Fluke 5440A repair

[bdunham7]

Wow, dedication pays off!  Just in time for your next project to arrive...

[Rax]

One may think seeing one of these may belong in a "Lord of the Rings" production, but when you see it repeatedly, sometimes during three consecutive 20s integrations, maybe it's objectively true?...
Nothing like enjoying the completion of one tough project, y'all.

[Rax]

when you see it repeatedly, sometimes during three consecutive 20s integrations, maybe it's objectively true?...

One more testimony added to Dr Frank's dedication to this unit. I'm not sure what others think, but IMHO, this may be in the 732A standard category (@ 10V)? I'd love to hear thoughts.

[MegaVolt]

Congratulations
It's a pity that we didn't think to check this earlier

Now you can update it to version 5440B as recommended here:
https://www.eevblog.com/forum/repair/fluke-5440b-psu-fault-check-gaurded-power/msg3071346/#msg3071346

[Rax]

Congratulations
It's a pity that we didn't think to check this earlier

Now you can update it to version 5440B as recommended here:
https://www.eevblog.com/forum/repair/fluke-5440b-psu-fault-check-gaurded-power/msg3071346/#msg3071346

Interesting, I was not aware of this. It seems to require an upgrade to the firmware, isn't that a fact?
I think my original firmware is 1.0, I wonder what others have seen on their 5440As. Maybe I need to flash all the EPROMs... I only did U23/704114 to make this work.

[MegaVolt]

It seems to require an upgrade to the firmware, isn't that a fact?

Yes.

I think my original firmware is 1.0, I wonder what others have seen on their 5440As. Maybe I need to flash all the EPROMs... I only did U23/704114 to make this work.

I find it difficult to say what exactly needs to be flashed to get version 2.1 (5440B). Boards A15 and A16 should survive flashing without problems. And perhaps they will be able to work with the old A2.

But I'm not sure if A2 can be updated. Unfortunately this will be an experiment. Which may end in failure.

[Rax]

But I'm not sure if A2 can be updated. Unfortunately this will be an experiment. Which may end in failure.

I'll seek to apply as much as possible the healthy principle of "if not broken, don't fix it," though that's a particularly challenging goal for people with our mindset... 
First step on that path is - research the subject until you feel you have a reasonable handle on it! 

[Dr. Frank]

when you see it repeatedly, sometimes during three consecutive 20s integrations, maybe it's objectively true?...

One more testimony added to Dr Frank's dedication to this unit. I'm not sure what others think, but IMHO, this may be in the 732A standard category (@ 10V)? I'd love to hear thoughts.

Well, I own my 5442A since about 2009, and often compared its +10V output to other volt-nuts standards.
From those data, I estimate its stability to +/- 0.2ppm/y, although it's only powered on, when to be used.
The ratio coefficients for the higher ranges (22V, 250V, 1kV) seem to be very stable as well, <1.5ppm over many years
I think I published these results as well.

Frank

[Rax]

Now that I have a functional 5440A (it feels good to say that) I realize I never really looked for an Operating Manual. Does anyone know a source?

I can find 5440Bs, and I assume it's probably almost the same, though I'd still prefer a 5440A specific version. Looked at Artek, and even they don't have it.

[Rax]

From those data, I estimate its stability to +/- 0.2ppm/y
Frank

What I'm seeing right now is pretty amazing. It's largely staying within the last count on the 20V scale of the Prema 6048, and oftentimes, as I posted above, it may register up to three (to my observations this far) 20 seconds integrations at 10.0000000V. This is with low-emf cables, in a relatively warm garage (temperature cycling is inevitable, but doesn't typically exceed 5C). I had 27C last night, today we were at 25C in the morning and I see 26C now.

This is with a modest warmup, no selfcal or really anything done to the unit. Another thing I should mention is the two halfs of the case are not installed, the unit just has the internal shields on. A little confusingly, it stays closer to 10.0000000V if I don't try to put something on top of the area where the fan is. I'd want to that so airflow is properly occurring inside the unit. But if I do, the unit adds quite a bit of error from the perfect 10V (at least by my Prema's opinion) - a few ppms or more.

Is this something that the internal calibration is addressing? I'm a little apprehensive about doing it, as the unit seems to be so dead on as is (but without the case on....). 

[Dr. Frank]

Last time I forgot to do the Int Cal. Difference was about 0.3ppm
The higher ranges may show more deviation w/o Cal.

[Rax]

Last time I forgot to do the Int Cal. Difference was about 0.3ppm
The higher ranges may show more deviation w/o Cal.

