Fluke 8558A/8588A 8.5-digit DMMs

[TiN]

e61_phil, now I see where your disappointment in 3458 ACAL comes from. If your data indeed correct and base DCV gain drifted +3 ppm in just 3 months, then your meter's ADC is very broken.

CAL72? data from rusty 3458A:



And I beg you, please, create separate thread. This is so offtopic in this one. Also answer to

Do you think not all 3458A are much better than specified?

Is obvious as No, many old 3458A's cannot even meet current published specifications, leave alone better ones. And good ones - how better would they specify "updated" spec? Entering realm of Vishay specmanship on this one, since Keysight cannot guarantee anything about meters already in the field. Take simple example: 10VDC TC. Current spec is 0.5 ppm. Better spec, let's say 0.25 ppm/K? My three meters meet that spec, Dr.Frank's does not. If he sends his meter to calibration and pay lots of gold for it, he will expect to see nothing else than "calibrated, in specification" without notes "apply old specification from 1989, not the new one from 2019".

Btw, here's actual real benefit of having ACAL in meter = you can see drift/errors and correction factors for every function/range in 3458A (K2002 can give you constants too, but have ACAL only for ACV) without ANY external ultra-super-stable standards. But Fluke 8508A (and I expect new 8588/8558A too) which goes for double of the price hides all that, so if you want to plot similar 10VDC range drift you will be stuck with 732's and need to connect stuff everytime and hope errors from cabling/user does not creep into your sub-ppm measurements.  My point here is that I want to know or at least to have reasonably easy ability to characterize my DMM (buying and maintaining Fluke 734A/C bank is not reasonable), not just trust manufacturer's marketing department with their "our meter is super-stable enough not to need ACAL".

[e61_phil]

If the ADC alone is the problem I would expect that all ranges behave equal. But they don't. But, you are right let's start a new thread for that kind of discussions.

Has anyone an example cal sheet for a 3458A? I saw one online which doesn't include values. Only "passed".

I also think no cal lab will check the temperature coefficient of the meter. But I understand the problem with newer specifications. It confuses more than it helps.

[e61_phil]

Btw, here's actual real benefit of having ACAL in meter = you can see drift/errors and correction factors for every function/range in 3458A (K2002 can give you constants too, but have ACAL only for ACV) without ANY external ultra-super-stable standards. But Fluke 8508A (and I expect new 8588/8558A too) which goes for double of the price hides all that, so if you want to plot similar 10VDC range drift you will be stuck with 732's and need to connect stuff everytime and hope errors from cabling/user does not creep into your sub-ppm measurements.  My point here is that I want to know or at least to have reasonably easy ability to characterize my DMM (buying and maintaining Fluke 734A/C bank is not reasonable), not just trust manufacturer's marketing department with their "our meter is super-stable enough not to need ACAL".

That isn't true. The only thing the 3458A gives you is what it means relative to its LTZ1000 and 40k references. That is not more than a Fluke 57XX will give you with calibration check or what you can do on your own with some stable sources. There is no need for ultra-super-stable standards.
If you own a controllable calibrator and a linear DMM you can run through this ACAL also fully automated with any meter and gain these constants.


But it's on you if you like it better if manufacturer say: "Our ranges are that drifty, you have to adjust them daily to get good performance. We also cannot check if the ADC still behaves linear, but the whole concept relies on that fact". Muuuuucccchhh better
And of course is it cheaper to have a drifty meter which correct itself daily.

[TiN]

If 8508A ADC is drifty or got bad linearity, you'll never know without high-end external gear.
If you get 3458A with bad drift/linearity, all you need to do is run bunch of ACALs procedure. Don't even need calibrator.
What I really meant is that you can verify 3458's A9 reference stability or A3 ADC stability, without needing 57xx/other good 3458A/reference DMM. But yes, choose your poison.

No amount of ACAL will fix broken meter, that is last thing I'll say about this in thread about 8588/8558A. I'm lost already on what we disputing about, anyhow. More meters to everyone, with or without ACAL.

[e61_phil]

I don't take it as a dispute. It is interesting to discuss the pros and cons, I think.

A function that compares the ranges against each other like ACAL is great, no objections! But you need a lot of knowlegde and effort to gain that information. The 3458A don't give it soo easy. But it is an old instrument and one cannot compare it to newer ones with a lot of software like the 5730A calibrator. And I don't see how ACAL can warn you if your ADC isn't linear anymore. The results are just false. But if you have a constant non-linearity that wouldn't show up in the CAL values.

The only thing you can detect on the 3458A is a drifty ADC. If the reference will drift the CAL values will not show that. And you have to read out the data and monitor that, there is no warning lamp on the meter. Neither an Error message.

And having a just stable 100mV, 1V and 100V source isn't ultra-super-stable stuff. That is everything you need for such a test. If you don't have that, you probably don't need it

But I don't want to get stuck on the 3458A. My point is more in genereal ACAL vs. a stable meter. Perhaps that isn't that offtopic anymore, because Fluke says they don't need ACAL


My points are (Perhaps a wischlist for the next generation of meter ):
- I would like to have a function that runs something like ACAL, but don't adjust anything on the meter. Just reports "largest drift: 4% of spec on 1kV" range, like the 57XX does. And of course give access to all the gained data. With this data you can calculate corrections if you want, but nothing disturbs your calibrated (by a proper calibration) ranges.

- I don't like the concept of adjusting everything automatically with no chance for corrections. That has several drawbacks:
1. Nothing can be better adjusted as the transfer concept is able to transfer it from the artifacts. That means you are not able to charactize any range much better than the transfer can do, because ACAL will destroy that every time you run it. That doesn't matter, because the 3458A ranges aren't better than the transfer (at least our 3458As), but that don't need to be true for better meters (stability wise) like the 8508A.
2. If one range will run out of spec, you have to adjust the whole meter and you lose all your history.
3. ..

[maxwell3e10]

It would be best if the meter could spit out all calibration constants (offsets/gains) for all the ranges in a user-friendly format (better than a calibration memory dump). That would allow one to keep track or potentially go back to a known previous state.

[Magnificent Bastard]

What behavior of the 8508A do you mean?
I am using ACAL on my 3458A once every day and it has shown to be working perfectly, based on resistance measurements.

I meant the stability of the 8508A. The 8508A is stable without daily ACALs. The fact that the CAL? constants move quite a bit and the reading is stable on a 3458A (if you use ACAL) means that the internals of the 3458A drift by the same amount as the "constants" drift.
If you don't use ACAL anymore, the 3458A will drift like the shown constants (which are constant without running ACAL). My point was only that a 3458A isn't nearly as stable as a 8508A. The 3458A (at least ours) really need ACAL to compensate for drifting components.

There are two approaches to engineering DMMs--- the first is to use low (or medium) quality components in the critical areas; with a high-spec voltage and resistance standard; then use auto-cal to compensate for time and temperature drift.  The second method is to use ultra-high-spec components in all of the critical areas; and these keep time and temperature drift to a minimum.

There are two different intended use cases for these DMMs.  The 3458A was meant to be a high-spec systems meter-- used on the production floor with only mild control of ambient temperature and humidity.  The 8508A/8558A/8588A DMMs are all meant to be mollycoddled in a nice cozy calibration lab, where the temperature and humidity does not change much at all.

95% of the market for the 3458A has been (and still is) as a systems meter for semiconductor companies-- out on the production floor.  The 3458A *CAN* be used for metrology-- but that is a very small segment of the market, and I don't think HPAK ever cared about it very much at all.  This is why they designed in artifact calibration-- to keep the end-user's production cost down.  A big semiconductor company can have over a thousand of these meters-- can you imagine what the cost might be to adjust each one of these against primary standards for each range in each function?  Wow!

The 8508A/8558A/8588A DMMs are an entirely different matter-- and they are specifically designed to support metrology labs--- so, they must remain stable (in the calibration lab) and have calibration traceability to primary standards.  In other words, each range in each function must be measured against primary standards before, during, and after adjustment-- hence there is absolutely no reason to build in artifact calibration, since the full complement of primary standards are right there (and handy) to make the adjustments anyway.

Apples and oranges people.

I would love to see Keysight come out with an 8.5 digit meter that is specifically designed for metrology use (and then maybe another similar model for systems use).  I would still like to have the artifact calibration myself-- but real calibration labs would probably rather use individual primary standards for adjustment.  In the new meter, the artifact calibration should create a "traceability report"-- showing the uncertainties of the standards used, and the uncertainties of each range after adjustment.  Probably, this could be shown on the screen (with realtime updates) as you are performing a measurement, because the final measurement uncertainty can be dependent on what is being measured.

[e61_phil]

@Magnificent Bastard: I don't see much contradiction to what I said. I'm arguing only from the metrology side of view. But, at least here in germany, ACAL isn't enough if you need traceability. There is no way around a proper calibration if you are an accredited company in germany.
And the Fluke 8558A is designed as a 3458A replacement. Hence the name. And that is not only for the metrology applications, also for the applications which needs very fast DMMs. -> System-DMM

use low (or medium) quality components in the critical areas; with a high-spec voltage and resistance standard; then use auto-cal to compensate for time and temperature drift.

That is exactly what I said: You cannot use a 3458A without ACAL.
And what can be wrong with a meter which is stable without ACAL? That gives only more confidence when you make range transfers, because that really shows up something odd. If you meter is build with medium quality parts you will always assume that some little shifts are normal and that can cover problems.

hence there is absolutely no reason to build in artifact calibration, since the full complement of primary standards are right there (and handy) to make the adjustments anyway.

Nothing to add


I think we are around the circle with the discussion. Main points are on the table. We all would like to have some Cal Check function which reports drift. And if you have something like this it is just software to use the latest findings to correct for the actual value or switch the function off and display the values with the CAL constants found during the last calibration.

[MiDi]

SN18A states 0.43ppm/day average for A3 in spec -> 90d ~40ppm, 1y ~150ppm 

[Kleinstein]

[quote author=e61_phil link=topic=174129.msg2289000#msg2289000 date=1553279985
....
I think we are around the circle with the discussion. Main points are on the table. We all would like to have some Cal Check function which reports drift. And if you have something like this it is just software to use the latest findings to correct for the actual value or switch the function off and display the values with the CAL constants found during the last calibration.
[/quote]

An internal cal check would be really nice for a metrology grade meter. It may be there as part of the self test. However it may need a little extra hardware to provide the internal test signal - not much, so one would hardly notice this at the price point of a 8 digit meter. As it helps to have the same internal reference, an external source may not be a full replacement.

Depending on the degree of test, it might also need things like a second voltage reference and thus possibly a major addition. The Datron 1281 had 3 voltage refs (2x LTZ, 1 x LM399) and from the HW side the possibility to read them separately. It is still not really possible to show the actual drift, more the indication of something to be wrong - like having two clocks and still not knowing the exact time. It would be only for amplifier gain that one could show inconsistency with the ADC  - it could still be the ADC aging, though not very likely.

The Fluke 8588/58 could also profit from a kind of internal cal: they seem to use different ADCs for the slow (> 100 µs aperture) and fast conversions and the digitize mode. The specs for the fast conversions are not that great, and at least the longer term drift or TC could really gain something from an internal comparison of fast and slow conversions.  The fast modes are likely rarely used for metrology applications and may not have the strict traceability needs.

It is a little odd to see 2 years specs for the reference meter - for real cal lab use those meters are more like on a less than 1 year cal cycle. I would see more use in specs for a longer cal cycle for the lower resolution meters. Also the longer the time, the more attractive ACAL gets - resistors / dividers tend to drift over time, while the ADC's INL is expected to be rather stable over time.

