Fluke SL935 Resistance Standard project (rare prototype teardown included) - Page 1
Forum section: electronics / general

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 04:06:58 am
content: Wonder what TEA got to greedy TiN this time? You guys will never guess, but many would surely want this!Hint, it made by Fluke, uses something from Fluke 732B, but it is no 732B.Read the rest about SL935EDIT 8 May 2017:Livestream recording of SL935 cable connections fix and assembly in 732B-7001 chassis.YoutubeSchematics for resistor standard was recovered, and oven settings captured.Initial data after reassembly with oven working revealed <0.5ppm difference to standalone measurement I made week ago.

author: TheSteve
author_rank: Unknown
timestamp: April 28, 2017, 04:42:05 am
content: I know! But I won't say...

author: tszaboo
author_rank: Super Contributor
timestamp: April 28, 2017, 09:01:24 am
content: Something with a battery, powered all the time?

author: Echo88
author_rank: Frequent Contributor
timestamp: April 28, 2017, 09:03:17 am
content: You must have a very good position on Santas Naughty or Nice-List.

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 11:02:08 am
content: Yes, battery, and supposed to be powered all the time.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: April 28, 2017, 11:25:45 am
content: Hmm... 5790B?CheersAlex

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 11:28:00 am
content: 5790B don't have battery to power.Actually the thing it rather small. It's only 30% of the package on the photo on the left side, rest is 5700A transformer assembly

author: dr.diesel
author_rank: Super Contributor
timestamp: April 28, 2017, 11:33:31 am
content: No idea, but I already want at least 3-4 of them.

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 12:25:09 pm
content: I wouldn't mind few spares too.Oh, did I mention it's black?

author: Kefka Palazzo
author_rank: Newbie
timestamp: April 28, 2017, 01:13:43 pm
content: Fluke 732a?

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 02:00:12 pm
content: You saw black Fluke 732A's?Last time I've checked those are beige white.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 28, 2017, 02:18:44 pm
content: “I know what this is. This is an espresso machine. No, no wait. It’s a snow cone maker. Is it a water heater?”

author: nadona
author_rank: Regular Contributor
timestamp: April 28, 2017, 02:19:22 pm
content: 732B

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 02:21:22 pm
content: It's not 732B, but it does have three digits in model number.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 28, 2017, 02:23:50 pm
content: Something made by a competent artisan?

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 02:26:05 pm
content: I've heard so. Surely parts used came right from some serious gray beard-designed gear.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 28, 2017, 02:28:10 pm
content: 792?Else why even make us?Quote

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 02:33:30 pm
content: Nope, 792A is about twice as large than this, even without battery block.And I've already posted about 792A, sothat cat is out...I'm just curious who is hardcore enough precision-nut to know about this thing, as I discovered it just few weeks ago. Was enough for me to start throwing cash at seller though.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 28, 2017, 02:42:12 pm
content: It's either long EOL or my google skills are in poor shape today. I'm not a precision-nut either.But my last guess is an 752. It has no battery though.Nothing else really fits the shape that is in catalog today. And you don't have pictures of it on your website.

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 02:45:34 pm
content: 752A not black either.

author: SvanGool
author_rank: Regular Contributor
timestamp: April 28, 2017, 03:20:50 pm
content: Fluke 731B

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 03:31:39 pm
content: Hm, it's sorta black. But no, I have no interest in 731's, sorry.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 28, 2017, 03:37:11 pm
content: Did you buy a temperature reference?

author: HighVoltage
author_rank: Super Contributor
timestamp: April 28, 2017, 03:38:37 pm
content: Quote from: TiN on April 28, 2017, 02:21:22 pmMay be 4 x 732B to make a 734A full rack?

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 03:47:19 pm
content: Left 732B is not in the sequence.No, it's not one 732B, not two 732B, not any amount of 732B'sWell, maybe it's 30% of 732B, but anyhow it doesn't have this model number.

author: ap
author_rank: Frequent Contributor
timestamp: April 28, 2017, 03:52:14 pm
content: 732B external battery charger?

author: tszaboo
author_rank: Super Contributor
timestamp: April 28, 2017, 03:54:09 pm
content: So it is 3 digit, blacknot a 732Bnot a 731Bnot a 734A because wrong shape and even you are reasonable.not a 792A because you already have one.and battery powered, so probably not their shunt resistor.Must be the battery pack for a 792A.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: April 28, 2017, 03:56:11 pm
content: So simple.Transfer switch for 792A.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 28, 2017, 04:10:02 pm
content: You are liking this aren't you?

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2017, 04:23:39 pm
content: NANDBlog, doktor pytaSorry folks, it's nothing related to 792A, that would be too easy guessapQuoteThis one is on Fedex now, delivery target next Tuesday

author: SvanGool
author_rank: Regular Contributor
timestamp: April 28, 2017, 04:35:58 pm
content: Quote from: NANDBlogQuote from: Tin1 The heater of a 732B: an Alox (aluminum-oxide) substrate based power resistor ?or2 The front panel of a 732B?

author: Vgkid
author_rank: Super Contributor
timestamp: April 28, 2017, 05:25:08 pm
content: Was it the prototype precurser to the 732. I saw a teardown on the volt-nuts mailing list/bbs-38.

author: mimmus78
author_rank: Unknown
timestamp: April 28, 2017, 08:38:48 pm
content: Two pages and still no reply.This is a torture.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: April 28, 2017, 09:08:55 pm
content: SL935

author: CalMachine
author_rank: Frequent Contributor
timestamp: April 28, 2017, 11:24:39 pm
content: Quote from: ZeTeX on April 28, 2017, 09:08:55 pmTell the man what he has won!

author: Macbeth
author_rank: Super Contributor
timestamp: April 29, 2017, 01:37:21 am
content: Quote from: TiN on April 28, 2017, 03:47:19 pmThis must be the world famous Fluke 219.6B, surely?

