Fluke 730A DC Transfer Standard

[branadic]

Good evening,

I've noticed that there are almost no images of Fluke 730A on the web, except this



It just so happened that a unit arrived on my desk (/AH 13508). The batteries had leaked and were already removed, but other than that the unit was working.
I already replaced the HP connector by an IEC connector, etched away the residue that the NiCd had left on the aluminum of the battery compartement with go-devil, re-newed every single solder joint on the mainboard, gave the complete board a thoroughly clean, replaced the cables from the mainboard to the batteries and today removed the switch assembly to maintain it, as the springs were corroded and had left corrosion on the board. Most likely I have to replace all the springs of the switches, nothing impossible. Almost there to power it on myself.
What I found interesting though is that the "Mean Output" switch was factory locked, but I couldn't find a hint in the manual about it.

-branadic-

[Vgkid]

For the mean , there could be an averaging amp / or voltage divider.
edit: apparently it puts the in parallel 
http://www.ko4bb.com/manuals/47.134.114.28/Fluke_730A_Voltage_Reference_Operator_Manual.pdf

[branadic]

By locked I mean the switch was physically locked by a plastic washer instead of having a spring and that washer was designed for the switch, so nothing that looks like a hack by someone to prevent the operator from pushing the switch. Hence why I'm curious if there were options the F730A was delivered with.
During the process of maintaining the switches one of the rods broke. 
Super glue didn't fix it and epoxy based glue didn't work either. I guess the rods are made of resin, so I will try UV curing resin as glue next. In worst case I have to cast the rod, as 3D printing probably won't work due to the very small features on the rod.
More images about to come, once I've managed to complete my overhaulin'.

-branadic-

[alm]

The reference board looks quite a lot like the Fluke 731B, although clearly with a different layout. Except with the DH80417B which was also used in the 731A and some early 332/335 series calibrators instead of the SZA263. I have an early 731B which also has the DH80417B refamp (see attached pics).

[Rax]

More examples of early reference boards pre-SZA263 (this is from my Fluke 332D). I didn't take good pics of the reference itself, but one pic depicts 4ST1-2 (just as the manual states), which I assume to mean it's the DH80417B? 

[branadic]

The reference is A3, it is located inside the black component, which is an oven/thermostat made by Klixon.

-branadic-

[Rax]

The reference is A3, it is located inside the black component, which is an oven/thermostat made by Klixon.
-branadic-

Yes, it is - I just meant I didn't open my "4ST1-2" part to see if there's indeed a DH80417B inside it, or there were other variations using a different reference (which I don't think is likely).

Frank has that documented very neatly at https://www.eevblog.com/forum/testgear/fluke-332baf-in-the-slaughterhouse/msg393627/#msg393627.

Interesting to observe about the F730A is that its reference is not ovenized.

[branadic]

UV resin didn't work to fix the shaft, it was fairly easy to remove it once cured. The resin the shaft is made of seems to be rather "special".

I then started making a mold using alginate. This worked, but since the mold releases water all the time neither UV curing resin nor epoxy felt happy with that and the casted shafts looked like a mess. What I learned in the process: Forget alginate as a solution for a mold, it simply doesn't work out.
Already ordered some RTV silicone (https://www.silikonfabrik.de/silikone/silixon/silixon40-silikonkautschuk-rtv2-giesssilikon.html?number=SILIXON40-500-0709), but wanted to finish the project this weekend. I remembered to have some RTV blue silicone and took that to make a mold. This works to some extend as it is not that liquid. However, it takes 24 h for it to cure, so this also would have been a "finish the project this weekend" blocker.

Eventually, I looked inside a Fluke 8000A I had sitting in the shelf and to my surprise found the very same switches. So for the time being the Fluke 8000A had to serve as a donor for the shaft and the springs until I have made and organized replacements. I also removed the lock on the Mean switch and replaced it with a spring.

The unit is mostly back together and I could turn it on without having to fear something goes up in smoke and yes, she is working  

There is still some work to do before I can call it finished, but I'm close to aquire some data like noise, short-term and mid-term stability.

-branadic-

[branadic]

I made some progress.

