Data Precision 8200 calibrator - repair and other fun stuff

[DavidKo]

In the manual to old Metra L110 decade, they have recommend to use ordinary grease dissolved in petrol to create thin layer of lube for moving parts lubing .

If the switches were not intended to be serviced, there will be a lot of lube, which had slowly solidified after some time. Less lube they use, quicker it gets dry.

[Rax]

I wonder if anyone in this community has one with the HV option. Which I can't yet quite find spelled out in the service manual.

It'd be interesting to give a shot at creating a PCB for it. I assume it should essentially be a 10X, or maybe 100X (if taking its input from the main 10V output, which I think it should) upscaler/amp.

[eliocor]

I would be interested in the HV option too....

[vtp]

I wonder if anyone in this community has one with the HV option.

I have one DP8200 with HV option. It's 100X.

[vtp]

And the last picture

I did not remove the HV power supply cover at that time so no picture of the other side. It isn't that difficult to figure out what is going on inside from tracks. Looks to have a push-pull drive for potcore transformer, possibly using SG2525.

If disassembled it should be relatively easy to recreate that. Something would need to be substituted for the 100:1 feedback divider and thick film resistor network.

[Rax]

Thank you, vtp. Currently in business travel, but will get a chance to look at these soon.

If anyone was able to identify the corresponding circuitry from the SM, I'd love to hear it.

[JK21]

@Rax
Do you know this thread:   https://www.eevblog.com/forum/testgear/data-precision-8200-with-1kv-option/  ?

[Rax]

You'd be way better off to find a good KVD and reference, and do it yourself.

Well, Conrad, I may have just grabbed a KVD... An ESI RV722, apparently. Do you mind sharing what was your standard voltage source ("reference") you used for doing the cal?

[Conrad Hoffman]

I have a 722. It's decent but I can't remember the specs. At the time my voltage reference project was going on and I probably still had an ovenized cell bank and recent calibration.

[Rax]

Moving the topic of field calibration of the Data Precision 8200 back to this thread - I feel it rather belongs here?...

I've went ahead with this and here are some results.

• I've adjusted the 10V point to agree with my just-verified 8502A. I seem to be able to keep it within about +1/-2ppm from 10.00000V, which I feel is probably tempco driven more than anything (confirming Testtech's testimony).
• Adjusted also the 100V range. This one fluctuates quite a bit more, and it needs a good amount to settle to a value (I feel the settling starts occurring a minute or two after switching the range on and setting the value, but I essentially adjusted it to a sweet spot - so the accurate 100V point would be met at a point where the settling curve is almost done moving and the time passed is reasonable for a measurement situation. Have others observed this behavior? Maybe I'm looking too close, what I'm talking about is I believe essentially within the 10ppm spec.
• The 100mA is yet a bit more slippery, but I'd wager not outside of bounds for a DCA measurement vs. DCV
• There's a bit of offset (which I adjusted one time recently) which seems to come back and then go away without a trace as soon as I grab the tools to adjust (kind of literally). Maybe there's some noise leaking in in some way, maybe something environmental is happening, maybe I should also just come down with this one aspect. Or maybe I should look closer at Z19?...

[Rax]

(further log...)
It seems the tempco is negative - I see this 2-3ppm variation in output across the about 3 degrees of temperature fluctuation at the bench (all this is F, so between 75F and 72F across 24hrs yesterday and today). So the voltage out slightly increases with the temperature decreasing.
Which is good, the lab doing the cal is maintained at 22C, which is also where my adjustment hits 10.00000V exactly. We'll see!

[Conrad Hoffman]

I don't think the 8200 has great quality banana jacks, but you'll still benefit from using cleaned bare copper wire for your interconnects. It doesn't take much temperature difference to move things by a couple ppm and this is often where inexplicable offsets come from.

[Rax]

I don't think the 8200 has great quality banana jacks, but you'll still benefit from using cleaned bare copper wire for your interconnects. It doesn't take much temperature difference to move things by a couple ppm and this is often where inexplicable offsets come from.

Thank you, Conrad, good point. FWIW, I'm using a set of shrouded Probe Master "all copper" interconnects for this. But I have not necessarily conditioned the 8200 jacks.

[Rax]

I don't think the 8200 has great quality banana jacks, but you'll still benefit from using cleaned bare copper wire for your interconnects. It doesn't take much temperature difference to move things by a couple ppm and this is often where inexplicable offsets come from.

One other thing that came to mind just now is I should maybe unstrap the GUARD from LO and connect separately with multimeters? I think if I want to get so down into the weeds ("grass"), this may be a requirement? I think the very careful are running shielded wire, but I've no such cables (though I should probably make myself some).

I've been strapping GUARD to LO/VOLTS on all my meters, and for the DP8200, I've been running the thing with just stranded copper wire connecting the SENSE and GUARD with the respective HI and LO. This is because my unit came without straps the low-emf copper bridges - where can one buy a bag of these?... I can't find any anywhere!).

[Rax]

One other thing I'm trying to wrap my head around - a lot of these these days  - is calculating the tempco of this calibrator.

The spec says +-(10ppm/C + 2ppm/C range). Does this mean 10ppm + 2ppmx10V (that being the range I want) = +-30ppm?