author: TiN
author_rank: Super Contributor
timestamp: April 29, 2017, 05:49:47 am
content: ZeTeX wins a thank youAll my money budget depleted to thank any more.It's only oven assembly with resistor standard guts inside and refaced 732B front panel.That's why I bought 7001 battery block, which is essentially everything else. So I can plonk this prototype inside, hook it up to oven and get it nice and stable.Maybe I can find a spot for KX LTZ reference inside the oven, so I can get 10V out of it too. That would be perfect 5700A calibration travel standardAt least that's how I comfort myself doing such purchases.

author: Vgkid
author_rank: Super Contributor
timestamp: April 29, 2017, 06:09:49 am
content: Woah, I'm really looking forward to this one.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 29, 2017, 11:46:46 am
content: S/N 001 ?

author: CalMachine
author_rank: Frequent Contributor
timestamp: April 29, 2017, 01:15:24 pm
content: Quote from: TiN on April 29, 2017, 05:49:47 amShe's a beauty!!I am interested in what its values are

author: tszaboo
author_rank: Super Contributor
timestamp: April 29, 2017, 01:15:49 pm
content: Let me get this straigt. It is a resistance standard, with battery backup and heater. That sounds just bad. Although, I understand you have all the tools to calibrate 3458As now.

author: EEVblog
author_rank: Unknown
timestamp: April 29, 2017, 01:29:56 pm
content: Quote from: Jeroen3 on April 29, 2017, 11:46:46 amYeah,

author: TiN
author_rank: Super Contributor
timestamp: April 29, 2017, 05:18:28 pm
content: I don't know any history or previous owner of this unit but my best guess of this was something like this:One of Fluke standards/metrology lab managers got tired of hauling SR104s and packs of oily Fluke 742A/Thomas resistors around to calibrate 5700A/5720A, gather a team and said :- M: Hey guys, we have those nice 732B's, which are real bobby dazzlers, how about we take one 732B and butcher it up to convert into resistor standard- Somebody from calibrator repair line: Hmm, I can donate stash of dead ohm boards from 5700A's for this fun- Somebody from assembly line: sounds like a one shift break job to me..- Somebody from ID team: I can stick some black tape and add some funny looking silkscreen, no worries.- Accounting: Hey wait, what I do for missing parts in database?- M: Just put it under some unused model number, let's do it! Call it 744A...- DBA: mm,, 744 already used for calibrator...- M: Whatever, call it Standards Lab 935 then! I need this thing tomorrow to calibrate that stash of 5700As!...week after...- Here's the box, we made it for 1 ohm and 10Kohm, stable enough to transfer resistances for 5700A cal. So it's a perfect match for 5700A....year after...- New accounting hire: What is this SL935 thing? We don't sell this product, what to do with it?- Just toss it into reject bin, I don't know what that is.... some time after ...Box travels around swapping owners, till finally ends up in my greedy handsMy best guess. If somebody from Fluke reads this, and actually knows, I'd love to hear.Oven and resistors might sound bad, but it may not be that simple. For calibration or transfer purposes it might be better to have larger but known drift of resistance, instead of varying output due to tempco. Oven can be set low enough, to be just over the ambient. I don't know how hot 732B ovens usually run (yet).

author: HighVoltage
author_rank: Super Contributor
timestamp: April 29, 2017, 05:26:00 pm
content: And how should we ever have guessed this one?And how exactly did this one end up in your hands?Amazing!Can not wait for tear down pictures.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 29, 2017, 05:28:43 pm
content: At least I know how I came across that lone reference oven on ebay. Some sacrifices must be made.

author: TiN
author_rank: Super Contributor
timestamp: April 29, 2017, 05:45:41 pm
content: Many sacrifices are required. That's the way it works.HighVoltageI paid in gold for it, it wasn't easy, but my grip was firm. I was hunting down the 5700A transformer assembly, and after deal was already done, guy sending a photo of this thing asking "maybe I want this too?". Hell yes, I want, especially after seeing what's inside.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 29, 2017, 05:48:11 pm
content: It's almost believable but I don't think you could ever come across a stash of dead 5700A boards.

author: TiN
author_rank: Super Contributor
timestamp: April 29, 2017, 05:54:16 pm
content: That's one mean joke... I hold EEVBlog responsible! Chassis under bag unfortunaly not Fluke's, that's semiassembled 8753A VNA, which just sits there for almost a year already. Have nice thick layer of dust on it.

author: Vgkid
author_rank: Super Contributor
timestamp: April 29, 2017, 06:12:30 pm
content: I'm looking forward to this.Heck I have an ovenized resistance reference. Ok it is not overly accurate, resistors are not low TC(2 are Vishay hermetic power resistors, Why they could use more precise resistors + external trim network)left box

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 29, 2017, 06:16:22 pm
content: They need to be organized by slot number.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 29, 2017, 07:05:50 pm
content: As far as I know, the 732B runs a 45°C, it's described somewhere in the manual, I think.The 5440B at least also keeps its reference ovenized at 50°C, and its resistors at about 55°C, so that the T.C. of the resistors is eliminated, as well as any power dissipation (esp. at 1kV output).Therefore, the stability is greatly increased, and I don't think, that the drift is greatly enhanced at these temperatures, as resistance wires are much more stable compared to silicon structures, at comparable temperature elevations. Therefore, drift should be < 1ppm/yr. as well.Compare that to Edwin Pettis' very interesting description of PWW technology.Frank

