Data Precision 8200 calibrator - repair and other fun stuff

[Rax]

Hi all,
I was very lucky to score one of these calibrators during the slow days of holidays - I'm more convinced every year that's a very good time to be combing through listings and get good deals - and, as they seem to typically need, the only real issue was a complete restoration of the switches. All of these seem to look like they've been immersed for years in households of heavy smokers or something, as the grime on those switches is just incredible.

Enclosed pics depict some of this work, though not the perfect cleanliness of the finished product after I switched to using an eraser. I simply forgot that I used to do this (I even have an electric eraser and a full set of tips...) - I guess sometimes one forgets their own figured out methods. In any case, with the eraser, the circular concentric lines are gone too and the tin surface is perfectly clean and shiny. I used IPA and ammonia alternatively to clean this, before the eraser, with a good wash of IPA wrapping it up every time, so if there's anything left from the eraser, it'd be removed.

I'd be interested in hearing some overall thoughts on this calibrator. My units are up to 6.5 digits, so this seems to be perfectly adequate. This far, everything I measured generated by this unit has been absolutely perfect to all digits (by instruments' agreement). I may bite the bullet, and, when everything is confirmed working, have this calibrated (meaning, verification) and tagged as such for high confidence provisions.

One thing I'm not really sure of is its 100mV output. I don't seem to measure it at the front terminals - but some sources seem to indicate that should only come out at the back. If that's the case, does anyone have some info how to achieve this? Is there some proprietary cable? I am not sure what needs to be connected to the "J301" and/or "J302" ports at the back of the unit.

Thank you for your input in advance.

[jwet]

Don't know what you paid but that's a great score- first class calibrator.  Basic spec is 10 ppm and 1 ppm/C drift which is 5 digits worst case.  You generally want a standard to be 10x of your DUT so you're probably shy of 6-1/2 digits technically.  I wouldn't hesitate to send it to a cal lab once you've got basic operation- see if they can give you actual readings rather than just running the standard cal.

The 100 mV output is indeed only available on the back.  Its kind of an unbuffered output vs the front panel kelvin 4 wire stuff- two wire only and 100 ohm output Z.  Don't know why its done this way.

You might add some anticorrosion lubricant to the switches on reassembly- Boeshield T-9 or Deoxit D5.  Most common alcohols are 91 or 99% with the rest being water.

Have fun.

[Rax]

Don't know what you paid but that's a great score- first class calibrator.  Basic spec is 10 ppm and 1 ppm/C drift which is 5 digits worst case.  You generally want a standard to be 10x of your DUT so you're probably shy of 6-1/2 digits technically.  I wouldn't hesitate to send it to a cal lab once you've got basic operation- see if they can give you actual readings rather than just running the standard cal.

The 100 mV output is indeed only available on the back.  Its kind of an unbuffered output vs the front panel kelvin 4 wire stuff- two wire only and 100 ohm output Z.  Don't know why its done this way.

You might add some anticorrosion lubricant to the switches on reassembly- Boeshield T-9 or Deoxit D5.  Most common alcohols are 91 or 99% with the rest being water.

Have fun.

Thank you, jwet.

I actually forgot to mention that I did indeed recondition the contacts with Deoxit. To do that, I used cotton swabs just to keep the Deoxit on the metal surface only. The switches work great now (I still have to do the +/0/- and the range... which are working fairly OK but I can't resist!).

[Conrad Hoffman]

It's a great unit. Those switches are the weak point and I didn't know you could get them apart for cleaning. Mine are terrible and no amount of soaking or Deoxit has gotten them back to reliable. Still, whatever the display says, is correct, even if you have to fiddle the switches a bit to get there. The reference is a LM399. I suspect a cal house would charge an arm and leg to properly calibrate it, as all the (clever) octal? ranges need to be adjusted. You'd be way better off to find a good KVD and reference, and do it yourself. Does yours have the HV or GPIB options?

[Rax]

It's a great unit. Those switches are the weak point and I didn't know you could get them apart for cleaning. Mine are terrible and no amount of soaking or Deoxit has gotten them back to reliable. Still, whatever the display says, is correct, even if you have to fiddle the switches a bit to get there. The reference is a LM399. I suspect a cal house would charge an arm and leg to properly calibrate it, as all the (clever) octal? ranges need to be adjusted. You'd be way better off to find a good KVD and reference, and do it yourself. Does yours have the HV or GPIB options?

