Fluke 5440A calibration - Page 1
Forum section: electronics / general

author: Rax
author_rank: Super Contributor
timestamp: September 20, 2023, 01:17:00 am
content: Hi all,Having just repaired my 5440A, I'd like to get it up to snuff.There seem to be a few stages to this:Power Supplies (3-16, p.3-7) - pretty straight forward. This unit's levels were quite off when I checked them (before the repair). The unit passes all internal tests and measured exceptionally well before its first Int Cal (in my possession)Square Wave Generator (3-19, p.3-9) Not quite sure what the impact of this would be. Whether it absolutely needs to be completed.A bunch of others I may not focus on, at least in planning stages.External Calibration (3-27, p.3-18) Major ticket item, of course. A couple of basic questions here is that it's not able take a specific value close to 10V (such as, for instance, the Cal Club could provide). My solution to this - which I'm not sure how feasible, so I invite input - is to dial in my 731B to 10,0000000V, as indicated by my Prema 6048 (which I trust, don't REALLY ask me why) and use that for the 10V step. Still thinking through the procedure, but do I absolutely need a null detector?- For the higher ranges, I can likely use my DP 8200's 100V output, though I don't think it'd be any improvement over just relying on the 5440A's own scaling linearity, as Dr Frank suggested on a different thread. I don't have anything for 1000V.- For the lower ranges, I'd use by KVD to divide down the 10V from the 731B.Thanks for sharing your input.

author: bdunham7
author_rank: Super Contributor
timestamp: September 20, 2023, 03:08:06 am
content: Quote from: Rax on September 20, 2023, 01:17:00 amI'd be reluctant to actually make a calibration adjustment to either of those two sources until I had a decent history on the unit and knew its behavior (stability and tempco) over some time. The 5440A is probably your most stable and accurate device by OEM specifications. It is using the same reference as the 731B but with an oven. And at this level, you start to really need a temp-controlled environment.Are you absolutely sure about the inability to take voltages that deviate from nominal as a reference? This would seem to be a huge oversight and this ability appears as step 9 of every 5440-series manual I could find, although I'm not at my normal computer at the moment and don't have an actual 5440A service manual handy. After all, every other Fluke microcontroller operated device that has software calibration entry has this ability, even the old 8500-series DMMs.

author: Rax
author_rank: Super Contributor
timestamp: September 20, 2023, 04:53:09 am
content: Quote from: bdunham7 on September 20, 2023, 03:08:06 amWhich is why the way I envisage doing this is relatively consequently (within a day or, say, a weekend; even, if possible, in immediate sequence). I think I'd be able to complete the procedure with temperature variations of less than 1C.The 5440A is, from my observations this far, in a completely different league than what I've seen before. I think the 731B is possibly not too far, but essentially, I'd use it purely as a transfer standard. I think as such it's intended to travel, be shipped maybe, experience some temperature variations, etc., but in my case it'd experience none of that.Quote from: bdunham7 on September 20, 2023, 03:08:06 amI'm not, this is from a relatively cursory read of the SM. Currently traveling for work, so limited capacity for this, but was hoping for some input from those with experience on this unit.But the 5440A SM I have doesn't have a step 9 at the External Calibration procedure... ?... (mind you, the 5440A SM is only available as an Artek PDF, and is definitely different than the Bs or the 5442). Only seven steps in that one. May be a difference in software?

author: Rax
author_rank: Super Contributor
timestamp: September 20, 2023, 01:39:38 pm
content: Here are the pages on the "External Calibration" from the 5440A SM.

author: bdunham7
author_rank: Super Contributor
timestamp: September 20, 2023, 02:04:09 pm
content: It's in the second sentence of step 6.c.I think the USA Cal Club FX standard is the best possible answer for 10V, something recently transferred from that might be next-best. But on those lower ranges are your substitutes for the 752A really adequate? Personally I would only be adjusting it's calibration if I was reasonably confident I knew both how stable it was and approximately how much it was off--after comparing with multiple independent references. Your 5440A may well turn out to be the most accurate instrument of your entire lot, especially after a 30-day power on bake out.

author: Rax
author_rank: Super Contributor
timestamp: September 22, 2023, 03:24:55 am
content: Interesting stuff here: "calibrate the calibrator"

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 22, 2023, 12:13:30 pm
content: At first, you only should calibrate your 5440A externally (@ 10V range) if you have an external standard which is uncertain relative to NIST lesser than 2ppm.If you assume that your PREMA is uncertain to that level, you can use it directly, by measuring the 10V output from the 5440A during external calibration, and correct the 10V cal constant of the 5440A accordingly.0.2 and 2V ranges always need such an external calibration as well, i.e. they also could be directly measured by a calibrated DMM. The 3458A would be suited best, as it auto calibrates its 100mV and 1V ranges, and therefore transfers its 10V uncertainty to these ranges. Its 1V range should be used only, for both ranges of the 5440A. Removal of offsets greatly enhances the uncertainty of the 5440.As said, the 250V and 1kV ranges of the 3458A have too high an uncertainty, see its specifications vs. the required ones of the 5440.The 20V range of the 5440 is additionally quite difficult to calibrate with a 3458A, as this would be done on the 100V range, and the 100:1 divider in ANY long scale DMM deteriorates its uncertainty, due to the high level of internal offsets, and impact from internal bias currents, because all applied voltages are measured in its internal 1V range only.Anyhow, you only need to calibrate 0.2, 2, 10V ranges externally, and the 20, 250 and 1000V ranges are sort of auto-calibrated by INT CAL, so usually need no additional external calibration any more, if they are once properly calibrated at FLUKE. That's called the abbreviated external calibration, as can be found in the calibration chapter of the operation manual:'The principal function of External Calibration is to correct for any shift in the Calibrator's internal Voltage reference.A second function is to correct for long-term drift in the internal voltage divider resistors used for the 2.0V and 0.2V divided output ranges.All other time and temperature dependent changes in the Calibrator are corrected by the Internal Calibration procedure.'The differential method of full calibration originates from the old days, when there were no long scale DMMs, i.e. Fluke 335D, 720A, 752A, 732A and 845A made up a complete 7.5 digit calibration and measuring system from 100mV to 1kV. See:'Calibration: Philosophy in Practice', 1stand 2ndEdition, FLUKE.I have fully calibrated my 5442A after 13 years, for the first time ever, because HighVoltage kindly lent me his 752A, and I had a quite reliable 10V source available at that time, FLUKE 7000, which was calibrated by TiN to < 1ppm.I have to say, that the deviation in all ranges were very minute. If I remember correctly, the shift of its internal 13V reference (i.e. its 10V range) was below 0.5ppm. The deviation of the higher ranges was about 1.. 1.5ppm, I guess. I have to search, but I think I published the calibration setup and results.In summary, I would recommend to not re-calibrate your 5440A, as its uncertainty in its 10V .. 1kV ranges is probably much better than your PREMA.Please get a calibrated 10V reference from your US CAL Club, to importThe Voltinto your lab, as bdunham7 already proposed.Frank

author: Rax
author_rank: Super Contributor
timestamp: September 23, 2023, 06:07:34 am
content: Quote from: Dr. Frank on September 22, 2023, 12:13:30 pmWould it be difficult to find a link to those results, please? I've dug pretty hard, and I found different references to that thread (?), but I don't think I quite located the actual one. I'd appreciate some assistance with that.Thank you.

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 23, 2023, 03:42:44 pm
content: Quote from: Rax on September 23, 2023, 06:07:34 amI did not publish a dedicated thread about the calibration of my 5442A, so it's hard to find. Sorry that I sent you astray.It's contained in the discussion about the Hamon Divider:https://www.eevblog.com/forum/metrology/influence-of-switch-resistance-in-hamon-dividers/msg4207093/#msg4207093Therefore, the basic 10V calibration probably changed around 1ppm over 13 years, and the ratios of the upper ranges 1.6ppm at most, maybe caused by the assumed leakage or linearity fault of my box.Anyhow, all ranges would still have been inside the 5440B, 30d Uncertainty specification, even before the full external calibration.The ratio change would only violate the 30d Stability specification (0.5 .. 1ppm).The 1kV linearity specification (1ppm) is not fulfilled, so that's another hint for a possible fault inside the box.But that's all extremely stable, so my advice holds, to rely more on the 5440A, than on your PREMA.Frank

author: Rax
author_rank: Super Contributor
timestamp: September 24, 2023, 06:02:52 am
content: I've looked a bit closer at my initial "post INT CAL" measurements, which were concerning with an almost 12ppm delta (just earlier tonight, 9.9998785V as read on the Prema for a dead-on 10.000000V output by the 5440A). Mind you - I've, in a less than ideal discipline of methodology, done both a re-zeroing of my Prema and the INT CAL on the 5440A at the same time, between the "pre INT CAL" and the "post INT CAL" measurements collection.Tonight I tackled this again, as I got a bit more and better time to do this, re-zeroed the Prema on specifically the 20V range over 20s integration, left the low-emf AB cables with my weighty short contraption (= thermal inertia) rest to temp-equalize for few minutes every time I touched them, and benefitted from a more temperate and steady evening temperature in Southern California (= my garage @ a pretty steady 26C), and I seem to be within less than 5ppm of 10V.Given the .5ppm of reading spec of the Prema for stability on the 10V range, the 5ppm on the 1yr accuracy, the 3.5ppm + 5uV 1year uncertainty of the 5440A/B, I think what I'm seeing qualifies.I think in practical situations with a known instrument that's been performing well for a solid time and has experienced no major faults that may throw it off, one may see less than the above, but for the intents and purposes of a repair pursuit this I think tells me this is not out of the ballpark. If I get the chance of an objective reference at hand for comparison, I'll leverage that. Meaning I'd compare the reading of that and the 5440A 10V output on the Prema and draw some comparative conclusions.But for now I'll be seeking feedback on my thoughts above. Thank you much in advance.