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: April 29, 2017, 08:33:29 pm
content: For a precision wire wound resistor, the operating temperature is not particularly a concern, whether operated at 23°C or 60°C or something else, as long as the resistor is rated for that temperature and properly processed (if intended as a reference resistor) it will remain stable with stable temperature, the higher temperatures do not affect the wire as far as aging characteristics and if processed correctly, the remaining stresses, whatever they may be, will also be stabilized to a high degree. A well designed and processed PWW resistor will exhibit very minimal drift as long as its environment is also stable. The resistor must be designed for the specific intended use, a standard off the shelf resistor, even a very good one, will not be quite as stable in the short term at least.If you are going to insist on a high standard performance level, you are going to have to specify the conditions and pay for the extra needed processing to achieve it. You cannot compare one grade of resistors against another with different performance parameters and expect the same levels. You aren't going to get an SR-104 for $100, maybe a good used one for $2,000, you have to pay for the performance you want, it doesn't come cheap. It is apples and oranges, they are all resistors but they are not all the same.I have built high performance resistor standards in the past, they cost a lot more than the regular grade resistors I normally sell and take time to manufacture. Just because they are PWW resistors and similar, they are not the same.

author: nidlaX
author_rank: Frequent Contributor
timestamp: April 30, 2017, 09:21:27 am
content: Goddam. TiN always delivers!

author: TiN
author_rank: Super Contributor
timestamp: April 30, 2017, 11:16:07 am
content: Some first checks..1 Ohm: Median 1.000059 Ohm vs 3458A, TC <2ppm/K over 3C span, can't tell, readings too noisy10 KOhm: Median 9999.990 Ohm vs 3458A, TC <0.3ppm/K over 3C spanNo special processing/connections, no shielding from drafts, etc. Oven not connected to anything. 3458A ACAL ALL every 0.4c, so essentially it's comparison of SL935 vs HP's 40K reference resistor TCR.I'll need to code some python to use 6221 as reversible current source to get much better data off 1 ohm, with Delta-measurement method.

author: VintageNut
author_rank: Frequent Contributor
timestamp: April 30, 2017, 06:06:05 pm
content: Quote from: TiN on April 30, 2017, 11:16:07 amThe micro-ohm errors in the 1-ohm measurement can have very long time constants to settle to zero IF you can get all of the connections of the circuit to be at the same temperature (no thermal gradients). Otherwise you are measuring the 1 ohm resistor and some number of thermocouples.The 6221 can help, but the uncertainty of the 6221 is not metrology-grade.

author: TiN
author_rank: Super Contributor
timestamp: April 30, 2017, 06:16:27 pm
content: Uncertainty of 6221 wouldn't matter in bridge configuration or even in simpler setup with two 3458A's monitoring both resistor and current source.

author: e61_phil
author_rank: Frequent Contributor
timestamp: April 30, 2017, 07:12:20 pm
content: Quote from: TiN on April 30, 2017, 06:16:27 pmIsn't your HP3245A a better 100mA source?

author: Cerebus
author_rank: Super Contributor
timestamp: May 01, 2017, 03:12:04 am
content: Quote from: mimmus78 on April 28, 2017, 08:38:48 pmNo,thisis torture - three pages and not a glimpse of the insides!

author: Pipelie
author_rank: Regular Contributor
timestamp: May 02, 2017, 06:03:53 am
content: I got a offer for this unit last year.The price was acceptable, but the unit is incomplete, and no Fluke WW resistors inside at all. So,no,Thanks.Frankly, I was disappointed when I Saw what‘s inside.

author: TiN
author_rank: Super Contributor
timestamp: May 02, 2017, 04:19:26 pm
content: Quote from: Pipelie on May 02, 2017, 06:03:53 amWell, I'm sure happy that you didn't snag it, otherwise this thread wouldn't happen.But it would be interesting to know why disappointment?Unit is complete enough for me, as I just received 732B-7001 today, which is a perfect match now. Just add somewaterbatteries...

author: TiN
author_rank: Super Contributor
timestamp: May 02, 2017, 04:46:17 pm
content: Pics removed, thread derailed.

author: manganin
author_rank: Regular Contributor
timestamp: May 02, 2017, 06:08:06 pm
content: (Sorry)

author: Vgkid
author_rank: Super Contributor
timestamp: May 02, 2017, 06:15:12 pm
content: I mean if it works.:hide

author: TheSteve
author_rank: Unknown
timestamp: May 02, 2017, 09:17:19 pm
content: Ouch - why post that crap in TiN's thread?

author: Macbeth
author_rank: Super Contributor
timestamp: May 03, 2017, 12:08:50 am
content: Because it's hilarious?I'm sure TiN will appreciate good humour, though the purveyor of "10.00000V 2ppm" crap on ebay that relies on the sellers extreme lack of soldering skills and his belief in God will be offended.ETA: 6ppm to 2ppm. OMG!http://www.ebay.com/itm/10-Volt-10-V-DC-Prec-Voltage-Reference-Standard-Nulled-to-Fluke-732A-or-732B-/251756273626

author: TheSteve
author_rank: Unknown
timestamp: May 03, 2017, 02:46:33 am
content: Oh I get it. It's just that the Fluke is a work of art even if portions were hand assembled, that other voltage ref is just junky sadness.

author: manganin
author_rank: Regular Contributor
timestamp: May 03, 2017, 12:51:57 pm
content: No way a real R&D prototype or even a mockup. Fluke is the major player in the high end voltage standards but not in resistance metrology. Who would buy a thermostated 742A for $6K?Must be some DIY enthusiast in the service department who has access to spare parts / leftovers.Quote from: TiN on May 02, 2017, 04:46:17 pmGood deal if you find a totally smashed 732B needing a new enclosure. Or an LTZ1000 based "732B" would be cool too.I think that the Fluke divider hybrids find better use in some ratio related application rather than as a mediocre resistance standard. 14 pcs total !!!And sorry again. I know that religion and politics should be kept out of the forum. But I couldn't help myself...

