Fluke SL935 Resistance Standard project (rare prototype teardown included)

[TiN]

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 SL935

EDIT 8 May 2017:

Livestream recording of SL935 cable connections fix and assembly in 732B-7001 chassis.

Youtube

Schematics 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.

[TheSteve]

I know! But I won't say...

[tszaboo]

Something with a battery, powered all the time?

[Echo88]

You must have a very good position on Santas Naughty or Nice-List.

[TiN]

Yes, battery, and supposed to be powered all the time.

[Alex Nikitin]

Hmm... 5790B  ?

Cheers

Alex

[TiN]

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 

[dr.diesel]

No idea, but I already want at least 3-4 of them. 

[TiN]

I wouldn't mind few spares too.
Oh, did I mention it's black?

[Kefka Palazzo]

Fluke 732a?

[TiN]

You saw black Fluke 732A's? Last time I've checked those are beige white.

[ManateeMafia]

“I know what this is. This is an espresso machine. No, no wait. It’s a snow cone maker. Is it a water heater?”

[nadona]

732B

[TiN]

It's not 732B, but it does have three digits in model number. 

[ManateeMafia]

Something made by a competent artisan? 

[TiN]

I've heard so. Surely parts used came right from some serious gray beard-designed gear. 

[Jeroen3]

792?

Else why even make us?

You guys will never guess

[TiN]

Nope, 792A is about twice as large than this, even without battery block.

And I've already posted about 792A, so that 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. 

[Jeroen3]

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.

[TiN]

752A not black either.

[SvanGool]

Fluke 731B 

[TiN]

Hm, it's sorta black. But no, I have no interest in 731's, sorry.

[Jeroen3]

Did you buy a temperature reference?

[HighVoltage]

It's not 732B, but it does have three digits in model number. 

May be 4 x 732B to make a 734A full rack?

[TiN]

Left 732B is not in the sequence.

No, it's not one 732B, not two 732B, not any amount of 732B's
Well, maybe it's 30% of 732B, but anyhow it doesn't have this model number.

[ap]

732B external battery charger?

[tszaboo]

So it is 3 digit, black
not a 732B
not a 731B
not 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.

[doktor pyta]

So simple.
Transfer switch for 792A.

[Jeroen3]

You are liking this aren't you? 

[TiN]

NANDBlog, doktor pyta
Sorry folks, it's nothing related to 792A, that would be too easy guess

ap

732B external battery charger?

This one is on Fedex now, delivery target next Tuesday 

[SvanGool]

- It is 3 digit, black
- Not a 732B
- Not a 731B
- Not a 734A because wrong shape and even you are reasonable.
- Not a 792A because you already have one.
- Battery powered, so probably not their shunt resistor.

- Many would surely want this
- It's made by Fluke
- Uses something from Fluke 732B, but it is no 732B
- Something with a battery, and supposed to be powered all the time.
- Parts used came right from some serious gray beard-designed gear.
- 792AIs about twice as large than this, even without battery block.
- It's 30% of 732B
- It's only 30% of the package on the photo

1 The heater of a 732B: an Alox (aluminum-oxide) substrate based power resistor ?
or
2 The front panel of a 732B?

 

[Vgkid]

Was it the prototype precurser to the 732. I saw a teardown on the volt-nuts mailing list/bbs-38.

[mimmus78]

Two pages and still no reply.

This is a torture.

 

[ZeTeX]

SL935

[CalMachine]

SL935

Tell the man what he has won!

[Macbeth]

Well, maybe it's 30% of 732B, but anyhow it doesn't have this model number.

This must be the world famous Fluke 219.6B, surely?

[TiN]

ZeTeX wins a thank you All 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 standard 

At least that's how I comfort myself doing such purchases.

[Vgkid]

Woah, I'm really looking forward to this one.

[Jeroen3]

S/N 001 ?

[CalMachine]

ZeTeX wins a thank you All 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 standard 

At least that's how I comfort myself doing such purchases.

She's a beauty!!       I am interested in what its values are   

[tszaboo]

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.

[EEVblog]

S/N 001 ?

Yeah, 

[TiN]

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 hands 

My 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).

[HighVoltage]

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.

