With a bit of searching I came across the following:
It is a nice simple example of a PID controller.
When looking on Figure 1.b you will see the schematic.
This schematic has 5 different parts:
Please keep in mind that the input is the error signal. To get this signal you need to subtract the desired value from the actual value.
Have a look at the following:
Lastly I made the following example:
(You may want to switch around the reference and input temperature depending if you have a positive or negative feedback)
This should be enough to allow you to create your PID controller