author: Echo88
author_rank: Frequent Contributor
timestamp: May 03, 2017, 01:40:06 pm
content: Indeed, the SL935 shown here is nothing more than a prototype nobody would dare to sell to customers. "Work of Art"If TheSteve would like to invest in art, i suggest this:https://en.wikipedia.org/wiki/Artist%27s_Shit

author: TiN
author_rank: Super Contributor
timestamp: May 03, 2017, 02:08:03 pm
content: Too bad there is no "Unthank post" button. After all this is electronics community section, not the general chat.And calling Fluke not a player in metrology is fun, sure folks at Everett will have good laugh reading this.People and market seem not to mind using Fluke resistors in 720A, 752A's, which are still up for today's standards.Are these resistors from 5700A worse? Maybe. Ask that question in 5 years if you really care that much, when we see actual data.Would I buy such a unit as stated "thermostated 742A for $6K"? No, not really. And why 6K? Why not 3K or 15K?I've heard IET charges more for magical SR104, no?Something tells me that people here that able to measure visible difference between SR104 and 10xF5700 network array can be count on one hand (me excluding, I don't pretend to have time or gear for that).If you guys not interested, let's get this prototype project closed and all move tothis magical thread.I've got a tool to transfer calibrations for 5700A. No SR104 replacement or magical best in the world resistor statements were made.

author: VintageNut
author_rank: Frequent Contributor
timestamp: May 03, 2017, 02:32:37 pm
content: TinAs always, without exception, I thoroughly enjoy following your projects.This particular Fluke resistance box is very interesting. It shows intelligent design and access to lots of the best resistors fluke uses.Please continue to share what you are doing with this resistance box.

author: CalMachine
author_rank: Frequent Contributor
timestamp: May 03, 2017, 03:16:23 pm
content: Quote from: VintageNut on May 03, 2017, 02:32:37 pmI agree. I thoroughly enjoyed seeing what was inside of that Fluke prototype and was intrigued by this prototype in particular. I would take what some people are saying, with a grain of salt... It, clearly, wasn't a production item.

author: Echo88
author_rank: Frequent Contributor
timestamp: May 03, 2017, 03:31:37 pm
content: I might have been a bit harsh. Of course the stability/accuracy of those paralleled resistors should be very good and TiNs teardowns are always worth the read. I just expected a working glorious device after 3 pages of guessing and it looks more like what i would build in my sparetime, if i would work at fluke and had those resistor-networks laying around.

author: manganin
author_rank: Regular Contributor
timestamp: May 03, 2017, 03:44:24 pm
content: Quote from: manganin on May 03, 2017, 12:51:57 pmQuote from: TiN on May 03, 2017, 02:08:03 pmFluke has one of the best primary levellabsin the whole world, but their best resistance standardproductis still the 742A. The small size and low temperature coefficient makes it an excellent transfer unit also used in the highest level. But even though sometimes marketed as a replacement for the SR104, there is a magnitude difference in stability.Quote from: TiN on May 03, 2017, 02:08:03 pmAll those products rely on regular relative adjustment or calibration with more stable standards. But I agree that Fluke (or their subcontractor) makes very good resistors.Quote from: TiN on May 03, 2017, 02:08:03 pmMy intention was not to be rude, but challenge you to think how to get the best out of the purchase. I think in this case the value of the complete instrument is less than the sum of those high end parts it was made of. The divider hybrids alone are probably worth the money that you paid. How about building ten new instruments instead of stacking all together to make one mediocre standard resistor? Especially for you it would be easy to find a number of new interesting metrology applications.And sorry for injecting noise in this thread with the "Totally looks like" meme.

author: TiN
author_rank: Super Contributor
timestamp: May 03, 2017, 03:54:02 pm
content: Thanks, I'll go with mediocre standard resistor, as I don't have SR104, nor seeing it for sale anywhere in <1K$. Also SR104 is useless as 1 ohm, without current comparator or bridge, none of which I have yet.SR104 without calibration is just a box with wire and oil tank too.And anyhow, my purpose was clear from the start, and that was never a replacement for SR104, which is not really a primary standard anymore since the QHR adopted, unless I got that wrong too?

author: TheSteve
author_rank: Unknown
timestamp: May 03, 2017, 04:13:27 pm
content: Quote from: Echo88 on May 03, 2017, 01:40:06 pmI'm willing to agree to disagree. I think finding a prototype(hand built or not) from a company such as Fluke is a real treat. We'll likely never know the true intentions of the device but it still gives an idea into what at least one person in the calibration department was thinking or dreaming of. Art doesn't have to be pretty.I think it was a great find for TiN, and am glad he shared it with us.

author: HighVoltage
author_rank: Super Contributor
timestamp: May 03, 2017, 04:35:02 pm
content: TiNYour posts are amazing, please don't be discourage by some messages and keep going with your project.

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: May 03, 2017, 05:17:14 pm
content: @TiN,As far as I know, the SR-104 is still considered a primary resistor standard, for two good reasons, first, the jump from a JJ resistance to a 'standard' value resistor is not direct, JJ resistors are very odd values and secondly, they are extremely expensive and compared to a JJR, an SR-104 is very cheap. Because of their reputation, an SR-104 holds its value very well over the years and an older unit often has stability around 0.1 PPM/year and even less. The only time you might find an SR-104 going for less than about $2,000 is if it has been messed up by an idiot, in which case, you avoid it like the plague. For most hobbyists, even the more serious, a very good L&N standard of the 40xx-B series (for example) have very good stability and generally cost less to have calibrated than an SR-104. These can be found for even a few hundred for brand new ones, I purchased a brand new, in the sealed bag, 4025-B for under $100, made in March 1992. It came with a really nice calibration chart for temperatures above and below the nominal 23°C in 0.1°C increments.The trick is, don't buy a standard that is far above your real needs, the higher grade standard, the more it is going to cost, new or used. I have an SR-104 because I needed it for my work, same thing for the 242D bridge, at times I need PPM accuracy for sure and the SR-104 is calibrated accordingly (that costs more than many other resistor standards). If you seriously need that high of precision resistance readings then you need an SR-104 and an appropriate resistance bridge.....no a 3458A is not a resistance standard in and of itself, although it can be used as a short term transfer standard if calibrated against an SR-104 or equivalent. While it is possible to do a very accurate ratio transfer up and down from a given standard (such as the SR-104), the accuracy and uncertainty does increase a little bit for a 10:1 and you lose a little bit more for a 100:1 ratio, generally that is about the limit for high accuracy ratio transfers, you can do higher but you rapidly lose accuracy and uncertainty increases faster. I use the SR-104 for the reference for 10:1 and 100:1 ratios and I can maintain accuracy and uncertainty to under 3 PPM (carefully), for low ohms, I use low ohm calibrated L&N standards to transfer with to maintain high accuracy.I think the SL935 is definitely a prototype and a very neatly done prototype as it should be. It is not uncommon for a company like Fluke to build prototypes and try them out before deciding to go further but it is also very unusual for a prototype to find its way into private hands. I would surmise Fluke was possibly attempting to produce a resistance standard that could possibly compete with the SR-104 and provide two resistor values in the bargain. Since an actual product never made it out of engineering, I think they were unable to meet whatever design goals they had in mind. It isn't easy making a standard like the SR-104, otherwise there would be more of them out there at a lower price (perhaps).

