Controlling heating elements

[aaronhance]

Hello eevblog forums! I was wondering what would be the best way to control a heating element with an mcu? I would like to be able to achieve and sustain a set temperature, with the help of a sensor of-course.

[Tomorokoshi]

1. What voltage for the element?

2. What power of the element?

3. What type of temperature feedback?

4. What process parameters - stability, heat-up time, etc.

5. Ambient conditions?

[Richard Head]

It depends on your intended level of accuracy of the setpoint temperature and the thermal time constant of the thermal mass.
If you require sub 1 deg C stability then you probably require proportional control (ie thyristors/triac with phase control).
If your setpoint stability isn't too critical you can use bang-bang control and use a relay to switch the element on and off. This is the most popular type and most industrial controllers use this technique.
If you go for proportional control then I would be inclined to use an analog control loop and a micro with PWM (or DAC) to generate the adjustable setpoint voltage.
If you go for bang-bang control the the micro can do everything. Just remember to include some hysteresis or the relay will open and close very often.

[aaronhance]

1. What voltage for the element?

2. What power of the element?

3. What type of temperature feedback?

4. What process parameters - stability, heat-up time, etc.

5. Ambient conditions?

12v, 150w and 30w heaters.
thermistors
+/- 10*C for 150w, +/- 5*C for 30w
room temp 18*C - 26*C~