Fluke 8558A/8588A 8.5-digit DMMs

[e61_phil]

That might be true for two resistors equal in value, but that isn't specified by Fluke. They specify a range. So one have to be careful what specifications are compared. I would assume the Fluke would behave also much better for equal values.

I also ran into this trap as I tried to transfer 1k to 10k with my 7081 (sold now), which has also transfer specs and behaved very bad on this 1:10 transfer. We discussed that on another thread here.
I would say the 8508A and 8588A TRANSFER specs aren't comparable to any STABILITY specification.

btw: Solartron called it also "transfer" Spec, which seems to be only valid for equal values.

To get an idea of stability (of one or very equal resistors) it should be ok to make some measurements and calculate the standard error of the mean for a given time.

[maxwell3e10]

If you read Fluke 8588 specification notes, it says: "Transfer specification for DCV, DCI, and Ohms applies to measurement made between 10 % and 120 % of range for deviations of up to 10 % of the initial measurement made using the same configuration for range, filter, aperture, delay etc. Specification accounts for linearity and noise but excludes temperature coefficient which should be calculated from the data provided according to the environment in which the instrument is used."
So it only allows values different by 10%, which is not much of a test of linearity.

[e61_phil]

yes, and there is an ongoing disussion with Fluke about that. But even 10% is more than the same value.
And that 10% isn't specified for the 8508A.

[niner_007]

Seems incredible - the 8508A adds 0.3ppm and the 3458A adds 2ppm for NIST traceability.

Is that because of the uncertainty of the equipment used for calibrating the 3458A?

[EEVblog]

Fluke Australia have just offered a short loan of the new 8588A Reference Multimeter, I can only have it for a day or two. Presumably only one in the country and it has to go around the country doing a dog and pony show.
Obviously an actual full review is out of the question (and pointless), as I have no other bleeding edge voltnuttery gear to measure it against.
What would you want to me to do with it?

[TheSteve]

Fluke Australia have just offered a short loan of the new 8588A Reference Multimeter, I can only have it for a day or two. Presumably only one in the country and it has to go around the country doing a dog and pony show.
Obviously an actual full review is out of the question (and pointless), as I have no other bleeding edge voltnuttery gear to measure it against.
What would you want to me to do with it?

Will they let you open it and take detailed shots of the inside?

[TiN]

Take it apaaaaart :-D. But I'd expect that is out of question for a demo unit either. 

Like you said, anything else is kinda pointless, it would take a week only to warm-up and settle for any meaningful measurements.
I'm working on making review comparing old classy Datron 1281 vs newer Fluke 8508A and touching a bit on 8588A (which I don't have access for).
Sadly some of the metrology key parameters such as transfer specifications for resistance and DCV are getting worse and worse with every new meter.

[EEVblog]

Fluke Australia have just offered a short loan of the new 8588A Reference Multimeter, I can only have it for a day or two. Presumably only one in the country and it has to go around the country doing a dog and pony show.
Obviously an actual full review is out of the question (and pointless), as I have no other bleeding edge voltnuttery gear to measure it against.
What would you want to me to do with it?

Will they let you open it and take detailed shots of the inside?

Don't know yet, I've asked.

[amspire]

Fluke Australia have just offered a short loan of the new 8588A Reference Multimeter, I can only have it for a day or two. Presumably only one in the country and it has to go around the country doing a dog and pony show.
What would you want to me to do with it?

I guess you will be calibrating some of your references with it. It is interesting to see how accurate some of your references and meters actually are.

You could show how the references change with temperature.

Also, perhaps you could demonstrate the very low frequency noise of zeners and compare the noise ordinary zeners to the buried zeners found in the good references.

Richard

[e61_phil]

Fluke Australia have just offered a short loan of the new 8588A Reference Multimeter, I can only have it for a day or two. Presumably only one in the country and it has to go around the country doing a dog and pony show.
Obviously an actual full review is out of the question (and pointless), as I have no other bleeding edge voltnuttery gear to measure it against.
What would you want to me to do with it?

Hi Dave,

it is a very nice meter. I had it for 1.5 weeks and now I ordered one. It would be nice if you could compare the sampling against your 7.5 digit keysight meter. The fast sampling will not suffer from short warming up.

