KX Reference PCB shared order ; who is interested? - Page 1
Forum section: electronics / general

author: voltampere
author_rank: Regular Contributor
timestamp: June 23, 2017, 08:24:22 pm
content: I already ordered all the parts to build some voltage reference boards according to user TIN´s design.These are the links :https://xdevs.com/article/ltz_tale1/#calservhttps://xdevs.com/article/kx-ref/Next step for me would be ordering the PCB from a chinese factory.Increasing the quantitiy of the order does increase the total costs only minimal.So i thought it would make sense to share the costs with other users.Total cost ( incl. shipping to germany and import duty/tax ) will be divided by total quantity.Shipping to you will be on top of course!Anyone interested please state the number of pieces you are interested in.I will place the order in a week from now.RegardsJoerg

author: Kleinstein
author_rank: Super Contributor
timestamp: June 24, 2017, 07:13:02 am
content: TiNs KX -ref board looks nice, however it is using two single OPs instead of the more convenient dual OP (LT1013). There is essentially no good reason to use the LTC2057 for the LTZ1000 circuit.So I am not sure it makes much sense to do a direct copy of a circuit with known issues.For a new board one might consider space for different resistor sizes - e.g. PTF56 for the 70 K and maybe the three pin divider for the temperature setpoint. With precision resistors it is not a good option to bend the pins too much - it is much more viable to have alternative positions for the resistors on the board or a separate layout for much larger resistors (like the PWWs).

author: voltampere
author_rank: Regular Contributor
timestamp: June 24, 2017, 02:43:51 pm
content: Thank you very much for your input.I just managed to get through ( at least roughly... ) the "KX LTZ1000A fairy-tale" thread.Is anyone so far using that "upgrade" ( LT1013 ) to the original TIN KX design?I can´t find any report of success.Is there a way to "replace" the LTC2057 without changing the PCB layout.Unfortunately i am lacking the skills and knowledge and experience to do my own design.So i have to stick with what others achieved so far.It seems that still a lot of enthusiasts are building the KX -ref according TIN´s design.So i will probably just stick with it for my first adventure into voltnutting.joerg

author: Kleinstein
author_rank: Super Contributor
timestamp: June 24, 2017, 07:21:01 pm
content: In principle one could use LT1006 instead of the LTC2057. They are rather close to the LT1013, with the additional option to reduce the operating current. AFAIK there was at least one successful try with these OPs.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 24, 2017, 07:28:17 pm
content: LT1413 *maybe* a better choice.regards.

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: June 24, 2017, 07:39:31 pm
content: Zhtoor,That would be a no, the LT1013 was specifically designed with the LTZ in mind, there are no better chips. We've gone around this merry-go-round before, just use the LT1013.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 24, 2017, 07:49:23 pm
content: Quote from: Edwin G. Pettis on June 24, 2017, 07:39:31 pmthanks you sir!,but it looks like at least designers of FLUKE 7001 thought so, or maybe not.regards.

author: try
author_rank: Regular Contributor
timestamp: June 24, 2017, 08:14:08 pm
content: Hi Jörg,Quote from: voltampere on June 24, 2017, 02:43:51 pmthere is no need for a professional board during that early stage.Build the circuit on a strip board "Streifenrasterplatine", p.e.. You can draw your personal design on squared paper.That works astonishingly well and leaves you all the options for modifications.If you already have a sufficiently precise multimeter (6 digits), you could build your prototype with the cheapest available resistors and measure how it behaves and then gradually improve part by part.The build process will last longer but you will learn more.Use a socket for the reference (you can remove it and solder the reference later).Build a reference simulator (like Andreas described it somewhere) that can be plugged into the socket.Consider a jumper on your board to be able to cut off heater power.Put everything into a (metal) case that allows for upgrades. Once everything runs fine you might want to insert a voltage regulator for the power supply and some op amps behind the outgoing seven something Volt.Think about the direction you wanna go: Either McGyver style like Conrad Hoffmann (building everything out of nothing) or Andreas style (buying a dozen of each part and selecting one out of them thereafter).Don't use up your expensive parts for you prototype, use them for your final version.Have fun!Regardstry