First of all, thanks to user beanflying the instrument is now standing on its own feets:
https://www.eevblog.com/forum/testgear/replacement-knobs-feet-and-fittings-for-test-equipment/msg2502039/#msg2502039

Next, I have checked the output voltages, which were quite different on all four channels. I was able to adjust at least 3 of them to what I assume to be 10 V. Reference board 2 however was way out of adjustment range. So I looked on the board and found that the reference boards are Rev. C, which has nothing to do with the schematic in the Fluke 730A manual. After some reverse-enginerring and comparison I found that the schematic matches the one given in the Fluke 731A manual, but uses Flukes hermetically sealed resistors as in Fluke 731B. After I found that I've added a 4R7 resistor in series to R7, which brought back the adjustment capabilities.
I was now able to also bring channel 2 to 10 V, which allows to parallel (Arithmetic Mean) all four reference boards without huge changes. From here we can now take some measurements, intercompare the channels and look at stabilities. But before that, I'm planning to add a temperature sensor (thermistor GA10K3A1) to the unit and to connect it to some unused pins of the Centronic connector. This way no extra holes have to be drilled.

-branadic-

[branadic]

Attached is a first result of a 1h stability measurement of all channels one after the other after an initial adjustment of the ouput voltages. There is room to improve and to do better, I know.

-branadic-

[branadic]

I today worked a little bit more on the adjustment and repeated the measurements, this time only half an hour on each channel. The outputs are now way closer. I think I will leave them just there and observe their drift from here.

Some of these 2x10 pin card edge connectors were ordered, so I can put each reference individually into the thermal chamber and we can check how they perform over temperature. The connectors should arrive soon.

Meanwhile, I can focus on measuring low frequency noise.

I wonder if someone else with such a unit has results to share, too. 

-branadic-

[Bill158]

I have one of these 730A.  The S/N is #331 and it has the round precision resistors.  Attached is the ".xls" file I have generated from a much larger set of data on all of my various voltage references.  The value axis is in uVolts or "0.1 ppm" per division.  This is because I collect all my data using the NBS 430 technical note as my guide.  This takes the errors out of trying to get a reading at 10 volts with the DVM (i.e. H3458A).
This data has been collected over 12 years or more against my most stable f732A  S/N 3435xxx.  This 732A has show it's self to be extremely stable for about 20 years now, using the NBS430 note, against 4 other 732As.
As you can see the maximum deviation has been about 1.5 ppm max and those outliers are due to mainly "MEAN" switch contact problems.  This unit needs some work for sure.  Exercising the "MEAN" switch takes care of this issue.  Some day Real Soon Now I will work on this.
Bill

[branadic]

I today performed low frequency noise (0.1 - 10 Hz) measurements of the 10V outputs and repeated it on each channel. Here are the results:

Mean:
rms = 179.20 nV
std = 178.87 nV
pp = 1.2344 µV

rms = 167.78 nV
std = 167.16 nV
pp = 1.1632 µV

Channel1:
rms = 335.30 nV
std = 335.28 nV
pp = 2.4805 µV

rms = 338.79 nV
std = 338.74 nV
pp = 2.1987 µV

Channel2:
rms = 297.15 nV
std = 296.80 nV
pp = 1.9943 µV

rms = 294.98 nV
std = 294.49 nV
pp = 2.3202 µV

Channel3:
rms = 286.60 nV
std = 283.83 nV
pp = 1.9611 µV

rms = 275.13 nV
std = 272.28 nV
pp = 1.9004 µV

Channel4:
rms = 297.94 nV
std = 297.96 nV
pp = 1.9335 µV

rms = 332.34 nV
std = 332.31 nV
pp = 2.3700 µV

So far, all measurements were performed with the NiCd batteries removed, replaced by some electrolytic caps and the unit running from mains. I'm still thinking about a proper battery repacement, be it NiMH or Supercaps. I was told that Conrad replaced the NiCd in one of his references with batteries plus zener diode.

-branadic-

[alm]

How did you measure the noise? AC-coupled LNA?

Much better noise figures than I've seen reported before on the DH80417B (though that was a 2 hour measurement). A bit less than sqrt(4) improvement in noise of the mean output compared to the individual channels. Which makes sense, given that not all noise will be uncorrelated.

[branadic]

The measurement was done using pipelies 0.1 - 10 Hz, 80 dB LNA in front of an R9211E, so yes, AC coupled.

I'm not sure why Frank reported worse results, it could be partially due to less quality resistors in Fluke 332? 

-branadic-

[branadic]

Today a second unit (SN 302), that was donated to me, arrived. It has even older turn counting dials, but they could have been replaced at some point in the past by a previous owner, as the top cover has some cutouts to make them fit, that don't look very original to me.

This unit obviously is revision A that is shown in the figures given in the manual. There are some bodge resistors on the back, for which I need to figure out if they are an original afterthought or something that was added by a former owner.
Attached some very first impressions with the Mica resistor goddies on the reference boards.