Sadly some of the metrology key parameters such as transfer specifications for resistance and DCV are getting worse and worse with every new meter.

TiN, you write that again and again, but I think that isn't true. The Datron 1281 hasn't any transfer specs at all and the 8588A has a limited range for compararison (that is really a pity). Which means you have to apply 24h specs if you want to make 10:1 transfers.

The 1281 is the winner in the 100mV range. The other ranges are divided by the 8508A and the 8588A (that's why I keep the 8508A). The 3458A is still unbeaten on paper up to 100V.

I also think that Fluke has very carefull specicifications on the meters. I did some linearity/transfer tests and there is no visible difference in transfer accuracy between the HP 3458A and the Fluke 8588A loaner.

[TiN]

TiN, you write that again and again, but I think that isn't true. The Datron 1281 hasn't any transfer specs at all and the 8588A has a limited range for compararison (that is really a pity). Which means you have to apply 24h specs if you want to make 10:1 transfers.

Maybe so. We already discussed this before  . I tend to be more interested in design capability and actual performance, rather than careful specmanship from Fluke, which is so careful, that even critical specification like linearity are nowhere to be found. Again, I don't say that 8588A is bad meter, I just disappointed in lack of transparency from metrology targeted product. So I've used 10 minute stability for D1281 and same 10 minute stability for 3458A/HFL specifications to compare with + INL specification. And unlike 3458A, Datron and Fluke is easier to apply for transfers because internal GPIB-controllable switching for inputs. I love using 1281 to compare three references together (with 8508/001 or 8588A can do only two references comparison).

[e61_phil]

From my side of view the most interesting "INL spec" is the transfer spec. Saying 0.1ppm INL on the first page of the 3458A datasheet is only marketing and you can't use that number for any calculation. But, you are right we already discussed that over and over

What kind of specification are you missing? Perhaps one can ask to publish that. My "feeling" is, that Fluke Calibration is really knowing what they do and you can get support from people with metrology know how. My experience with Keysight is the complete opposite.


How do you connect a third reference to the 1281? Sounds interesting

You can compare Ref A against the internal Ref and Ref B against the internal. This way you can also compare"three", but I guess you want to do something else
For this purpose, I build a small box with low thermal relays to compare references with my 3458A at home.

[TiN]

That is secret knowledge of xDevs IRC team 



I just use both rear inputs on 1281 and scan each channel in sequence.

[e61_phil]

Very nice!
Do you know what kind of relays they use? The best ones I could find (thanks to Johannes!) are specified with 300nV typical. It seems that my box is better, but perhaps there are better ones..

[maxwell3e10]

I did some linearity/transfer tests and there is no visible difference in transfer accuracy between the HP 3458A and the Fluke 8588A loaner.

Could you explain what is going on in the attached plots and table. I am not quite following what all the numbers refer to.

[niner_007]

Saying 0.1ppm INL on the first page of the 3458A datasheet is only marketing and you can't use that number for any calculation.

My "feeling" is, that Fluke Calibration is really knowing what they do and you can get support from people with metrology know how. My experience with Keysight is the complete opposite.

The unpublished INL spec is suspect, my feeling is that the Flukes have more marketing on their back that anything else, it's 2019 after all. My feeling is that the ADC in the 3458A is still unbeaten and Fluke is still playing catch up.

[niner_007]

Very nice!
Do you know what kind of relays they use? The best ones I could find (thanks to Johannes!) are specified with 300nV typical. It seems that my box is better, but perhaps there are better ones..

Which relay are these? The COTO 3500 are < 500nV, that's the only ones I'm aware of with such low emf spec.

[e61_phil]

Saying 0.1ppm INL on the first page of the 3458A datasheet is only marketing and you can't use that number for any calculation.

My "feeling" is, that Fluke Calibration is really knowing what they do and you can get support from people with metrology know how. My experience with Keysight is the complete opposite.

The unpublished INL spec is suspect, my feeling is that the Flukes have more marketing on their back that anything else, it's 2019 after all. My feeling is that the ADC in the 3458A is still unbeaten and Fluke is still playing catch up.

If the INL number (I wouldn't call ist spec) is that important could you tell me how I can derive the transfer specification of 0.05ppm + 0.05ppm (10V range -> direct ADC) from that "0.1 ppm dcV linearity"? Or any other way of calculation, if I want to compare two voltages?
How do you define the INL number given in the marketing section of the datasheet?