author: branadic
author_rank: Super Contributor
timestamp: September 24, 2023, 06:55:41 am
content: As far as I remember you neither know anything about the accuracy and/or linearity and/or t.c. of your Prema 6048 nor have you changed the opamps as suggested by dieter1 to improve its INL.So I totally agree with Dr. Frank, don't trust your meter unless you have it verified against a well known programmable source to answer the open questions, as it is probably way off from being trustworth and rely on the calibrator instead.-branadic-

author: Rax
author_rank: Super Contributor
timestamp: September 24, 2023, 04:01:36 pm
content: Quote from: branadic on September 24, 2023, 06:55:41 ambranadic - yes, all that's [sort of] true. I do have corroborating evidence the Prema is in the ballpark (I'm actually looking up records, both written up and in memory, to reassess that), but no hard evidence of exactly where it is with traceability and uncertainties and all that attached to it. As we all know, getting a Prema calibrated is actually a challenge today, and very few places would even touch it. I only have access to verified (17025 data attached) "up to 6.5 digit" meters, so that's pretty severely limiting my options.It's entirely possible that, after I get the 5440A fully assessed, it could serve as the reference to calibrate/adjust the Prema. At that juncture, I'll be happy to do the mod nailed down by dieter1. A bit of a chicken and egg situation, for sure.

author: Rax
author_rank: Super Contributor
timestamp: September 24, 2023, 05:40:44 pm
content: Quote from: branadic on September 24, 2023, 06:55:41 amI've been going through some records I have from earlier in the year, when it was my turn to have the FX and the rest of the kit (I have not been very good at submitting these to the Cal Club database, but maybe this is a good opportunity). To be noted, I got the Prema 6048 at the very end of the custody, so very little quality time was spent then with both overlapping, and this was a new to me meter, etc. So grain of salt below.One 04/08, at 22.8C, after a fresh zeroing and using the low-emf AB cables I have (where Guard was floated as the FX obviously is a two wire deal), the FX was saying 9.9999712V on the Prema. Given the FX was presented as 9.99996194V, that's a hair below 1ppm off of 10V. I have other measurements that are not so close as this, but they are less trustworthy as they were done the day before with less experience on the 6048 etc.This above is one data point I have that can be brought up to establish the credentials of the Prema (all its issues set aside for a moment).

author: Rax
author_rank: Super Contributor
timestamp: September 24, 2023, 07:22:58 pm
content: Here is another reference point from the overlap time of my FX custody and very early ownership of my Prema. I posted these pics on the Cal Club USA #3 thread at the time.I think this other reading shows the Prema - (can someone please confirm my math?... I apparently can never get ppm calcs to be second nature) - being .6ppm? off of the FX, but the cables are not low-emf (just decent quality ones).Also, this obviously does 80s integration, while the example in the post just above I believe was - maybe? - 20s integration. IN my experience with the Prema, everything above 20s (providing all digits) is very consistent all the way to 80s. I'm only using 80s these days as a final vetting step when a critical reading is registered.

author: leighcorrigall
author_rank: Frequent Contributor
timestamp: September 24, 2023, 10:24:47 pm
content: Congratulations on obtaining such nice equipment. I definitely enjoy my 5440B; it is excellent.These are just random thoughts ...Make certain to reapply the thermal paste to all components that require it before worrying about performance. The original thermal paste dries up and no longer effectively dissipates heat. You want to minimize heat buildup on the PCBs before considering calibration.I heard from a former NRC meteorologist that these Fluke calibrators, in particular, should beinternallycalibrated every couple of weeks if they are left continuously in operation. I'm unsure of the reasoning because I had to move along in the tour, but I thought it interesting. Something about how they were designed, I guess. This meteorologist used the 5440B for voltage comparisons with some fancy equipment, which caught my eye. They are still very applicable in today's labs and outperform 5700A DCV specifications. The trouble is performing external calibrations if you don't have the right equipment (i.e., a null detector, voltage reference, and a voltage divider).Assuming you do not have the appropriate equipment, perhaps the best choice is to verify the output voltages for each range instead of performing an external calibration. For the most part, if the instrument has not undergone serious refurbishment and one has confidence in the internal references, the calibrator should be well within the specifications after an internal calibration. As someone noted above, two SZA263/LTFLU references make the calibrator highly stable and with excellent linearity.You will not be able to verify an unknown calibrator with an unknown meter.

author: Rax
author_rank: Super Contributor
timestamp: September 24, 2023, 10:47:05 pm
content: Quote from: leighcorrigall on September 24, 2023, 10:24:47 pmIn my understanding, the INT CAL mostly addresses (= measures) miscellaneous drifts (internal reference resistors, for instance) such that zero and gain shift errors are factored into the calibration constants (which the procedure updates in memory). The manual actually requires it as often as daily (!) after warmup and before use. Thank you for confirming the importance of this requirement with feedback from the field team. The SM says do it daily, but I think that's under the assumption it's off every night - it sounds like the team you talked to said every two weeks if running constantly, which makes perfect sense to me.What I haven't quite figured out is, in case the internal references are themselves subject to drifting, whether that throws off the INT CAL enough to essentially require the EXT CAL be performed to realign the instrument. I believe the INT CAL relies on internal voltages to calculate the revised cal constants. Sort of a chicken and egg situation, unless there's some other consideration here I'm not factoring in.In this unit's case, running the INT CAL had a dramatic effect (as high as about 12ppm!), but that could be explained by decades of being stored in miscellaneous and uncontrolled conditions. Before INT CAL, the agreement between this and my Prema 6048 - as I explained previously - was nothing short of breathtaking. But I don't put much more currency on that, other than some sort of unlikely, but not impossible occurrence/coincidence.

author: Rax
author_rank: Super Contributor
timestamp: September 24, 2023, 11:56:09 pm
content: Quote from: leighcorrigall on September 24, 2023, 10:24:47 pmGood point. Along similar lines, I've seen some carelessly placed electrolytic capacitors (in terms of PCB design) - too close to heat sinks for long life, and therefore looking pretty toasty - and I've had to mitigate that somewhat (use 105C caps - though I use that by default for recapping - and tilt them to keep them as far away from heat as possible). As we all know, a lot of equipment from the time rather optimistically sized heatsinks, underrated tantalum caps, and made other similar design decisions.Quote from: leighcorrigall on September 24, 2023, 10:24:47 pmI have a verified 731B (by means of Keysight calibrated 6.5 digit meter), the Prema 6048 (which we're trying to assess the trustworthiness of), and few other standards to go by (obviously, I need to keep an eye on any circular reliance as I do this). Unless one has access to a metrology lab, I don't think doing this kind of thing (in a hobbyist lab) is ever easy.Quote from: leighcorrigall on September 24, 2023, 10:24:47 pmOf course!

author: Rax
author_rank: Super Contributor
timestamp: September 25, 2023, 12:31:46 am
content: Aside from the FX comps, my main bench reference point (DCV) is a 731B. I got this a few months ago, and before handover it was adjusted by a good friend and former metrology lab engineer/tech. The adjustment was with respect to a Keysight calibrated 34410A, and accounted for known deviations from the normative 10V (per Keysight's almost precisely one year old long form cal cert).To gain more insight into my available DCV standards, I hooked it to the Prema 6048 today, and got readings between about 9.9999825V and 9.9999831V, which is about 1.75ppm to 1.69ppm off of 10V. This is at about 26C (one downside of the 731B is its less than stellar tempco compensation hardware provisions... though I think it's a pretty incredible performer particularly given that). For instance, a few hours later in the evening and a couple of degrees lower in the lab I see no discerning variations in the output of the 731B.Over my entire ownership of the 731B (must be about a year now?), I've mostly been seeing te 731B within less than .5ppm off of 10V, though sometimes that may show a larger spread. But that was typically triggered by a change in contingent conditions - re-zeroing the meter, disconnecting (for a different project, etc.) and reconnecting the 731B, environmental conditions variations, etc. - so by itself the 731B is very consistent, at least as observed by using the Prema 6048.To summarize, I'm taking this as another confirmation the Prema is reasonably within accuracy.I am editing that, as it may sound conclusive, which is certainly not my intention. In my prior two or three posts, including this one, I am simply accruing as much data as I can to establish trustworthiness of my bench references, and the 5440A alongside with that.I am looking forward to any thoughts and interpretations of the data presented this far.

