Time Proportional Control is pretty much a slower version of PWM where the duty cycle is varied by on and off time. For example, if the time span is 10 seconds and I want 90% on time then, that converts to 9 seconds on and 1 second off.

So, the output of the PID routine would span between 0 and 10 seconds for on vs. off time. To accomplish this, I need a way to make a guess as to whether the SSR should be on or off based on the output of the PID loop.

See this link, this link, and this link for the Arduino example.

Thanks for the help,
Curtis