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: June 25, 2017, 03:23:07 am
content: I love it! At the day job they say if I'm going to machine a part, the first thing I do is go out and dig the ore for the metal.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 25, 2017, 09:46:08 am
content: The LT1413 and LT1013 are rather similar - so both should work and it would essentially make not difference. The LT1013 is well tested - not sure of the LT1013 was specially made for he LTZ1000, but it is a very good match if single supply operation is wanted. It is well tested and well good enough - so there is not much another OP could do better. So at best you might save a buck or so, but at the risk of possible strange behavior during turn on or with transients.The point with the Kx board is that it it used single OPs, which is kind of inconvenient.Using vero board might be actually an option if this is only for a single. It is still better than using a board design made for other resistors and bending the leads to the extremes.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 25, 2017, 11:33:39 am
content: Quote from: Conrad Hoffman on June 25, 2017, 03:23:07 amI once visited a master-machinist in Multan / Pakistan. This is what he told me to do:-"If you want to drink a glass of water, first dig a well."regards and may the likes of Conrad Hoffman be more common!.

author: TiN
author_rank: Super Contributor
timestamp: June 25, 2017, 12:27:02 pm
content: "If you want to have a LTZ ref, first lay your PCB board as well and wound resistors from a wire"Anyhow, I'd love to see more open-hardware LTZ1000 projects available to new-comers.

author: dr.diesel
author_rank: Super Contributor
timestamp: June 25, 2017, 12:52:43 pm
content: I've had plans to respin the board with Edwin's WWs and the community in mind, maybe/hopefully somebody beats me to it.

author: Echo88
author_rank: Frequent Contributor
timestamp: June 25, 2017, 01:57:41 pm
content: *beats you*

