Fluke 332D minimal calibration - Page 1
Forum section: electronics / general

author: Rax
author_rank: Super Contributor
timestamp: February 03, 2024, 05:56:15 pm
content: Hi all,I repaired this 332D a little while ago - seehttps://www.eevblog.com/forum/repair/fluke-332d-leds-repair/- which included new LEDs for the ranges and spacers between the internal enclosure and the external one and some other minor things. BTW - I think some of these may be a serious liability, due to these spacers getting frail and often times lost. Mine didn't have nearly enough for what I'd regard safe.In any case, I'm seeing this quote off from nominal out. My line voltage at the bench is relatively low (to contemporary US standards) - about 116VAC, but that should be almost exactly what this unit wats to see. May also be worth checking the rails, and tweak the two adjustments available for that.I've reviewed the calibration instructions, and, as everyone knows, they're pretty invested. I read through the forum and didn't find a lot on the adjustments/calibration procedure.I'm trying to figure out if an abbreviated procedure is possible. I think this would be useful to others seeing old units like this one is. For instance, I assume the linearity may still be OK (though I could test it with my Prema 6048). I'm considering only performing the "Range Zero Output Adjust" and the "Range Cal Adjust" and call it a day.Looking forward to your shared thoughts.

author: Rax
author_rank: Super Contributor
timestamp: February 04, 2024, 08:19:17 pm
content: Linearity looks good to me. I don't see a reason why the linearity would be disturbed by adjusting the zero and the range resistors for accurate output.

author: alm
author_rank: Super Contributor
timestamp: February 04, 2024, 08:36:57 pm
content: What is the max INL (integral non-linearity): the maximum difference of these points from a straight line between 0 and full range? From reading table 4-12 of the manual, the linearity adjustment appears to be within 0.5 uV/V for decks A, B and C. What is the INL of your P6048? You might get a better linearity measurement if you use your Fluke 5440 and a null meter as a pseudo-differential voltmeter, like how they used the Fluke 720A in the service manual (adjust F5440 until the null meter reads zero, and read voltage from F5440 setting).I haven't used these series of instruments, so I can't comment on how much adjustments interact. A quick skim suggests that in the Fluke manual linearization is the last step, but in the military manual it is one of the first steps, so you may be right that range adjustments may not affect linearity, although both manuals make you perform zero adjust before linearization. Of course there is no guarantee that the resistors in the switches may not have drifted, so I would argue you should verify linearity of all decks given how long ago last adjustment must have been.

author: Rax
author_rank: Super Contributor
timestamp: February 04, 2024, 09:44:10 pm
content: Quote from: alm on February 04, 2024, 08:36:57 pmInsightful points, alm - thank you - and, granted, my linearity plot looks great as seen from a... helicopter. But a "reasonable effort" with this instrument (a "10ppm instrument" - or 20, depending how you look at it) is what I'm, at least initially, looking for. It'll never be my "go-to" DCV calibrator (unless, gods forbid, the 5440 takes a dump). At best, a backup, though the space it takes is frankly a bit of a nuisance.But ideally, the adjustments would not interact too much, and the "linear slope" would just shift up and down linearly (maybe change the sloping a bit) without creating any wrinkles in the plot. Of course, all this put crudely and wishfully.Maybe the least "intrusive" adjustment is the nominal output range resistors as a first step. Then check the zeros and see if they're non-compliant. If they are - great - an instrument which may fall in spec already; if not, proceed to the zeros, etc.I think the zero adjustment will in most cases be the first adjustment - in my experience - though in some cases they then have you go back and check it after other adjustments (= interaction). But a bit of that may be just starting with a clean baseline.The linearity check methodology you point out is a great idea (I do have a K155 here, so that'll come in handy). I think on its main thread we were assuming the Prema has a .5ppm linearity, though I searched through the thread to remind myself how we arrived at that conclusion, and didn't find the pertinent posts. If I find enough time, I could at least try it both ways and see if they both point on way or the other.

author: Rax
author_rank: Super Contributor
timestamp: February 05, 2024, 04:37:42 am
content: Quote from: Rax on February 04, 2024, 09:44:10 pmThis is not meant to detract from the engineering considerations over where the zeroing belongs in the adjustments sequencing.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 05, 2024, 10:10:52 am
content: The way the Fluke 332D is build (mechanical switches for resistors or maybe a KV divider) there should not be much effect of a full scale or zero adjustment on the linearity. Bothe the zero an linearity are rather basic adjustments. For the zero it makes sense to do it first and if needed redo it again (or at least check) as one of the last steps. A linearity adjustment could effect the gain, but should not really effect the zero.The Prema meter should be well good enough for a check of the INL. The FLuke 4550 may be comparable but would be a bit more tricky to use. It would only be the high voltages >20 V, where prema meter may not be that good and the 4550 maybe really better linearity. For the other ranges it would be likely easier to check the 4550 and prema meter against each other and than use the DMM.The linearity plots are rather crude - not really showing if the linearty is good. This type of plot is more suitable for a low end analog meter or see if something is really broken. I doubt one would see an error <10% from such graphs.The more normal plot to look at the linearity of better instruments is to plot the INL or an approximation to this. So the difference, corrected for a possible wrong scale factor.

author: Rax
author_rank: Super Contributor
timestamp: February 05, 2024, 03:13:54 pm
content: Quote from: Kleinstein on February 05, 2024, 10:10:52 amTrue, and my intention with this was to see if there are gross deviations anywhere. But it'd be more appropriate to employ the general methodology I used for checking the INL of my Prema 6048 to make the plot more legible.