author: mimmus78
author_rank: Unknown
timestamp: May 03, 2017, 07:47:14 pm
content: Quite interesting thingy, especially because it's a prototype.Who cares if not so nice and up to the Fluke standard?!

author: Dr. Frank
author_rank: Super Contributor
timestamp: May 03, 2017, 09:21:11 pm
content: TiN,many thanks for sharing this very interesting prototype.Especially the 732B oven construction is now transparent to the public, which is the best feature here.I'm interested in the schematic of the oven..And I wonder what the T.C. of the resistors are.. and at which temperature they are kept in this instrument.Aren't these single arrays also inside an oven in the 57x0A instruments?Frank

author: lukier
author_rank: Unknown
timestamp: May 03, 2017, 11:32:50 pm
content: Quote from: Dr. Frank on May 03, 2017, 09:21:11 pmHere's free_electron's teardown of 732B.https://www.eevblog.com/forum/testgear/fluke-732b-dc-standard-teardown/I wonder what's the insulation material. It looks like polyurethane foam made in some form.TiN:I too don't get the sniggering in this thread. This are not only great resistors if they are used in 5700A but the whole thing is an extremely rare collectable - some companies have strict policies to destroy such prototypes.While this might not be SR-104 I wonder how it compares to 742A. It might be even slightly better, but not better enough to justify possibly much higher price (742A is just 4 fluke wire-wounds AFAIR and here custom laser trimmed resistors, oven assembly, controller, battery etc) - maybe that's why Fluke dropped the idea.

author: Cerebus
author_rank: Super Contributor
timestamp: May 04, 2017, 01:25:38 am
content: Quote from: lukier on May 03, 2017, 11:32:50 pmI concur. I've used a lot of 2 part polyurethane foam over the years and, based on the appearance, I'd be very surprised if that's not what that is.

author: TiN
author_rank: Super Contributor
timestamp: May 04, 2017, 05:06:22 am
content: Quote from: Dr. Frank on May 03, 2017, 09:21:11 pmI'll restore schematics of both resistor arrangement and oven. I plan to get it done and ready on this weekend, need to get few parts and battery that fits the chamber.Those hermetic resistor arrays are not heated in 57x0As, just free standing. Z5 (90K/10K) is between relays on A9 CAL OHM board and Z1 is on A10 Main OHM board.I have both boards, so they are exactly the same resistors, no doubt.Fluke's ACAL study document mentions these hybrids are designed to have zero TCR in 22-26C region, and Z3 from A10 which I tested few weeks ago indeed confirmed that, with total worst TCR -0.6ppm from 20C to 40C (box math). I'll have to see how hot the oven runs, maybe tweak it for 40-45C tops, to keep things lower power and reduce possible thermal EMFs effects.Edwin G. PettisThanks for info, as I was under impression that national standard labs switched to QHR similar timeframe as DCV PJVS. Few years ago I was quoting measurement/comparison of resistance standard to Taiwan metrology body, and it sounded like no big deal to compare ohm vs QHR, if you happy to fork 400$ per measurement point. So guess that depends on what is the definition of primary standard, as many 732B/734A's surely considered primary in many second-level calibration labs.

author: carl_lab
author_rank: Frequent Contributor
timestamp: May 04, 2017, 05:46:15 am
content: Quote from: HighVoltage on May 03, 2017, 04:35:02 pmI totally agree!

author: Pipelie
author_rank: Regular Contributor
timestamp: May 04, 2017, 07:59:57 am
content: Quote from: TiN on May 02, 2017, 04:19:26 pmI was going to share it in Metrology section with you guys,but I get busy after Chinese new year holiday and forgot it.until I saw the front panel of this unit.obviously, this resistor box was designed to use to calibrate the Fluke 57x0, I think!I didn't expect to see those hermetic resistor arrays siting on the general-purpose board, I big fan of hermetic WW resistor but not these .that‘s why!and of course, I don't span another $400 to build or find the missing parts. I already have SR-104 (calibrated in HK 2016) and SRL-1.here is the photo from seller, P.S. you can find it in 38HOT.

author: Echo88
author_rank: Frequent Contributor
timestamp: May 04, 2017, 09:07:53 am
content: @ Dr. Frank: The oven-schematic should be the one described in the 732B-Manual i think?https://xdevs.com/doc/Fluke/732B/FLUKE_732B_734A_INST.pdfPage 115

author: Dr. Frank
author_rank: Super Contributor
timestamp: May 04, 2017, 09:14:39 am
content: Quote from: TiN on May 04, 2017, 05:06:22 amTiN,the schematics of the oven is inside the 732B manual (LTFLU reference is missing), so I don't want to create unnecessary work.It's explicitly mentioned in the manual, that the oven runs on 45°C, that means that the fixed resistor Z401 is equivalently 41.3k, which is the resistance of the NTC @ 45°C.That's also the reason, btw., why I let my LTZ1000 reference also run on 45°C.Frank.