author: Rax
author_rank: Super Contributor
timestamp: September 26, 2023, 12:33:44 am
content: I hope I'll be forgiven, but I've been editing the last couple of posts for form and clarity, and also data included. May not be the most conducive way, but as I solidify some of this data I feel revising the original post accordingly is the way to go. I think it'd worth taking a second look for those interested.

author: bdunham7
author_rank: Super Contributor
timestamp: September 26, 2023, 01:11:10 am
content: Quote from: Rax on September 25, 2023, 12:31:46 amI haven't the time or energy to read the 5440A manual (actually I don't think I have it...) but I'd like to know exactly--in minute detail--how the INT CAL process works and what it depends on, etc. I have some idea what it does for the 100V and 1000V ranges, where I think it is just using the linearity of the DAC to to a 1:10 transfer and comparison, but I don't grasp the details of the rest of it. I'd certainly want to understand all of that in detail before doing any external calibrations. Also, perhaps try the INT CAL again and see if it moves again or holds steady. If it keeps changing, perhaps there is trouble somewhere.

author: Rax
author_rank: Super Contributor
timestamp: September 26, 2023, 02:24:02 am
content: Quote from: bdunham7 on September 26, 2023, 01:11:10 amThis is why I'm saying this is in a different league in stability than anything I've seen before (and probably puts a good word for the Prema, as I wouldn't see it unless the DMM could read it).Once I connect the 5440A which has been running for a few days now, it goes rock solid to the 9.9999500V I know it registers on the Prema. I am seeing variations of less than .1ppm as it cycles through 20s readings for a while as I'm doing other things around the bench (I've been watching it for maybe 15 minutes now). This is on a hot summer night in Southern California, (27.7C in the garage). I've seen the exact same value, within those variations, since its first INT CAL from a few days ago.I am doing this to be sure what to expect after another INT CAL if I run it right now.

author: Rax
author_rank: Super Contributor
timestamp: September 26, 2023, 02:50:49 am
content: After the INT CAL, the 10V out of the 5440A seems to be pretty solidly at 3.1ppm off of a perfect 10V (in Prema's opinion) at 9.9999687V. So a bit closer to spec than the 5ppm I saw prior. Current variations are of less than .04ppm (...684 to ...692). We'll see...I'll let run it until the morning and see what it thinks then. But maybe it just needs a good "30 day bake," as you put it, bdunham7. And maybe a few more INT CALs to really hone into the drift as the unit expels any moisture and crud and bad spirits by running for a while.

author: Rax
author_rank: Super Contributor
timestamp: September 26, 2023, 12:45:46 pm
content: Quote from: Rax on September 26, 2023, 02:50:49 amAfter running all night, at currently 25.6C, I'm seeing it somewhere near 9.9999648V (between ...44 and ...50). That's about 3.5ppm from 10V.

author: Rax
author_rank: Super Contributor
timestamp: September 26, 2023, 01:52:34 pm
content: Here are the corresponding pages describing in detail the internal calibration to facilitate the analysis.

author: Rax
author_rank: Super Contributor
timestamp: September 28, 2023, 01:17:01 am
content: Quote from: branadic on September 24, 2023, 06:55:41 amGetting more time to be thinking on this, branadic, that's not quite accurate. I am one of the contributors to the Prema 6048 with linearity tests based on my KVD measurements. I was able to replicate the "zero crossing" non-linearities observed with the Prema. I think only two or maybe three of us undertook that test.I think I've also presented some TC data on that thread. Besides, if you have access to the Cal Club #3 dataset, you'll see some relative TC measurements that compare the Prema with a DP 8200 over a pretty wide range of temperatures.Overall, I know far more on my Prema than I do on the 5440A. I do understand the 5440A has a following, and that some issues were determined to effect the Prema, but I don't think those really intersect this exploration here.But as long as we're talking about the INL issue the Prema has, if I get a trustworthy 10V reference at my bench (which is at least partly why I'm doing all this), I'll then be able to tackle that upgrade to the Prema dieter1 figured out. I am not at all convinced the INL issue with the Prema impairs its ability to measure 10V accurately.

author: Rax
author_rank: Super Contributor
timestamp: October 01, 2023, 06:08:28 am
content: Well, maybe the extended "bake-out" bdunham7 is what was needed here?...After being on for about two weeks now, and creeping ever so slightly to perfect agreement with the Prema (from about 5ppm after the first INT CAL, to then 3ppm), it's now at just about perfect agreement.I did one more INT CAL this morning - may be the 4th or maybe 5th - and then I saw it coming essentially dead onto Prema's 10V (within a measured +.09ppm and -.05ppm). Overall, today I saw these infinitesimally small variations around 10.0000000V. Far less than .1ppm for all of the time. Less than .05ppm from 10V actually, most of the time, on either side of 10.0000000V.I'll keep on watching it for the next few days or maybe weeks, but the trend seems very positive.

author: Rax
author_rank: Super Contributor
timestamp: October 01, 2023, 04:07:34 pm
content: I wonder if anyone's aware of a way to output the cal constants generated during the last INT CAL. Either displayed on the screen, or saved in a way that can be extracted from the instrument. I think they are being automatically printed (or can be) when the procedure is being completed. Also, supposedly, they can also be displayed on the screen (though I can't find any indication how that's supposed to be performed). Until I'd run the INT CAL again, it seems reasonable to believe the last generated cal constants should be available to be displayed.Given how close the measurements are currently, I'd want to have those saved somewhere, in case they need to be resurrected somehow.

author: Dr. Frank
author_rank: Super Contributor
timestamp: October 01, 2023, 05:57:05 pm
content: The Cal Constants can be printed via serial interface. Print is accessible via instrument Menu.That's they way how I calculated the calibration shifts of my 5442A.Did not figure out yet, if there's away to access via IEEEFrank

author: maat
author_rank: Regular Contributor
timestamp: October 01, 2023, 05:58:39 pm
content: The Calibration constants can be extracted via GPIB. Do you have a GPIB adapter and know you way around in Python? If you are using Linux, you may directly use my Fluke5440B libarary:https://pypi.org/project/fluke5440b-async/and seehttps://github.com/PatrickBaus/pyAsyncFluke5440B/blob/master/examples/test_functions.pyfor a full example.Otherwise, check out theGCALGPIB command and my implementation of extracting the parameters here:https://github.com/PatrickBaus/pyAsyncFluke5440B/blob/64f4869891e0b51c1e66b73948303a7bed34eab8/fluke5440b_async/fluke_5440b.py#L974

author: Rax
author_rank: Super Contributor
timestamp: October 01, 2023, 07:48:01 pm
content: After some fat-finger fumbling with the Prema - such a half-baked software/menu system...how does one exit, or cancel out of unintended modes on PROG/CONT?... - I've decided to redo INT CAL (after all, it seems to be recommended as a daily procedure per SM) and I'm a bit less dead on at around .7-.6ppm off of a perfect 10V on the Prema. My plan was to somehow record those "near perfect" INT CAL-generated cal constants, but I don't currently have a way to read GPIB. I do have a kit of parts for the "USB GPIB" but never got around to putting it together.If anything, I think this solidifies its closeness to either absolute/nominal 10V, or at least to Prema's 10V. I'm still looking for input on whether all this stuff I'm seeing is expected behavior from a fully working but recently resurrected unit. I'm inclined to think it is.Also note the Prema was re-zeroed, both in auto and 20V manual mode. To snap it our of its bonkers programming place (I have no idea where it entered, but I couldn't figure a way out), I also had to restart the Prema once. I keep it permanently on as I see not reason for it to not be perpetually warmed up.

author: Rax
author_rank: Super Contributor
timestamp: October 01, 2023, 08:12:55 pm
content: Quote from: Dr. Frank on October 01, 2023, 05:57:05 pmFrank - can you please share more on how exactly you're reading that? What sort of cable, how do you connect it to a computer, etc? I assume you don't actually use a serial port printer (which I think is how they intended it).

