem to be within tolerance. Even at just 5pmm, we may be able to create something cool with a combination of them.

here's the eBay link:  https://www.ebay.com/itm/253445474469 (https://www.ebay.com/itm/253445474469) (edit: all lots are gone)

Title: Re: 10k precision resistor project
Post by: ArthurDent on February 25, 2018, 02:10:11 am
I have 2 HP 11104A 10K standard resistors I picked up some years ago that are nice. They are adjustable and quite similar to the one described in the OP. You can read the technical data and see the innards (starting on page 8 ) at:

http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1966-04.pdf (http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1966-04.pdf)
Title: Re: 10k precision resistor project
Post by: ramon on February 25, 2018, 03:57:55 am
And please can anyone provide detailed information about the thin material layer too. As I don't believe it is polyester (as stated in the HP journals) due to it's high coefficient of linear expansion. Or does it has some glass reinforcement? When I was looking information about the lowest CTE plastics (without glass reinforce) the only one I found was Kapton (Polyimide). And it's CTE is not that low (20) compared to 14 for Evanohm.

High-spec-(unobtanium) space materials (like Novastrat 905 datasheet) says 0 ppm/k between -120 and 20C. Does anyone has a sheet of this? I can provide 0 ppm/k nikrothal lx (evanohm) wire.
Title: Re: 10k precision resistor project
Post by: ramon on February 25, 2018, 04:45:04 am
That's correct. Evanohm (-R and -S) datasheet says 7.22 x10^-6 in/F (12.996 x10^-6 ppm/k). And Nikrothal LX says 14 x10^-6 ppm/K (between 20-300C)
Title: Re: 10k precision resistor project
Post by: Gyro on February 25, 2018, 10:44:13 am
...Remember that a "Standard" reference resistor doesn't necessarily mean "Low TC".  That's why SR-104's have a temperature compensation curve right on the cover.  L & N standard resistors are actually pretty good thermometers too.  It's up to you to maintain the proper lab temperature for best performance.

What you're talking about in a "standard" resistor is -low- long term drift @ a certain fixed temperature.  Normally you want that close to around 20 ~ 25C, 40C is going to probably cause accelerated drift depending on what resistor material you're using.  Devices with very low long term drift aren't that common in the commercial market.

A "Precision" resistor might be something that you could trim up and null out on a resistance bridge to match a good resistor (like an SR-104) for a short term transfer;  the word "short" might be up to interpretation - depending on what you really need and at what uncertainty, since this is the metrology section.

...

Just an off-the-cuff comment... Doesn't that open the option of Copper, at least for some lower value resistors. Granted you need a decent length but it certainly helps with termination and thermal EMFs.

I would have thought that, not being an alloy, it would be very long-term stable and measurable at a specified temperature.

An ovened copper resistor?
Title: Re: 10k precision resistor project
Post by: Echo88 on February 25, 2018, 11:35:09 am
Copper has a coefficient of 4250ppm/K (according to zlymex), so in order to hold the value stable (<= 1ppm) with temperature regulation you would need an absolutely amazing oven to stabilize the resistor within <0,2mK.

Title: Re: 10k precision resistor project
Post by: Gyro on February 25, 2018, 11:44:09 am
Well, that's maybe a small issue (I didn't realize off-hand that Copper was that high!) :D
Title: Re: 10k precision resistor project
Post by: ramon on February 25, 2018, 12:40:21 pm
If I have a 100k wirewound resistor with -4.25 ppm/K, then I just need a 100 ohms copper resistor with 4250 ppm/K to match 0 TCR.
Title: Re: 10k precision resistor project
Post by: cellularmitosis on February 25, 2018, 01:47:05 pm
Title: Re: 10k precision resistor project
Post by: Edwin G. Pettis on February 25, 2018, 05:27:08 pm
Actually, copper's TCR is +3900 PPM/°C, ±5% for 25°C to +125°C and the TCR is +3600PPM/°C. ±5% for +25°C to -55°C, obviously there is no abrupt change in TCR at the 25°C reference point.  One problem with using copper as a compensation resistor is the end product is very non-linear in overall TCR, at and near the reference temperature it will produce a fairly close approximation of a nearly flat TCR curve but it will be very much hyperbolic like Manganin.  So if you're expecting a nice linear compensation curve, it isn't going to happen.  You may get a fairly low TCR over a few degrees but if you're expecting zero TCR, you've got great expectations and little more.

The idea of using copper for compensation is old, been around for decades and in certain circumstances it provides a neat solution but not usually for high precision applications where the temperature is going to be moving around some and you're looking for very low TCR.

