[volt-nuts] introduction

Wed Apr 27 03:34:46 UTC 2011

Hi Fred,

Well, it sounds like the people that had this equipment really had no idea how to care
for it properly.  It also suggests that they did not know what they were doing and just
bumbled along.  Could be the reason the operation was shut down at some point.

No special manuals exist for the 731, 845 or for that matter most of all of the old
Fluke equipment.  Any inside understanding was gained through experience.

The best method you have for comparing against the cells is to use the 750A divider.
This divider is very high quality and hopefully the previous owners did not go inside
it.  The only truly accurate and stable output on the 731 is the 10 volt posts.  I
would hook up the cells and the 845 to their respective connections on the 750A and
then attach the 731's 10 volt posts to the divider string's main input terminals (as
shown on page 2-5) with the switch set to 10 volts.  Then do your inter comparisons
with the different cells in the Guildline.  You can use the cell voltage level switches
on the 750A for determining the cell values with the 731 acting as the reference.

The best you will be able to do (unless our 731 is calibrated) is to determine
differences between cells.  By taking readings several times a day over many days and
weeks you can get a picture of the cell activity and their stability.

If your Fluke 731 is not calibrated, hopefully you may find a known quality Cal Lab
that would provide you access to adjust your 731 to a known value.  Then that would
become your main reference.  Then you could assign values to the cells in the
Guildline.  From that bootstrap you should be able to arrive at a confidence level to
trust what is happening with the Guildline and eventually make it your Lab reference.
Or at least make the Guildline a faithful sanity check.  The problem with cells is you
need to constantly inter compare them to make sure they are behaving correctly and
remaining stable.

As the equipment, presummably, has not been compared or adjusted against a real
standard, I am not surprised by the offset readings you measured.  The best stable
voltage reference you have is the Fluke 731.  It would be well worth the expense to
have it calibrated with a high quality Lab if you have one near you.

Regarding the 720, Fluke was making those until just very recently.  I would see if
they could still provide you with the necessary parts to rebuild it.  It would be well
worth the effort in my opinion.

73....Bill....WB6BNQ

Fred wrote:

> I think I have the manuals complete, they are original and I do not miss
> pages but maybe there is also a real extended service manual for the
> 845AB.
> In my schematic there is a A and a AB powersupply schematic. The A has a
> zener and no battery. They removed the battery in mine, that was also
> written on the cabinet and placed two zeners. I think they did not get
> it right anymore and then bought the Fluke 8500 that was part of the
> setup (in the drawings I had in the documentation it was coupled to the
> 750)
>
> Tonight I did some first measurement. The Cells are now about a month or
> two operational and heated. They are very carefull moved to a special
> made shelf two weeks ago. But now I have a problem. It's like the man
> with just 1 clock, he think he does know the time, the man with two
> clocks has a problem. I have 4 DC calibrators and 4 Weston cells so I'm
> lost :-)
>
> I first measured 1 cell from the Guildline using the 845 and the 731. I
> turned the 731 dial until I had a zero in the 3uV range and allmost zero
> in the 1uV range. I took that value as a reference. Following the trend
> in the graphs from this cell (from 1977 upto 1987) the value could be
> realistic. The oven temp is 30.07 degrees. The philips was about plus
> 250uV, the 332 was minus 160uV. But if I connect them through the 750 I
> get a 25uV difference. I have not tried to calibrate it, it is always
> kept in the same clean room and never messed around so it will be
> probably better if I leave it like this because the 720 is not usefull
> and needed for calibration.
>
> The 720 is strange, it is clean as a baby inside-out. It is not been
> dropped or so. But all the plastic is cracked and broken. If you touch
> it it crumbles. Maybe someone back then cleaned it with some solvent.
> It's a pitty because it is a beautifull instrument. I must find some
> teflon or poly-ethilene to make new ones (I have a lath and a mill but
> is is a lot of work) Some are possible repairable using 2K-epoxy. One
> switch, number 1 from right, is very bad, I had to take it out because
> the centre-follower is crumbled. The others still work and are in place
> but the studs have cracks and pieces allready missing.
>
> 73
>
> Fred
>
> WB6BNQ schreef op di 26-04-2011 om 13:20 [-0700]:
> > Hi Fred,
> >
> > Looks like you got lucky with such a nice collection being offered.
> >
> > I am confused on why additional zeners would be added to the 731 and 845.  Both
> > were made to work without batteries.
> >
> > The 731, if it is in good shape, is an extremely stable reference source.  Well
> > able to transfer a known value from a competent calibration Lab to use for
> > establishing the value of your Guildline cells.
> >
> > As I am sure you know, the 845 is the only high impedance DC NULL meter available
> > that was worth a damn.  The first mains power transformer (and battery with its
> > charge circuit) is just to supply a power source for the 84 hertz transistor
> > inverter to the neon's.  That same inverter is also used to power the all of the
> > circuitry.  That is part of what provided the extremely high input isolation.
> > The noise you see on the 1 uv scale is normal.
> >
> > The 720 switch problem sounds interesting, I wonder what caused the switches to
> > be so bad ?  In a clean environment there should be no reason for them to have
> > disintegrated.
> >
> > The Guildline was a very nice catch.  Have you had an opportunity to determine if
> > the cells are in good shape ?  Hopefully nobody loaded them with a low
> > resistance, that would have messed them up for sure.  In conjunction with the
> > 845, 750 and the 731 you have yourself a nice voltage reference system.
> >
> > As for cables, well, I would not worry about that.  Just use normal copper wire
> > and you will not go wrong.
> >
> > From your comments I am wondering if you have the full manuals for the 731 and
> > 845 ?
> >
> > 73....Bill....WB6BNQ
> >
> >
> > Fred wrote:
> >
> > > Hello,
> > >
> > > My name is fred, PA4TIM, I'm a volt-nut. Took a lot of therapy to
> > > confess ;-)
> > >
> > > I was already fascinated by calibrations because I restore measurement
> > > equipment. I collected some old calibrators like an old one from Philips
> > > using nixies as indicator, a Tek AC calibrator ment for internal factory
> > > use.
> > >
> > > But a few months ago a got a mail from a stranger who noticed my website
> > > and asked if I was interested in the stuff from his companies old
> > > calibrating lab (for free !!!) The lab was closed 25 years ago, but the
> > > stuff stayed there unused. Now they needed the room and "found" this
> > > stuff but almost nobody knew what it was so a lot was thrown away. He
> > > thought that was a shame and asked if he was allowed to find a
> > > collector. Al stuff including manuals and calibration history and in
> > > state like new. But not used for 25 years and some stuff suffered from
> > > sleeping or was maybe already death when parked away
> > >
> > > It started with a Guildline 4 cell unit. In perefect condition. I had to
> > > repair the heater and some minor aging things.
> > >
> > > A tek 576 curve tracer came as a bonus with a box new Tek parts.
> > >
> > > Then things speed up, if I wanted some more. A complete Fluke
> > > calibration setup. To bad they tossed away all cables.
> > > -332B voltage standard, worked like a charm after changing one cap.
> > > -760A meter calibrator, worked for a week, now constant jumps in
> > > protecting and the home fuse blowes even if I put the plug in powered of
> > > so I think a Y capacitor is leak. I will find that, no problem (I hope)
> > > -510A AC reference standard, dead batteries but I just removed them
> > > because they are optional. I left in the option board. Still not sure if
> > > that is wise.
> > > - 731A, also dead nicads. I removed them and put in a 12V voltage
> > > regulator. Also had to replace a paper-foil capacitor.
> > > - 750A voltage divider. There is room for two strange batteries but as
> > > far as I understand it also workes without as long as you are sure You
> > > do not over voltage
> > > -some HP stuff like a 20 penta Ohm elctro Ohmmeter/voltage source, a
> > > time standard, pindiode modulator and low distrotion sinewave generator.
> > >
> > > But then two very important parts of the set up. A 720 kelvin Varley
> > > divider. All see-through plastic isolator standoffs and centre coupling
> > > parts of the switches are desintegrated. That will become a hell of a
> > > job.
> > >
> > > The biggest problem was my 845AB, they allready removed the nicads and
> > > added two extra 10V zeners. Thick metal multi-amp ones.  The problem is
> > > the manual is very limited. There are some scope pictures and a small
> > > trouble seek section.
> > > I had to replace allmost every cap, so did them all. Then I kept
> > > problems with stability. Then I took my lab-supply and put 10V over the
> > > capacitor. It drew about 30mA and was stable. Then I raised the voltage
> > > and when the zener started conducting the 845 draw 600mA. I think the
> > > 10V mega-zeners started drawing so much current the transformer
> > > saturated or at least power got unstable. Could not close the top lid,
> > > as soon as it came near the transformer the meter went nuts. I now
> > > placed a 7812 and it is stable over the whole range I think. At 1uV full
> > > scale with shorted input and knob at zero the meter deviated plus/minus
> > > 0,1 uV max, most times about 0,05uV. I think that is not bad but this is
> > > my only null-detector so I do not know for sure.
> > >
> > > Now I have to find out how to make cables to connect everything, find a
> > > way to determine what will be my  STANDARD VOLT. I have the calibrating
> > > history upto 1988. I can measure the differences between the cells but
> > > first have to find out the safest way, and if that is comform the old
> > > papers I think I take that as a basis. Then adjust the calibrators to
> > > that value. This will probably still be more accurate as the average
> > > multi or bench meter. I have a 6,5 digit as best one.
> > >
> > > Does some one has a better way ?
> > >
> > >
> > > For my collection See www.pa4tim.nl Not all the fluke stuff is on it
> > > yet.
> > >
> > > 73
> > >
> > > Fred
> > >
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