author: TiN
author_rank: Super Contributor
timestamp: May 04, 2017, 10:28:28 am
content: Dr.FrankSchematics of oven is indeed in 732B, but there is no Z401 anymore in this proto, just few 5-band metal films instead and thru-hole thermistor hanging on the inner side of oven chamber.So actual oven setpoint might be lower or higher than original 732B. Might pimp up a setting resistor a bit with some suitable BMFR..

author: tszaboo
author_rank: Super Contributor
timestamp: May 04, 2017, 11:16:25 am
content: Quote from: TiN on May 02, 2017, 04:46:17 pmCan you please find a nice place for the pictures, and share their location with us?Thank you.

author: TiN
author_rank: Super Contributor
timestamp: May 04, 2017, 12:10:41 pm
content: Check on the first post in this thread.

author: tszaboo
author_rank: Super Contributor
timestamp: May 04, 2017, 12:19:47 pm
content: Quote from: TiN on May 04, 2017, 12:10:41 pmWell hidden.

author: TiN
author_rank: Super Contributor
timestamp: May 08, 2017, 04:19:51 am
content: During yesterday's livestream on my Youtube channel, I got SL935 cable connections fixed up and all assembled in 732B-7001 chassis.YoutubeSchematics for resistor standard was recovered, and oven settings captured. Oven inside SL935 is set to run at +35 C, instead of warmer +45C like 732B.Lower oven temperature make sense, as main purpose why this prototype was build is metrology, and majority of metrology labs running 20-24C lab temperature. So +35C setpoint allow good 10C headroom against ambient and does not introduce too much thermal stress into the resistor assembly.This also meant that I had to add 25.5Kohm resistor in series of R547 on charger board, to make IN CAL led working as expected, otherwise it detected thermistor temperature signal is too low and IN CAL was off.Initial data after reassembly with oven working revealed <0.5ppm difference to standalone measurement I made week ago.1 Ohm resistor is just simple parallel connection (maintaining 4-wire Kelvin layout) to 10 x 10ohm from networks.10 KOhm output is taken using 9 x 19 ohm series from network + 10K+10K/10K+10K calibration network. 2.111111 Ohm from 19R network is likely just a trim to get <1ppm accurate 10K.According to my 3458A (DIY calibrated in January 2017 vs double 10K foil resistor transfer vs 0.55ppm uncertainty calibrated SR104 (August 2016)) median resistance settle around 9999.9944 Ohm, just half a bee's dick short of ideal 10KWill swap to another 3458A (same date calibration) to log for longer time.I'm happy with the investment so far, given that I spent half of the price of Fluke 742A/IET SRL-1 and get both resistances.For tempco measurements probably best way would be to collect some 24-48h data with oven ON, and then repeat same 24-48 measurement with oven OFF, keeping room temperature same (to reduce chance of error due to own HP 3458A tempco). 40K VHP103 inside 3458A expected to be worse than this SL935 box, so ACAL can't help much here either.Eventually I plan to send this box for low uncertainty calibration lab over few years, to establish drift and long-term stability rate of both 1 Ohm and 10Kohm, but for now I'll just log it for few months to make sure it's stable.

author: VintageNut
author_rank: Frequent Contributor
timestamp: May 08, 2017, 12:59:12 pm
content: Hi TinExcellent job re-working the box to your needs. And fast work!I look forward to your results from a calibration lab on this box.

author: Pipelie
author_rank: Regular Contributor
timestamp: May 08, 2017, 03:27:48 pm
content: excellent job, nice Rebuilding!

author: TiN
author_rank: Super Contributor
timestamp: May 10, 2017, 04:37:11 am
content: 1 Ohm data arrived.How about adding 16.8K VPG foil in parallel with it, to get perfect 1 ohm?

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: May 10, 2017, 05:34:53 am
content: How about 6 parallel 100k resistors? You must have some in there somewhere?

author: Dr. Frank
author_rank: Super Contributor
timestamp: May 10, 2017, 06:32:38 am
content: Quote from: TiN on May 10, 2017, 04:37:11 amHow about adding 10k+6k8 thin film resistors?That's sufficiently close within your uncertainty, and T.C. and drift of the T.F. will be attenuated by a factor of 16800 to an unmeasurable level.Frank

author: TiN
author_rank: Super Contributor
timestamp: October 13, 2017, 02:58:30 pm
content: Little follow up, as SL935 prototype is now charged up and ready to travel for it's first metrology-level calibration.Will be interesting how she handles the trip.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: October 13, 2017, 03:01:53 pm
content: Beta testing the 732C?

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 13, 2017, 04:36:32 pm
content: Quote from: ManateeMafia on October 13, 2017, 03:01:53 pmI think he is a super secret Fluke spy

author: texaspyro
author_rank: Super Contributor
timestamp: October 13, 2017, 10:55:45 pm
content: Quote from: Edwin G. Pettis on May 03, 2017, 05:17:14 pmOr was listed on Ebay by somebody that could not type. I got my SR-104 for around $200. The auction listing title was incorrect and nobody else bid on it. doG loves dyslexics...I asked IET about calibration. I think that they originally quoted around $1100 and I did not respond. After a few weeks they came back with an unsolicited $800 offer.I have the SR-104 mounted in an insulated box along with a Thunderbolt GPSDO and a 10V reference. I use the temperature control feature in Lady Heather to control the temperature in the box at one of the two temps where the SR-104 is at "exactly" 10K using the Thunderbolt as a heater and a PWM fan to control the temperature. Seems to work rather well. Temperature swing is less than 10 millidegrees and 24 hour RMS temperature is in the low tens of micro-degee range of the setpoint. Of course, those are not absolute accuaracy, just a relative indication of stability.If you have the cal data (ALPHA, BETA, R_DEV. TEMP_DEV) for your SR-104 (on the chart in the lid) this program will calculate the resistance over a range of temperatures. You need to change the #defines at the start of the code to match your device's cal constants and re-compile the program.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: October 13, 2017, 11:05:36 pm
content: I send mine to Process Instruments. Their pricing is almost half of IET. I just sent mine today with a few other standards and they have been great to deal with on the phone and email. IET quoted me a similar price as yours a few years ago.The pricing is fair and they can do tempco's if needed. They also work with lab built standards if you want it calibrated.

