with that PAC i linked, theres a potentiometer for varying the 'intensity' between 0 and 100%. im liking the PAC instead of the standard PWM just because its much more fine-grained control. with PWM its only on or off, which when you slam 20 or 50 amps on and off rapidly it can effect other things in the house (lights pulsing, havoc on digital voltage regulation circuits on your TV or computer, etc). a phase angle controller is more gentle; instead of just varying the rate and time of the on/off switching to equal the overall desired duty cycle, a PAC actually modifies the waveform to equal the % power you set.
One more question: PWM / PAC for oxygen solenoid so O2 can remain on for duration of transfer to fermenter or regulated pressure?
you dont want to pwm a solenoid. if you want to adjust the flow rate ofa gas you can use a needle valve, especially for the flow rates you will probably be using with oxygen (low flow). once you set the needle valve to the rate you want, you can control the gas line with an on/off solenoid if you want it to interface with the BCS. a solenoid doesnt control the flow rate though.
and remember to use oxygen-rated equipment! pure oxygen can be very dangerous and can cause regular valves to spontaneously catch fire (thats right- steel or brass valves can spontaneously catch fire