DIY 10K low TC home lab referance - Page 1
Forum section: electronics / general

author: kj7e
author_rank: Frequent Contributor
timestamp: May 17, 2018, 11:07:46 pm
content: I put together a simple yet very stable, low TC home lab 10K reference just for the heck of it. The centerpiece is a Vishay VHP101 oil filled hermetically sealed 0.005% tolerance part - Y407810K0000V9L. While this is no replacement for a real secondary standard with a linear TC and predictable drift, this will make a nice cost effective reference to use around the shop with more than acceptable performance. The case is a small but heavy duty (thick wall) plastic Hammond box with a copper EMI/RFI inner coating - 1594RBBK. The thought here was to provide a slight amount of thermal stability at the same time as provide a guard path around the resistor. The posts are Pomoa 3770's for the 4W and 3760 for the guard. The only down side with the plastic case is the binding posts can be forced to apply mechanical stress on the leads to the resistor, I tried to add some strain relief on the leads. Most of the time I will be using a shielded 4w lead with spades, so binding post stress should not be a big issue.A few days ago I did a TC sweep and comparison to a Visahy Z201 (10K, 0.005%), I was impressed with the results;Z201: 18-28C = 0.8ppm/C. 10-40C = 0.7ppm/C.VHP101: 18-28C = 0.05ppm/C. 10-40C = 0.05ppm/C.Anyway, if your like me you rather look at the photos than read about it;

author: CalMachine
author_rank: Frequent Contributor
timestamp: May 17, 2018, 11:33:15 pm
content: Lookin good!!

author: hwj-d
author_rank: Frequent Contributor
timestamp: May 17, 2018, 11:46:33 pm
content: QuoteMaybe an inner steel plate with flattened holes, like the molds from the Pomona plastic bushings?

author: kj7e
author_rank: Frequent Contributor
timestamp: May 17, 2018, 11:51:49 pm
content: Quote from: hwj-d on May 17, 2018, 11:46:33 pmI actually thought about doing just that, but after it was assembled.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 18, 2018, 12:18:52 am
content: That fancy copper lined case probably cost more than the die-cast aluminum ones I use for everything.Nice project. Thanks for showing pictures. One day I'll be able to make charts like that but not yet.Respectfully,George Dowell

author: kj7e
author_rank: Frequent Contributor
timestamp: May 18, 2018, 12:27:39 am
content: $11 from Mouser for the Hammond 1594RBBK box.$61 from Texas Components for the Vishay Y407810K0000V9L resistor.$10 each for the 3770 binding posts and $5 for the 3760.

author: zhtoor
author_rank: Frequent Contributor
timestamp: May 18, 2018, 12:48:14 am
content: @kj7enice buildhow about a precision 10K thermister (kelvin sensed) also?btw. what is your measurement setup?best regards.-zia

author: kj7e
author_rank: Frequent Contributor
timestamp: May 18, 2018, 02:19:26 am
content: A temp sensor here wont yield much benefit with this build. There will likely be more annual shelf life drift than the TC within the normal room temp range (23C +or- 5) and the TC for the VHP101 is not very linear, so computing projected TC error is not very accurate here.I use a Keiithley DMM7510 and Keysight 34465A. My TEC box is a bit crude at the moment, but I have a new project on my bench I started on today to address this

author: HighVoltage
author_rank: Super Contributor
timestamp: May 18, 2018, 11:53:22 am
content: Nice and compact built!Your VHP101 seems to be right in the middle between the binding posts.How did you decide which side to use for sense and which side is force?I have always placed the resistor as close as possible to the force terminals.May be it is not needed.May be even better for mechanical stress to keep the resistor in the middle?

author: eurofox
author_rank: Unknown
timestamp: May 18, 2018, 12:10:59 pm
content: Quote from: HighVoltage on May 18, 2018, 11:53:22 amI place the resistor in the center as well and always use tick copper conductor.