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: October 02, 2023, 02:08:38 am
content: Quote from: Rax on October 01, 2023, 04:07:34 pmPage 3-5 of the operators manual tells you how to display on the screen. Give it a try and just write them down! Also you should probably start logging the temperature to make sure your 5440 output is as stable as claimed around that magic 10 C band.

author: Rax
author_rank: Super Contributor
timestamp: October 02, 2023, 04:29:26 am
content: Quote from: RandallMcRee on October 02, 2023, 02:08:38 amThank you, Randall, that's it! And I can't even invoke the differences between the "5440 series" Operating Manual vs the "5440A" specific one (though the latter has it at p.3-9), 'cause... the latter has it at p.3-9!Thank you for going into it and digging that up. Very helpful.Quote from: RandallMcRee on October 02, 2023, 02:08:38 amGoop point, and I always do! Truth be told, given I haven't completely closed this up (no top and bottom cover yet on, though I'm doing my best to direct design airflows through its innards, and shields are on, etc.), the ambient air temperature and airflows may have a higher than designed impact on its stability... One could tell via GBIP if the garage door was opened to get the car in by my better half!In any case, I've taken notes of its - apparently - 20 calibration constants and given it's displaying 10.0000000V right now on the whole 8 1/2 glory of the Prema, I think I'll call it a fruitful day!

author: Rax
author_rank: Super Contributor
timestamp: October 02, 2023, 04:47:29 am
content: Quote from: RandallMcRee on October 02, 2023, 02:08:38 amThinking a little more about this, Randall - it's likely why I'm seeing these excursions on the low end of a reading on my meter for the 5440A output. It seems that typically, a warmer environment would trigger lower readings for a certain voltage output (at least with my units here), which may be counter-intuitive for most (including me). So if I, say, see 28C at my bench (hot for all lab typical conditions), I'll likely see a "lower than 10V" reading on the Prema (for instance, 9.9999995V, therefore lower than 10.0000000V).Importantly, I should probably suspect the Prema for this tempco far more than the 5440A, with its ovens for all critical stuff.The Prema has the famously uber-stable LTZ1000, but none of its circuitry is temperature stabilized. Almost everything of substance on the 5440A is.Stepping back, there's all sorts of thermal inertias of things from heavy walls to slabs to... instruments to air convection and whatnot, so it's a bit hard to really grasp how this plays into a metrology reading, but my background in both physics and building engineering (HVAC etc.) helps. I mention it because that's what I think needs to be considered.

author: Dr. Frank
author_rank: Super Contributor
timestamp: October 02, 2023, 01:13:27 pm
content: Quote from: Rax on October 01, 2023, 08:12:55 pmI have an older OKI LASER printer which still features an RS232 interface, so you just need a serial cable which fits both sides. I don't know the exact configuration of this cable, i.e. if it's got twisted TX / RX lines, handshake lines, etc. With RS232 you always have to try out, or read that d...ed manual.On the front panel, there is a menu to print all cal constants. Again, the operations manual is your friend.I'm adding a photo of the different snippets here, documenting the calibration progress of my unit.Frank

author: Dr. Frank
author_rank: Super Contributor
timestamp: October 02, 2023, 02:27:32 pm
content: Quote from: Rax on October 02, 2023, 04:47:29 amWell, I've got a basement lab which features ultra stable room temperature all over the year, i.e. basically +/- 1°C.You can have constant temperature over days and weeks within +/- 0.2°C, w/o any HVAC, only heating in winter time.Unstable room temperature, i.e. variations > 0.5°C over the measurement run (even with ACAL instruments) will ruin your day.Variations of more than +/-2°C make precise/stable absolute measurements nearly impossible. Transfer / difference measurements are another story.The 5440 might be more stable with his ovens, but my hp3458A has a (typical) T.C. w/o ACAL of +0.5ppm/°C, which you directly see in your measurements.My better half once opened the small basement windows to get fresh air inside, when my 24h stability measurement was running.That -0.5°C r.t. change created a -0.3ppm dip, so I was able to calculate the T.C., which comprises of the T.C. from the LTZ1000A circuit, plus the T.C. of U180, which can be separated by monitoring CAL? 72 and sketching that over TEMP?The heating of the room by the instruments (200W in total, I guess), plus the 36W neon lamp, plus the 100W from the operator therefore pose a real problem for high stability and transfer measurements. You first need to let the room temperature stabilize to the new level, and then you have to make your transfers quickly and monitor the temperature to make sure it doesn't change more than 0.2 .. 0.5°C.I append the temperature log from last month.At the beginning, the data logging stick had to cool down from the temperature in my office upstairs, @ over 25°C, where I always read out the data.Then you see weeks of mostly constant temperature. Outside it was quite warm, over 30°C, I think.In the 2nd half of September, the outside temperature went down below 20°C. I have not yet switched on the gas heating, which stabilizes the r.t. of the lab even more.On October 1st, I made my regular measurements, where you clearly see the warm-up by the instruments in the night before, starting @22:30.Next morning ~ 8:15 ACAL ALL with fluorescent lamp on, 7x Ohm comparisons 8:42 .. 9:00, 3458A TEMP? increase by 0.1°C.A break-fast later, there's the comparison of 13 volt references between 9:38 .. 10:06. Temperature increase inside the 3458A was +0.1°C only, but R.T. changed by +0.3°C already.ACAL temperature had been 0.6°C lower, but the absolute reading of the 3458A does not interest here, only the transfer between the 13 sources.I recently had sent two of my references to a fellow volt-nuts, together with another temperature logger.I got very similar temperature profiles from his lab, and from his measurement session.It would be helpful to make remotely controlled measurements, no lighting and no operator in the lab, but then you'd need a precision scanner.Frank

author: Rax
author_rank: Super Contributor
timestamp: October 02, 2023, 05:26:21 pm
content: Thank you, Frank, for sharing that data.In my case, I'm relatively lucky to be located in Southern California - BTW, for some mysterious reasons I have some possible explanations for, there's almost no basements here!...- which may have some of the steadiest, mildest weather on earth. This year's been extreme by our standards, so it's been unusually difficult in the lab - and who knows what the future holds - but usually I'd be well within a very modest variation (maybe 2-3C tops during a certain cycle, like a day or even a week). It does tend to be rather hot for a mysterious reason (it's on a concrete slab with two fire rated, exposed masonry walls on each side and a garage door that's receiving a fair amount of sun in the afternoon; there's a master bedroom above, that's it, and somehow it's by far the warmest space in the house!). But I have a heat pump in there, with both cool and heat cycles, so I can shave off the worst of spikes. The car does need to go in and out, so far from ideal. Home metrology!

author: Rax
author_rank: Super Contributor
timestamp: October 02, 2023, 06:20:23 pm
content: As I'll continue evaluating the state of both accuracy and stability of the unit, one other possible action item along the lines of bringing it back to spec is adjusting the power supplies. Thoughts?...I'm of two minds on this, on one hand I really like to see power supplies readjusted to specifications, on the other I'd hate to fix what's not broken and maybe create some problems.

author: bdunham7
author_rank: Super Contributor
timestamp: October 02, 2023, 06:47:48 pm
content: Quote from: Rax on October 02, 2023, 06:20:23 pmAre they out of specification now? What is your mains voltage measured inside the unit (if you can measure that reasonably safely)?

author: alm
author_rank: Super Contributor
timestamp: October 02, 2023, 07:28:57 pm
content: Quote from: Rax on October 02, 2023, 06:20:23 pmIn general, if a power rail is within tolerance, like 11.5-12.5V, then adjusting it to the middle of the tolerance band won't make a circuit work any better and may require adjusting other parts of the circuit. If it's outside specifications, then I would first look into a component defect like a dry electrolytic or drifted resistor before adjusting.

author: Rax
author_rank: Super Contributor
timestamp: October 03, 2023, 12:20:48 am
content: Thank you both - bdunham7 and alm.In a nutshell, some of the rails were not drastically off, but definitely out of spec last I checked. Some were spec'd very tightly, and that's how I mean out of spec. I'm not sure why some would need to be like "5.15V" (from memory)... . [later: (+-0.00V?... really?!)] I'd need to dig out my readings from some bottom of a pile of handwritten notes [see just above].That said, I fixed a busted rail and recapped the entire unit (with some small exceptions) since - aside from just making it work. So it's possible whatever stressed parts were there before - caps, though I'll still be suspicious of drifted or just stressed carbon comp resistors - they've been replaced.I'm pretty reluctant to mess with it very much from this point. But may take a hard look as some of the carbon comp power resistors, which I regard as just unfit for the kind of service they're in. Sign of the times to employ them.__________________________________________________________________________________Actually, I found my notes. Mind you, at the time I was still using the "5440 series" SM. I'll have to cross check to see if all applicable to the 5440A, but I don't expect many surprises. [later: no surprises]As the notes say, this is from back in April, when I was just embarking on this behemoth of a project. I have not gone back in there and rechecked the rails.