As I've indicated before, there are no free lunches, there is always a trade off that has to be made, no way around it.  Don't put too much weight on simulation, those are only approximate at best when it comes to resistance and many other components as well.  I'm not trying to throw water on ideas here but I'm talking from many years of experience, I'm not talking into my hat.
Title: Re: 10k precision resistor project
Post by: MasterTech on March 04, 2018, 02:48:02 pm
Let’s go with an update of the project. Eventually I went with a slightly different approach and components. This is the final schematic:

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=400815;image)

Resistor enclosure
The container is made of copper sheet and the sides will be terminated with precut PCBs. Tin solder is used to avoid leaks. Eventually the enclosure will be covered with a thermal insulation sheet.

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=400819;image)

Heating element and temperature sensing.
I decided that I’d need a heated device cause I can’t control very well the temp everywhere at my lab over the year and because I’m more interested in short term accuracy rather than long term drift. At the lower end of the oil tank I’ve placed an aluminum housed power resistor and a RTD sensor at the top. The RTD sensor is a PPG102A1. The resistor terminals cross the copper wall with a couple of Tusonix feed throughs model 4101-002, small but rated for 10A. Still haven’t decided the RTD amplifier to use. The heating resistor and the 10k adjustable resistor will be separated by a metallic mesh for EM shielding.

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=400821;image)

Eventually I went with the Vishay acccutrim trim for its smooth travel, was tempted to use a bourns wire wound though. The 1ohm resistors are wire wound from Welwyn AS21R00FTR. The trim needs an internal support so I made that with my mill in bakelite. The adjusting shaft was made in the lathe with aluminum rod and features 2 o-rings. This shaft is contained in a methacrylate cylindrical shell.

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=400823;image)

The adjustment range is as follows:

this design: 0.416 ohms
HP 11104A: claims +-30ppm, so 0.6ohms
SRX-10k: 0.666

Main resistor
I chose here a well trusted and very stable wire wound from the HSP series of Ohmite, model HS520A10K00B and manufactured 1 year ago. Internally it is made of 6 sections similar to other resistors seen on this forum (standard resistors thread).

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=400817;image)

This is a 0.1% resistor so depending on the measured value I’ll have to select an appropriate ‘compensation’ resistor. With the 3458A working at a stable TEMP? 34.5º, the resistor at 19º and after proper configuration (ACAL, OHMF, APER 1, DELAY 1, OCOMP ON, NDIG 8, it reads a very stable 9999.55. After heating the resistor at 40º (planned heating temp) it goes down to around 9998.4, so this equals about 6ppm/C for this range. After cooling of the resistor and another ACAL the original value is read back again although it takes nearly an hour to do so.

Given the value obtained after heating the 10k resistor I need to use a 1ohm series resistor, same type as before.

To be continued...
Title: Re: 10k precision resistor project
Post by: amspire on March 04, 2018, 03:21:13 pm
This is a 0.1% resistor so depending on the measured value I’ll have to select an appropriate ‘compensation’ resistor. With the 3458A working at a stable TEMP? 34.5º, the resistor at 19º and after proper configuration (ACAL, OHMF, APER 1, DELAY 1, OCOMP ON, NDIG 8, it reads a very stable 9999.55. After heating the resistor at 40º (planned heating temp) it goes down to around 9998.4, so this equals about 0.06ppm/C for this range.
Don't you mean 6ppm/C ?
Title: Re: 10k precision resistor project
Post by: SirAlucard on March 04, 2018, 05:07:03 pm
So what would you do with such a highly accurate resistor?
Title: Re: 10k precision resistor project
Post by: Edwin G. Pettis on March 04, 2018, 05:28:08 pm
MasterTech,

Your TCR calculation is way off, using your measurements and a 21°C temperature variance, that comes out to 5.476PPM/°C not .06PPM/°C.  Not a bad TCR for an Ohmite resistor.
Title: Re: 10k precision resistor project
Post by: MasterTech on March 04, 2018, 05:40:52 pm
True. Should not be working on sundays... That makes me think because that resistor is 3ppm from -10 to 80deg. Will have to revise the setup
Title: Re: 10k precision resistor project
Post by: Gyro on March 04, 2018, 05:46:44 pm
Good idea on the sealed copper shield, if you want to avoid indeterminate metallic junctions, you can get hollow solderable hermetic feedthroughs too... https://www.ebay.co.uk/sch/i.html?_odkw=glass+hermetic&LH_PrefLoc=2&_sop=10&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xglass+hermetic+feedthrough.TRS0&_nkw=glass+hermetic+feedthrough&_sacat=0 (https://www.ebay.co.uk/sch/i.html?_odkw=glass+hermetic&LH_PrefLoc=2&_sop=10&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xglass+hermetic+feedthrough.TRS0&_nkw=glass+hermetic+feedthrough&_sacat=0)

Title: Re: 10k precision resistor project
Post by: BNElecEng on March 04, 2018, 06:29:54 pm
Hi everyone, pardon the intrusion. I've been following this topic with interest. Since you mention hermetic feedthroughs, does that imply that a vacuum would be useful or is it purely to stop airflow around the resistor?

Title: Re: 10k precision resistor project
Post by: MasterTech on March 04, 2018, 06:31:40 pm
Hi,

because the can will be filled with oil (Shell Diala), that's why the adjusting shaft for the trim has o-rings also.
Title: Re: 10k precision resistor project
Post by: BNElecEng on March 04, 2018, 07:34:25 pm
Got it, thanks. I missed the part about it being filled with oil.
Title: Re: 10k precision resistor project
Post by: Edwin G. Pettis on March 04, 2018, 07:42:28 pm
By the way, that resistor is actually made by Ultronix and labeled Ohmite.....Ohmite bought Ultronix from Vishay a tad over 10 years ago.  Ohmite was strickly a power resistor house before then.  They wanted the rheostat manufacturer that Vishay was wanting to sell and had to take Ultronix as part of the bargain.
Title: Re: 10k precision resistor project
Post by: MisterDiodes on March 05, 2018, 05:09:11 pm
MasterTech,
Just a suggestion:  Watch your current flow on that pot wiper, especially at max rated power dissipation of your box (max voltage input).  You don't want a dry wiper contact, nor do you want over around 200uA.  Otherwise you'll lose stability at that wiper, no matter what pot you use.  "Some" wiper current flow as some 10's uA is always desired during operation, and just keep an eye on that when you turn the pot to its max/min stops.

As a rule of thumb, that resistor just to the right of your pot would normally be -at least- 10X the pot value, or around 100 ohms as a bare minimum value - but that depends on the trim adjustment range you think you need for the resistors you have on hand.

In other words - keep the adjustment range as small as possible.

Title: Re: 10k precision resistor project
Post by: MasterTech on March 05, 2018, 06:08:15 pm
True, I also realized that by using those values Im pushing things a little bit, however for the intended use it should be fine. But maybe I should consider changing those 1s to 5s or 10s at least...
Title: Re: 10k precision resistor project
Post by: zhtoor on March 06, 2018, 01:12:47 am
I thought about buying some VAR resistors, and dipping them into molten PCTFE (aka: "Kel-F")-- this material absorbs and/or adsorbs ZERO water vapor-- this is the only alternative I have found to a glass/Kovar hermetic package.  This idea needs testing though...  ::)

hello,

regards.

-zia
Title: Re: 10k precision resistor project
Post by: TiN on March 08, 2018, 06:02:19 pm
Thank you, Inverted18650! Got my set of neat Caddock resistors to try for stability. Got them started now to add into my temperature coefficient measurement database (https://xdevs.com/article/tcr_test/),

These will take someo 60-120 hours of my four 8.5-digit DMMs to get all data collected.
And as good excuse, I also got myself new PTFE silver-plated copper kelvin cable to build some fixtures.
This is nice cable, fully shielded and robust to use. I'll be making multiple variants, using both Pomona 5406, Pomona 4892 banana jacks (which have BeCu spring contacts) for poor meters like Keithley 2002 and Advantest R6581T. Best performance cables will also have bare-copper spade lugs for proper connections on devices like Keysight 3458A (https://xdevs.com/fix/hp3485a)

Each cable is Kelvin-connected, with four separate conductors to utilize highest precision of the benchtop meters.
I also want to try alternative idea with reverse-connected spade lug as thermal anchor for DUT-resistor mount.