author: TiN
author_rank: Super Contributor
timestamp: November 11, 2017, 10:07:45 pm
content: Aren't they beautiful together? SL935 is out for proper calibration now.Will be very interesting to see standard's alpha/beta values.

author: TiN
author_rank: Super Contributor
timestamp: December 01, 2017, 12:07:38 pm
content: Okay, Fluke SL935 standard is now back from calibration atProcess Instruments Inc.It didn't go 100% smooth, as unit arrived from CAL with LOW BAT light on and no IN CAL light. Perhaps calibration tec did not hook it back to AC power after the measurements.It was shipped to calibration lab fully charged, with battery life minimum 120 hours. That was enough time for SL935 to receive calibration in "hot" state, without any temperature interruptions,even if it was never plugged into mains. Shipping back from PI was 2-day service, which took just 52 hours from pickup to delivery.Click for full PDF-report data, on both resistors.My loved resistor data is available for amusement now, with amazing tempco. Thanks to integrated +35C oven.I mean, really, just look at these alpha and beta coefficients.Worst error is +0.07ppm on 10 KOhm with temperature from +23.00 to +28.9C.Overall I think it was worthy calibration investment (bit over $1K total for cal+tempco measurement+shipping), as now I have solid resistance reference to take care of. Will be interesting to monitor it's long-term stability, as I do plan to send it for same cal next years as well.As bonus, we can perform some math acrobatics, to attempt our own meters accuracy, using previously captured data.Here are my own measurements which I did at home, prior to sending SL935 for calibration + ManateeMafia's meter:HP 3458A, meter 2over 10KOhm, direct 4-wire, OCOMP ON, DELAY 3, NPLC100 =9999.971 Ohm, +26C ambient, 18 May 2017. Error from PI value :-0.37 ppmHP 3458A, meter 1over 10KOhm, direct 4-wire, OCOMP ON, DELAY 3, NPLC100 =9999.985 Ohm, +25C ambient, 20 May 2017. Error from PI value :+1.03 ppmHP 3458A, meter 2over 10KOhm, direct 4-wire, OCOMP ON, DELAY 3, NPLC100 =9999.965 Ohm, +24.5C ambient, 25 Sept - 28 Sept 2017. Error from PI value :-0.97 ppmMeter 1 calibrated by using Vishay VHP103 resistor at 10Kohm as transfer standard, which are in turn measured against 90-hour fresh cal'd ESI SR104 (by PI too) in August 2016. Meter is 24/7 powered.Meter 2 calibrated directly vs same ESI SR104 back in January 2017, shipped to me in Feb and in 24/7 powered use since then.HP 3458A, ManateeMafia's meterover 10KOhm, direct 4 wire, OCOMP ON, DELAY 3, NPLC100 =9999.966, +26C ambient, 3 Nov - 7 Nov 2017. Error from PI value :-0.87 ppmBased on this brief data, with adding uncertainties and error factors, I'd have pretty good confidence stating that such transfer path can provide <8 ppm absolute resistance accuracy at 10 KOhm. Noise + short-temp variations are usually under 3 ppm.Now similar data for1 Ohm.HP 3458A, meter 1over 1 Ohm, direct 4-wire, OCOMP ON, DELAY 3, NPLC100 =1.00006111 Ohm, +22C ambient, 5 May - 25 May 2017. Error from PI value :+2.1 ppm, noise about 30 ppm.HP 3458A, meter 2 + TE 9823 calibrator sourcing +100mA and -100mAover 1 Ohm, direct 4-wire, NPLC 100 =1.00006657 Ohm, +23.5C ambient, 13 October 2017. Error from PI value :+7.5 ppmHP 3458A, meter 2 + TE 9823 calibrator sourcing +20mA and -20mAover 1 Ohm, direct 4-wire, NPLC100 =1.00006574 Ohm, +21C ambient, 21 Sept - 22 Sept 2017. Error from PI value :+6.7 ppm, noise around 2 ppmHP 3458A, ManateeMafia's meterover 1 Ohm, direct 4 wire, OCOMP ON, DELAY 0, NPLC100 =1.00005831, +24C ambient, 31 Sept - 3 Nov 2017. Error from PI value :-0.7 ppmNoise is around 30ppm.Looks like despite the large noise impact from the 3458A (because 1 ohm is just 10% of the minimum range), calibrated 3458A still able to resolve better than 10ppm accuracy for 1 Ohm resistors, if proper care is taken. Bodging external calibrator to source +/-current into 1 ohm resistor rendered worse absolute accuracy, so this remain to be investigated further.I'd also like to thankManateeMafiafor great help with measurement, testing and support.

author: Vgkid
author_rank: Super Contributor
timestamp: December 01, 2017, 02:32:06 pm
content: That is impressive , thanks for posting that.

author: babysitter
author_rank: Frequent Contributor
timestamp: December 01, 2017, 08:49:25 pm
content: Quote from: TiN on December 01, 2017, 12:07:38 pmI think thats enough reason to ask for a partial refund. A full refund if you told them about the Battery.