author: Rax
author_rank: Super Contributor
timestamp: October 05, 2023, 04:08:14 am
content: Not sure if anyone has any fresh thoughts on the PS measurements. Both bdunham7 and alm made very pertinent comments, I think. I'll have to evaluate my odds (and star alignments) before poking on the rear side for the line voltage as it comes in. There's more truth to it than most of y'all know, there's some fairly long extending cords providing power to my gear. Garage setup all the way.Tonight though, following a fresh INT CAL for the 5440A and a fresh 20V zero for the Prema 6048, they got very quickly within less of .1ppm of 10V (and each other, of course). Most evening they hanged out together somewhere less than .07ppm of perfect agreement on 10V. I didn't quite get 10.0000000V (got some 10.0000002Vs), but that's like winning the lottery. But I confess being just captivated by seeing that many zeroes!

author: Rax
author_rank: Super Contributor
timestamp: October 18, 2023, 12:50:26 am
content: Long(er) term observations leave me pretty floored.Given relatively fresh INT CAL of the 5440A and zeroing of the 6048, their agreement is just about as high as ALL of their 8 1/2 digits allow them to agree. Literally, most of the time they agree on all digits (and be on 9.999999V or 10.000000V). If I see variations around that, they'll be typically within less than .1ppm of 10V (sometimes the same reading over multiple 20s integrations by the 6048). If things "slide down a bit" (wilder variations of temperature, no recent INT CAL, etc.), the highest divergence I would see may be as high as .5ppm - but this is very, very rare, and easily corrected by cursory operations as described.I wanted to make sure I accrue some statistical relevance for this data over some time period and temps, and I can pretty much "provisionally conclude" based upon a few weeks the agreement on an "8 1/2 digit worth" accuracy on 10V (factor in here my "932B level stability" 931B which is agreeing to sub-ppm levels too with these two) is solid.As branadic and Dr Frank argued, the 5440A is, in (now, also my) opinion as accurate as it can possibly be. I think it's about as accurate as when it last left the Fluke cal facility in Everett WA. I definitely don't think any calibration is needed (at least at 10V; other outputs rely on linearity of the instrument as Dr Frank stated and so they're probably best left alone). I feel this also vets my Prema and the 931B. I am happy to have a few solid references (at least I feel I can qualify them as such).

author: alm
author_rank: Super Contributor
timestamp: October 18, 2023, 07:20:56 am
content: While seeing all nines or zeros is certainly satisfying, I don't see it as anything but coincidence. It's like saying you and another person are driving the exact same speed on the highway: not something I'd adjust a speedometer to.The way I look at it, the P6048 was compared to the traveling reference X days ago. This reference's value was known within u1 ppm. After X days, the P6048 drift will be within u2. The uncertainty due to tempco of the P6048 based on the difference in temperature when measuring the reference X days ago is u3. The noise in your measurement (standard deviation over samples) is u4. The uncertainty due to non-linearity (depending on how different the voltage of the reference and 5440B) is u5. Then add up all type A and type B uncertainties as standard errors per GUM and multiply by coverage factor, and the result is a statement like "The P6048 at this point in time and temperature will measure 10V as 9.99995V +/ 5 uV/V (k=2), and based on that the 5440B's output when set to 10V is 9.99995V +/ 5.5 uV/V (k=2)".The 5440B is certainly very stable and linear. So if it were 100 uV/V out, I'd suspect a defect. And the fact that it's quite close gives confidence that it's working properly (in that range). But that doesn't mean it's within 0.1 uV/V either. And I wouldn't want to run it 24/7 for most predictable drift given the noise and power usage

author: Rax
author_rank: Super Contributor
timestamp: October 18, 2023, 12:45:20 pm
content: Quote from: alm on October 18, 2023, 07:20:56 amI [consider I] understand your point, but I think ultimately, this is not unlike statistics as an epistemological approach in physics - as much as it can do all of the things physics is expected to do (predict phenomena which can then be verified in experiments to check the validity of a theory based on statistical thought), it still essentially doesn't have ontological substance (it doesn't positively say an individual event will take a certain course). Differently put, just because metrology is based upon thought articulated around uncertainties, it doesn't mean one's volt cannot objectively be accurate. It just doesn't. I'd definitely adjust my volt around conclusions such as the above, and expect it'd pass calibration checks against traceable standards.What I posit above is:the accuracy of both the 6048 and the 5440A (and the931B731B and the FX) is very high (at 10V!)their aging is infinitesimally small at this point (to borrow a term from differential calculus, which was created for no other reason than deal with physical phenomena such as this) and it's been so since their last "calibration with adjustment" (this is intended to address the comment on highway driving)Also differently put, the fact that a reference (FX) adjusted decades after these two above agrees with them as closely as it does (my own measurements of the FX) points to the same. The likelihood of all these references across years of adjustments and checks to be wrong by the same infinitesimally small amount diminishes the likelihood they're all wrong (a statistical formalism statement) by an amount proportional to the size of that differential (smaller differential = higher likelihood of accuracy). Therefore, it's likely that they're right (I also posit the two are logically exclusive).It's why voltnuts accrue multiple932Bs731Bs at their bench - to diminish their divergence from the objective volt by averaging, evaluating (collective) aging, etc. Diminish the likelihood of them being wrong.

author: Rax
author_rank: Super Contributor
timestamp: October 18, 2023, 01:02:44 pm
content: Quote from: alm on October 18, 2023, 07:20:56 amI'm building the guts to turn them off....I promise.

author: Rax
author_rank: Super Contributor
timestamp: October 18, 2023, 04:04:07 pm
content: Quote from: alm on October 18, 2023, 07:20:56 amThe actual (= based on reason) motivation for having all these on for so long is accruing the hundreds of hours of observation I have piled up with them, in various combinations of measurements and configurations. My WFM situation (I am currently still hybrid), and the fact that WFM occurs at the same desk which is my bench, allows me to monitor these things for many hours at a time (while not yet having the capacity to automate this empirical data accrual).

author: alm
author_rank: Super Contributor
timestamp: October 18, 2023, 05:07:22 pm
content: Quote from: Rax on October 18, 2023, 12:45:20 pmThere are two reasons why we need statistics in metrology:Any measurement you do, with the exception of some fundamental measurements like counting atoms, has some variability associated with it. If you measure a block of jelly ten times with a tape measure, you'll likely get ten different outcomes based on the compression of the jelly, the angle at which your eye looks at the tape measure, how hard you pull on the tape measure, etc. If you have ten different people measure ten times, you'll get even more variation. We use statistics to describe such processes.We can not predict exactly what all atoms in a voltage reference or resistance standard are going to do. Or how every standard is going to change over time, temperature, air pressure etc. So what the manufacturer does is based on their own testing and their process control, they will specify a number that if you measure 100 standards, at least 95 will stay within. In generalthey will guard band this numberso their process control doesn't have to be so tight. This is the number you will see as specifications. They might say an instrument will not drift more than 10 uV/V/year.The alternative for modeling 1 using statistics is saying you have a perfect model that can predict all the noise and other contributions to the variation in measurement. I would love how you built such model. Regarding #2, you are right to say this is describing a population, not a single instrument. Characterizing an individual instrument's performance like short term and long term drift, tempco, etc is certainly viable. Usually it means having to acquire a sizable volume of data against an independent, much more stable reference. For example, you could measure the drift of a 3.5 digit meter against your P6048 by measuring it now, again in 1 year, and seeing how much the 3.5 digit meter changed. The drift of the P6048 is likely to be negligible compared to the 3.5 digit DMM. Or you could have your voltage references calibrated against a much more stable reference (like the Fluke reference bench that's regularly compared to their Josephson voltage standard. Seethis Fluke articleon how well they can estimate the drift of their voltage references after a series of calibrations. But stupid Fluke still uses uncertainties for these estimates. What data do you base your "better" estimates on?Quote from: Rax on October 18, 2023, 12:45:20 pmAging is a motion. Since it's hard to measure the velocity since we're talking about very small velocities, one generally measures it based on multiple points over time. Ideally spaced a fair time apart (months at least) to reduce the requirement on how accurate you need to measure the difference. What are your multiple points?In metrology, you normally would ask a cal lab to never adjust, so you can track the drift yourself. Do you have access to a previous cal certificate that says what the measured value was and with what kind of uncertainty? Even cal labs have uncertainties, and when calibrating high-accuracy instruments their uncertainties may not be that much better than the meter. Even when it was adjusted, the cal tech has no interest in putting it at exactly the nominal value. Any value within the specified uncertainty will do, and no adjustments will be made as long as it's within specifications. So all you can say as that during the last calibration, it was likely in specifications. Hopefully 24h, but maybe 1 year, depending on how good the cal lab was and what the customer asked for. Add to this that a DMM or calibrator is a complicated instruments with a lot of components that can affect aging, and you can't assume them to drift monotonically, never mind linearly like the Fluke 732B voltage reference in the article above. There will be multiple components with their own drift rates and time constants. Think multiple springs with different spring constants in series. Based on this, I'd say any statement about drift of the P6048 (that you compared to the FX reference once) and 5440 (that you compared to the P6048 over a short stretch of time) is pure fantasy.Quote from: Rax on October 18, 2023, 12:45:20 pmWhile it may be plausible, you just can't make any definitive statements based on that. Certainly not at the sub-ppm level. You're operating at the edge of what's physically possible with zener references. If you had a series of comparisons against a Josephson voltage standard (see Fluke article on predicting drift of voltage references, which are much easier to predict for reasons I just mentioend), then it would be a different matter. But you really can't claim sub-ppm uncertainties based on some hand-waving.Quote from: Rax linktopic=393472.msg5120175#msg5120175 date=1697633120The 932B, is that a newer, unreleased version of theFluke 931B RMS differential voltmeter? While averaging multiple references can certainly reduce drift, since the variance of the average of N independent normal distributions is s^2/N, the references are never truly independent. Standards labs like the NBS (now NIST) used to maintain quantities like Volt and Ohm using a pool of artifacts, like Weston Cells or standard resistors, that were very carefully monitored and averaged. They used two different kinds of Weston cells to balance out systematic factors. Yet when more stable quantum standards were developed, it was found that both theNBS VoltandNBS Ohmwere drifting relative to the quantum standards. You just can't know for sure, regardless of how many references you compare, without an external validation or your own quantum standard.