If yes, wow, that's a lot, but I am definitely seeing a thermal behavior that's well within those limits. That said, even if I'm looking at this through 7.5 digit readings (8505A on 1V or 10V range), it's pretty amazingly stable.

[alm]

Where do you see that? In the copies of the data sheet and service manual that I downloaded at some point, it gives a tempco of 1 ppm/°C of reading + 0.2 ppm/°C of range, so for a 5 V setting on the 10 V range, the tempco would be 1 ppm * 5 V / °C + 0.2 ppm * 10 V / °C, or 1.4 ppm of 5 V/°C. For 10 V it would be 1.2 ppm/°C (of 10 V).

[srb1954]

One other thing I'm trying to wrap my head around - a lot of these these days  - is calculating the tempco of this calibrator.

The spec says +-(10ppm/C + 2ppm/C range). Does this mean 10ppm + 2ppmx10V (that being the range I want) = +-30ppm?

If yes, wow, that's a lot, but I am definitely seeing a thermal behavior that's well within those limits. That said, even if I'm looking at this through 7.5 digit readings (8505A on 1V or 10V range), it's pretty amazingly stable.

The spec sheet I am reading says:
   +/-(1ppm/℃ +0.2ppm/℃ range) on the 10V range.

[Rax]

You both are right. I was reading the wrong part of the spec sheet.

So for 10V on the 10V scale, 1ppm of reading (assuming reading is 10V) would be 10ppm, no? Plus .2ppm of range would add 2ppm, so overall +/-12ppm for full scale on the 10V range?

As I look at what the DMM is displaying, I am looking for a shorthand way to tell if things are in good order. So to me, ppms are certain digits of the DMM reading (obviously, the last or last two, depending).

[alm]

No, 1 ppm of 10 V is 1 ppm. ppm is like percentage, it's one millionth of something. What that something is, is usually clear from the context. Normally if you say 10V +/- 10 ppm, you mean 10V +/- 10e-6 * 10V, or +/- 100 uV. If this confuses you, then it might be easier to convert everything to absolute (i.e. volts). For 10V output on the 10V range, the tempco is 1.2e-6 * 10V / °C, or 12 uV/°C. Does that clear things up?

[Rax]

No, 1 ppm of 10 V is 1 ppm. ppm is like percentage, it's one millionth of something. What that something is, is usually clear from the context. Normally if you say 10V +/- 10 ppm, you mean 10V +/- 10e-6 * 10V, or +/- 100 uV. If this confuses you, then it might be easier to convert everything to absolute (i.e. volts). For 10V output on the 10V range, the tempco is 1.2e-6 * 10V / °C, or 12 uV/°C. Does that clear things up?

Thank you, alm. I do understand the fact that it is a ratio, or percentage of a value. However, I may be misreading this, but I thought there's a multiplier attached to it by stating it's 1ppm/C (of) rdg, so it's 1ppm times the actual reading (otherwise it's just say "1ppm/C" period, no?). Meaning, if I was looking at a reading of 1V, a 1x multiplier applies, a 10V reading would have a 10x attached to it. But it's entirely possible I'm reading it wrong.

[bdunham7]

1ppm of 10V is 10µV, not 10ppm.  1ppm of reading of x.xxxV  is x.xxx µV.  Which seems obvious except that it does get confusing if you aren't careful.  Some standards bodies have gone to specifying µV/V as the method of expressing proportional uncertainties, but I don't see that as being any clearer.  IMO the easiest way to keep it straight when struggling with ppms is to convert to either voltage or counts.

So, on a 6.5 digit instrument and the 10.00000V scale,  1ppm of range/C  works out to 10µV/C or 1 count/C. 

[alm]

Let's change it to percentages. 1% of 1V is (1% * 1V) = 0.01V, but this is still 1% of 1V, not 0.01%. 1% of 10V is (1% * 10V) = 0.1V, but this is still 1% of 10V, not 10% of 0.1%. Does that make sense? The ppms are relative to the reading. So 1 ppm of reading if the reading is 1V is (0.0001% * 1V) = 1 uV, but it is still 1 ppm of the reading. And 1 ppm of the reading if the reading is 10V is (0.0001% * 10V) = 10 uV, but this is still 1 ppm of 10V. Maybe it's easier to understand if you use absolute values (uV) instead of fractional values (ppm/%).

[Rax]

Thank you both, yes, I need to do some practice exercises and also commit to some "consistency decisions..."

[Conrad Hoffman]

Much as I like ppm, here's what NIST has to say about it. See section 7.10.3:
https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-7-rules-and-style-conventions-expressing-values

[Rax]

Apologies to those reading this thread for the subject.... I take ownership for going on tangents, though hopefully (which I'm sure of, at least in what regards me, personally) it's all been very interesting and a great learning opportunity. 

Taking it back to the specific topic, I wonder if any of the long term owners of the 8200 have had to deal with persistent offsets on output? Per Conrad's input, I just took a stab at the banana jacks - and extracted some pretty serious gunk from there - but planning for more serious work need be.

I've adjusted it a week or two ago just to find it now throwing me off with (mis)interpreting something else. I wonder if I'm seeing some parts failures I may have to address before attempting to have this taken in for calibration.