I highly recommend doing the switches - not a difficult job and shouldn't take long (there are some youtube videos on this). Getting to them is pretty straight forward and even the switches are pretty clearly intended to offer the possibility of servicing (which, really, applies to the entire unit). Once done, all switches will operate flawlessly and done with care - for instance, I've obstructed the adjustment holes through the shielding inside to protect the reference circuitry during the work - nothing else should be disturbed.

I'd probably just have a cal house check their performance, not adjust them - I am in Southern California and, with all the wealth of them around, I am not aware of any here willing to adjust something like this. But checking and possibly providing long form data paperwork for not much $ is possible. As the unit seems to close or dead on, I think I'd be willing to risk it.

That said, if anyone in this community is near me and would have what it takes to adjust this to calibrated state, please do let me know.

[Rax]

Does yours have the HV or GPIB options?

The sticker in the back is a bit hard to read, but it seems to say the "100V" and "HV1" options are present. That said, I am getting 100V out of this, but not HV (as expected if that board's not in, I see "Error" on the display if I switch to the corresponding mode). GPIB option is present.

[Conrad Hoffman]

Yes, mine has 100V but no 1000 and no GPIB. Note this was sold as Data Precision 8200 and also Analogic AN3200 (mine). Not sure if there are any significant differences.

[Rax]

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

So, is a preferred adjustment method for a unit like this? It seems to be what the SM indicates. I am unsure what the possibilities are in my neck of the woods - whether it's more likely to find a high end reference AND a KVD, or other options (?). Still looking for anyone with the right equipment (high end voltage standard, KVD, 8.5 digit calibrated DMM, etc.) in Southern California to assist with this, but hopeful some options will emerge.

[Conrad Hoffman]

Anybody with an 8.5 digit meter can set this up. The problem is it's the sort of manual thing that cal labs do less and less of, and probably charge more and more for. Certainly call around and get some quotes. My experience with a sample of one is that the unit handily beats its specs over quite a few years. It's old, so things have drifted and settled about as much as they're going to.

[Rax]

Anybody with an 8.5 digit meter can set this up. The problem is it's the sort of manual thing that cal labs do less and less of, and probably charge more and more for. Certainly call around and get some quotes. My experience with a sample of one is that the unit handily beats its specs over quite a few years. It's old, so things have drifted and settled about as much as they're going to.

I've called around last year - maybe I'll give it another shot now - but I was unable to find even one facility willing to calibrate AND adjust an older unit such as this. They're willing to take it through verification, but not adjustment. If anyone's in my neck of the woods and knows differently, please pitch in.
My current solution is to have it adjusted as close as possible within a community member's bench, and then possibly bite the bullet and have it verified and hopefully stickered.
And so I just had my ol' 8502A gone through this treatment - you know who you are! And thank you!! - and it seems to be very, very close (or dead on in some ranges and values, such as 10.00000V) - to the 8200. Which confirms both the quality of the treatment and the excellent condition of the 8200. Though I still have to verify the 100mV is present at the back.

[branadic]

Sorry for highjacking the thread.
I eventually received a Data Precision 8200 branded as Analogic AN3200. Overall, the unit is in good shape and working. However, it needed a bit of a clean and adjustment to bring it back into spec.
The encoder disks of the conductive encoders were slightly tarnished but some polishing and bending of the fingers brought them back to operation. Different to videos on YT



the metal plates that hold the encoder together don't have the notches that are bend over, but rather have a dent to hold them in place.

The unit has the LM299 installed. It comes with the GPIB interface, is missing the 1000 V option, but doesn't throw out an error when the switch is set to the 1000 V position. Also, the unit resets the voltage setting if the polarity switch is changed in position, which is a bit unfamiliar to work with.

It won't win a design award and is rather ugly looking to be honest. However, it works a treat.
So the question arises, can it be improved (noisewise) by some component upgrades? The 20 bit DAC is pretty simplistic and there are some circuit design choices that I would have probably done different. One of which is, the reference voltage is divided first to be then amplified again, but also the way the divider and its adjustment is implemented.
Upgrading the unit with a lower noise ADR1399 would also require replacing Z6 (AD517, TO99 package). The lower noise OP(A)27 comes into mind. This however also requires adjustment of R7/R8/R9/R10/R12. Replacing Z14-Z19 would probably be a good idea too, to decrease noise. Are there other suggestions?

http://www.ko4bb.com/manuals/2.205.134.124/8200_20_BIT_DAC_A1_PN_60-1090_REV_0AD_Schematic.jpg

-branadic-

[Kleinstein]

The OP27 would not be a good replacement for most of the OP-amps: with the higher speed there is a chance it would oscillate. A more suitable replacement would be more like OP177 and similar low bias precision OP-amps of comparable speed.
Even for Z, some 5 K input impedance are a bit on the high side for an OP27 with little advantage over an OP07.
For the overall noise Z14 and Z19 also contribute comparable (depending on the DAC setting more or less).

The capacitor C19 likely has to go with a new OP-amp for Z6.
The ADR1399 of cause needs the RC for damping.
If the voltage is not too different, one may get away with the same old R8.

The system with divide first and than using a tap of the precision resistor chain is not that bad. The extra divider has not that much effect (only goes from some 7 V to 6 v)  and the resistor chain for the gain is anyway there for the DAC.

I don't see decoupling capacitors for the 4051 and 4094. One could consider to add some and a few ohm series resistor to the emitter of Q11.

For the current shunts / resistors one could think about adding some protection - though this may not be easy.

The question is if a new ADR1399 is really that much better than a well aged LM299. It would be lower noise, but likely more drift for at least the first few years.

[JK21]

I have a DP8200. Few mechanical repairs (a few screws and bolts) were needed. However, I have replaced the 100mV output connector on the rear panel.
I didn't like the original connector design, because the connections of the divider resistors were always bent when the connector was plugged in.
I used an XLR connector with gold-plated contacts and a small hand-made auxiliary board. The leads to the contacts are made with short strands and the divider resistors are no longer mechanically stressed.
This also improved the divider ratio from 100.0060 to 100.0011.

[Rax]

I have a DP8200. Few mechanical repairs (a few screws and bolts) were needed. However, I have replaced the 100mV output connector on the rear panel.

Can anyone provide some indication as to why this design choice? And also, what exact connector or dongle was being used there.

[JK21]

And also, what exact connector or dongle was being used there.

Sorry, I can't remember where and what exact type I ordered. There are various manufacturers of XLR audio connectors.

[Rax]

Sorry, I meant the original design choice. Ultimately, why route the 100mV range all the way to the back and on a J301 connector? Can this be efficiently rerouted to the main posts up front?
I have never even seen how a jack and/or dongle for that looks like.

[JK21]

I have never even seen how a jack and/or dongle for that looks like.

My first reason to swap the connector.

[Rax]

100mV range is now back online.

The range and polarity switches were not addressed at the first go at the switching assembly - as at the time they seemed to be mostly working OK. But upon later examination, I couldn't output proper levels on the back. After fixing the range switch, proper levels are now present at the rear output. Before this repair, I had some intermittent activity of the relays when using that switch, and I don't think the 100mV relays were ever properly actuating.

Stepping back - I can't believe how much grime and crud were on all of these switches. The polarity switch seemed to have some sort of grease smeared all over the inner PCB. I just can't explain it. But it seems to be a widespread problem with all these calibrators, so I really think one of the best immediate improvements possible are cleaning and conditioning the switches. Once that's done, the unit seems to come back to operation that's very close, if not outright within spec.

[Kleinstein]

Some switches intentionally use some special grease. It protects against corrosion and reduces the wear / friction, so that a higher contact pressure can be used.  A switch designed to work greased may show quite some wear when used dry.

[srb1954]

I have a DP8200. Few mechanical repairs (a few screws and bolts) were needed. However, I have replaced the 100mV output connector on the rear panel.

Can anyone provide some indication as to why this design choice? And also, what exact connector or dongle was being used there.

It might be a low thermal EMF connector. With the 100mV range the LSD resolution would be 100nV so you would definitely have to worry about thermal EMF voltages if you wanted to get reliable measurements at that level of resolution.

