Single component temperature testing station - Page 1
Forum section: electronics / general

author: ftransform
author_rank: Frequent Contributor
timestamp: May 11, 2012, 08:26:54 pm
content: I was interested in perhaps building a tiny thermal chamber in order to test one component at a time.The idea is to take one of these 20$ cartridge heaters, a short one,http://www.omega.com/pptst/CSS_CSH.htmlI am unfamiliar with this component though, a maximum sheath temperature of 760 C is listed, and I would like the ability to test component up to say 500C.My idea is to suspend the component (with a thermocouple attached) several milimeters above the heating cartridge (perhaps a thin wire mesh could be used) and heat it via radiation.Can a cheapo ebay PID controller accurately regulate this when combined with a nice thermocouple? Or does my device need a bigger heat sink before the temperature can be precisely controlled? I am worried that the thermal capacity of the heating cartridge by itself is too small to regulate well. My goal is to be able to control the temperature by 1-2 deg C. The thing being tested will have a cover put over it so air currents in the room do not cause erratic temperature changes.I am also not sure about what wattage I will need to control this accurately... I do not mind overshooting it so long the system is stable.Any hints and tips?I would also like to use this device to measure the melting points of things like plastic, solder by using microscope slides.I would really like to maintain the ability to heat things to ~ 500C though, so please do not suggest oil submersion devices. That should have its own thread if it needs to be discussed.

author: SeanB
author_rank: Super Contributor
timestamp: May 12, 2012, 07:03:47 am
content: Better is to decide how big a chamber you want, and to get a replacement oven element of the right length and wind it into a cylinder of the right diameter so as to make a tube of a diameter and length that will be your oven. Then you measure the temperature of the steel element and use that to drive the PID controller to heat it up. Radiation will heat the inside to nearly the same temerature, and you can reduce heat loss by using a quartz or Pyrex window at one end and a asbestos or mica barrier at the other end.

author: Unknown
author_rank: Unknown
timestamp: May 12, 2012, 08:01:28 am
content: Quote from: ftransform on May 11, 2012, 08:26:54 pmBefore you worry about the controller you need to establish the capabilities and performance of your process. How long will it take to heat and cool, is the system well enough insulated from external environment. How many switching cycles will be required to maintain temperature within your allowable tolerance. How quickly will your sensor element respond? If correctly sized and matched then the better of the WunHug-Lo PID controllers (Which are rarely true PI) should be adequate for control with some reasonable tolerance. Without looking too deep into it, I'd doubt a single element of the type shown would be practical. Maybe several element on a heatsink would be useful for a shoebox sized enclosure. You'll have to do your sums and/or be prepared to experiment a little.A larger mass with reasonable thermal inertia in a well insulated enclosure will be easier to control, and keep operating reliably, than a tiny element.