[#3300] Wavetek 7000, the hidden gemstone. - Page 1
Forum section: electronics / general

author: TiN
author_rank: Super Contributor
timestamp: May 14, 2018, 05:04:11 am
content: Yay, post 3300...As some already know, MM Labs got greedy hands on (not cheap at all) Wavetek 7000 cells, sold recently on ebay.While I'm working on the article and study of design, here's glimpse on data over last few days:Two W7000 cells are measured.Cell 1 TW7000 measured by calibrated 3458A in differential to calibrated Fluke 732B (9.99992738 V).Cell 2 MM7000 measured by calibrated K2002 in differential to same Fluke 732B.Environment suboptimal due to ambient temperature oscillation from aircon, but even then output is within+/-0.2 ppmwindow.More to come..

author: Pipelie
author_rank: Regular Contributor
timestamp: May 14, 2018, 06:01:05 am
content: cool!I think the resolution of the y-axis (voltage) is too small to read.HP3458A hates air condition... for sure. at least mine does.

author: kj7e
author_rank: Frequent Contributor
timestamp: May 14, 2018, 03:57:27 pm
content: When I was a kid, I would read the old HP catalogs cover to cover. I remember seeing in the 1969 catalog how they kept the Cal Lab room held to + or - .03deg C, IIRC they used water pipes in the walls and floor to regulate temp. Think I was 9 when I first saw that, it amazed me then and still does now.

author: quarks
author_rank: Frequent Contributor
timestamp: May 14, 2018, 05:24:17 pm
content: looking forward for more to come

author: Pipelie
author_rank: Regular Contributor
timestamp: May 16, 2018, 06:00:21 am
content: Quote from: kj7e on May 14, 2018, 03:57:27 pmI think that's how we do in the north of China in winter.

author: TiN
author_rank: Super Contributor
timestamp: May 16, 2018, 09:45:14 am
content: More ppm hunting commited.Allan deviation plot on data also shows that at short observation time &tau;, the ADEV is higher due to reference and meter noise. At longer &tau;, instability slightly decrease because the noise averages out. At still longer &tau;, the ADEV creep up again, suggesting that the meter stability is gradually drifting over time and impact from other factors.Here was result with ADEV of same 3458-002 measuring reference directly on 10V range.

author: TiN
author_rank: Super Contributor
timestamp: June 25, 2018, 03:56:44 pm
content: Completing expensive inner-circle USA cal club round for 2018, box with my Wavetek 7000 is on the way to me, yayBefore thing arrives, I can share the following photos taken during the calibration in May 2018.Since 7000 has no history or calibration certificate, decision to adjust it was made.Prior to adjustment value was measured on direct DCV range, with in-cal 3458A/002 (KS Loveland annual service).After this, Wavetek 7000 was connected opposite to in-cal Fluke 732B, which has assigned value with uncertainty 0.33ppm and accumulated few calibrations to establish predicted value at the time of W7000 cal.732B value is expected to be 9.99992738 VDC.Wavetek 7000 was adjusted 78.3 uV higher than 732B, to result new calibrated value+10.00000568VDC. (ignore incorrect multiplier on VFD).Resulting direct measurement: +10.0000056 VDC, which is spot on.I plan to calibrate some of my LTZ references , one 3458 and one 2002 to this Wavetek, and then ship same 2002 to calibration, to increase confidence that DC Volt import this year for my lab is good.Once all is confirmed, this will be used as my primary reference, together with my zombie 792X battery-backed LTZ FX 10V-reference box.

author: TiN
author_rank: Super Contributor
timestamp: July 03, 2018, 12:01:57 pm
content: Another day, another Doug.W7000 finally delivered to me today. Now it's going thru it's conditioning thing.Once it finishes conditioning (that takes about 8.5 hours) logging will start in both direct measurement and differential to my 792X LTZ-box (large scary box on top of 3458As).You can see K2400 powering the unit on backstage right. Keep heatsources like SMU far from precision stuff

author: doktor pyta
author_rank: Frequent Contributor
timestamp: December 08, 2018, 05:09:17 pm
content: TiN,can we expect photos of the PCBs of this rare device?Existing ones don't satisfy my curiosity...

author: TiN
author_rank: Super Contributor
timestamp: December 08, 2018, 06:03:29 pm
content: Yes, you can expect photos and schematics. It's just too muchdistractions here, sorry... Silly equipment from ebay keep coming and coming...