author: eurofox
author_rank: Unknown
timestamp: May 18, 2018, 12:25:35 pm
content: I just order a 10K 0 PPM resistor:Resistance 10 kOhmsTolerance ±0.005%Power (Watts) 0.3WComposition Metal FoilFeatures Moisture Resistant, Non-InductiveTemperature Coefficient 0.0ppm/°COperating Temperature -55°C ~ 125°CPackage / Case RadialIs 0 PPM really possible?

author: kj7e
author_rank: Frequent Contributor
timestamp: May 18, 2018, 12:52:35 pm
content: HV, in theory it would be best to place the resistor as close to the sense binding posts as possible. With a 4W Kelvin setup, the Force side should burden all lead resistance and the Sense side should be as close to the DUT as possible with minimal lead resistance. After reading the Standard Resistor teardown thread about 20 times, I decided it must not make much difference in the real world and to follow the examples from Fluke and others;https://www.eevblog.com/forum/metrology/teardown-standard-resistors/It really does not matter which side is force or sense in my case. So again I followed what seams to be the industry standard and put the Force on the Left.eurofox, no such thing as a 0ppm TC. Also, the best TC specs from Visahy are typical values, not factory tested and guaranteed. You will need to do your own testing to really know what you have. I think I got lucky with my sample.

author: quarks
author_rank: Frequent Contributor
timestamp: May 18, 2018, 12:56:47 pm
content: Looks nicely made, possible improovements could be to add a heatsink and a temp sensorsee example from Dr. Frankhttps://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg464413/#msg464413

author: kj7e
author_rank: Frequent Contributor
timestamp: May 18, 2018, 02:26:17 pm
content: Quote from: quarks on May 18, 2018, 12:56:47 pmHi quarks,I think that device of Dr. Frank was for TC testing, so high thermal conductivity and low gradient was important. This box is just a reference and not for TC testing use. The enclosure design goals for this project was, remove air drafts, static field and some EMI/RFI protection, and add some additional thermal stability from outside ambient influences (such as the A/C coming on or the shop door opening with a cool air draft). This is why I chose the copper lined plastic enclosure over aluminum. Also, this gives me a true guard path around the resistor. It seems to work well, its not sensitive at all to handling the enclosure while measuring, but if you put your hands near the unshielded test leads you will see the static charge influence.For TC testing, I have a new thermal box I'm building on my bench now. That WILL have a 4 wire PT100 and other sensors, its a heavy thick wall aluminum box with uniform heating elements, but this will be saved for a separate thread.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 18, 2018, 03:49:13 pm
content: "For TC testing, I have a new thermal box I'm building on my bench now. That WILL have a 4 wire PT100 and other sensors, its a heavy thick wall aluminum box with uniform heating elements, but this will be saved for a separate thread. "I for one can't wait for that report.George Dowell

author: martinr33
author_rank: Frequent Contributor
timestamp: June 14, 2018, 03:40:29 am
content: I made a copy using a Vishay 0TC part - much appreciate the idea! Mine's in a metal box with a thermistor. I used the 0.0% TC unit from Digi-Key.

author: kj7e
author_rank: Frequent Contributor
timestamp: June 14, 2018, 05:10:28 am
content: Quote from: martinr33 on June 14, 2018, 03:40:29 amPosting this now requires you to post up a photo.

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 14, 2018, 06:17:02 am
content: Quote from: kj7e on May 18, 2018, 02:26:17 pmWell , my design is indeed intended as a secondary resistor standard, not only for T.C. testing, and temperature balancing and measurement is strictly required for any reference resistors, see esi SR104 box.Your box has several bugs:- Too thick copper wires .. these are heat sinks and create temperature imbalance via the measuring cablesDue to 4 wire Kelvin connection, location of soldering does not play a role.You also should have avoided heating the VHP resistor during soldering, so these thick copper wires are no good.- missing aluminium or copper block, assembled to case - your setup creates further temperature imbalances between case and resistance element.The oil filling would also short temperature gradients- missing thermometer to precisely determine T.C. in first place, and in use would give the opportunity to precisely determine its R(T), again see esi SR104.The oil filled hermetically sealed Vishay resistors are extremely stable over time, the specification is < 2ppm / 6 years for shelf life, which seems to be correct from my long term monitoring of five VHP202Z.So it's really a pity that you regard this resistor as being shabby.

author: kj7e
author_rank: Frequent Contributor
timestamp: June 14, 2018, 06:32:42 am
content: All good points Dr. Frank. Ill keep these in mind for v2.

author: eurofox
author_rank: Unknown
timestamp: June 14, 2018, 01:10:36 pm
content: Quote from: Dr. Frank on June 14, 2018, 06:17:02 amI build one using the same resistor but mount it in an aluminium box, use wires with similar diameter of the resistor wires, use the full length of the resistor wires and put clip on the wires to bypass the heat during soldering.

author: 001
author_rank: Super Contributor
timestamp: June 18, 2018, 01:02:06 pm
content: Sorry for stupid question:Can I buy similar resistors on Ebay?Can I use some wirewound resistors from old resistance decade?

author: eurofox
author_rank: Unknown
timestamp: June 18, 2018, 04:43:54 pm
content: Quote from: 001 on June 18, 2018, 01:02:06 pmYou can buy it from Mouser, they ship free of charge above 50€ to Europe in just 2-3 days and since this resistor cost almost 50€ you just need to ad some small parts.With respect to old wire wound resistor you can use it but will not be the same result

author: pizzigri
author_rank: Regular Contributor
timestamp: January 18, 2022, 05:06:09 pm
content: Sorry to reply at such an ancient post, but was thinking about using a low tempco trimmer to trim a slightly lower 10k resistor to tune it to a perfect 10k.I wanted to use a standard 71-Z201T10K000VB Vishay resistor with a 0.2ppm, choosing one that measures around 999,995 or so and add something like this: Y005610R0000K0L 10R Trimmer so that I can reach a perfect 10k... the tempco of that trrimmer is 15ppm but on 10 Ohm, and it's really cheap compared to the 10ppm part which is like 60 Euro each. This one goes for around 18 Euro.And obviously ask the help of some merciful soul here so that it can be tuned to that value on a real voltmeter, 7.5 or even 8.5 digit machine - without spending a fortune.Nicest machine i own is a 34410A, plus another classic 34401A.Reasoning behind this and not choosing a single fixed resistor of the correct value, maybe with like 1PPM, to trim the Foil resistor: I dont want to make it hard for whoever is doing me this favour to do a very tedious operation of soldering the tuning resistor(s) or purchasing lots of different and expensive parts to do this. All the friend would have to do is leave it on a bench for a day or so and then tune it with the trimmer noting the temperature at which the calibration was done.what do you think?

author: Harfner
author_rank: Contributor
timestamp: January 18, 2022, 07:21:25 pm
content: Why do you need exact 10K? A known (small) difference works as well in most cases.

author: mzzj
author_rank: Super Contributor
timestamp: January 18, 2022, 08:26:36 pm
content: Quote from: pizzigri on January 18, 2022, 05:06:09 pmtrimmers are usually bad idea for anything super accurate. Secondly it is usually better to add large value resistor+trimpot in parallel to trimmed resistor to make the contact resistance variation smaller.Sneaky bastards at Vishay specify C.R.V 3 to 10 ohms without telling what it means (contact resistance variation)10 ohm random contact resistance would make your project futile if you used 10 ohm trimpot in series. Better way would be something like 100M fixed resistor and 10k trimmer in parallei with your precision resistor.