Unfortunately the BOM in the service manual doesn't offer any information as to the manufacturer merely quoting the Analogic part number, 25-321036

[Rax]

Some switches intentionally use some special grease. It protects against corrosion and reduces the wear / friction, so that a higher contact pressure can be used.  A switch designed to work greased may show quite some wear when used dry.

That's a possibility, though given the distribution of that (all smeared on one side, mostly away from the contacts), it looks more like a spill of sorts - such as from maybe lubrication on the shaft or something like that. Also, that's the only switch showing that - the rest have only some sort of tar deposit - and I'm not entirely sure why that one switch only (the range switch) would have grease on it.
 
I hope I won't have to open this back up one more time to apply some grease, but I'm not very concerned. It just doesn't seem a very sensitive application. Before the cleanup, the switch was acting extremely sticky and was also downright defective regarding actuating the 100mV mode. I also can't imagine me, or any future user, would actually use this in an extremely high demand capacity (the switch being used hundreds of times a day) like a calibration shop would.

[Conrad Hoffman]

Those switches are just PCB with maybe some special tinning or plating. IMO, fragile enough that a grease is highly recommended. You can get various special Nye products at high cost, or maybe use common Superlube grease. I've talked to their app people and they say it's good as an electrical switch grease and generally safe for plastics. It's a PAO/mineral oil with a fumed silica thickener, plus 5 micron PTFE particles.

[Rax]

Those switches are just PCB with maybe some special tinning or plating. IMO, fragile enough that a grease is highly recommended. You can get various special Nye products at high cost, or maybe use common Superlube grease. I've talked to their app people and they say it's good as an electrical switch grease and generally safe for plastics. It's a PAO/mineral oil with a fumed silica thickener, plus 5 micron PTFE particles.

Well, that explains everything. The main failure mode of these units seems to be the aging of this grease - the "crud," and "tar," etc. I found on these switches was just that - grease that dried, or thickened and whatnot. It degrades so much that it starts both interfering with the electrical contact, and the mechanics of the movement of the switch.

The kind of thing I wish I'd figured at the beginning of this saga - I'd have a figured out a proper grease and have at hand before the surgery and would have applied it as the last step on my restoration work. Well, maybe I'll open this thing at some point later for the third time and go through the switches once more.

That said, I'm pretty sure this is good for a very long time as is. And it works 100% at this point. Happy camper here.

[Conrad Hoffman]

Possibly a squirt of Faderlube could be gotten in there without disassembly? It contains a light oil, which should be better than dry.

[Rax]

Possibly a squirt of Faderlube could be gotten in there without disassembly? It contains a light oil, which should be better than dry.

I did use Deoxit D5 on all contact surfaces of all switches - both PCB traces and the spring leafs - but I guess the difference from that to an actual viscous grease would be enhanced mechanical lubrication.

For now I'll just settle for the level of mechanical lubrication the Deoxit will provide (as a "surfactant" of sorts).

[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.

[Conrad Hoffman]

FWIW, other than the intermittent switches, mine's been as reliable as a cast iron boat anchor. Long ago it needed a single 1k precision resistor, but other than that, nothing.

[Rax]

FWIW, other than the intermittent switches, mine's been as reliable as a cast iron boat anchor. Long ago it needed a single 1k precision resistor, but other than that, nothing.

This far, within the limits of the instrument, though pending further checks and empirical data around some suspicious datapoints, I feel this has been doing really well.

But thank you for confirming your good track with it.

[Rax]

One thing I'm seeing as I've adjusted and now I'm observing it relatively short term is that the 100V range seems to need quite a bit of time to settle down. Assuming I'd shoot for 100.0009V with my 100V field adjustment (which is my absolute characterization point per my 8502A long form cal), it'd start at about 99.9999V or so and it'd need maybe 5-10 minutes to get to the 100.0009V.

I'm considering adjusting it a little high to shoot for a reasonable amount of time before I would expect it to be accurate (I'd ideally want it to be pretty quickly ready after the 100V range turn on, in a day-to-day switching between ranges situation, which doesn't easily accommodate 10 minutes for switching the 100V range).

Is this something others have seen, or is it an issue in mine indicating a need to repair?

[Le_Bassiste]

might be worth checking as to whether extra settling time for ranges 100V and above are partly caused (or even cancelled) by the DMM's input divider.

