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: <[email protected]>
To: <[email protected]>
Sent: Thursday, June 28, 2012 7:04 PM
Subject: [volt-nuts] Thermistor value for 732A Reference 10V Standard
Hi!
Can anyone give me a rough value of the thermistor resistance that is
brought out to the front panel of a Fluke 732A DC Reference Standard
(lower
left-hand side)? The thermistor is for the user to monitor the
temperature of
the oven that contains the voltage reference. I see a resistance that
starts out at 6600 Ohms (unit was nearly cold) and climbs and levels out
at
about 8400 Ohms after a day, or so. Is this reasonable? The thermistor
is
given in the parts list as RT2, a Fenwal JA41J1 (no longer made) and on
the
schematic as a 10K @ 25C unit. So this doesn't make sense.
Does anyone have any experience with this? Or is just simpler to replace
the thermistor with a 100 Ohm RTD and be done with it? Or would this
drive
the calibration labs nuts?
Any references or advice would be appreciated.
Tom Leedy
Clarksburg, MD
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