[ManateeMafia]

At least I know how I came across that lone reference oven on ebay. Some sacrifices must be made. 

[TiN]

Many sacrifices are required. That's the way it works.

HighVoltage
I 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. 

[ManateeMafia]

It's almost believable but I don't think you could ever come across a stash of dead 5700A boards. 

[TiN]

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.

[CalMachine]

 

[Vgkid]

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

[ManateeMafia]

They need to be organized by slot number.

[Dr. Frank]

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

[Edwin G. Pettis]

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.

[nidlaX]

Goddam. TiN always delivers!

[TiN]

Some first checks..

1 Ohm : Median 1.000059 Ohm vs 3458A, TC <2ppm/K over 3C span, can't tell, readings too noisy
10 KOhm : Median 9999.990 Ohm vs 3458A, TC <0.3ppm/K over 3C span

No 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.

[VintageNut]

Some first checks..

1 Ohm : Median 1.000059 Ohm vs 3458A, TC <2ppm/K over 3C span, can't tell, readings too noisy
10 KOhm : Median 9999.990 Ohm vs 3458A, TC <0.3ppm/K over 3C span

No 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.

The 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.

[TiN]

Uncertainty of 6221 wouldn't matter in bridge configuration or even in simpler setup with two 3458A's monitoring both resistor and current source.

[e61_phil]

Uncertainty of 6221 wouldn't matter in bridge configuration or even in simpler setup with two 3458A's monitoring both resistor and current source.

Isn't your HP3245A a better 100mA source?

[Cerebus]

Two pages and still no reply.

This is a torture.

 

No, this is torture - three pages and not a glimpse of the insides!

[Pipelie]

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.

[TiN]

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.

Well, 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 some water batteries...

[TiN]

Pics removed, thread derailed. 

[manganin]

(Sorry)

[Vgkid]

I mean if it works. :hide

[TheSteve]

Ouch - why post that crap in TiN's thread?

[Macbeth]

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   

[TheSteve]

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.

[manganin]

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.

Total spend just bit over 1K$ for something that should be good enough as transfer standard for 3458A/5700A/5720A calibrations. I wish there would be room inside to put LTZ module as well...

Good 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...

[Echo88]

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

[TiN]

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 to this 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. 

[VintageNut]

Tin

As 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.

[CalMachine]

Tin

As 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.

I 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.

[Echo88]

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. 

[manganin]

Fluke is the major player in the high end voltage standards but not in resistance metrology [products].

And calling Fluke not a player in metrology is fun, sure folks at Everett will have good laugh reading this. 

Fluke has one of the best primary level labs in the whole world, but their best resistance standard product is 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.

People and market seem not to mind using Fluke resistors in 720A, 752A's, which are still up for today's standards.

All 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.

Too bad there is no "Unthank post" button.

My 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.

[TiN]

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?

[TheSteve]

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

I'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.

[HighVoltage]

TiN
Your posts are amazing, please don't be discourage by some messages and keep going with your project.

 

[Edwin G. Pettis]

@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).

[mimmus78]

Quite interesting thingy, especially because it's a prototype.
Who cares if not so nice and up to the Fluke standard?!

[Dr. Frank]

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

[lukier]

Especially the 732B oven construction is now transparent to the public, which is the best feature here.

Here'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.

[Cerebus]

I wonder what's the insulation material. It looks like polyurethane foam made in some form.

I 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.

[TiN]

TiN,
Aren't these single arrays also inside an oven in the 57x0A instruments?
Frank

I'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. Pettis
Thanks 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.

[carl_lab]

TiN
Your posts are amazing, please don't be discourage by some messages and keep going with your project.

I totally agree!

[Pipelie]

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.

Well, 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 some water batteries...

I 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.

[Echo88]

@ 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.pdf Page 115

[Dr. Frank]

I'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.
...

TiN,

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.

[TiN]

Dr.Frank
Schematics 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.  .

[tszaboo]

Pics removed, thread derailed. 

Can you please find a nice place for the pictures, and share their location with us?
Thank you.

[TiN]

Check on the first post in this thread.   

[tszaboo]

Check on the first post in this thread.   

Well hidden.

