Harun,

As Kai pointed out, the basic algorithm is easy. But since this equation does not have the "thermal inertia " factor of your load, real time tuning based on system behaviour cannot be eliminated.

What I am trying to say is this:

1. Assume that the heater is heating a thin copper foil of 0.1mm thickness and 10sqmm area.

2. Assume that the heater is heating a block of 100mm thick and 100 sqmm area.

Can the same algorithm work OK in both cases ? You get what I am saying ? What can be done simply is to modify Kai's equation ( I have no right - only suggestion )

Duty cycle = ((SP-T) / PB x 100%)xTIF + 50%

Where TIF is the thermal inertia factor. Start with a value of 1.00 and adjsut it based on real time trials.

Raghu

Raghu