author: Rax
author_rank: Super Contributor
timestamp: October 18, 2023, 05:50:29 pm
content: Quote from: alm on October 18, 2023, 05:07:22 pmThank you very much for your thoughtful points. I don't know, though, what to make of your assumption the typo I had in my post was more likely of the third digit in the model number, than the much more obvious first? In case there was any doubt about that, I was referring to the 732B, which is in the business of sub-ppm voltage standard duty. I don't see how a 932B (which doesn't exist) would arrive in this conversation at all.

author: Rax
author_rank: Super Contributor
timestamp: October 18, 2023, 06:36:26 pm
content: Quote from: alm on October 18, 2023, 05:07:22 pmA couple of further notes on that.In your quote of me above, if you read carefully, you see there's no sentence that includes definitive language, so I think we agree on definitive statements, but apparently not on close reading of each other.I do have a few measurements against the FX, which I believe was measured against a JJ standard, and which I'm using for substantiating my thoughts.You're making some really insightful, well documented points - thank you very much for that. But overall, really, all of my notes - observations and commentary around them - should be taken as just that: observations with commentary. I don't claim to have a JJ array tucked in a corner in my garage. But based upon my observations and a few other voltunuts from this community and other communities (not unlike I am aware of other such communities in different regions or countries, and their own "relative volts" and whatnot, making similar observations, relative comparisons in their groups with their gear, and oftentimes "sub-ppm" comments), their calibrated instrumentation, TiN's reference, and my local cal lab, I have a fairly reassuring evaluation of my bench volt, and I'm fairly certain I have exceeded what my local calibration lab can do (DCV-wise). I am "fairly certain," just about how much they're off too.Sub-ppm graphs and evaluations are pretty common-place on this community (including my own data contributions on other threads). Some relative, some not so much.

author: Rax
author_rank: Super Contributor
timestamp: October 20, 2023, 12:36:55 pm
content: I've done a couple of power cycling experiments. As expected, the 5440A has about four hours warmup before it's fully stabilized - exactly as much as Dr Frank indicated - while the Prema 6048 seems to be fully up in maybe about an hour. At the end of that, they're in the exact same agreement as before. The 731B I didn't power cycle, but the agreement stays exactly as tight with it also.Other than energy savings, I am not convinced I should continuously power cycle these every day. I tend to use them daily, and to me the frequent power cycle - with the oven cooling down and then warming up again - seems more radical and introducing more wear than keeping them on. I do think they're in the part of their career where there's very little aging to still occur.On our different takes above, alm - to me, it's pretty obvious we're both correct. We just adopt points of view from two different paradigms, and have not truly shifted our universe/domain of discourse to really meet. You, as a metrology guy (I assume), adopt a mindset where statistics dominates all the way to an ontological relevance. I, as a physicist, set limits to what statistics can say will or will not happen.I appreciate your points and have carefully read all the resources and articles you've presented here.

author: Rax
author_rank: Super Contributor
timestamp: October 20, 2023, 08:27:46 pm
content: Quote from: Rax on October 20, 2023, 12:36:55 pmLet me flesh that out a little more. Typically what this paradigmatic shift means in physics is, if you apply a limit condition to a certain paradigm, it needs to blend seamlessly into the other paradigm for both to be correct (see Special Relativity vs. Newton's Mechanics).In our case, with your "highway speed" point, alm, you assume all of these decades-old instruments still have relatively large (or: "significant") drifts. And maybe they do - I don't have many years experience in this field - but I have not seen them drift in months' long, daily observations accruing hundreds of hours (as I said). I may still be wrong (maybe my methodology is faulty), but if they still significantly drift, I should either observe it, or they all drift exactly the same (which I think is impossible, as they don't share the same references, design is completely different, even their age is likely different, etc.).So if you take your assumption of drifting and instead assume it's insignificant, my point on accuracy and reliability of my bench volt becomes valid.To bring a metrology point in this conversation, let's look at what Solartron-Schumberger says relative to their 7081 8.5 digit meter (see attachment). I'd love to hear others' experience with drifting references (particularly decades-old), but SS states past nine years the drift is "insignificant." This is on a chart including sub-ppm quantifications, and for an instrument qualified to measure sub-ppm quantities.

author: Rax
author_rank: Super Contributor
timestamp: October 20, 2023, 11:48:42 pm
content: Quote from: Rax on October 20, 2023, 08:27:46 pmI think the 5440A was made in 1981, so nine years past that is in 1990. We're 30 long years further down the line past that.I should also say, I've just probably just contemplated a quick, 3ppm drift from a brand new (probably aged) Fluke reference in a recent production Fluke meter.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: October 22, 2023, 02:58:15 pm
content: Quote from: Rax on October 20, 2023, 11:48:42 pmWhen comparing old and new devices you should take into account the change in the volt standard in 1990 to 9.3ppm

author: Rax
author_rank: Super Contributor
timestamp: October 22, 2023, 03:09:31 pm
content: Quote from: MegaVolt on October 22, 2023, 02:58:15 pmGreat point! I never quite got to a point where I feel I incorporated that into all this.Does that mean all calibrations prior to that change's date are off by today's standards?

author: MegaVolt
author_rank: Frequent Contributor
timestamp: October 23, 2023, 09:02:23 am
content: Quote from: Rax on October 22, 2023, 03:09:31 pmYou must take into account the correction if you take old data. This is a simple arithmetic correction.

author: Rax
author_rank: Super Contributor
timestamp: October 25, 2023, 01:37:41 am
content: I tried to shake my 5440A and the Prema 6048 out of agreement (curiosity?...), and I must confess I haven't had much success.I kept them off for a day or two now and then (different times!), not run INT CAL, or zeroing, and then did, vary temperatures at the bench a bit wilder than before (plus airflow). I was able to run a slightly over 1ppm disagreement by running the Prema on its back (seems pretty impactful, BTW), and varying the temperature gradients in the garage pretty wild (door open to allows drafts to shower the instruments, etc.). The latter is also pretty impactful.But I guess they just designed both the 6048 and the 5440A too well... The most I could shake them off balance is by a bit over 1ppm. Of course, this says nothing about long term this and that (or absolute accuracy), but just to assess short term variations on ovenized instruments. Variations turn out be difficult to quantify (being as small as they are).Once I ran both instruments a bit more civilized - constant/stable, though admittedly high - about 27C - temperatures, though their evenness helps zeroing on the Prema and the INT CAL on the Fluke deal with it - they settled back to under .2ppm agreement.

author: Rax
author_rank: Super Contributor
timestamp: October 26, 2023, 05:05:26 am
content: About those 27C... In case that was a point of contention, I am at 22.8C right now and see the exact same agreement between the Prema 6048 and the Fluke 5440A. On the dot 10.0000000V, +-.05ppm all night tonight.Hopefully, this is not construed as obscene.

author: Dr. Frank
author_rank: Super Contributor
timestamp: October 26, 2023, 07:01:50 am
content: Quote from: Rax on October 26, 2023, 05:05:26 amHave you already checked their agreement on the other ranges?Frank

author: Rax
author_rank: Super Contributor
timestamp: October 26, 2023, 11:33:31 am
content: Quote from: Dr. Frank on October 26, 2023, 07:01:50 amYes, but not as systematically (though I must have some notes somewhere). But for instance, this morning - they've been running overnight - at 25.6C I found the P6048 indicating about .2ppm high at 10V (fluctuating between .15ppm and .23ppm from integration to integration).And then, if I apply:100V: 99.998724V1000V: 999.98352VI am not positive I gave them enough time - I think there's a bit of settling time needed for higher voltage measurements - as I'm right before a flight to a conference across the States, but that's probably close enough to what I've seen those ranges typically doing.