author: dr.diesel
author_rank: Super Contributor
timestamp: June 25, 2017, 02:04:27 pm
content: Quote from: Echo88 on June 25, 2017, 01:57:41 pmPlease share! My plan was to utilize the most convenient/open/easiest EDA tool, something completly free or possibly online/web based so everyone could play without OS ties. Then vette it through the experts here in hopes of capturing the majority of the thoughts in the LTZ mega thread.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: June 25, 2017, 03:33:03 pm
content: Please, Over and over again: Do as what LTZ datasheet tells you: '1013 amp in DIP package is right in the sweet spot for low current noise and high stability. NO available amp is better right now for LTZ. Don't use an AZ amp for best long term low drift. Follow the lead on the most successful 8.5 digit DMM - the 3458a. Do you notice the -02 option High Stability Vref board is no different than the standard issue board?? It's just a selected LTZ chip, because that is what dictates the drift, mostly - and far beyond your control. Even the expensive high stability board uses the same plastic package amp as they have for 10's of thousands of instruments for decades...if there were a terrible problem with that, we'd know. The Voffset of the amp has no effect on output voltage as it is used as a current driver. It is not uncommon for 3458a's to have drift on the order of a ppm per year and they are decades old, and that tells you how the circuit works. We have a few of those 3458a's in the lab, and all they do is work for a living, 24/7. The weakest part of that instrument is the display - if they had built it with LED's, a lot of those would never need parts replacements.All the elements that need a hermetic seal is already inside the LTZ can for you. As long as the resistors are fairly stable, the they don't need to be high tolerance, or oil filled or expensive. Stay away from SMT for precision circuits (in general), especially ceramic caps After building hundreds, I can tell you: no real need for a fancy board, no need for crop circles, no need for voodoo slots, no magical guards, no sockets or anything like that unless you have some specific thermal flow requirement. Keep it compact and practical, use star grounds. Plan for a cover on the LTZ chip on top and bottom to keep air drafts away. If you over-insulate the thing it won't be able to regulate it's own heat. Build it and start letting it burn in for several months before your even start measuring it. Don't touch it with a a soldering iron after that. Just move on with whatever is downstream of the LTZ.If you're going to build one board it's no more effort to built 5 or 10, and if your time is worth anything the cost is nothing compared to anything else you're doing. Select the best performers for yourself and give your buddies the rest. Real precision and low ppm's do not come cheap. The only "Poor Man" about this level of precision is what you'll be after you start doing it. Guaranteed.Most people here won't even have the resources to measure down past 2ppm absolute anyway, and you'll never really know how good your LTZ circuit is until you have something really better to compare it to - which would be something like at least three cal'd 732's and/or four ~ five cal'd 3458a's, etc. In fact, I'd say that if you don't have those resources, I wouldn't bother building an LTZ, but do whatever you want. You need to realize that it is -very- difficult to measure a finished LTZ circuit to even 2ppm absolute accuracy, if you're doing it right. If you're going for 1ppm absolute accurate, then you probably have local access to a JJ-Array, or a lot of 732'sI'm sorry, but my opinion is: if you need a GOOD precision Vref, quit wasting time "digging the ore" and build a known good circuit for far less effort and cost - and put that energy into the other much more difficult parts of your application. You're not going to build anything better than a basic LTZ if that's what you need. Once you start looking at other areas of precision circuitry, there are MUCH more difficult areas to look at - like converting the stable 7V into another voltage for instance. That's not trivial. Dr. Frank has one approach here but there are other ways also. Or building a front end for that high resolution ADC that matches the stability of the LTZ, etc.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 25, 2017, 04:00:04 pm
content: Quote from: MisterDiodes on June 25, 2017, 03:33:03 pmthanks.could you elaborate on Dr. Frank's approach?regards.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 25, 2017, 04:03:39 pm
content: Quote from: MisterDiodes on June 25, 2017, 03:33:03 pmagreed.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: June 25, 2017, 06:08:46 pm
content: Quote from: zhtoor on June 25, 2017, 04:00:04 pmREAD the LTZ thread - from the beginning. Around 2013 - or google it. That's one way. But if you think a $6 precision resistor is too expensive (THE best value / bang for the buck in the precision world is a PWW from Edwin Pettis) you maybe won't like the approach. But it's a technique that works. It'll get much more expensive from there, if you want even tighter stability.A 732a/b is the ultimate example of a stable 7V to 10V converter, and it takes much more thoughtful design than the Vref itself.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 25, 2017, 07:45:02 pm
content: Quote from: MisterDiodes on June 25, 2017, 06:08:46 pmi agree about Edwin's bang/buck, simply the BEST.i do like the approach, actually i was thinking of a design with 3XLM329's = 6.95 X 3 = 20.85V brought down using a precision divider to 20Vand from then on self-checking ratio's (more than one way to skin the cat there.)regards.

author: voltampere
author_rank: Regular Contributor
timestamp: June 25, 2017, 08:16:19 pm
content: Thank you very much guys!!!I am about to rethink my strategy.My choices :A) Stick with my original plan. Just copy TIN´s REV 3 board ( with the LTC 2057, like many others already did).B) Copy TIN´s board and squeeze two LT1013 in ( and use only half of their two Op Amp´s ).C) Find the guy who designed a board with the LT1013 and copy that. ( any hint who did it ? ).D) Design my own on a prototype board. ( i will probably do that anyway at some point... )By the way...Are you sure you want to move the discussion about the proper OpAmp for LTZ1000 circuit to this thread?Wouldn´t it be better to keep it in the original LTZ1000 thread?RegardsJoerg

author: Andreas
author_rank: Super Contributor
timestamp: June 25, 2017, 08:45:56 pm
content: Hello,E) if you really are afraid using LTC2057 then you could also use a LT1006 (= half 1013). (See cirquit on page 1 of the LTZ1000 datasheet).After 1,5 years running 2 references with LT1013A (hermetically) and 2 with LTC2057 I still see no correlation of ageing to the OpAmp used.The only correlation is to the datecode of the LTZ1000A (2 datecodes mixed among the Op-Amps).Dont make yourself shy up to now I have not seen any prove that choppers are worse than the LT1013.By the way: On the newer Fluke 8508 you can see a LTC1150 on the reference board. (its somewhere in the LTZ1000 thread).The real disadvantage of the KX-board is that you are very limited with populating reasonable resistors.With best regardsAndreas

