As the load is purely resisitive it would be very simple to use phase control with an opto coupled triac (better than an SCR (in my humble opinion) as they self commutate at the 0v crossing - from what I remember, just not as high in the current rating) then you could control the temperature very consistantly by varyting the phase angle, no switching noise either as it is at the 0v Crossing that you turn the triac on.



I would also use the RS485 method suggested as this is less hardware to implement (the Max chips need external caps for the RS232 levels - unless you buy the flash new models with them all built in)and it is good for up to 1200m with good noise immunity



Regards

Marshall