[TiN]

During yesterday's livestream on my Youtube channel, I got SL935 cable connections fixed up and all assembled in 732B-7001 chassis.

Youtube

Schematics 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 10K  Will 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.

[VintageNut]

Hi Tin

Excellent job re-working the box to your needs. And fast work!

I look forward to your results from a calibration lab on this box.

[Pipelie]

 
excellent job, nice Rebuilding!

[TiN]

1 Ohm data arrived.



How about adding 16.8K VPG foil in parallel with it, to get perfect 1 ohm? 

[ManateeMafia]

How about 6 parallel 100k resistors? You must have some in there somewhere?

[Dr. Frank]

1 Ohm data arrived.



How about adding 16.8K VPG foil in parallel with it, to get perfect 1 ohm? 

How 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

[TiN]

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.

[ManateeMafia]

Beta testing the 732C? 

[CalMachine]

Beta testing the 732C? 

I think he is a super secret Fluke spy   


 

[texaspyro]

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

Or 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.

[ManateeMafia]

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.

[TiN]

Aren't they beautiful together? SL935 is out for proper calibration now  .
Will be very interesting to see standard's alpha/beta values.

[TiN]

Okay, Fluke SL935 standard is now back from calibration at Process 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 2 over 10KOhm, direct 4-wire, OCOMP ON, DELAY 3, NPLC100 = 9999.971 Ohm, +26C ambient, 18 May 2017. Error from PI value : -0.37 ppm 
HP 3458A, meter 1 over 10KOhm, direct 4-wire, OCOMP ON, DELAY 3, NPLC100 = 9999.985 Ohm, +25C ambient, 20 May 2017. Error from PI value : +1.03 ppm   
HP 3458A, meter 2 over 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 ppm  

Meter 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 meter over 10KOhm, direct 4 wire, OCOMP ON, DELAY 3, NPLC100 = 9999.966, +26C ambient, 3 Nov - 7 Nov 2017. Error from PI value : -0.87 ppm 

Based 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 for 1 Ohm.

HP 3458A, meter 1 over 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 -100mA over 1 Ohm, direct 4-wire, NPLC 100 = 1.00006657 Ohm, +23.5C ambient, 13 October 2017. Error from PI value : +7.5 ppm
HP 3458A, meter 2  + TE 9823 calibrator sourcing +20mA and -20mA over 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 ppm

HP 3458A, ManateeMafia's meter over 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 ppm    Noise 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 thank ManateeMafia for great help with measurement, testing and support  .

[Vgkid]

That is impressive , thanks for posting that.

[babysitter]

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.

I think thats enough reason to ask for a partial refund. A full refund if you told them about the Battery.

[Macbeth]

The type of resistors inside are not likely to show any temperature induced mechanical hysteresis, and so I think this adds up to a big "nothing burger".  The calibrated value should be good after it heats back up to calibration temperature-- then let it sit for a day.

I 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? 

[HighVoltage]

Those are some very impressive calibration data
Thanks for sharing the PDF

[TiN]

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.

Macbeth
I did sent article covering desired calibration procedure to 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  .

How do you measure such uncertainties?

Is 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.

[ManateeMafia]

So, "she'll be alright". Next step would be comparing it to freshly calibrated SR104 and SRL1  .

Sounds like the 242D is going to be put to use.

[dl1640]

VERY amazing re-work.

I wonder what kind of cabling PI used in this calibration
not sure if they did as you requested of using clean copper spade lug

next time you better send in your cables for combined calibration with the SL935

[Andreas]

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 regards

Andreas

[CalMachine]

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 regards

Andreas

That's got to be a typo.   I would think that the certificate not including a 10 kOhm reference, is also an error.

[Dr. Frank]

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.

Don'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 deviations

Frank

[babysitter]

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.

[ManateeMafia]

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.

[ManateeMafia]

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.

[Andreas]

Does anyone have any objective evidence that a hermetically sealed (or even a non-hermetic) thin-film (aka: metal-film) resistor exhibits any mechanical hysteresis due to small temperature excursions? 

Hello,

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/#msg1143103

Hysteresis 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/#msg1170353

I 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/#msg462301

But 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 regards

Andreas

[TiN]

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: