[volt-nuts] Fluke 732A Questions

J. L. Trantham jltran at att.net
Tue Dec 31 08:22:45 EST 2013


I would like to find the mating plug for J10 for several reasons, being able
to get it to calibration being just one of them.  However, I was hoping it
would be good enough to make it to calibration on the internal batteries.

I seem to recall reading that the internal batteries were good for a few
hours but nothing like what the 732B would do, which sounded like the 732B
could make the trip on the internal batteries.

Where did you find the resistance of the thermistor 'as shipped'?  I saw
mention of being supplied to the original owner when shipped as well and I
have had the top cover off and the battery module out to replace the
batteries and found nothing to suggest a thermistor value.  I have also
lifted the top layer of insulation off the oven to move the cal-jumpers but
did not see anything that suggested a thermistor value.

My 'metrology level' standards are my HP 3458A's, calibrated by Agilent, and
Solartron (Ametek) 7081's calibrated by Ametek.  I have been thinking of
getting the 732A calibrated by Fluke but I didn't know if they would still
calibrate the unit.  I wonder if they would have the 'as shipped' thermistor
value on file for my specific serial number?

I, too, read about the stability of the thermistor being the most important
measurement.  That was in the 'change sheets' attached to the manual on
Didier's site.

The 'cal-jumper' was at '40' when I got the unit.  Per my 3458A, I could
only get it down from about +220 uV to about +100 uV with the front panel
adjustment.  By moving the jumper to '20', I could only get it up to about
-12 uV below 10 V by turning the adjustment all the way in the opposite
direction.  However, by connecting jumpers for both the '20' and '10', I was
able to get it at 10 V with the front panel adjustment at about center
position.  I have not 'logged' any values yet but every time I go to the
shop, it is about +/- 1 or 2 uV from 10 V.  I do the 'AUTO CAL' on the 3458A
each morning I go into the shop.  

I measure the resistance with a Fluke 8050A (simply because it is the
closest DMM to the standard) and it is 4229 to 4230 ohms each day.

Interestingly, when I got the 732A, undisturbed Fluke Calibration stickers
were in place over each of the adjustments on the front panel, on a back
screw on the top cover, and 'half' of a sticker on the back over the power
supply module, as if the other half was lost when someone removed the
battery module.  Somehow, I find that comforting, given that it now seems so
stable, making me think it is 'normal aging' that is responsible for the
values I measured rather than a problem with the oven, etc..  IIRC, the spec
is 6 ppm per year for 10 V, or 60 uV per year.  I'll have to look at the
power supply module to see if I can find some date codes but I suspect the
unit is 25 to 30 years old.  Unfortunately, there were no 'dates' on the
stickers to tell when the unit was last calibrated.

I was thinking of sending the 3458A's and the 732A out for calibration
simultaneously and seeing what I find when they get back.  

I'll call Fluke and ask about their Cal services, the plug, and the shipping
case/battery pack issues.

Thanks everyone for very useful information.


-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
Behalf Of Charles Steinmetz
Sent: Monday, December 30, 2013 11:23 PM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Fluke 732A Questions

Joe wrote:

>Also, how do you get your 732A calibrated?  Do the batteries last long 
>enough to ship overnight to a facility?

No -- I assumed that was why you were looking for a battery connector.  You
install an external battery for shipment overnight.  Fluke can supply a
complete external battery with cable and plug ($375, last I knew), or you
can make your own.  I believe they can also supply a shipping container,
which has a dedicated space for the Fluke external battery.  (If you don't
use Fluke's container, build something very sturdy with wood and padding and
with handles that make it hard not to carry it and set it down right side

I wouldn't have anybody but Fluke calibrate a 732A.  There are 3 levels of
calibration, all with data, from about $700 to about $1500 (the last is
calibration by Fluke's Primary Standards Lab).

As far as thermistor values go, the relevant question is not what is the
value in absolute terms, but rather what is the value in relation to the "as
manufactured" value, which was provided by Fluke when the unit shipped.
This had been recorded by the original owners of each of my units, and they
are all within 2 ohms of the original value today.

If you do not know the original value, then your original measurement is a
"going forward" value and it cannot tell you anything about where you are in
relation to  the original manufactured value.  The fact that you had to
change cal jumpers suggests that either the oven temperature has shifted
since manufacture, the reference assembly has shifted, or both.

Fluke has said various things in various places about how far the thermistor
readings can drift before you have a problem.  +/- 20 ohms over the unit's
lifetime seems to be a good consensus value.  If it changes fast -- say, 10
ohms or more in a month -- you have a problem.

Best regards,


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