I'll try to first understand better exactly what the Int Cal is doing (there isn't anything useful in the Operations - unless I missed it - and will dive into the SM next to get a handle on that).

But I imagine it's exactly the first thing to do after closing up the case, to mitigate and adjust for slight differences due to internal air movement, parasitic external air/temp gradients, etc. Should I expect the output to be brought about as close to what my Prema says is 10V as I see it currently (while running it open and with a leaky path for the forced air for cooling)?

[Rax]

On further progress report, I've executed both the Digital and the Analog Self-Test Procedures. The unit passed both with no issues.

The manuals are not very clear on what the Analog above contains, but is the Internal Calibration part of it?

[Dr. Frank]

Last time I forgot to do the Int Cal. Difference was about 0.3ppm
The higher ranges may show more deviation w/o Cal.

I'll try to first understand better exactly what the Int Cal is doing (there isn't anything useful in the Operations - unless I missed it - and will dive into the SM next to get a handle on that).

But I imagine it's exactly the first thing to do after closing up the case, to mitigate and adjust for slight differences due to internal air movement, parasitic external air/temp gradients, etc. Should I expect the output to be brought about as close to what my Prema says is 10V as I see it currently (while running it open and with a leaky path for the forced air for cooling)?

The IntCal basically re-measures the resistor ratios of the different ranges, and corrects the gains versus the stored ratios.
 As the reference is very stable, as well -probably-  the DAC , this function corrects for drifts in the gain resistors.
This method is similar to the HP3458A and the Fluke 5720, but it can not fully calibrate its ranges like these, only correct for small differences.

You find a description at the end of the Service Manual, appendix A called: Recent Innovations in Direct Volts Calibrator Design.
Frank

[Rax]

I guess we've also passed the HV self test.

[Rax]

I've done an Int Cal, and I've also re-zeroed the Prema yesterday, and as I feared, I'm no longer seeing the spectacular 10.0000000V measurements. I'm a few ppms off now. What gives?

Were they a fortunate coincidence? Has the Int Cal misfired?

I'm not terribly upset by this, my interpretation is #1 above (coincidence). Though, what are the odds?...

I've launched an inquiry with Fluke for a calibration quote. I think if I'd drive this to their main lab, it'd be a very long, but not unmanageable trip. But this definitely deserves that treatment.

[Dr. Frank]

I've done an Int Cal, and I've also re-zeroed the Prema yesterday, and as I feared, I'm no longer seeing the spectacular 10.0000000V measurements. I'm a few ppms off now. What gives?

Were they a fortunate coincidence? Has the Int Cal misfired?

I'm not terribly upset by this, my interpretation is #1 above (coincidence). Though, what are the odds?...

I've launched an inquiry with Fluke for a calibration quote. I think if I'd drive this to their main lab, it'd be a very long, but not unmanageable trip. But this definitely deserves that treatment.

It is usually necessary only to calibrate the basic 10V range, the other ones are so stable (the range coefficients), that those might not need a special calibration by a 752A. See calibration procedure, in which cases you can abbreviate the external cal.
200mV and 2V ranges need to be calibrated more frequently, anyhow, best with a 3458A.
The 3458A can be used for 10V range calibration of the 5440, anyhow. (Better don't use it for calibration of the higher ranges, esp. 1kV is very bad)

Didn't you have access to a 3458A, or another calibrated precision DMM, or an external 10V reference?

That'll be much better than shipping this beast to a cal lab.

Frank

[Rax]

Didn't you have access to a 3458A, or another calibrated precision DMM, or an external 10V reference?

That'll be much better than shipping this beast to a cal lab.

Frank

I have my own characterized 731B. I could readjust it to match my Prema (once the 5440A is all buttoned up, which is not yet). Then I'd do the 10V cal, like you point out.

For the lower ranges, I could then use my KVD and extract them from the 10V (and still can use the Prema to characterize those).

I have a bunch of other standards (including a null detector), but I think the above is what applies best to this.

[Rax]

In the direction of "buttoning it up," a few possible action items:

• finish the recap (just a few caps left on a board or two)
• EPROMs... Shall I try to replace them all with my NOS ICs after reimaging? I imagine the rest of the EPROM ICs have a likely failure in the short/medium term.
• Also, is it possible to reuse the EPROM that lost its bits? (pun intended). I got some cheap UV erasers, I could use that to blank it and then rewrite.
• MAYBE: perform the output current upgrade mod. How useful is this, really?

