XPost: sci.physics, alt.solar.thermal   
   From: muratlanne@gmail.com   
      
   "Morris Dovey"  wrote in message   
   news:j903e2$bak$1@speranza.aioe.org...   
   > ... My thinking is that I can use the heat transfer information along with   
   > predictive logic to project what temperatures /should/ result from the   
   > heating so that significant variances from the predicted values   
   > (signalling ignition) can be identified fairly quickly. Knowing the heat   
   > transfer rate should allow me to shorten the delay between powering down   
   > the heater and capturing the heater resistance, and to use that value in   
   > context to accurately /infer/ the temperature in the reaction chamber.   
   >   
   > Morris Dovey   
   > DeSoto Solar   
      
   If I were doing this I would scare up a surplus PID temperature controller,   
   Omron is a good name, a thermowell for the temperature sensor and a vacuum   
   oven feedthru for the heater power leads. The rest can be fabricated,   
   including the thermowell if you have a decent thread-cutting lathe (almost   
   essential for physics experiments). The feedthru on my vacuum oven was a   
   pipe plug with Glyptal sealing the wires. It leaked and thus I bought the   
   oven cheap, but making a new one fixed it fine.   
      
   If you attempt to measure temperature from heater wire resistance you will   
   have to wait many seconds for it to cool down exponentially to the internal   
   temperature. You could sacrifice one to find the input power that damages it   
   and stay below that with the second one.   
      
   Usually we keep the heater and sensor separate, with the heater upstream and   
   the sensor in a location that better averages the temperature of the   
   contents. Applications that measure and control the heater resistance   
   generally keep its temperature constant and read out the necessary power,   
   for instance the hot-wire detector in a mass spectrometer or the mass air   
   flow sensor in a car engine. Otherwise PID control which avoids temperature   
   overshoot is much better.   
      
   The two accessible controls on your A/D converter are gain and offset. Use   
   the offset to get your zero and the gain, the reference voltage, for full   
   scale.   
      
   jsw   
      
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