[TiN]

INL (of the ADC or meter, it's an important difference) is the total error of the range, while transfer specification is much more limited parameter, that applies only for specific conditions.

By means of verification ADC's INL (which comes from ADC design and hard to improve) and verification of DMM front-end path INL and error factors (which we can work to improve/workaround weak spots), one can determine and get characterized actual transfer specification.

E.g. ADC can have INL 5 ppm over its input range, that looks like a smooth curve, and with doing the smart math and digital equilibristics you can get 0.5ppm transfer spec out of it. But you cannot do the opposite.

Relays in 1281 (and 8508 too) that handle inputs are S4-L's. We did repairs and teardowns of 1281 multiple times before. There is no much need is super-low emf, since errors from thermal EMFs are not changing faster then the measurement cycle.

Could you explain what is going on in the attached plots and table. I am not quite following what all the numbers refer to.

Not sure what is difficult here? This is same Datron 1281 DMM measuring three different 10V voltages.

[e61_phil]

Nice information with the relays! Thanks.

The datasheet 0.1ppm is meter INL for sure, nothing else makes sense.

How do you define "total error"? My question is simple, I guess: What is the "0.1ppm dcV linearity" useful for? I don't know how I should use that to calculate the error of a 3V to 6V transfer for example.

And I guess the definition is not everywhere the same. The Fluke calibrators also have a linearity spec in ppm, but it seems that these values are simply added to the error from the rest.

[TiN]

You need to know all error contributors to arrive at actual transfer error of 3V to 6V. INL alone is not enough, otherwise you wouldn't have all those limitations in transfer specifications.
The whole reason why limitations are specified - so other error contributors are minimized. It is that for high end DMM or MFC, short-term stability often limited only by signal path noise and INL.
Noise we can attempt to average/filter out. INL you cannot filter out or predict, so that's why I think it's one of the key design parameters that can be helpful to know in uncertainty calculations.

Of course, most of the calibration applications don't go down this rabbit hole and direct you just using manufacturer's specification like 24-hour stability or 15 minute transfer specification, so manufacturer already did the calculation and estimation of the worst-case error for you. Knowing INL and actual errors from DC amplifier, switching circuits, thermal stability, reference noise, ADC resolution and so on is important if you want to verify manufacturer's specifications instead of just trusting datasheet's numbers like 0.05 ppm Umeas + 0.05 ppm Urng.

Fluke 57xx MFC already have included INL errors in the specifications, you don't have to add anything. You can review ACAL function verification paper for some more details, how transfers are actually covering various functions in MFC.

[e61_phil]

TiN please make a point. It is again only "it is important"-bla bla (sorry). If you want to verify the manufactures data you should start from scratch and then you don't need a ADC INL spec (which is also not given for the 3458A. The 0.1ppm are for the meter). If you want to make transfers between standards with least possible (specified) uncertainties you need transfer specs not marketing 0.1ppm INL nonsense. There are measurements shown by Fluke for the 8508A INL. http://support.fluke.com/Calibration-Sales/download/asset/2114953_a_w.pdf
I don't know what specification is missing here.


The Fluke 57XX and also the old 5440B have linearity specs. You can use that if you want to verify linearity of a meter for example. The 5730A specifies linearity with 0.3ppm + 2µV on the 11V range. That is a spec you can simply add to your measurements. It is not the span of an error.
Here is an example with applied calibrator linearity uncertainties: https://www.yumpu.com/en/document/read/11827423/a-wheatstone-bridge-for-the-computer-age-les-huntley-fluke

[Kleinstein]

The INL error can be a relevant part of the transfer specs and also limit the accuracy of the ACAL method. However if the type of INL is known the transfer specs can be tighter than just the INL number would suggest, as linearity has more aspects than just the upper limit of the INL curve.
For the INL specs 0.1 ppm of a 10 V full scale would mean a possible 1 µV error from nonlinearity. For the example 3 to 6 V transfer this would be some 0.3 ppm contribution to uncertainty.