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: June 25, 2017, 10:07:29 pm
content: To stay on track: The point is, IF you're spinning a new board, use the '1013. That is exactly what LT will tell you. There is absolutely -zero- reason to use anything but that.If you want to re-use a not-optimum designed board, that's fine also. You probably won't see the change in drift over time unless you're setup to measure for that, and not unless you're comparing to other board designs. The change in drift is small with choppers, but there, and different LTZ die will react differently. If you're just playing with old un-cal'd eBay stuff to measure with, then you would never know the difference anyway. Ignorance is bliss.But the circuit is simple and it's not like its a big deal to bang out a board to fit what you need, and do it right. It's not like the boards cost anything compared to whatever else you're doing. I like to do it right, when I can. If you can't spin you're own board, then just use the existing design. It's still fun!Andreas: We've covered this before. Any amp will work OK and you might not see the difference with -your- measuring equipment, but the current noise is in choppers inputs is really -very- high at chopper freq. And yes you can very much see the stress effects on the LTZ crystal lattice in the lab. All the chopper current does is prevent the LTZ die from relaxing completely over time - and the other reason is we don't ever want to add UN-necessary current flow loops into the otherwise pristine analog system. I know you have extra caps on your amp inputs, but there wasnevera good reason to change the amp in the first place. In any case, I'm glad it worked OK for your needs and for your measuring uncertainty, at least for a few boards. Make a few hundred of various LTZ versions and you'll see a bit different story when looking close at accurate, calibrated ppm changes over 5 / 10 / 20 years or more. You'll learn that you want the lowest possible added noise in the zener current flow.In fact we've pointed that ancient chopper amp mistake Fluke made back to Fluke engineers, years ago - that's not a new circuit design. A lot of design engineers don't have a clue what the charge injection noise is on those choppers, and when you finally look for that... Holy Smokes!. Don't hit your circuit with that unless you are ready for it!There's a reason the lab is full of 3458a's also...really the most successful and profitable design over decades. They are showing you how to make a very good and stable Vref circuit. It's not hard learn from that. The next thing to study is observe how they get 28 bits resolution from a 12 bit ADCYes - This thread along with the Jumper thread probably all belongs over in the big LTZ thread.

author: TiN
author_rank: Super Contributor
timestamp: June 26, 2017, 12:25:33 am
content: Quote from: Andreas on June 25, 2017, 08:45:56 pm8508A is using LTFLU reference, not the LTZ1000.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: June 26, 2017, 01:34:21 am
content: Quote from: TiN on June 26, 2017, 12:25:33 amFluke had tried choppers for replacements on lots of other equipment also with less-than-perfect results, and Fluke engineering got in a hurry sometimes - and they really had a period of floundering for a while. Their are good places for zero/drift chopper amps but really watch out for input current spikes - that part is glossed over on the datasheet about how big those spikes are - and how temp. dependent they can be. '1150 / '1151 are relative duds compared to the newer stuff. Late 80's / Early 90's. Everyone thought these would replace all amps.At least marketing thought so.We even had one affecting the signal from a laser diode test setup - the AZ amp was supposed to be watching some steady current flow on a low power chip-scale diode, and the dammed thing was modulating the laser output with those input current injection noise spikes, which then showed up on the optics. Oops. Learned an expensive lesson on that one. Since then we've been very wary on where they are used.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 26, 2017, 03:12:18 am
content: Quote from: MisterDiodes on June 26, 2017, 01:34:21 aminteresting "dimples" on the interferogram

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 26, 2017, 03:17:04 am
content: Quote from: MisterDiodes on June 25, 2017, 10:07:29 pmmaybe we should ask kleinstien to do a spice model for that one!regards.

author: voltampere
author_rank: Regular Contributor
timestamp: June 28, 2017, 10:00:51 am
content: Quote from: Andreas on June 25, 2017, 08:45:56 pmThat should be the easiest compromise for the beginning!Thank you...Joerg

author: SvanGool
author_rank: Regular Contributor
timestamp: June 28, 2017, 11:09:21 pm
content: For the statistics:I got reported today that there are more than69 KX V3 referenceboards already purchased fromOSH ParkThere were already more than40 KX V1 referenceboards around from the group buy bymimmus78CongratulationsTiN, you have gotmore than 100 KX boardscircling around, we might see some real LTZ1000 traction in the coming months, what a motivating initiative you started!