[TiN]

The Datron 1281 had 3 voltage refs (2x LTZ, 1 x LM399)

Sorry, only 2 x LTZ in 1281/4950. That was 1271 replaced "check" LTZ with LM399 instead.
However 8508A cheaped down and used only single LTZ1000A (LTFLU in later revisions).

And the Fluke 8558A is designed as a 3458A replacement.

If early 8558A specs are close to the truth, then 8558A is not that good competitor to working 3458A (DCV/Resistance), unless cheaper than 10K$ to fill tiny market spot above 7.5 benchtop meters but below metrology/reference meters.

[e61_phil]

The 8558A will cost ~10-11k€. Therefore, almost the same price but RoHS compliant.

I haven't checked everything in detail, but it seems they gave the 8558A the same specs as the 3458A opt 2

[Magnificent Bastard]

In the "things that I would like to see" department, my wish to Santa Clause would be an 8.5-digit SMU.  This would be able to generate as well as measure Ohms, DCV, ACV, DCI, and ACI.  Since it would already have the sources, then doing a "Cal Check", or "A-Cal" or even an "Artifact-Cal" would be possible.  This could be used to calibrate "lesser" DMMs-- 6.5 or maybe even 7.5 digit meters-- as well as measure all kinds of things.  It would be the ultimate machine for a volt-nut.  Unfortunately, the market is so small for something like that, we will never see it happen.

[TiN]

my wish to Santa Clause would be an 8.5-digit SMU.

Like we engineers say - When you want something...you build something.
I would laugh together with Santa too...if I didn't build 5720A last year... 

[e61_phil]

CalPlus send me Product Specifications today (I think they are online now?).
Unfortunately, the footnote 15 (transfer within 10%) is still there, I will ask...

[TiN]

Yes, it's online public now.
Documents published are byte to byte exact to ones posted few weeks ago, that we already discussed nicely.
I cringed a little on advertisement video:

6.5-digit 5522A workhorse calibrator with Pomona banana jack + Belden cable, while voice behind the scenes says "designed by metrologists for metrologists". I'm used to make same cables for my K2002's. Aww...

Promo PDFs show proper 5730A's , 5790B's and Fluke Everett JJ system and "Fluke Volt" to as reabilitation tho.



Keysight, now eyes on you. Let's see 9-digit meter, pretty please. 3458A after all already gives 9.5 digits of noise over GPIB.
Year 2019 => SI Volt 2019 => 9-digit, get it ?     Just don't use LM399 , and we are golden.

[e61_phil]

Hopefully your picture should show how a 5522A is calibrated 

[mzzj]

30 amp range on 8588 is quite exceptional on dvm.

And I feel sorry for that poor bastard who has to enter all the data from the calibration certificate to stability tracking file 
675 calibration points in the certificate..  Fluke rep wasn't sure if the calibration certificate is available as file but agreed that it would be a good idea

[ScoobyDoo]

Hello Voltnuts folks,

                              The Fluke 8588A demo video is up and running again:



Further info:
https://us.flukecal.com/fluke-calibrations-8588a?lcid=778c7b5f-7d67-e911-80cd-00155d027460&utm_source=YouTube&utm_medium=Social-Media&utm_campaign=Video

Herzliche Grüße/Meilleures salutations/Best regards

ScoobyDoo

[srnec]

some pics from inside of beast

[bsdphk]

I must admit that I have a hard time recognizing the picture you two guys paint of HP3458's ACAL.

While you two focus on the "top line" specs for DCV and OHM stability, in the 3458 ACAL firmware those are almost a detail.

The real meat of the ACAL code, and what makes the 3458A special because of it, is things like calibrated zero offsets for all the relay combinations, all the AC* gains and so on.

Likewise to claim that the new Fluke does not do ACAL flies in the face of the laws of nature:  There is no way they can deliver the stated specs without doing some kind of ACAL on a lot of the parasitics.