author: Macbeth
author_rank: Super Contributor
timestamp: December 01, 2017, 10:55:36 pm
content: Quote from: DiligentMinds.com on December 01, 2017, 09:36:17 pmI disagree. The amount of work TiN put into this making sure the battery and charging circuitry would be perfect, ensuring the logistics, and I can only imagine a sick feeling to the pit of his stomach when after all that work and cost he finds the device returned with a LOW BAT and OUT OF CAL indication.Yes, perhaps you can surmise that the SL935 contains resistors that "shouldn't" drift once they get back up to temp, so no harm done - but the cal technician is not the one to make that judgement at all and TiN went to best efforts to make sure it would remain powered all along - just like a 732B would be. Perhaps he didn't specify that the battery should be charged while in the cal lab, but surely this is standard procedure on any Fluke "732B like" device and plainly obvious?It brings into question how you can trust this firm at all if the technician is so slovenly. How do you measure such uncertainties?I do think some compensation is in order - perhaps a free recal next year, with maybe only shipping to be paid for?

author: HighVoltage
author_rank: Super Contributor
timestamp: December 01, 2017, 11:21:15 pm
content: Those are some very impressive calibration dataThanks for sharing the PDF

author: TiN
author_rank: Super Contributor
timestamp: December 02, 2017, 06:25:32 am
content: I'd agree with DiligentMinds.com that it should be fine, and this theory also backed by the actual measurement.SL935 now is connected to MM's 3458A which just completed fresh calibration at Keysight last week.After few ACAL's deviation is <1ppm already at 10K.MacbethI did sent article coveringdesired calibration procedureto PI prior to shipping unit. I don't expect their resistor calibration tech calibrate prototype ovenized standards very often, so I'm not filing any complains or refunds at this time. Many labs may not even accepted obscure non-production unit for calibration in the first place (since they cannot be sure of performance or stability of unknown device).IN CAL light is just driven by simple comparator, that will trigger if oven temperature go too much outside of +35C NTC reading. It doesn't really mean that it's out of cal.Keeping constant temperature is more important for DC zener reference, and bit less so for hermetic film resistors.So, "she'll be alright". Next step would be comparing it to freshly calibrated SR104 and SRL1.QuoteIs indeed a bigger (and expensive) question there, as I have no any forecast for ability to measure even at this noise resolution, leave alone uncertainty.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: December 02, 2017, 12:59:51 pm
content: Quote from: TiN on December 02, 2017, 06:25:32 amSounds like the 242D is going to be put to use.

author: dl1640
author_rank: Regular Contributor
timestamp: December 02, 2017, 01:28:04 pm
content: VERY amazing re-work.I wonder what kind of cabling PI used in this calibrationnot sure if they did as you requested of using clean copper spade lugnext time you better send in your cables for combined calibration with the SL935

author: Andreas
author_rank: Super Contributor
timestamp: December 02, 2017, 07:39:37 pm
content: Hmm,what I do not understand at the 10000 Ohms resistor how they get that resolution:8,9 nano Ohms! per deg C as alpha on a 10K resistor sounds incredible to me.but in the formula they use the value obviously as 8,9 ppb / K.with best regardsAndreas

author: CalMachine
author_rank: Frequent Contributor
timestamp: December 02, 2017, 07:52:08 pm
content: Quote from: Andreas on December 02, 2017, 07:39:37 pmThat's got to be a typo. I would think that the certificate not including a 10 kOhm reference, is also an error.

author: Dr. Frank
author_rank: Super Contributor
timestamp: December 02, 2017, 08:28:05 pm
content: Quote from: TiN on December 02, 2017, 06:25:32 amDon't you have before / after travel comparison data, to check whether your SL935 has the same value, or may have been altered by the loss of power?Your VHP203 should be stable enough to identify such small deviationsFrank

author: babysitter
author_rank: Frequent Contributor
timestamp: December 02, 2017, 08:43:21 pm
content: Do you know the conditions - e.g. temperature extremes, mechanical shocks - during transport? Also, it proves some level of "sloppy work" if they were aware but neglected it.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: December 02, 2017, 09:00:24 pm
content: The box was shipped 2nd day. The packing was in the original box and showed no signs of external damage.The temperature on the day of delivery was ~27C.A mistake was made on my part because of the holiday delivery workload and my expected work schedule. I anticipated being away from home that day and depended on them to deliver it to my home where someone would sign for it. Since it was under battery power, I didn't want to hold it for pickup and not make it to FedEx that day. They ended up delivering it in the evening (8pm) when I typically get it around noon.I hold all my standards and 3458A for pickup except the 732B. I usually hand deliver it to Tektronix and then drive there a couple of hours on the day it is picked up. This will definitely be an issue shipping the 732B to Fluke since they will probably ship it without asking for special delivery instructions. This is the first time I have had to receive a reference under battery power where it was unplugged for more than a few hours.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: December 02, 2017, 09:07:56 pm
content: DiligentMinds,I would think that there would be some mention about this potential issue in the Fluke MFC manuals. Power cycling a 57x0A calibrator should show signs of shifting since there are so many heated hybrids inside these units.

author: Andreas
author_rank: Super Contributor
timestamp: December 02, 2017, 10:50:40 pm
content: Quote from: DiligentMinds.com on December 02, 2017, 08:56:16 pmHello,My measurements of (metal foil) VHP202 resistors show 1-2 ppm hysteresis over a 30 deg C temperature span:https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg1143103/#msg1143103Hysteresis gets much better when the temperature excursion is reduced to a 14 deg C span:(with my setup I cannot measure it)https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg1170353/#msg1170353I have also some results of molded metal film (UPF50) which were not too bad (mostly below 1ppm over 30 deg C) regarding hysteresis on slow temperature gradients (0.12 K / minute).https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg462301/#msg462301But if you let rest the resistors over night most of the hysteresis is usually gone the next morning.Of course there is also some permanent (ageing) drift.with best regardsAndreas

author: TiN
author_rank: Super Contributor
timestamp: June 27, 2018, 05:43:32 pm
content: The magical resistor box today arrived back to lab, finally.Second calibration report included in selfie:Now it's time to determine error on my 3458A/2002's and transfer ohms to the SR104 and my other resistance standards.Previous cal data for reference: