Originally Posted by varocketry
This type of controller is discussed in great detail in threads at homedistiller.org.
MATTD2's comment is completely wrong. This design adds a resistive load to continuously vary the power to the heating element. [A PID works via on/off.]
If your setup only turns on/off, it's not wired properly or it's not the right SSR.
Some SSRs have different control methods.
Sorry but I don't understand why you think my comment is wrong? A TRIAC (as use in SSR, SCR, Phase Angle Controllers) are either off or on, do you agree with that? It does not add a resisteive load at all.
Can you explain what parts of my post you think are wrong.
A PID uses proportional-integral-derivative control to give more precise control of a process value to a set value without excessive ramp time or overshoot. Most PID use by homebrewers use a 5VDC PWM output to control a SSR. This is something completely different (the control method) to what was being asked(the switching method).
With the linked controller it is using phase angle control like you say, but that is still, as I said, turning the output on/off really fast. Basically it turns it on at some point ("set" by the potentiaometer) through the phase cycle, it then stays on until that one half cycle is completed and the voltage crosses the zero volt again. It then waits to turn on again when it hits the set point again = turning on/off really fast, not adding a resistive load.
more info - http://www.learnabout-electronics.org/diodes_07.php