INL specs are tricky, as it is rather difficult to really test INL and not all units may be the same. One can do a rather time consuming test at some 1000 point's with a very accurate source (JJA), but this still is only a partial (though usually sufficient) test and not at all practical for every unit or even a larger sample. So I can understand that Fluke is reluctant to give INL specs, as they may still have to measure more units.
With an ADC like in the 3458 there is a chance that a drifting resistor array may also effect the INL - so it may change over time. Not so much in the 3458 but more like the Datron1281 and ADTV6581, there could also be aging (ingress of humidity) of the integration cap that can make INL worse over time.

A special test point for linearity is the turn over error (comparing positive an negative reading). However a good values for the turn over error does not guarantee good INL: a good example are integrated SD ADCs with differential inputs that often by design have a very low turn over error, much better than the full INL.  Also some thermal effects are not caught by the turn over specs.

There are measurements shown by Fluke for the 8508A INL. http://support.fluke.com/Calibration-Sales/download/asset/2114953_a_w.pdf
I don't know what specification is missing here.

The INL error curve is just an example - other units may and in some aspects will behave different.

There is no absolute need for INL specs. Transfer specs for enough cases would be sufficient. However these are usually only give for a few conditions and not even the same for all meters. Not sure if this is more like cherry picking or just manufacturer specific preferences.

[TiN]

My point is very simple. I repair and test 8.5d meters and 7.5d calibrators, so as part of troubleshooting I always have to do INL test on DUT, to ensure functionality built on top of INL performance are correct. Using full transfer spec as a limiter in such tests is not adequate. You should be able to understand why already. Testing INL shows dodgy out of spec 3458 ADC very easily, even though meter still meets transfer specifications, thanks to ACAL.

There would be no reason in testing any calibration issues or ACAL or transfer features if core ADC or DAC cannot deliver the required sub-ppm INL performance. Since my tests are also automated, I use two or more verified 3458A's as "composite 0.1ppm 10V INL standard" in such tests, with two DCV meters confirmed lack of the temperature dependency. This is why INL number in datasheet is important for me. Don't have my own JVS yet. Other alternative is manual labor-intensive testing with 720A, SR10*0 and alike. As your Fluke linked doc outlines, INL is also not a problem for transfer between the same nominal value standards, typically used in metrology.

and not all units may be the same.

Precisely! I'd say 2 meters are never same, actually.

Manufacturer specifications apply for most of the units out there. But each particular unit still behaves little differently. More listed design parameters in documentation help me to separate expectations, as I obviously can also perform measurements inside the DMM to find out each domain error and compare that to expected manufacturer values.

With an ADC like in the 3458 there is a chance that a drifting resistor array may also effect the INL

.
My measurement results (from >8 different ADCs, good and bad) show that all drifty/bad ADCs cannot meet 0.1ppm INL in -11 to +11V sweep. Good ADCs have no problem with this.

There is no absolute need for INL specs. Transfer specs for enough cases would be sufficient. However these are usually only give for a few conditions and not even the same for all meters. Not sure if this is more like cherry picking or just manufacturer specific preferences.

It is more of a desire item, then actual metrology field need. We are deep down the rabbit hole for this one here.
Maybe I'm expecting too much, thinking about a customer who paid $20k+ for "reference DMM" and not having that little bit of optional information? Kind of same goes to traceabillity in calibration reports. Desired wish - to see data of all upstream standards chain to SI, so one can calculate own numbers for U. Like open-source calibrations, sorta. Actual metrology field tho provide you only final measurement result with assigned uncertainty and expecting you to trust the lab in their measurement. Lab is audited by accredited body to ensure their measurements are in order, but there is no way to be 100% sure your particular calibration report is correct. Maybe the calibration tech had bad mood during your DMM calibration So it's all marketing and specmanship, one would say, no any different to Vishay's "typical 0.0 ppm/C TCR" resistors? Truth is hiding somewhere in between... .

[e61_phil]

I never said it doesn't make sense to measure linearity of a meter. This is done in every proper calibration. (And that is why you need linearity specs of the calibrator)

I don't get your point why it is so important to write in the marketing section of a datasheet 0.1ppm linearity (they don't tell it INL). Both (Fluke and HP) showed "typical" values of their meters against a JJA.

You pretend that Fluke wants to hide something. That isn't the case in my opinion. I think it is more the other way around. Why aren't there absolute specs on the 3458A datasheet? There is only a footnote that you should add 2ppm to be traceable.