Hi Tom,

Definitely not good! The thermistor is supposed to be an NTC, so seeing
the value
rise from cold means there's something very wrong indeed.

If you want to replace it, this might be a good alterative:
http://www.digikey.nl/product-detail/en/192-103LET-A01/480-3158-ND/1886044

Kind regards,
Rob Klein.

Op 29-6-2012 1:04, Leedyt@aol.com schreef:

Hi Tom,

According to the Fluke 732A manual page 2-6 the nominal value is between
3k - 4k with the oven at normal operating temperature.  Mine checks 3.545 k
and has been within a few ohms of that reading each year for five years. You
may have a heater problem.  There is a protective thermal fuse which can go
open, in series with the heating elements.  It's purpose is to prevent a
runaway oven from cooking everything.  Once it opens you will never get any
heating until it is replaced.

Regards,

mitch

----- Original Message -----
From: Leedyt@aol.com
To: volt-nuts@febo.com
Sent: Thursday, June 28, 2012 7:04 PM
Subject: [volt-nuts] Thermistor value for 732A Reference 10V Standard

Are you reading this in-circuit and operating? The current flowing through
the resistor will skew the reading.

Stupid question I know but had to be asked...

DaveH

Rob Klein <rob.klein@...> writes:

of

nuts

Many thanks to all for the advice.  I suspect that somebody "replaced" the
original thermistor with another unit and didn't know what they were doing.
Since the unit seems to put out 10 Vdc (+/- less than a ppm or so) at ambient
temperature, I suspect that the internal oven is operating correctly.  But I
might investigate further by raising and lowering its ambient a few degrees and
checking to see that temperature of the oven remains constant.

Has anyone actually measured the internal temperature of the oven (in degrees
C)?  Since the operating temperature of the 732A is spec'd at 40 C, I suspect
that it is about 45-50 C, or so.  And I also suspect that temperature stability
of the oven is more important than absolute accuracy.

I'll let you know what I find.  Thanks to all again -- I didn't expect the
large outpouring of knowledge!

Regards -- Tom

Op 29-6-2012 6:34, Tom Leedy schreef:

According to the manual it's 48 ± 2°C

You'd be correct :-)

Nobody expects the large outpouring of knowledge! (with apologies to
M. Python)

Rob.

I think monitoring the 1V or 1.1V is a better test over temperature than
monitoring the 10V.  It's quite stable even without the heater.

----- Original Message -----
From: "Rob Klein" rob.klein@smalldesign.nl
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Friday, June 29, 2012 6:29 AM
Subject: Re: [volt-nuts] Thermistor value for 732A Reference 10V Standard

Op 29-6-2012 6:34, Tom Leedy schreef:

According to the manual it's 48 ± 2°C

You'd be correct :-)

Nobody expects the large outpouring of knowledge! (with apologies to
M. Python)

Rob.

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and follow the instructions there.

Mitch,

Quite the contrary.  The 10 volt output is the master output and therefore the
most stable.  The others are derived from dividers and thus add additional error
terms due to the tempco of the divider string and any possible loading presented
to those outputs.

Bill....WB6BNQ

Mitch Van Ochten wrote:

Bill,

I had to read it twice myself, but that was Mitch' point. When you want
to check the performance
of the oven, you want to measure something that has a decent bit of
variation over temperature.

Rob.

Op 29-6-2012 13:33, WB6BNQ schreef:

Hi Rob,

Yes, now I see the point !  My apologies to Mitch for misunderstanding his point.

Bill....WB6BNQ

Rob Klein wrote: