[volt-nuts] Fluke 732A Questions

Bill Gold wpgold3637 at att.net
Tue Dec 31 19:26:23 EST 2013


    The NIST notes can be downloaded from this site.


    Here is the battery check paragraph.  I check mine once and month and plot performance using Excel.

2-48. Prior to operating the 732A on battery power, the following procedure should be followed.

    1. Connect a voltmeter at the rear terminal POWER INPUT jack to monitor the battery voltage.

    2. Note the voltage while the battery is on trickle charge (the AC PWR LED is on, but BTRY CHG off).
        The voltage should be around 27V.

    3. Disconnect the line cord, wait 10 minutes, and then monitor the battery voltage for one-half hour.
       The battery package may have to be replaced if the voltage decrease by more than 0.2V during
       this period and the load represented by the 732A is correct ( see Section 4, Battery Discharge).

2-49. It may be advisable to perform the above procedure periodically to ensure battery backup capability is maintained.

    While the Fluke manual maintains that the battery life is 24 hours, the reality is that you can get maybe 12 to 15 hours on a fresh set of cells.  I think that the engineers didn't figure on the total heater current being around 240 ma in the final design.  The batteries are rated at 4 AH and some simple math says that 4/.24 = 16.67 hours to a battery voltage of 5.25 V.  But the "In Cal" LED will turn off around 22 volts so maybe 15 hours at best.  The batteries will continue to supply heater current so it might keep the +18.6 volt regulator working for a few more hours, but when the batteries are down that far it is hard to calculate remaining life.  This is why there is a Fluke 732A-7003 Transport Case and Battery Charger and you can have up to 4 battery packs in the case.  This gives you a total of 72 hours transport time, according to Fluke.  I have seen people take a couple of 12 volt high capacity SLA and duct tape them to the top of the 732A to increase transport time.  I am not too sure what the AH capacity is of the 12 volts cells.  I would guess that 12 AH might do the job but I have never gone that far to figure out.

    The 24 hour spec is probably based upon the NIST Technical Note #1239 (Solid-State Voltage Standard Performance and design Guidelines) which recommended at least 24 hours of battery life for transport.  You can get this from the same website as above.

    I never had to worry about this (battery life) as Fluke used to have a repair and cal facility in Milpitas, CA and I worked in Morgan Hill, CA.  I would either hand carry the unit to be certified, or Fluke would pick it up and deliver it back, under power.  Then Fluke decided to sell the whole operation to FLW Service Corp who finally dropped the whole operation around 2005.  I also retired around that time so I didn't care to pay for all of this myself ( I was having the Company pay ).  Since then I have not had a "Certification" of any 732A units and just relied upon the inter-comparison method to hopefully keep a reasonable value of the "Volt".  I have looked around the South SF Bay Area for a Cal Lab who could "Certifiy" one of my units and the only place I could find would be Simco in Sunnyvale.  I will have to ask them what they charge for a "Certitication" of a 732A.  The local Fluke place used to charge $500 but then that was using 732As that they had sent into Fluke in Everett WA.  But then since this is just a hobby anymore I don't need, and didn't need while I was working, the full blown services and accuracy of Fluke in Everett.  I guess a 732B would be a way to get all of this but who needs it right now, not me.  Of course I could always get my own Josephson Junction but then I would be a real crazy "Volt Nut" and certifiable at the same time.

    I have never even heard about the Fluke 735C until I saw one on fleabay, and I assume you were the one who bought this when I saw you asking about schematics.

Happy New Year


----- Original Message ----- 
From: "J. L. Trantham" <jltran at att.net>
To: "'Discussion of precise voltage measurement'" <volt-nuts at febo.com>
Sent: Monday, December 30, 2013 6:28 PM
Subject: Re: [volt-nuts] Fluke 732A Questions

> Bill,
> Sounds like you are further along in the 'volt-nut' process than I am.  I'll
> have to chase down the NIST paper.  I have been very impressed by the
> stability of the 732A and the 735C.
> Unfortunately, I don't have any documentation on the 735C and only the early
> manual for the 732A.
> I would be interested in the specifics of the battery check procedure in
> your manual.  Unfortunately, my manual does not have a page 2-9.
> I note that there are two banana jacks on the front of the battery module,
> both black, one connected to ground and the other not connected to anything.
> Any idea of what they are for?
> I always like to keep equipment as 'original' as possible.  If I can't find
> the correct connector, I'll find something similar that will fit in the same
> hole and use it instead.  We'll see what I hear from Fluke and Hypertronics.
> Also, how do you get your 732A calibrated?  Do the batteries last long
> enough to ship overnight to a facility?
> Thanks for the info.
> Joe
> -----Original Message-----
> From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
> Behalf Of Bill Gold
> Sent: Monday, December 30, 2013 7:03 PM
> To: Discussion of precise voltage measurement
> Subject: Re: [volt-nuts] Fluke 732A Questions
> Joe:
>     My 732A units vary in thermistor resistance from 3.408K ohms to 4.514K
> ohms and have been extremely stable to with in +/- 5 ohms for years now.  I
> did measure the oven temperature of the one with the 3.408K ohms just to see
> what was causing the thermistor resistance to be a little low and came up
> with about 47 degrees centigrade, as best as my equipment would allow me to
> measure it.  Equipment was a Fluke 80TK thermocouple module, a Fluke 80 PK-1
> thermocouple bead and a HP 3456A DVM.  I put shrink wrap around the bead and
> then threaded the bead into the temperature oven through one of the
> adjustment holes in the front panel and made sure that it was far into the
> oven, probably around the middle.  Then I checked another unit that read
> 4.5K ohms and it read around 43 degrees C so all of that made sense.  I
> believe I saw somewhere that the spec was 45 degrees C +/- 2 C.
>     I did have to change the jumpers on the "Calibration PCB Assembly" on
> one of my units so that it would match other 732A units that were "In Cal"
> and had certified values.  But that unit has since drifted down at a rate of
> around 1.2 ppm per year which is with in specs but a little more than I have
> seen from other units.  Recently this unit has suddenly quit drifting down
> and seems a lot more stable now.  That was S/N 459xxxx.  I have a S/N
> 343xxxx which has been proven rock solid for years now at around +/- .3 ppm
> and just seems to have "DC noise" stability as it just goes up a little and
> then down a little and never needed any adjustment.  I also have a S/N
> 460xxxx which is extremely stable also.  So I guess that age does seem to
> factor into stability as well as how long they have been powered up.  But
> the only way to insure that you have a good "volt" is to have at least 4
> units and then inter-compare them periodically following NIST (NBS)
> Technical Note #430.  While 430 was written for Saturated Standard Cells,
> the technique seems to work just fine at 10 volts also.  You can also find
> this measurement technique in the 1st Fluke "Calibration - Philosophy in
> Practice" book published around 1974.
>     I gave up on the "unobtainium" connector on the back of the battery pack
> very quickly.  I drilled a 1/4 " holes on either side of the "unobtainium"
> connector, after removing it, and used two single miniature banana jacks to
> allow me to connect to the batteries for the purpose of checking their
> performance as described in the 732A manual page 2-9 in manual P/N 788414
> May 1986.  I should probably turn in my resignation as a "volt nut" for this
> action but it works.  KISS.
> Bill
> ----- Original Message -----
> From: "J. L. Trantham" <jltran at att.net>
> To: <volt-nuts at febo.com>
> Sent: Saturday, December 28, 2013 2:51 PM
> Subject: [volt-nuts] Fluke 732A Questions
> > I have reviewed the prior postings on Volt-nuts (a very rewarding review,
> > BTW)) regarding the 732A and have two questions:
> >
> >
> >
> > 1.        Has anyone determined the part number, or a source, for the
> mating
> > plug to J10, the external power connector for the 732A-7005 battery pack?
> I
> > noted some postings recently about this but did not find a definitive
> > response regarding the identity of this plug.  The alternative would
> appear
> > to be a complete replacement of J10 and its plug, as long is it all fits
> in
> > the opening in the panel.  I hate to 'bore holes' in vintage equipment.
> >
> > 2.       The oven thermistor in my 'new to me' unit measures 4229 ohms
> (+/-
> > an ohm or two) after the unit has warmed up for a week or so.  I note the
> > manual refers to 3K to 4K for the value of this thermistor when the unit
> is
> > 'stable' as well as other's posting values in the mid 3500's ohms for
> their
> > units.  Should I be concerned?  The unit seems to be stable to within
> about
> > 2 uV over about a week (as measured by my 3458A - see below).  Should I
> open
> > the unit and try to measure the oven temperature or just be satisfied that
> > the unit seems to be working?
> >
> >
> >
> > I had to replace the four 6V 4AH SLA batteries and they charged up
> > appropriately as judged by the front panel LED's.  I had to remove the
> > 'jumper' for the '40' option on the A7 board and connect the jumper to the
> > '20' and '10' options (total of '30') in order to get the unit to adjust
> to
> > 10.0000000 VDC on my 'Agilent In Cal'd' 3458A.
> >
> >
> >
> > The need to change the jumpers, perhaps, could be just an ageing issue or,
> > on the other hand, a 'temperature' issue with the oven.
> >
> >
> >
> > Should I open the unit and directly measure the temperature (supposedly
> > about 48 degrees C) or just be satisfied with what I have?
> >
> >
> >
> > My recently added 735C also needed moving some 'jumpers' in order to get
> it
> > 'on scale', as determined by my 3458A, although it's thermistor measures
> > about 3330 ohms (after being on for several weeks).
> >
> >
> >
> > Thanks for everyone's help.
> >
> >
> >
> > Joe
> >
> > _______________________________________________
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