Tom Jenkins
Lifetime Supporting Member
This could get tricky depending on the thermal mass of the furnace contents and the energy capacity of your heaters. Expect a fair amount of dead time in your control response.
I'd calculate the rate of change as Dravik suggests. ROC = ΔT/Δt. The time interval t will have to be based on observation. You will need to have a long enough interval to get an accurate rate, but not so long your control can't respond.
I would use the ROC as the process variable for your control loop, with heater power the controlled variable. Then, when you get to, or close to, set temperature switch to another control loop with the actual temp as the process variable.
I'd calculate the rate of change as Dravik suggests. ROC = ΔT/Δt. The time interval t will have to be based on observation. You will need to have a long enough interval to get an accurate rate, but not so long your control can't respond.
I would use the ROC as the process variable for your control loop, with heater power the controlled variable. Then, when you get to, or close to, set temperature switch to another control loop with the actual temp as the process variable.