Code: [Select]
`-==================================================================================================¬¦  xDevs.com TEC Experiment kit        -i- Datafile teckit_caddock_test1.csv exists                ¦+--------------------------------------------------------------------------------------------------+¦    GPIB[25] : Keithley 2510                                                                      ¦¦    GPIB[ 2] : Keysight 3458A                                                                     ¦¦    GPIB[ 6] : Keithley 2002                                                                      ¦¦    GPIB[ 3] : Keysight 3458A                                                                     ¦¦==================================================================================================¦¦ Sample       :      169               Meter mode   : OHMFO            Set Temp     :  20.000 °C  ¦¦ Next temp    : 20.000 °C              Measured val : 999.97864710     Process Temp :  19.997 °C  ¦¦ Min temp     : 20.000 °C              OCOMP/DELAY  : 1, 0 sec         TEC Current  :  -0.3215 A  ¦¦ Peak temp    : 50.000 °C              Fixed range  : Configure        Status       :  Hold start ¦¦ Remaining    :  8h 25m 38s            NPLC         :  100.0000        Gain         :  140.0000   ¦¦ Elapsed time :  0h 12m 09s            Terminals    :   FRONT          Intergal     :    0.1000   ¦¦ Progress     :    2.35%               REL Value    :      1E-06       Derivative   :    0.9000   ¦¦                                                                                                  ¦¦  [   154] : S = 20.000 P = 19.998 I = -0.325 A  VAL = 999.9787099 R, PCB_T = 9004.961776 R       ¦¦  [   155] : S = 20.000 P = 19.998 I = -0.325 A  VAL = 999.9786758 R, PCB_T = 9004.962009 R       ¦¦  [   156] : S = 20.000 P = 19.998 I = -0.325 A  VAL = 999.9786614 R, PCB_T = 9004.961039 R       ¦¦  [   157] : S = 20.000 P = 19.998 I = -0.324 A  VAL = 999.9788573 R, PCB_T = 9004.960913 R       ¦¦  [   158] : S = 20.000 P = 19.998 I = -0.325 A  VAL = 999.9787782 R, PCB_T = 9004.962207 R       ¦¦  [   159] : S = 20.000 P = 19.998 I = -0.324 A  VAL = 999.9788177 R, PCB_T = 9004.962189 R       ¦¦  [   160] : S = 20.000 P = 19.998 I = -0.325 A  VAL = 999.9787513 R, PCB_T = 9004.962279 R       ¦L=========================================    -21.623==============================================-`
Will see soon.

Title: Re: 10k precision resistor project
Post by: cellularmitosis on March 08, 2018, 06:42:16 pm
Nice setup TiN  :-+.  Where did you get those bare copper spade connectors?  I had to make my own using acid... what a pain!  https://www.eevblog.com/forum/metrology/diy-low-emf-cable-and-connectors/msg1305061/#msg1305061 (https://www.eevblog.com/forum/metrology/diy-low-emf-cable-and-connectors/msg1305061/#msg1305061)
Title: Re: 10k precision resistor project
Post by: SirAlucard on March 08, 2018, 09:44:54 pm
Nice setup TiN  :-+.  Where did you get those bare copper spade connectors?  I had to make my own using acid... what a pain!  https://www.eevblog.com/forum/metrology/diy-low-emf-cable-and-connectors/msg1305061/#msg1305061 (https://www.eevblog.com/forum/metrology/diy-low-emf-cable-and-connectors/msg1305061/#msg1305061)

Bare copper is nice and all, but what do you end up doing to keep them from oxidizing? Dunno if I'd be able to use them all by the time they turned.
Title: Re: 10k precision resistor project
Post by: cellularmitosis on March 08, 2018, 11:37:40 pm
I know we are getting a bit off-topic here, but I do wonder if there is a counter-balancing effect -- if the thermal conductivity of the copper is so great that even a thin layer of oxide doesn't matter, because the two chunks of (oxidized) copper are held much closer to thermal equilibrium.

Then again, perhaps copper oxide is a thermal insulator?  Also, the thermal EMF of copper oxide is a killer (something like 4000uV/C?).

I also wonder what is meant by "copper oxide" when quoting that gigantic thermal EMF figure.  Are we talking about the slightly dull look on copper which has sat out for a few days?  Or are we talking about the green statue of liberty?
Title: Re: 10k precision resistor project
Post by: hwj-d on March 09, 2018, 12:36:05 am
(Should i post it?)  :)

OT:

use Coke!

