temperature sensor and feedback control

PeterGibbons

I am requesting some direction and advice on products available through parallax that will perform temperature sensor and feedback control.· In this particular project, I am looking to heat a copper heat sink to 50-120 degrees C in roughly 5 mins and then reduce power to my mica heater to reach steady state conditions on the heat sink thereafter.· Ideally, I am seeking a controller that is capable of holding a set-point temperature and maintain steady state conditions by either regulating voltage or resistance.· I would like the power source of the heater to be a 120 V standard plug outlet.· I have estimated that the desired power to the heater will be 12 to 63 watts depending on the final temperature of the heat sink.· Therefore voltage would need to be reduced to roughly 11 to 27 volts.· The heater can operate either in AC or DC power conditions.· I am fairly unfamiliar with the devises needed to complete this task (solid state relays, etc.), however, I am fairly familiar with BASIC language.· Any advice and links to products that may be of assistance is greatly appreciated.

Andy Lindsay (Parallax)

There is an example in the Stamps in Class Industrial Control text that has most of the elements you are asking about.· This text is available for download from www.parallax.com.· Select Stamps in Class Tutorials from the Downloads menu, then look for "Industrial Control" (266 pp.)...Download text (5.8 MB).· See Experiments 5 and 6.··Additional temperature measurement techniques can be found in "Applied Sensors 1.3" (216 pp.)...Download text (3.69 MB).

There will also be some useful devices in the Products menu (Select·Accessories Portal -> Industrial).· With a 24 VDC supply and a heater that could dissapate up to 63 W, the current draw will be

· I· = P / V
···· = 63 VA / 24 V·= 2.625 A

For direct digital control of DC, the solid state relay·Output Module 60 VDC·"could" do it, but the power supply might be a hassle.

I would take a closer look at the·Output Module 120 VAC.· Even with the root-2 thrown in the calculations,·63 W doesn't look like a problem.· These output modules are plugged into the Opto22 8-Channel I/O Module Rack, which is in turn plugged into the Stamp Controller Interface Board.· If you choose the 120 VAC solid state relay, the power supply requirements for the Stamp Controller Interface Board (and the BASIC Stamp·microcontroller) could easily be the 9 V wall wart (9VDC 300 ma Power Supply) featured on the Stamp Controller Interface Board product page.· The circuits and desgins for everything but the Output Modules are published (links on the various product pages).· If you need to look into a more economical solution, these documents should provide you with a starting point.

PeterGibbons

Thanks for the suggestions, i have purchased the devices and am currently researching the control techniques (proportional) for the setup you recommeded using the BS2, LM34 temperature sensor probe, and the ADC0831 analog to digital converter. Any additional links that you can provide with sample code for feedback control that may narrow my investigation would be appreaciated.

PeterGibbons

I have seen the example for the sensor using a transistor, however, sample code using the output 120VAC solid state relay would most likely demostrate the proper feedback and control techniques.

Ken Gracey

Peter,

I'd like to reinforce that Andy pointed out the Industrial Control text from Parallax. This book is free and will be useful no matter what hardware you end up connecting to the Stamp. The concepts are fairly portable and so much of it can be done the Industrial Control parts kit (one of my favorites).

Ken Gracey
Parallax, Inc.

Ken Gracey

Peter,

If I'm not mistaken, Industrial Control includes some schematics that show how to substitute solid state relays for the transistors in the kit.

Ken Gracey