Hey guys, i am currently messing around with a ceramic heater try to heat up a small volume of passing air in a tube.
I am trying to regulate the temperature the heater gets to so as to regulate the air temperature.
The temperature i was looking to achieve is around 200 celsius and i will be powering the circuit with 7.2 volts.
Now the issue i have is the regulating circuit, i can't figure out weather it is best to use a thermistor or thermocouple for this range and i am also not to sure how to implement/design a circuit to inhibit the heater when a set temperature is reached so as to maintain the temp. (i have done this previously with a microcontroller, but never just using an electronic configuration)

any help is greatly appreciated!

thanks

 

I'd go for a thermistor. One like this, for example, would be good up to 300C
http://uk.mouser.com/ProductDetail/...AlK6hOPG0DJp1AiadhaLJFLpEmh2eDE7axg/%2bYd1Q==

 

thanks!
for what reason would you choose a thermistor?
also any ideas about how i can configure the thermistor in a voltage divider or something to allow for control of the heater temperature

 

Use a comparator op amp, like an lm358, or Tlc272, with the thermistor and mosfet power transistor, or relay to feed the heater, alter the values or R1,R2, Vr1 to suit your temperature range.

 

for what reason would you choose a thermistor?

Resistance change per degree is much greater than a thermocouple's few micro-volts per degree. Easier to process, cheaper.

 

Resistance change per degree is much greater than a thermocouple's few micro-volts per degree. Easier to process, cheaper.

ideal, thanks for the info.

 

Use a comparator op amp, like an lm358, or Tlc272, with the thermistor and mosfet power transistor, or relay to feed the heater, alter the values or R1,R2, Vr1 to suit your temperature range.

This sounds like the thing i'm going for, using a simple circuit with variable resistor values to trigger an FDS4465 mosfet.

 

If you want to use a thermocouple use a K-type with the AD595 chip, use the circuit on page 6, figure 9.

 

If you want to use a thermocouple use a K-type with the AD595 chip, use the circuit on page 6, figure 9.

sweet, i appreciate all the info guys!

has anyone any views on the benefits of using a microcontroller to control heater temp in a portable dc powered unit vs simpler electronic implementation?

 

One benefit of the micro would be that you could implement PID control of the heater, hopefully for closer temperature control.

 

One benefit of the micro would be that you could implement PID control of the heater, hopefully for closer temperature control.

yeah i figured it would be beneficial to implement PID and PWM for power savings and accuracy.
cheers again

 

I did a project using the LM35 (which might not tolerate your temperature) where I achieved control to ±0.1°C using simple thermostatic control, no PWM. My point is, you don't have to use a micro is you don't want to. If I recall, I used an op-amp with a gain of ~20x on the LM35 output which is normally 10mV/°C, followed by a comparator controlling a MOSFET, switching the cooler load. PWM might have been more elegant, but ±0.1V is pretty darn good. Tough to even measure much better than that.