Howto use PID tune for the best results?

Hi. I have designed a system in simulink, which contains the transfer function of the real system and a controller block.a desired temperatue,and a scope, very simple.The real device is a heating device,which will be connected to the mains voltage and I will generate a PWM signal, according to its current temperature,in order to reach to the desired temperature. my question would be, when I am using the PID block from Simulink library, do I have also to include the mains voltage effective value, as a gain, which would be 230/sqrt(2) in the circuit, or not? since the real device would finally work with mains voltage and will receive the gain. any comment would help,Thanks

[Arkadiy Turevskiy]

Yes, sure you should make the model approximate the real system as closely as possible.