The device was missing the feets, so some 14 h later proper replacement was available. Furthermore, it was missing one of the Guard covers, which I've recreated from 1.5 mm aluminum.

-branadic-

[branadic]

I was asked to provide a comparison of the noise measurements above to my LTZ1000 references running on batteries. The noise floor of the LNA is known to be 100 nVpp with shorted input.

LT1000-1 (10.008658 V):
rms = 257.86 nV
std = 257.84 nV
pp = 1.5744 µV

LTZ1000-2 (10.008774 V):
rms = 283.23 nV
std = 283.22 nV
pp = 1.9169 µV

LTZ1000-3 (9.989901 V):
rms = 268.25 nV
std = 267.62 nV
pp = 1.6186 µV

I also attach results for the 10 V output of my ADR1000 voltage reference running on batteries for the measurement.
rms = 152.91 nV
std = 133.30 nV
pp = 919.21 nV

-branadic-

[doktor pyta]

The reference board seems familiar: https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg5208300/#msg5208300

[W6EL]

Greetings,

I have a Fluke 633A which seems to have two of the same reference boards. Mine are similar to the ones in the manual's illustrations, like your second set. I would guess that the dividers might be set differently on the output side though.

I am currently doing a test over the course of the day -- just one reading every hour or so, manually -- but I am curious as to how stable these things are without ovenization.

I'd like to hear your thoughts on the additional stability gained by parallel units and/or ovenizing. I too might order some extra sockets and build a little box inside this enormous 633A to house a pair in a controlled thermal environment.

I'll post clear photos of the reference boards once this set of tests is complete.

--E

[W6EL]

Alright, here are the reference cards from the Fluke 633A. They do look very similar to your set.

In the Fluke 633A, one card is run from about -10V up to ground, and the other card is form ground up to about 14 volts. I'm still trying to understand the 633A circuits, but I think ultimately I will ovenize the pair and "average" them in parallel. It seems like a good project for this rather spacious box. I could then create these odd-ball reference voltages that the 633A provides using the 10V reference output (but with more PPMs of course).

Oh hey, I also noticed that these boards say "730A" on them. So, there you go. The Fluke 633A is probably a great source for replacement reference boards, although they do not seem to show up on ebay much. Also 622A, and 644A likely.

[W6EL]

Also, I made some readings using my (uncalibrated) Fluke 8505A. All the equipment is in my garage, without any temperature regulation. Basically somewhere between outdoor (SoCal) temperature and indoor temps (two shared walls with the house). Pleasant but not exactly a controlled environment.

Note that the scales are not the same in these plots, so judge carefully. The Fluke 8505A uses the same reference as these reference boards, although the circuit is not exactly the same.

Standard deviation on both + and - outputs is about 17 microvolts. Span on the + was 54 microvolts, span on the negative 10V output was 58 microvolts. For these stats I only used the last half or so of the datasets, so as to not include the first day of "warm up" and all that.

[W6EL]

Today a second unit (SN 302), that was donated to me, arrived. It has even older turn counting dials, but they could have been replaced at some point in the past by a previous owner, as the top cover has some cutouts to make them fit, that don't look very original to me.

This unit obviously is revision A that is shown in the figures given in the manual. There are some bodge resistors on the back, for which I need to figure out if they are an original afterthought or something that was added by a former owner.
Attached some very first impressions with the Mica resistor goddies on the reference boards.

The device was missing the feets, so some 14 h later proper replacement was available. Furthermore, it was missing one of the Guard covers, which I've recreated from 1.5 mm aluminum.

-branadic-

Looks like R24 is broken on one unit, just in case you hadn't spotted that yet.

[branadic]

Looks like R24 is broken on one unit, just in case you hadn't spotted that yet.

No, it's not broken, that is one of the bodges I mentioned earlier. There is a parallel resistor on the bottom of the board, while the top one was lifted on one side.

Meanwhile, all electrolytic caps and carbon composite resistors have been replaced. The unit was already equiped with an IEC connector, which I replaced by an IEC connector with mains filter (1A) on both units. I yesterday performed very first measurements on the arithmetic mean, refboard 1 to 4 and arithmetic mean again over a course of 30 min each. As we can see at least one refboard seems to be suspices showing rather large noise.

-branadic-

[W6EL]

branadic, what are you using to make these measurements?

[branadic]

The 30min measurements were performed using Advantest R6581 8.5-digit multimeter.

-branadic-