[Kleinstein]

My suspicion is with a thermal effect. 10 minutes souds like a reasonable time frame for this.
The feedback divider in teh calibrator with 10K and 90 K is quite low value and thus quite some heating expected.
Compared to this the divider in the DMM is likely less of an issue as it is likely made also for higher voltage (e.g. 1000 V range).

For a test one could check what happens at a low voltage like 70 V: this would be about half the effect of heating, but a comparable fraction of the voltage for an effect due to amplfier settling or dielectric absorbtion.
The heating effect in nonlinear and not just a settling problem.

[Rax]

My suspicion is with a thermal effect. 10 minutes souds like a reasonable time frame for this.
The feedback divider in teh calibrator with 10K and 90 K is quite low value and thus quite some heating expected.
Compared to this the divider in the DMM is likely less of an issue as it is likely made also for higher voltage (e.g. 1000 V range).

For a test one could check what happens at a low voltage like 70 V: this would be about half the effect of heating, but a comparable fraction of the voltage for an effect due to amplfier settling or dielectric absorbtion.
The heating effect in nonlinear and not just a settling problem.

This makes sense.

[branadic]

I have upgraded AN3200 with an over 8000 h pre-aged ADR1399. I had to adjust R7 as well as R8+R9 from original 1.14kΩ to 1.7kΩ to have enough of margin left for adjustment on the 20Ω pot. Attached a 1h measurement taken with S7081 in 7.5-digit mode.

Edit: Repeated the measurement with S7081 in 8.5-digit mode and eventually verified the measurement with R6581D and indeed noise improved.

-branadic-

[Rax]

I have upgraded AN3200 with an over 8000 h pre-aged ADR1399. I had to adjust R7+R8 from original 1.14kΩ  to 1.7kΩ to have enough of margin left for adjustment on the 20Ω pot.
-branadic-

I'm not sure I follow - R7=3.01k, R8=5.3896k - how exactly did you have to replace these? Specifically, what were their replacement values?
Thank you for sharing these results and work.

[Rax]

-branadic-

branadic - this is completely unrelated, but I see all these cool graphs and charts on EEVBlog - what's the high level approach here? Automated readings over GPIB, logged some way on the computer and plotted through another something? I candidly am at this clueless level with this kind of data visualization, but I'd love to explore it.

[branadic]

It's actually a low level approach, some Raspberry Pi and GPIB magic in the background aquiring and storing data on a local drive, I still work completely script based, no fancy packages and libraries involved and the rest is simply LibreOffice visualization if I'm lazy re GNU Octave for the more interesting data, that I analyze each evening on the couch

-branadic-

[Rax]

I have upgraded AN3200 with an over 8000 h pre-aged ADR1399. I had to adjust R7+R8 from original 1.14kΩ  to 1.7kΩ to have enough of margin left for adjustment on the 20Ω pot.
-branadic-

I'm still interested in details on the resistors values revisions.

Have you seen any ill effects with doing this on the linearity of the instrument? Put differently, have you had to tweak the octade adjustments (within the "metrology calibration" procedure - R33, R30, etc.)? If not, this seems to be a pretty effective and relatively "low impact" upgrade to this unit.

R12 is part of the field calibration procedure, so I don't think that has bearing on the linearity of the instrument, and is obviously an expected adjustment to do given the change in the reference (in addition to the other resistors changes you mention).

[Kleinstein]

Changing the reference and accordingly adjust R7,R8 (or R9) and R12 should not have  an effect on the linearity. The change of R8,R9,R12 is to bring the ref. voltage seem by the divider back to the old value. So the octal divider chain would not see if the reference voltage changes (e.g. 7 to 6.9 V). The main change would be a slight higher current to the reference.

It is still a question if this would really be an upgrade worth while: the ADR1399 is lower noise, but the old LM299/LM399 is usually well aged, depending on how long the unit was powered on.
The lower reference noise would mainly make sense together with a change in the OP-amps (Z6,Z14,Z19) for lower noise.

