Did you check the relay? The solid state relay rarely goes wrong, but
it did go wrong in our machine. The resulting problem is similar to
yours. If there is no reading at the output while the heating
indicator is on, that is the failure of relay. To replace it is easy.
It costs about $50 at local electrical stores.
>There are two safety switches, the pressure transducer (carrier gas
>safety switch) and the temperature one on the top (thermo element
>switch). You may need to check/clean those connections. Unless you
>running at low pressures, the pressure transducer should not be
>causing problems (if it's ok). If the fan out the back isn't
>sucking air through the system fast enough to cool it, the top may
>get hotter than usual and trip the temperature alarm--so you might
>just need a new fan.
>If the K2 light it on, telling it to heat, then the controller is
>probably ok. But it would hurt to check connections between it and
>the solid state relay. And while you're at it, check the high
>voltage side too. If the relay itself is going, that can cause
>problems--but you should be able to pick one up at DigiKey. While
>your at it, re-seat the connections on the transformer too.
>You may also have cracks in the thermocouple and/or heating element,
>and they lose contact when the system heats up and expands. We just
>had the later happen with our system (a couple months old), and just
>replaced the heating element ourselves. If the thermocouple goes,
>you should see an error message on the controller.
>Richard Doucett wrote:
>>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
>>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.
>>/Richard (Rick) Doucett, Ph.D., Associate Director
>>Colorado Plateau Analytical Laboratory
>>Northern Arizona University
>>Tel: 928.523.0967 (lab)
>>Tel: 928.523.7265 (office)
>>/Stable Isotope Lab: http://www.isotope.nau.edu/
>>/Analytical Lab: http://www.research.nau.edu/cpal//
>>/Mailing address for packages:
>>Dept. Biological Sciences
>>Northern Arizona University
>>Building 21, South Beaver Street
>>Flagstaff, AZ, 86011-5640/