Hello Binit;

When you program a PID loop, your are trying to reduce the error between the sensor value and the setpoint you want to maintain.

Once the error is known (15 degrees in your example), you use the different gain parameters to calculate an optimum output to your output controller (your heater) to reduce the error, while trying not to overshoot (overheat the room) or producing oscillations of the output (heater turning on and off all the time). This is where the Gain, Ti and Td must be selected adequately (this is called "tuning" the PID loop.

So: what type of output control di you have, an electric coil, a gaz heater, a boiler...? How does your PLC increase or decrease the heat it produces (analog, or simple binary On/Off)?

It would be helpful if you showed us what parameters you have chosen already for your instance of FB 41, please take a screencapture and attach it here so we can examine it.

You cpould also take a few minutes to look at these FAQs on FB 41, they could be helpful:

https://support.industry.siemens.com/cs/ww/en/view/589983

https://support.industry.siemens.com/cs/ww/en/view/18459342

https://support.industry.siemens.com/cs/ww/en/view/17624666

Hope this helps,

Daniel Chartier