[Rax]

Coming back to this topic, as my F5440A is going back to a repair stage - at least I feel I need to assess if that's the case.

This is because it just experienced an apparent jump up of about 1.5ppm at 10V. I probably should check if all ranges have experienced the same, etc. (go in troubleshooting mode), though unfortunately I don't have as much solid data on the other ranges (<2V, including DIV, and 100V, 1000V, etc.). But all my meters this far (though still collecting data) - some of which are calibrated by different labs - seem to indicate the same jump.

The only other thing I can attach to this is that it happened during an unusually warm environment at the bench (over 28C). But it's permanent. Lower current temperatures have not restored the prior output value.

It's completely possible that the internal reference has just jumped by this much. From what I understand, this is rare, but not completely unexpected behavior. Crappy, for sure.

I'd appreciate input on this - what to look for, whether I need to look for anything, or it's all normal behavior, etc. Thank you very much in advance.

[Dr. Frank]

Hello Rax,
to answer your question in the mail: No I have not experienced a jump like that on my 5442A.
I always switch off my 5442A, when not in use, as well my working DMM, the 3458A.
All the references are running continuously, maybe I send one or two cold to another volt-nuts.
In case of low temperatures during transport, i.e. below 15°C, I might have a permanent upward jump of the LTZ1000 based reference on the order of +0.2 .. +1.5ppm, latter for temperatures around 0°C.

It's very uncommon, that the SZA 263s inside the 5440A just make just a jump out of thin air.
I also doubt that you would find a real damage inside your instrument.

I compare all my references once a month. The repeatability of the continuously powered references are around 0.2ppm or better.
The 5442A and the 3458A, after ACAL / INT CAL are on the same order, but tend to show bigger deviations up to 0.5ppm sometimes.
I assume that's due to the ACAL process, which sometimes get a hickup in the external circuitry.
This might be cured by repeating the ACAL process at a later time, but sometimes you have to wait for another day (with power / temperature cycling).

In the annual trend, you can then clearly see this single excursion of the instrument, so that you are able to distinguish between simple hickups and permanent reference shifts.
In your situation with greatly varying room temperature in your garage, it's very difficult to clearly exclude T.C. influences from your measurements.

Your 731B has 1ppm/°C, and very mediocre stability figures on the order of 10ppm/year, 2..5 ppm transfer stability (4h). Therefore, it's no proper voltage reference, but can only be used for transfer measurements when properly characterized for stability.
You definitely need a third stable reference to judge over the other two.

All my references are either specified, or validated to have around 0.02 .. 0.04 ppm/°C.
The 3458A, as already said, has around 0.25ppm/°C for its LTZ1000A reference, and 0.2ppm/°C for the ADC assembly, latter can be ACAL'ed.
 
In summary, your setup / environmental conditions is not good for sub ppm metrology, as I can tell you from experience, when my whole stuff was sitting in my office upstairs, with greatly varying R.T.
Only after I moved everything downstairs to the basement, where R.T. varies no more than +/- 1°C over the whole year, the transfer / comparison measurements were also stable, and such small deviations of 0.1ppm could be identified.

Andreas has a lot of experience with his very hot and unstable lab under the roof .. and he's got a lot of references as well, all have low T.C.
Maybe he can tell, how he deals with this problem. He's as well able to make smooth longterm stability measurements.

Frank

[Rax]

Hello Rax,
to answer your question in the mail: No I have not experienced a jump like that on my 5442A.

I must have misunderstood your recent point by email where you've identified - but not yet determined the cause of, last we talked - a 5.3ppm, then 3ppm, then 2.5ppm discrepancy with one of your other reference environments. Or maybe you've determined there was no jump and the cause was something else but didn't get a chance to share that with me.

Also, I think alm was making a similar point, I thought:

every time you switch a reference off and on there's a small chance it will jump in value.

Though I think the possibility of even apparently spontaneous changes in the reference voltage are not likely, but possible.

But I am pretty sure what I'm seeing is not tempco. It it were, I assume seeing some correlation between the reading and the ambient temperature would be expected. There's no relationship I can discern. It just switched to a higher reading on the Prema, period. The only temperature-related correlation I can think of is the higher than usual temperature at the time of the event, which, because it's such a distinct event and apparently not reversible, I assume could be caused by a part failure of sorts.

I also doubt that you would find a real damage inside your instrument.

If not that, and not tempco, then what is it?... I'm all ears!!

