Hi all,

I run my TC/EA at 1400 C for dD measurements.  Lately, the furnace will 
reach and remain on 1400 C for minutes to hours, but then something 
trips, and the furnace will drop temperature quickly until it reaches 
600-700 C.  Once at this lower setting, the furnace temperature will 
climb again and reach set point. It has continued this see-saw action 
for the past 48 hours now.   The furnace only seems to trip at the 1400 
C setting.  Meaning, I have set the furnace to 1200 C and it will remain 
there indefinitely.  However, for comparison, I have not tried leaving 
it at 1300 C.  

Last time this happened (6 months ago), I swapped temperature 
controllers with another instrument, but that did not help anything - 
the furnace still tripped.  Then I took my shop-vac and blew out a lot 
of dust on top of the furnace (the assumption being that dust was 
causing either an electrical short or added heat insulation).  This 
seemed to help at the time, but doesn't seem to be the problem this 
time, since no dust has dared return since the previous shop-vac incident. 

Coincidentally, my lab is running 3-5 degrees C warmer this week that it 
normally is, now that winter has reached Flagstaff, and building 
ventilation is receiving both heating and cooling air.   I've been told 
that the air-conditioning in my lab is maxed out, but my room temp still 
hovers around 24-26 degrees C (normally, it's between 21-23 C).   I 
doubt a small room temperature increase of this magnitude is enough to 
trip the TC/EA furnace sensor, but I can't help fixate on the coincidence!

Finally, like some of you, I do indeed have an external fan blowing air 
on top of the TC/EA at the neck of the autosampler where the sensor is 
supposed to exist.

If any of you have suggestions on how to problem-solve my TC/EA furnace 
woes, I (and my clients) would love to hear from you.

Best wishes,

/Richard (Rick) Doucett, Ph.D., Associate Director
Colorado Plateau Analytical Laboratory
Northern Arizona University
Tel: 928.523.0967 (lab)
Tel: 928.523.7265 (office)
Fax: 928.523.7500/

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/Mailing address for packages:
Dept. Biological Sciences
Northern Arizona University
Building 21, South Beaver Street
Flagstaff, AZ, 86011-5640/