author: branadic
author_rank: Super Contributor
timestamp: May 19, 2019, 03:42:48 pm
content: I pretty much appreciate tear down pictures. This unit is really interesting and with the upgraded battery pack with 1700mAh instead of 850mAh and thus 30h instead of previously 16h together with it's low power consumption <1W this is the perfect candidate by now for hot shipping. So Illya, you might want to put the teardown in the upper place of the priority list?I'd also like to know more about the recovery methode, especially the details not covered by the patent or the paper. Would be great. A live stream on that is also welcome-branadic-

author: TiN
author_rank: Super Contributor
timestamp: May 19, 2019, 06:01:18 pm
content: Okay, I'll try to move it up, sorry.I'm arranging my 732 calibration versus new SI Volt (Happy metrology day everyone!), so I want to close up 7000 as add it into my current 24/7 DC ref bank as 4th reference. So this has to be done earlier than later.Some of pictures are already taken:here

author: branadic
author_rank: Super Contributor
timestamp: May 26, 2019, 01:50:15 pm
content: So I was looking at the pictures and do wonder a bit.Around LTZ they use TDP16031000 and TDP16031002 resistor network as well as a 30k foil resistor. Can someone explain how they are arranged to set temperature? Is 100R network to form precision 120R resistor?Furthermore they have 3x TDP16031002 to form 7V/10V boost. Fluke shows, that they need 16 resistors to to do that, so third network must be wired in a different fashion, but I can't figure out how.Has someone a schematic of Wavetek/Fluke 7000 or an idea?-branadic-

author: branadic
author_rank: Super Contributor
timestamp: June 09, 2019, 11:20:58 pm
content: Reverse engineered front panel pcb by the pictures available onhttps://doc.xdevs.com/docs/Wavetek/7000/and simplified the resistor network arrangement.-branadic-

author: doktor pyta
author_rank: Frequent Contributor
timestamp: June 10, 2019, 01:22:30 pm
content: Tin, maybe I missed some thread but have You seen this burned resistor (pic) ?

author: TiN
author_rank: Super Contributor
timestamp: June 10, 2019, 01:47:26 pm
content: Yes, already fixed that. Onboard battery pack charger / power supply escaped some smoke.

author: TiN
author_rank: Super Contributor
timestamp: June 30, 2019, 02:46:40 am
content: In case somebody want to dig into reverse-engineering LTZ cell, here'sspaghetti-schematicsloosely based on physical placement.Will need to check all nodes again and redraw it all into human readable shape.

author: chekhov
author_rank: Regular Contributor
timestamp: February 07, 2021, 06:09:00 pm
content: Hi, it's been silent here for quite some time, let's add a bit more info about W7000.I thought it would be great to have 'complete' schematics of this little reference, at least to better understand what's going on.TiN and branadic did a great job posting schematics of reference board and front panel board, why don't add main board to the list ?So here we are. I drew traces how they actually go at the top layer of main PCB, put it all in KiCAD and tried to decrypt it.Main board image with traces and componentsSpagetti-schematics and following draft are as pdfs, too huge to be pictures:'(That's still looks like draft and will likely stay in that shape, but may help someone who curious about what's happening here.KiCAD labels are used absolutely improperly and component index may look weird, sorry for that.Most of the circuit is doing power-related job, a few places which control battery and input voltage and turn on/off other parts, there is a block that manages connection of the output to the back connector as well as helps control unit to get module's state. I haven't really tried to understand exact communication, anyway I don't have control module, and still there a few question about signals going from reference board.And of course output trimming circuit, the most valuable thing. Though it was already discussed in publication, here is how it looks in reality.I also added schematics of input part of power supply (made of separate components, though newer version uses LT1533) and front panel (keeping component names the same as in branadic's image).Though I tried to avoid errors, they are always may exist, obvious or not.Everything is also stored in our invaluable place -https://xdevs.com/doc/Fluke/7000/sch_chekhov/, including high-resolution images.

author: chekhov
author_rank: Regular Contributor
timestamp: February 07, 2021, 06:09:54 pm
content: Draft schematics of reference PCB was added.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: February 07, 2021, 07:20:26 pm
content: Thank You very much, chekhov !

author: branadic
author_rank: Super Contributor
timestamp: May 31, 2021, 10:53:58 am
content: Thanks for sharing your latest version, chekhov.Some good additional information on the design solution can be found inSetting New Standards for DC Voltage Maintenance SystemsandSetting new standards for DC Voltage Maintenance Systems - A Solid State DC Reference System-branadic-

author: dietert1
author_rank: Super Contributor
timestamp: June 03, 2021, 09:12:20 am
content: The LTZ1000 circuit shown includes TC compensation derived from the temperature behavior of Ube of Q18. The signal path is by R33. This is an improvement over the datasheet proposal, where TC compensation is derived from the heater voltage. While the first one is almost linear in temperature (at about 2 mV/K), the latter is proportional to sqrt(T) - an unnecessary complication.In my LTFLU references i am also using an Ube derived TC compensation and found it very convenient to first set TC compensation to near zero and then fine tune the oven set temperature to the min/max of the residual TC curve. Anyway one needs to vary the oven temperature to find the flat min/max of TC.Regards, DieterPS: Of course another point why deriving TC compensation from the heater signal is a mistake: When i wrote sqrt(T) in reality it is sqrt(TDUT - Tambient). Another complication, since Tambient will normally vary. In my opinion a clean design extracts a precise TDUT measurement from the reference together with the voltage.

author: branadic
author_rank: Super Contributor
timestamp: June 03, 2021, 10:03:50 am
content: I agree with you, but think it is much easier than one might think. It follows the approach, that you would do with any other temperature compensated reference. I always wondered where the z.t.c. temperature of the non-ovenized LTZ with R1=120 Ω as per datasheet schematic can be found. Unfortunately I don't have an oven going high enough in temperature to investigate that, but expect it to be around 80 - 90 °C.I've tested a simplified version of the W7000 schematic myself - doesn't include the conditioning and not all of the trimming - but was able to set the z.t.c. temperature of the non-ovensized zener to about 48 °C, measured with a temperature profile monitoring the LTZ internal temperature sensor. I've then adjusted the LTZ oven to that temperature and trimmed the remaining and already small and completely linear t.c. to -0.0106 ppm/K (see figure1).From there I've started with the amplifier stage to get the zener voltage to 10 V. This stage again needed t.c. trimming, but also trimming of the output voltage itself, which influence each other.Unfortunately, the classical resistor divider and mainly the output voltage trimming inside of it added a small portion of non-linear t.c.. The result I've reached so far is an output voltage of what I think is 10.000 005 4 V - average over 100 samples - with a linear t.c. of +0.0138 ppm/K, but containing a non-linear part (see figure2).-branadic-

author: dietert1
author_rank: Super Contributor
timestamp: June 03, 2021, 10:37:58 am
content: The Wavetek 7000 supports independent fine adjustment of TC (jumpers around RN3) and oven set temperature (jumpers around RN1). In this respect the LTZ1000 datasheet circuit is a mess and it's near impossible to demonstrate TC alignment or misalignment with that circuit.Regards, Dieter

author: branadic
author_rank: Super Contributor
timestamp: June 05, 2021, 10:20:56 am
content: Doing a lil' bit more of a tweaking and measuring this is what I ended up with, a linear t.c. of 0.0068 ppm/K (figure3). I do hate the higher order portion though. Stability is good, when comparing the reference inside the thermal chamber at 23 °C against my F7000-2 sitting at room temperature (figure4). So the variation that can be seen mostly comes from the meter itself.Am I'm happy with the result? Actually not, I guess I will remove the gain, turning it into a simple buffer for the zener, while scratching my had how to improve the gain stage without adding any high order t.c. component to it.There is so much to learn from the W/F7000.Edit: A full article about that reference is availablehere-branadic-

author: chekhov
author_rank: Regular Contributor
timestamp: September 12, 2021, 09:46:44 pm
content: Today little accident likely revealed the whole story of failure of this particular unit.Attempt to connect chassis to 10V LO output lead to immediate 'reboot' of the unit.Rather quickly the culprit was found, it was a battery pack:One of bolts that keep this battery pack shorts single cell to chassis, depending on how it was screwed and addition al unit movements.Thus, initially burned 1 ohm resistor was likely the consequence of doing the same what I did, but for a longer period of time. Could you imagine, this little mechanical issue lead to whole this story.

author: TheSteve
author_rank: Unknown
timestamp: September 12, 2021, 09:55:58 pm
content: Wow, a pretty terrible assembly job of that battery pack, nice job finding the fault.

author: branadic
author_rank: Super Contributor
timestamp: October 05, 2021, 09:49:44 am
content: Just thinking loud...When I've build the reference presented here, I was first measuring the initial and residual t.c. with the oven set to the z.t.c. point of the zener and found it to be at +0.175 ppm/K. The reference was buffered only.I've then compensated this t.c. and ended up at -0.0105 ppm/K after this step.Afterwards I've installed the boost to 10 V and found the t.c. to be -0.195 ppm/K, that was then trimmed within the boost stage.So question is, could the residual positive t.c. of the reference have compensated for the negative t.c. of the boost stage? Seems like I need more investigation to answer that question, so I've already removed the compensation on that board.-branadic-

author: Kleinstein
author_rank: Super Contributor
timestamp: October 05, 2021, 10:26:25 am
content: It is well possible that they only cared about the TC of the final result and choose the parts for the boost stage to compensate for the small TC of the zener part. The compensation could be intentional (select the parts before soldering) or just luck (some units work well, other may get a rework or selected trim parts).