[branadic]

R7 = 3.01 kΩ was replaced by 1 kΩ so roughly the same 3 mA through the zener as before.
R8 and R9 were replaced to the value given above to get back the adjustment range of R12. The noise went down significantly, even though Z6 wasn't replaced yet. I have an OP177 sitting on the shelf, but am not tempted to install it at the moment, also due to missing TO to DIP adapter and I don't like a dirty bodge to fit it in.
And as stated too, the ADR1399 saw a burn-in for over 8000 h before.

-branadic-

[Rax]

After having two units here to play with and assessing different things, I think it's very important for any of these to have its offset adjusted (4.3.3 in the manual).

It's technically part of the "metrology standard adjustment," but I don't think it affects anything on the linearity etc. of the unit. I may be wrong, but I think they should have included this in the "field adjustment." My standard tackle on these is currently the offset and the field adjustments. Once these steps are done, I'm finding this very well dialed in.

I've found the offset to be very high on these when they get to me - hundreds of uV - due to aging, lack of maintenance, etc. And this residual can throw all sorts of mayhem in the measurements, adjustments, etc.

[branadic]

I was asked to share some noise measurements with replaced reference, outputting 10 V.
Notice, the opamps are still original and have not been replaced. Please replace mV by µV and you end up with 3 - 4 µVpp.

-branadic-

[Rax]

I was asked to share some noise measurements with replaced reference, outputting 10 V.
Notice, the opamps are still original and have not been replaced. Please replace mV by µV and you end up with 3 - 4 µVpp.

-branadic-

branadic,
I may have missed it, but did you intend these to be compared with the "before" measurements? If yes, can you please point me to where they are available?
Than you.

[branadic]

It was way larger before, more in the 10 µVpp range, but I don't have an image of a measurement at hand.

-branadic-

[Rax]

It's been a while, y'all.

I have a second 8200, and got around to adjustments this weekend. It's a much cleaner unit and it seems to be working well overall. One issue I'm finding, though, is that I'm unable to get it to 70V when adjusting it per 4.2.3-9. The adjusting effect is very small, and I'm pretty sure I'll run out of range before I get to within 100uV of value. I'm typically finding an adjustment like this to be very close to the original pot position - more like a trim than a finger-spinning workout. This isn't acting like that, it barely moves in output value with vigorous spins of the pot adjustment.

I posted on this on the Repair group: https://www.eevblog.com/forum/repair/data-precision-8200-100v-range-out-of-pot-range-during-adjustment/.

Thank you for all input!

[branadic]

he lower reference noise would mainly make sense together with a change in the OP-amps (Z6,Z14,Z19) for lower noise.

As far as I understand you suggest OP177 for Z6, Z14 and Z19 and to remove C19 at Z6, is that right?

-branadic-

[Kleinstein]

Yes these 3 OP-amps will contribute to the noise. The original AD517 was a good OP-amp at it't time, but is still pretty noisey (2 µV_pp for 0.1 - 10 Hz). This may be acceptable for a LM399 or similar reference with some 5 µV_pp on its own, but an upgrade would make sense with an ADR1399 reference. With a change in the reference one would need to readjustst the voltage anyway and the different offsets should be no issue.
C19 is odd in the circuit, it reduces the phase reserve and not all OP-amps may like it - here it may be worth checking at least to check if it works better without or possibly oscillates with C19.

An OP177 would be a candidate that is also awailable in DIP.

[branadic]

I today received some DIP-TO99-adapters and desoldered the components on the board (Z6, Z14, Z19, C19).
Z6 was an AD517, while Z14 was an opamp marked AD40932, same as Z19, except it had a plastic cap/cover and was potted inside with some sort of silicone. When I removed the silicone I found that the leads on all pins were extended with 10R (brown, black, black, gold) carbon composite resistors, probably to reduce heat flow?, which I found pretty interesting. The three OP177 are now in place, we will see how that turns out.

-branadic-

[branadic]

After some zero point adjustments, I still use the original 50k at the offset trim pins of the opamps, I took some noise measurement data on the 10 V ouput. It seems like there is an improvement. 

rms = 388 nV
std = 387 nV
pp = 2.7 µV

rms = 500 nV
std = 500 nV
pp = 3.2 µV

rms = 401 nV
std = 401 nV
pp = 2.8 µV

rms = 382 nV
std = 382 nV
pp = 2.9 µV

rms = 399 nV
std = 399 nV
pp = 2.5 µV

-branadic-