author: Mickle T.
author_rank: Frequent Contributor
timestamp: October 26, 2023, 12:07:08 pm
content: Is there any chance we'll see short-term stability charts for the P6048+F5440A instead of a bunch of words about ppm's?

author: Rax
author_rank: Super Contributor
timestamp: October 26, 2023, 12:12:11 pm
content: Quote from: Mickle T. on October 26, 2023, 12:07:08 pmI'd love to be able to do that - and I've had some conversations on the P6048 thread on that topic - but I'm not currently able to read my P6048 over GPIB to automate collection of data and plot some charts.

author: alm
author_rank: Super Contributor
timestamp: October 26, 2023, 12:33:40 pm
content: You can make a chart the old school way by manually registering measurements, ideally something like 16 values per point so you can get a decent estimate of standard deviation, and then plotting the results.

author: Rax
author_rank: Super Contributor
timestamp: November 01, 2023, 01:25:05 am
content: Quote from: alm on October 26, 2023, 12:33:40 pmHere's a shot at that. Temperature is, unfortunately, 27.4C (I was at a conference in MN over an extended weekend of sorts, and was so happy to come back to 85F in SoCal from the high 20s!....).Both the 5440A and the P6048 have been off for about a week. I had my better half turn both on this morning (while I flew all day, so I couldn't handle that), to make sure they both plateau thermically ("warmup," of course). Upon arriving home in the afternoon, I only zeroed the P6048, nothing else (though it'd be interesting to see the effect of INT CAL on the 5440A). There's always a couple of readings initially that are a bit off, and so below I just started noting down at the point that the readings stabilized. Each one of the readings below is a consecutive 20s integration by the P6048.9.9999999V10.0000002V10.0000006V10.0000002V10.0000003V10.0000001V10.0000002V10.0000005V10.0000008V10.0000007V10.0000005V10.0000005V10.0000004V10.0000004V10.0000003V10.0000004V10.0000004V10.0000004V10.0000004V10.0000008V10.0000012V10.0000012V10.0000016V10.0000018V10.0000018V10.0000015V10.0000016V10.0000017V10.0000016V10.0000015V10.0000011V10.0000012V[here I had to deal with some Halloween guests, so I missed a few integrations]10.0000002V10.0000005V10.0000003V10.0000000V10.0000001V10.0000001V10.0000003V.....

author: Rax
author_rank: Super Contributor
timestamp: November 01, 2023, 01:39:44 am
content: ...I kept on going, but didn't see anything more than .13ppm of 10V on any integration I observed. It may wonder on the high end of a .01ppm variation from 10V (meaning, not on the 9.9999999V side), and then creep up to wondering around a .1ppm variation of the same. In that sense, that's a "high" variation. It's typically more stable than this on a given evening, but I blame the time they both were off with its moisture accrual, wet caps getting a bit wacky, etc., and also just general environmental conditions fluctuations in an unconditioned space.

author: Rax
author_rank: Super Contributor
timestamp: November 01, 2023, 03:56:48 am
content: I went ahead and also did the INT CAL and it seems, if anything, the agreement between the 5440A and the P6048is may be a bit tighter. For one, I don't seem to see those .1ppm excursions. I see it fluctuating in the ".01ppm range" (last count on screen) from 10V.

author: Rax
author_rank: Super Contributor
timestamp: November 01, 2023, 01:20:41 pm
content: Quote from: Mickle T. on October 26, 2023, 12:07:08 pmI was asked for a chart, so here's a quick one based upon the same readings. Note the first steeper slope is due to the units still stabilizing/establishing their first reading(s), while the second steeper slope on the downward trend this time is the jump from a "12" to a "02" which is much less steep (it occurred over several successive integrations, as I was away from the bench and dealing with guests).

author: Dr. Frank
author_rank: Super Contributor
timestamp: November 01, 2023, 02:09:52 pm
content: Hello Rax,what's the scaling and the unit of the X-axis?Is it possible for you to perform a stability measurement over 12 or 24 hours?You might monitor the environmental temperature as well.Frank.

author: Rax
author_rank: Super Contributor
timestamp: November 01, 2023, 02:17:15 pm
content: Quote from: Dr. Frank on November 01, 2023, 02:09:52 pmFrank,Every single point on the X axis is a successive reading at the end of a 20 seconds integration. On the Prema 6048, that's the shortest integration that brings all digits on the screen (8.5). So, essentially, X axis is time, discrete/quantified to 20 second units, if you will.

author: Mickle T.
author_rank: Frequent Contributor
timestamp: November 01, 2023, 02:24:31 pm
content: It makes sense to increase the integration time to 80 seconds.

author: Rax
author_rank: Super Contributor
timestamp: November 01, 2023, 02:27:44 pm
content: Quote from: Dr. Frank on November 01, 2023, 02:09:52 pmOn both of those accounts - not really. All this is manual harvesting of data, as I explained (I haven't yet been able to work out GPIB or other ways to automate my data harvesting). So to do 12 or 24 hrs continuously would require me to take vacation from my actual work, including time past those to 24 hrs to catch up with sleep!...Same applies to temperature, I can write down what my bench thermometer tells me every time I collect a reading, but it doesn't sort out the issue of "sweatshopping myself...."That said, I've found the instruments indicating about 10.0000020V this morning (at the end of a warm October night in SoCal) and I have no reason to think the overnight variations exceeded that (in my experience, largely speaking, when talking about an unconditioned garage, 5AM is usually the most divergent environmental condition of the night). And as environmental conditions in the room became more regular (with my presence in the room, etc.), the readings have gone closer to 10.0000000V than that. I've seen small variations of the last count as I had my first meeting of the morning.

author: Rax
author_rank: Super Contributor
timestamp: November 01, 2023, 02:30:31 pm
content: Quote from: Mickle T. on November 01, 2023, 02:24:31 pmI haven't personally seen the readings change much, if all all, by doing that, and it just makes collections of data painful and impractical. I'd almost rather stick with 20s and collect every fourth one... But is there another specific reason you think I should switch to 80 seconds? Tighter integration?

author: Mickle T.
author_rank: Frequent Contributor
timestamp: November 01, 2023, 05:48:19 pm
content: I suggest increasing the integration time, since your multimeter is quite noisy (not least due to the ICL7652 in the input amplifier). Based on the 10-minute chart you presented, it is generally not clear how you can talk about some *.01 ppm, when even 10-minute instability is an order of magnitude higher.

author: Rax
author_rank: Super Contributor
timestamp: November 01, 2023, 08:12:46 pm
content: Quote from: Mickle T. on November 01, 2023, 05:48:19 pmThat makes sense, thank you.Quote from: Mickle T. on November 01, 2023, 05:48:19 pmI explain that here, hopefully better:Quote from: Rax on November 01, 2023, 03:56:48 amMeaning, typically, and for relatively short stretches of time, the fluctuations are restricted to the "last count" on the 8.5 digit screen of the P6048. More importantly, before any critical work, I feel I can get these to agree very, very closely by running a fresh zero on the P6048 and an INT Cal on the F5440A. I wager that may also mean "more accurately," but that's a debatable point.But stepping back for a larger perspective over things, I think this is a fair statement for what I'm seeing and is confirmed days later by the chart I just posted:Quote from: Rax on October 25, 2023, 01:37:41 am

author: alm
author_rank: Super Contributor
timestamp: November 01, 2023, 09:22:27 pm
content: Quote from: Rax on November 01, 2023, 02:27:44 pmOkay, if you're not set up for short term drift measurements, how about long term drift?Quote from: Rax on November 01, 2023, 01:25:05 amLet's do this like a freshman physics lab. This is one point of data in what will be a long term drift chart, with a mean, standard deviation, a number of samples and hopefully a time and date. Now regularly, say every week or every month, do the same. And maybe after a number of months you'll be able to say something about the relative long term drift, analogous to how measuring variation in distance between two space ships will tell you relative velocity but not velocity relative to any other body. Unless the relative velocity is really high, you'll need to measure over a long period of time because even with a linear relative drift of 10 uV/V/year, the daily drift would only be 0.02 uV/V.Quote from: Rax on November 01, 2023, 01:39:44 amThis is not data however.Something to realize, is that running voltage references 24/7 creates a higher but more predictable drift. While switching them off reduces aging, but every time you switch a reference off and on there's a small chance it will jump in value. That's why Fluke 731/732 voltage references have a backup battery and an "in cal" light that goes off if the battery ever goes flat. Because only by maintaining power continuously between calibration cycles can they guarantee it will stay within specifications. Multimeters and multi-function calibrators generally have looser specs in the order of 1-10 uV/V/year, so this is less of a problem for them.

author: Rax
author_rank: Super Contributor
timestamp: November 02, 2023, 12:38:38 am
content: Quote from: Dr. Frank on November 01, 2023, 02:09:52 pmToday I got a glimpse of what excessive temperatures look like in the readings. Prior, I almost developed a sense of "invincibility" from the P6048/F5440A pair. But the temperature at the bench having exceeded 28C by quite a bit (SoCal heat wave), I saw an almost 1ppm divergence between the two, which is pretty unsettling, having seen such rock solid agreement this far.Hopefully, there's no other, more permanent, reason for this divergence.

author: bdunham7
author_rank: Super Contributor
timestamp: November 02, 2023, 12:51:43 am
content: Quote from: Rax on November 02, 2023, 12:38:38 amTempco within listed limits is going to be a big part of the specified tolerances. What you won't know is whether the tempco of your two units is complementary or oppositional. If the latter, you're in good shape, but if the former the actual values could be varying more than you'd like. The 8846A has very good tempco AFAIK (the old PCBA did for sure) but it certainly can't be the arbiter of a 1ppm discrepancy.For your data acquisition issue, how about just using time lapse video?

author: Rax
author_rank: Super Contributor
timestamp: November 02, 2023, 01:07:01 am
content: Quote from: bdunham7 on November 02, 2023, 12:51:43 amI think my observations this far point out oppositional tempco between the F5440A and the P6048 - by which I mean they seem to essentially compensate their T gradient - but they do that at slightly different rates. So over 28C this slight divergence starts becoming apparent. But throughout my usual "summer bench" environmentals (say, 24-28C, sunny with a slight breeze at the beach), they stick together very well. Data collection and "armchair processing" still ongoing.Quote from: bdunham7 on November 02, 2023, 12:51:43 amI'm not quite sure what you mean by this, but if you could elaborate?...

author: Rax
author_rank: Super Contributor
timestamp: November 02, 2023, 01:15:11 am
content: Quote from: alm on November 01, 2023, 09:22:27 pmFine. What I'm not sure I have a handle on, is how to subtract (or maybe "abstract?...") the drift you're talking about while, obviously, everything I could throw at this data collection has its/theirs own drift(s)?... Differently put, how can I guarantee I see the F5440A drift, vs. the (relative) P6048 drift?

author: bdunham7
author_rank: Super Contributor
timestamp: November 02, 2023, 03:37:26 am
content: Quote from: Rax on November 02, 2023, 01:07:01 amJust take a long video of the instruments and then fast forward through it later and manually record the readings every xxx seconds or minutes.

author: dietert1
author_rank: Super Contributor
timestamp: November 02, 2023, 08:54:28 am
content: When you go sub-ppm thermal EMF can get into the way, typical at a time scale of minutes.As the Prema doesn't come with binding posts but with copper safety sockets, you need copper banana plugs. And you want to wrap the connectors against air draft. Others made a small box to cover them.How is the Connection on the Fluke calibrator? Probably one needs copper parts, too.Regards, Dieter

author: Rax
author_rank: Super Contributor
timestamp: November 02, 2023, 01:39:04 pm
content: Quote from: dietert1 on November 02, 2023, 08:54:28 amDieter - definitely so; if I open the garage door, I see the draft and temperature gradient pretty quickly up to a level of a ppm or so I think - I mentioned this here before. My better half knows the car gets out first thing in the morning, and gets back into the garage last thing in the evening. When needed, I run the AC in the garage and I can also see those cooler drafts in the readings pretty distinctly.But to answer your question - I am using low-emf banana plugs fitted 1m cables by AB, so definitely up for this service. I think those are some really neat cables. I always leave enough time for temperature settling after maneuvering them, and the 20s integration I always use helps with that too.

author: Rax
author_rank: Super Contributor
timestamp: November 02, 2023, 05:31:06 pm
content: Quote from: Rax on November 02, 2023, 12:38:38 amOr, maybe I just ran out of luck. I've had these on since, ran zeroing on the P6048 a few times, INT CAL on the F5440A, also internal soft and hard checks, and I seem to see a permanent slide up of about 1.2ppm that's not going away. May try a cold boot or other cures. Pretty disheartening, to be honest.My other bench reference is a931B731B - and please recall it's a verified extremely stable reference relative to what's expected from a931B731B - is still in "under .5ppm" agreement with the P6048. Maybe the F5440A just experienced a slight reference jump?

author: Rax
author_rank: Super Contributor
timestamp: November 02, 2023, 05:32:44 pm
content: I should add the perfect agreement between the F5440A and the P6048 has been unshaken for almost two months of essentially daily checks. I probably should have never restarted the instruments.

author: bdunham7
author_rank: Super Contributor
timestamp: November 02, 2023, 05:42:47 pm
content: Quote from: Rax on November 02, 2023, 05:31:06 pmI don't think the SZA263/LT-FLU reference is all that prone to power cycle jumps like that because it isn't heated, at least not internally or to the same temperatures as the LM399 and LTZ1000 types. But there are probably good reasons that they assign the tolerances they specify. What would be your best guess as to your absolute uncertainty of 10 volts in your garage lab?

author: Dr. Frank
author_rank: Super Contributor
timestamp: November 02, 2023, 10:18:59 pm
content: Hey Rax,definitely you should acquire a cheap GPIB adapter, a monitoring program and a third reference source.You're turning in circles, not exactly knowing what your both instruments are doing.Frank

author: alm
author_rank: Super Contributor
timestamp: November 02, 2023, 10:30:44 pm
content: Quote from: Rax on November 02, 2023, 05:32:44 pmYet the only actual data you presented is in disagreement with this. This "almost two months of measurements" appears to have produced zero useful data. Could you have written a college lab report with "The mass of all the liquids I measured was in agreement with their density and volume"? That might be a conclusion, but that's not a report.I don't know the Prema 6048, but some Prema meters have fairly advanced math features, so it wouldn't surprise me if you could configure the P6048 to acquire say 32 samples and show the mean and sample standard deviation or variance. While not as good as acquiring individual samples, it could make manual registration more convenient until you set up automation.

author: Rax
author_rank: Super Contributor
timestamp: November 02, 2023, 11:20:10 pm
content: Quote from: Dr. Frank on November 02, 2023, 10:18:59 pmHi Frank,There's three instruments, and as I presented here before:Quote from: Rax on November 02, 2023, 05:31:06 pmThey've been in very close agreement until just now. Three instruments excludes a vicious circle fallacy.

author: Dr. Frank
author_rank: Super Contributor
timestamp: November 02, 2023, 11:31:13 pm
content: Quote from: Rax on November 02, 2023, 11:20:10 pmHi Rax,sorry, no, this 731B is a transfer standard at best, but not a reference standard.It's too much depending on temperature variations.And you know: A man with one clock knows the time, but a man with only two clocks is not so sure any more..Frank

author: Rax
author_rank: Super Contributor
timestamp: November 03, 2023, 02:03:08 am
content: Quote from: bdunham7 on November 02, 2023, 05:42:47 pmBut, as you know, this is ovenized inside the unit. I have two hypotheses to go by:The reference jumped by the observed 1.5ppm. I should have kept it running, minimizing the risk of this occurring. Sometimes learning to trust yourself over external input comes with tolls.The environmental temperature (28C at the time) triggered some sort of failure. I'll probably open the unit and see if there's any signs of trouble. I suspect something like power carbon comp resistors, one of the very few original wet caps leaking due to heat, etc.Thank you for your thoughtful points.

author: Rax
author_rank: Super Contributor
timestamp: November 03, 2023, 02:50:37 am
content: Quote from: alm on November 02, 2023, 10:30:44 pmIt's not, but I'm sure you'll tell me that it is (hopefully, also "how" it is, or "why"). If you could make that less of a "teaching down at you" moment, that'll drive your point a little better, and I mean this both respectfully and hopefully (if you're a tenth as prominent in what you do, as you seem to be, you'd know this. I am in what I do, and I do know it). It's a disservice to your knowledge to have this demeanor.But I haven't seen that this far (with all of your generous posting with resources, articles, and links, etc., which I appreciate every single one of), nor have I seen a close read of what I'm posting here. You're glazing over my discrete data or qualitative points concerning hours of observations I've made (none of which I can really substantiate, as they're "qualitative," and you'd just have to trust me that what I'm saying is the result of hundreds of hours hard work of "memorized" data accrual) to drive points you want to make regardless of any of it. That, in particular, is not helpful. It's disrespectful of my work.The ball is in your court, and I'm hopeful.