[volt-nuts] Thermistor value for 732A Reference 10V Standard

[DaveH]

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 

> -----Original Message-----
> From: volt-nuts-bounces at febo.com 
> [mailto:volt-nuts-bounces at febo.com] On Behalf Of Mitch Van Ochten
> Sent: Thursday, June 28, 2012 18:43
> To: Discussion of precise voltage measurement
> Subject: Re: [volt-nuts] Thermistor value for 732A Reference 
> 10V Standard
> 
> 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 at aol.com>
> To: <volt-nuts at febo.com>
> 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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