author: TiN
author_rank: Super Contributor
timestamp: June 28, 2017, 11:27:18 pm
content: Crazy, I wish we would ever see data at least of 20% of that...

author: voltampere
author_rank: Regular Contributor
timestamp: June 29, 2017, 06:26:57 pm
content: I promise to share my data.But first i need to build the KX-REF. ( and bring my meters into a trusting condition... )I have some questions regarding the fabrication of the board.allpcb.com is asking for details that i cannot give....So far i chose :Layers : 4Thickness : 1.6 ( other options 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 2.0, 2.4, 3.0 )Solder Mask : redSilkscreen : whiteSurface Finish : Immersion GoldNow the rest that i can only guess :Min spacing : 5/5 mil ; 6/6 mil ( 6/6 is the default )Min Hole Size : 0.25 mm ; 0.3 mm ( 0.3 is default ; do we need smaller Holes ? )Immersion Gold thickness : 1u" ; 2u" ( 1u" is default ; is that u" a micro-inch, a thousandth of an inch ? )Golden Finger Beveling : yes ; no ( *Both sides bevelling with 35°?Same treatment with chosen Surface Finish )Via Process : Tenting Vias ; Vias not covered ; plugged vias ( Tenting vias is default )Finished Copper : 1oz ; 2oz ( 1oz is default )I would appreciate some help here...Thank you very muchJoerg

author: TiN
author_rank: Super Contributor
timestamp: June 30, 2017, 04:30:41 am
content: Min spacing :6/6 mil( 6/6 is the default ) is OK.Min Hole Size :0.3mm will be ok.Immersion Gold thickness :1u" is OK.Golden Finger Beveling :No need, there is no edge connector.Via Process :Tent all via.Finished Copper :1oz finish.You should try blue or white soldermask. So we can have all color variants of KX'es running around.

author: Muxr
author_rank: Super Contributor
timestamp: June 30, 2017, 07:05:14 am
content: I've built my KX reference with some janky resistors for now.. she's burning in, while I wait for real resistors to arrive. Will share my findings as well.

author: voltampere
author_rank: Regular Contributor
timestamp: June 30, 2017, 08:05:00 am
content: Quote from: TiN on June 30, 2017, 04:30:41 amThank you ...So its pretty much default all the way....Soldermask will be blue then....Joerg

author: hwj-d
author_rank: Frequent Contributor
timestamp: June 30, 2017, 09:51:05 am
content: Quoteyesss...don't like this white ones

author: voltampere
author_rank: Regular Contributor
timestamp: July 12, 2017, 10:28:08 pm
content: I received the boards from allpcb.com.They are not perfect, but as far as i see it ( i am not experienced ) they should work.Compared to the pictures from TIN´s website the silkscreen has a slight "offset".I ordered a couple more boards than i need.If you are interested please send me a PM.Regards JoergEDIT:I just found out that i posted two pics of the backside of the board, now attached a pic of the frontside as well.

author: hwj-d
author_rank: Frequent Contributor
timestamp: July 12, 2017, 10:41:14 pm
content: Nice boards.

author: TiN
author_rank: Super Contributor
timestamp: July 12, 2017, 11:42:41 pm
content: Looking good to me. Silkscreen is not on the pads, so who caresWatch out on thin double trace to pin 3, make sure it's not open.

author: voltampere
author_rank: Regular Contributor
timestamp: July 13, 2017, 09:55:32 pm
content: Quote from: TiN on July 12, 2017, 11:42:41 pmI am not too worried about the silkscreen.Just wondering if it is their standard "quality" of if it is because of some file conversion trouble.They could not use the drill file of your Gerber archive without making some manual "adjustments".So maybe the silkscreen is also "adjusted" in some way?Thank you for ypur advice on the thin trace.I will check when i´m back home on saturday.Is it this one?RegardsJoerg

author: TiN
author_rank: Super Contributor
timestamp: July 13, 2017, 09:57:45 pm
content: Yes. Looks ok though on the photo.