I suspect the main reason for 3458As has the manual ACAL is that it takes a long time (mainly because of the ADC and averaging), because it puts wear on the reed relays and because you really should run it with nothing connected to the input terminals.

With modern computing power, a 10+ times faster ADC and solid state range/function switches I expect ACAL to be "hidden" behind function changes, and to deal with long term drift by periodically "stealing" single conversions to get zero/ref measurements as input for a real-time mathematical model of the measurement hardware.

In the 3458 that would have required at least a 68K20+FPU and caused constant clicking of relays.

What I'm most looking forward to in these new meters (not that I can afford one) is if they have for instance three ADCs running pipelined, each with its own voltage reference, to get the noise down by sqrt(3).

[Magnificent Bastard]

An 8.5-digit meter is more of a RATIO measuring device, and less of an absolute standard.  Even with these new Fluke meters, the absolute specs are +/- a few digits in the SIXTH decimal place.  The final 2 digits are useful for ratios.  These meters are NOT a "calibration lab in a box"-- please stop thinking of them that way.  Achieving uncertainty less than a few PPM requires different, more precise, (and mathematically provable) techniques than just whacking a resistor or voltage standard onto a "golden" DMM, and calling it "good".  That's why NMIs and Tier-1/Tier-2 calibration labs still use old-school techniques like bridges, null meters, and self-calibrating dividers.

[TiN]

srnec
Thank you for insight. Have any more? 

Resistor network datecoded 2017, so that gives an idea when Fluke had prototypes (if this is photo of prototype, not the production unit?) of this meter.
Bunch of LTC2057HV's spread around the board. Shunt near the relay looks like VPG BMF type.

bsdphk
To make ACAL useful ADC must be extremely linear. That often eliminates everything else other than SD or multislope integrating type.
FS Noise limitation also comes from DC reference, as it is hard to get noise lower than 1-2 uV, available from best of the best like LTFLU or LTZ1000 references.
So I doubt full ACAL can fast enough to be able run in background, even with solid-state switching. This class meters run autozero in background, and even just that already cuts speed more than in half.

[e61_phil]

This class meters run autozero in background, and even just that already cuts speed more than in half.

I fully agree to your post, but the Fluke meters (at least the 8508A) will not do auto-zero. That prevents the current spike, which comes from recharging the input.

[Kleinstein]

For using ACAL / internal cal measurements there is no simple yes or no. There are different steps where numerical corrections or internal adjustments are used. The simplest one is the auto zero - this could include the input amplifier (like with most HP meters) or just the ADC (e.g. Keithley 2000, Datron 1281,...).  Another point is the ADC gain - this is also quite fast and older meters like the Keithley 19x did that in real time (measuring signal , zero and reference - thus 3 conversion for a single reading). Another point are possible numerical corrections, e.g. for reference or gain drift - the Keithley DMM7510 seem to use this to some degree. These may be based on separate ADC for the temperature.

The ACAL step for the ranges like used in the 3458 is also not limited to non or all: One might use it for the high voltage input divider as these tend to be not that longtime stable, while measuring the high current range shunt's may be less desirable. Linking the ohms current sources to the shunts may be a good idea too.
Adjustments / calibration for the AC ranges are another point. This may not need a high accuracy ADC, but more like special hardware for the tests. The AC part may not have much in common with the rest up to the point of having a separate ADC. 

For all those extra measurements one could choose between in the background or as a special ACAL /zero step called by the user. Even if not used for ACAL essentially the same measurements could / should be used as a kind of self test in a really good meter.

I don't think a full ACAL in the background is feasible. Through thermal effects there can be some kind of slow settling and thus an effect on the next few measurements. Normally this would be a kind of slow settling effect, so it needs a few seconds to get better than ppm after a large jump.

As the new 8588 seems to be quite fast/ low noise I don't think they will use much adjustment in the background - maybe / likely AZ for just the ADC. For the old 8508 that was really slow, I would not be surprised to have the ADC gain adjustment in the background, as this can also help with linearity, as it can compensate some thermal effects.