Your 731B has 1ppm/°C, and very mediocre stability figures on the order of 10ppm/year, 2..5 ppm transfer stability (4h).

I have no doubt you didn't mean to literally state that above, as we both know that's not a correct statement. My 731B doesn't have a 1ppm/C tempco. In fact, probably no 731B "has that." That is a guaranteed minimum specification. My 731B may far exceed that - within some reasonable limitations of design, construction, and just... physics - and we actually well know all Fluke instruments tend to far exceed their spec. My sample is an exceptionally well performing one, particularly with regards to tempco, as confirmed by other voltnuts that have examined it and have far more experience than I do. Between mine and other samples seen in this group I'm talking about, there's been a wide variability in the observed performance of some 731B samples, and mine is a standout.

I'm not saying this 731 is a 732 in disguise - not ovenized, right?... - just that the baseline specification shouldn't be looked at as its actual performance, which it is not. For a delta T of just about 3C, the output of an unusually stable 731B may not vary as much as one would imagine just based on specs. This particular 731B was recently adjusted by another voltnut friend by transfer with a Keysight-calibrated meter at 23.3C, so not so far from my conditions, and with a respectable pedigree; I'm considering this datapoint when I'm evaluating some of the things I'm seeing. I do strongly trust it within the limitations I just described.

You definitely need a third stable reference to judge over the other two.

Absolutely I do - though my better half may go through with moving me with all my stuff, permanently, in the garage - and I am picking up a, supposedly working, 332D literally this Sunday. Not a 732, but another opinion of my volt at my bench. As it goes for a lot of us here, this is a hobby, so to just grab a 732C because I want my 5440A or 6048 characterized, is absolutely not a feasible scenario. I do the best I can with what I have at hand in a garage (still, just about +-1.5C!...), and I've also just started on this path, so have that in mind when reading on my work and challenges. I can't change a lot of my determinations.

That said, I do have two calibrated meters at my bench right now (one by Fluke), and will have a calibrated (by Keysight) 3458A/002 on loan soon. I'm presenting all this data I can humbly accrue (=0, apparently) based upon a pretty respectable number of instruments, some of which are "prime house" calibrated! 

Andreas has a lot of experience with his very hot and unstable lab under the roof .. and he's got a lot of references as well, all have low T.C.
Maybe he can tell, how he deals with this problem. He's as well able to make smooth longterm stability measurements.

Frank

Great point, thank you for sharing this. I'll seek to look over his posts, maybe, and the specific challenges he faced and how he sorted them out.

Maybe there's a chance for this aspiring metrologist!

[Dr. Frank]

Hello Rax,
if you just THINK, that your 731B is much more stable than specified, you can for sure simply present your T.C. and stability measurements on it, like most of the volt-nuts did on their "Super LTZ1000 references" in this said thread.
Ah, I forgot that you don't have GPIB and data acquisition yet .. that's the most urgent topic for you to solve.

The deviation problem I described to you was a completely different case.. I had sent two of my working references to another volt-nut.
He observed deviations with greatly varying results, also relative to recent comparisons he made before, and we both could not explain that effect. Other recent  ring transfers were successful to < 0.5ppm, instead.

This case is completely unrelated to comparisons of my 5442A, 3458A, or all my references, which are all still stable and consistent within 0.2ppm when compared in my lab.

Frank   

[Andreas]

Great point, thank you for sharing this. I'll seek to look over his posts, maybe, and the specific challenges he faced and how he sorted them out.

Hello,

I simply try to characterize and improve my measurement devices (e.g. by evaluation and compensation of T.C. and other effects).

https://www.eevblog.com/forum/metrology/project-pimp-a-keithley-2000/msg1106829/#msg1106829

Most of my measurements are only relative (not absolute) so they need only a (characterized) linearity.

For critical absolute measurements I make the measurements with more than one measurement device.
E.g. the K2000 the HP34401A + ADC13, ADC15, ADC16, ADC17 all in parallel and additional my most stable LTZ1000 references as comparison/adjustment.
Against noise I usually average the measurements over 1-5 minutes.

And of course all EMI related stuff like LED lamps, mobiles etc. are banned from my lab.

Most critical for me is a large temperature gradient. So I try to do critical measurements in summer in the morning when the temperature is still stable.

with best regards

Andreas

[branadic]

(e.g. by evaluation and compensation of T.C. and other effects)

Just to be crystal clear on that point, that is software compensation of measured data or hardware compensation, so that the reference exhibits almost no t.c.?

-branadic-