author: HighVoltage
author_rank: Super Contributor
timestamp: January 19, 2022, 08:15:24 am
content: Quote from: pizzigri on January 18, 2022, 05:06:09 pmWhen I started with precision resistors many years ago, I also had "only" a 34401A and a 34410A as my best instrument and a low Ohm series trimmer worked perfectly and I was really happy with my first 10k "standard".It's only when you go down the rabbit hole of more accurate ppm and higher precision of a 3458A that a series trimmer might not be the best solution.

author: pizzigri
author_rank: Regular Contributor
timestamp: January 19, 2022, 10:33:32 am
content: Quote from: mzzj on January 18, 2022, 08:26:36 pmUhh but what kind of resistors should those be? A 100M resistor with high accuracies and low tempco is likely going to be hugely expensive. Can you suggest a bom and example I could follow? And Ulf, I will never be able to afford a 8.5 meter, especially for the huge hurdle and cost of calibration.... I am just trying to have a better “standard” than the single Vishay resistor I built some time back without having any possibility to bave a real idea of its value.

author: KT88
author_rank: Frequent Contributor
timestamp: January 19, 2022, 11:36:15 am
content: There are (at least) two reasons for a parallel trimming arrangement:1. any series elements hamper the thermal conditions at the contacts of the main resistor like added TCs and different thermal conductivity...2. If the trimming range is say 10ppm only this part is affected bei variations of the large trimming resisor (100ppm of 10ppm for example).

author: pizzigri
author_rank: Regular Contributor
timestamp: January 19, 2022, 12:10:16 pm
content: However, the precise resistors to be used are going to be really difficult to find.... the proposed 100M +10K resistor +10K frimer is going to yield about 5000 ohms.... to have 10k the calculator at Digikey says I need a 20.1k resistor and 20k trimmer plus the 100M resistor. That really makes it complicated. And I do understand the advantages of parallel resistors, I have gone through the great post with the teardown of resistance standards, but my needs are of the simplest design possible for calibration so not to burden some merciful EEVblog member taht may want to help with the actual calibration and also ease of construction, availability of the resistors and reasonable cost - I would reuse as much as I can what I have, the metal box, Pomona contacts and maybe the Vishay resistor of my standard (which on my 34410 meters as lower than 10k, at least after a couple hours of measuring ). Both 34410 and 34401 are still in calibration.

author: mzzj
author_rank: Super Contributor
timestamp: January 19, 2022, 03:53:45 pm
content: Quote from: pizzigri on January 19, 2022, 12:10:16 pmI guess my explanation wasn't enough obvious: Connect 100M and 10k pot in series resulting adjustable resistor from 100M to 100.1MNow connect that parallel with 10k precision resistor and you get adjustment range from 10k||100M = 9,999k to 10k||100,1M 9,9990001kThat is actually way too small adjustment range even for super accurate resistor( I pulled the example numbers out of hat)Lets try again: Select 10,0155k precision resistor and connect 6M to 7M variable resistance parallel to that (6M resistor + 1M trimpot)You get trim range from 9998,8 to 10001,2 ohms.Now your 1M trimmer 100 ppm tempco has practically zero effect on end result(100ppm trimpot tempco would cause 0,0002 ohm error or 0,02ppm)6M resistor tempco is also largely irrelevant as 100ppm tempco would have 0.2ppm effect on the final value.There is also some traps with this approach if you go too deep in the ppm rabbit hole..

author: pizzigri
author_rank: Regular Contributor
timestamp: January 19, 2022, 04:38:17 pm
content: Ahhh i actually got it backwards, now it does make sense!!!OK so to go on to the practical side... I would need a resistor that gives me a 0.5% tolerance, so that buying like four/five of these resistors I could actually find a 10,0155k value, BUT with a good tempco of say 0.2%. I looked up on Mouser and could not find such a resistor... other possibility, contact Vishay and have them build a custom Z Foil resistor, doable but at unknown cost (and I suppose very steeeeep cost). I find it really difficult to do....and as I said, it would be used as a reference for my lab, which at best has good 6.5 digit capability.Im a bit demoralized.