author: dietert1
author_rank: Super Contributor
timestamp: October 05, 2021, 05:26:53 pm
content: As far as i remember we have seen schematics that included a nice measurement of zener temperature from the base-emitter voltage of LTZ1000 Q1 and then a resistor array used with jumpers to set TC in a binary fashion, with very fine LSB. No luck involved!By the way my LTFLUs include a very similar temperature measurement circuit, but i roughly compensated TC and then used the residual nonlinear TC to adjust the TEC oven for the zero TC temperature. In the LTFLU case the 10 V boost is included in the same oven.Regards, Dieter

author: aronake
author_rank: Frequent Contributor
timestamp: December 29, 2024, 03:20:23 pm
content: Does any of all knowledgeable people here know if there is any disadvantage of reducing what is called R2 in the LTZ1000 data sheet to 30K as Datron/Wavetek have down to 30K? Analog may just not have thought of the benefit of a much lower R2, but for the ADR1000 datasheet they just lowered it to 61.9K, and it ought to be well known to them with the benefit of lower R2 by the time they wrote the ADR1000 data sheet. And for ADR1000, there is even more benefit than in LTZ1000 as no need for the extra around 10 ohm resistor to bring the non heated TC to zero. Their unheated schematic in the LTZ1000 data sheet show they were aware of the benefits of the 10 ohm compensator and the lower R2.Amazing reverse engineering here by Chekhov of the schematics!And the "secret" final TC adjustment mentioned in some places mentioned in relation to this design, what is that?

author: Kleinstein
author_rank: Super Contributor
timestamp: December 29, 2024, 04:02:41 pm
content: Lowering R2 gives less noise from the transistor - usually more the higher frequency part, not so much the 1/f noise.At 100 µA a small transistor (e.g. bc847) should be at some 4 nV/sqrt(Hz) of white noise, which is way less than the LTZ1000 noise. So the transistor noise should not be that relevant.However it also comes with a slightly higher TC of the ref. part if not temperature stabilzed. The difference is not much: some 22 mV higher BE voltage, which results in 70 µV/K less for the temperture effect, or 10 ppm/K more for the overall TC (e.g. 60 ppm/K instead of 50 ppm/K). This makes the temperature stability and setpoint divider a little more relevant.The adr1000 has a different TC to start with, here more current could even lower the TC.

author: aronake
author_rank: Frequent Contributor
timestamp: December 30, 2024, 02:32:41 pm
content: Quote from: Kleinstein on December 29, 2024, 04:02:41 pmThanks for this! My pretty basic tests with ADR1000 seems to indicate 0 TC unheated at around 25K ohm for R2 though. So benefit would be lower noice and lower TC. One abvious disadvantage thugh is slightly more current draw, but that ought to be compensated by the heater drwaing less current. So still very unclear why data sheet say 69K, but there seems to be benefit in most areas by setting this lower.

author: chekhov
author_rank: Regular Contributor
timestamp: December 30, 2024, 04:46:53 pm
content: You may try different combinations of R2 and R1, can also decrease current back. Maybe question of time spent running thermal sweeps with different combinations in order to select desired temp set point.https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg5507800/#msg5507800Unfortunately that all does not help with LTZ1000, and upper Rz may add much more long-term instability and its own TC as well.

author: aronake
author_rank: Frequent Contributor
timestamp: December 30, 2024, 06:19:02 pm
content: Quote from: chekhov on December 30, 2024, 04:46:53 pmI am working on this now.I use an IET PRS300 for R2.https://www.ietlabs.com/prs-300-programmable-decade-resistor.htmlSo I can automate change of R2 as temperature goes up and down. Then trying 70, 80, 90 and 100 ohm for R1 which I change on the board. Using an ADR1000.I still dont see any benefit in such high R2 as 70K as per the data sheet.

author: aronake
author_rank: Frequent Contributor
timestamp: December 31, 2024, 04:06:24 am
content: I have found a VERY strong reason for not using too low R2. R2 is allready the resistor that have most impact on output voltage. Lowering this from 69K as per the data sheet to 24K where typically unheated TC is zero, dependence on the resistor increase more than 10 times! At 69K it is still very possible to make a very low heated TC, but lowering R2 to 24K would make this even better, but as R2 age with time and change resistance value this would have a much bigger inpact on outpur voltage so a much worse long term stability. And long term stability generally being much more important than 0 TC.What i did was to keep ADR1000 datasheet circuit at 65 degrees, then change R2 to some different values and measured voltage output.

author: chekhov
author_rank: Regular Contributor
timestamp: December 31, 2024, 07:24:11 am
content: Yep, that's true, if I'm not mistaken, around 20k R2 influence factor is smth like 55:1, far from what datasheet shows. But this is where 0 TC is located for me.I think that more relevant info for ADR1000 thread.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 31, 2024, 09:17:48 am
content: The increasing effect of R2 drift is indeed a reason not to lower the resistor. It is however not as bad as the numbers in the table suggest. The relevant part is the relevent change in the resistor, not the absolute change. It still gets roughly 3 times worse at 24 K.