This is really a PLC programming issue and not a technical problem. If you are willing to get paid helps from outside consultant we can ask some of the consultants we know to help you write the initial part of the program.
Otherwise, we can only offer you a description of how to control your ramp up cycle (ramp up from temperature -45 to temperature B+40 degree C within 1080 minutes). Normally your measured ADC reading is between 0 and 4092. You need to do some scaling to convert them into degree C. Assuming that each digit represent 0.1 degree after scaling, i.e. -45.0 degree means -450, and +40.0 degree is represented as 400:
At the ramp up cycle, the starting temperature is -450.
The end temperature is to be +400
Ramp up time = 1080 minutes
==> increment = 400-(-450)/(1080*60) = 0.0131 per second.
You can use a 1 second clock pulse to periodically execute a custom function. Within this custom function, you will increment a variable (say N) to keep track of the elapsed time from the start of the ramp up cycle. You will then compute the desired temperature at this instant and compare it to the measured temperature, then decide if you want to turn ON or OFF the heater:
N = N+1 ' keep track of elapsed seconds from start of cycle.
IF N > 1080*60 ' times up
..... ' do whatever necessary
ENDIF
S = -450 + N*131/10000 ' S is desired set point.
T = ADC(1) * (some scale factor to give readings in 0.1 C)
If T < S ' Temperature is below set point
SETIO Heater
ELSE
CLRIO Heater ' temperature is above setpoint
ENDIF