No joke, i use it for my motorbikes alloy wheels and spokes, old chromium car bumpers, and other valuable scrap metal stuff. For that i always have a coke spraybottle and a rag with me.  ;D

But hold on, what the heck does my sister doing there in YT...  :-DD

;)
Title: Re: 10k precision resistor project
Post by: Inverted18650 on March 09, 2018, 01:15:36 am
Its hard to rationalize the silver plate, and then gold plate but I see how it important it is for this level of accuracy. I just ordered some kaowool to improve my mini-foundry and want to experiment with pouring my own pure copper spades as well. I do have some old scrap gold I could try, but truthfully, not only would I literally be throwing away gold, but if I went that far, I would have to go and spend another \$500 on cables. I am not sure I can justify it. Stoked to see the results and thank you for all the hard work.
Title: Re: 10k precision resistor project
Post by: Vgkid on March 09, 2018, 03:16:02 am
You guys know you can buy copper spade lugs , right. :o
Slcp-20 is what you need. 8)
Title: Re: 10k precision resistor project
Post by: SirAlucard on March 10, 2018, 06:55:47 am
I also wonder what is meant by "copper oxide" when quoting that gigantic thermal EMF figure.  Are we talking about the slightly dull look on copper which has sat out for a few days?  Or are we talking about the green statue of liberty?

I don't think we'd be able to get it to a green oxide like the statue of liberty. However definitely the darker dull copper look. I mean imagine it would actually insulate the copper a bit. Since it's forming a layer on top of the copper.
Title: Re: 10k precision resistor project
Post by: MasterTech on March 17, 2018, 12:33:25 pm
To give shape to the copper enclosure I took a plastic rod and milled it to have a planar face and two longitudinal groovings

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=404539;image)
(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=404541;image)

After that I inserted in the bottom side of the enclosure a PCB with a conductive mesh soldered to it, this separates the heater from the resistor itself

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=404543;image)

After putting all in place, filling with oil at 45º and sealing the fill gap, this is the result. All the feedthroughs in the upper side are Tusonix 2461-001-X7V0-102PLF

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=404545;image)

I also took 4 golden binding post from a broken advantest R8340A I have, they are thicker than pomona 3770, so 40€ saved there.

(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=404547;image)

Now I'll have to build container box, temp control, etc...
Title: Re: 10k precision resistor project
Post by: TiN on March 17, 2018, 08:58:55 pm
Nice SFRS (Smiley face resistance standard)  :-+.
Title: Re: 10k precision resistor project
Post by: quarks on March 18, 2018, 06:25:47 pm
your binding posts look very much like BP-1000 which are available from IET (see att.)
(https://www.eevblog.com/forum/metrology/10k-precision-resistor-project/?action=dlattach;attach=404894;image)
Title: Re: 10k precision resistor project
Post by: Inverted18650 on March 18, 2018, 11:51:24 pm
MasterTech: this is great. Thank you for posting.
Title: Re: 10k precision resistor project
Post by: Conrad Hoffman on March 19, 2018, 03:00:52 am
\$69 for a binding post? Each? Seriously?
Title: Re: 10k precision resistor project
Post by: TiN on March 19, 2018, 04:11:45 am
Yea, I'll go with Low Thermal ones for 36% of that cost. They also look much nicer than these.  :-/O
Title: Re: 10k precision resistor project
Post by: MasterTech on March 19, 2018, 07:49:20 am
your binding posts look very much like BP-1000 which are available from IET (see att.)

Based on dimensions it seems so. The pomona 3770 look like a kids toy compared to these sturdy ones.

Quote
MasterTech: this is great. Thank you for posting.

Thanks. There are a couple of details when building hermetic oil cans like these. Specially the thermal expansion coefficient of oil is not negligible. That's why I made that planar face with groovings, and thats why it was filled with warm oil, I prefer it to shrink when it is cool rather than expand when heated
Title: Re: 10k precision resistor project
Post by: eurofox on March 19, 2018, 08:01:39 am
Yea, I'll go with Low Thermal ones for 36% of that cost. They also look much nicer than these.  :-/O

Where do you get those "cuties"?  :-DD
Title: Re: 10k precision resistor project
Post by: SirAlucard on March 19, 2018, 03:23:13 pm
\$69 for a binding post? Each? Seriously?

I was thinking the exact same thing.. >.< I mean I guess they're gold plated so ehhh? I wouldn't really want to pay that much regardless for some bindings.
Title: Re: 10k precision resistor project
Post by: Edwin G. Pettis on March 19, 2018, 04:56:27 pm
ESI/IET binding posts have always been over priced, nothing exceptional except the cost.  I've seen the BOM pricing on things like a SR1 transfer standard, if you bought all of the parts separately it would cost much more than what they charge for the SR1.
Title: Re: 10k precision resistor project
Post by: qihe_kim on March 27, 2018, 07:26:32 am
This new design is pretty good .
Title: Re: 10k precision resistor project
Post by: HighVoltage on March 27, 2018, 09:38:45 am
\$69 for a binding post? Each? Seriously?
And I thought that \$20 for a LowThermal binding post was a lot.