So when you use the PID in manual mode and dial it down, doesn't it simply cycle the element on and off? Is this "fast switching"?
Part of me thinks that adding a contactor to the RIMS side of things may be a better way to go. This way I have a physical switch to make sure the element in the tube isn't firing if the SSR fails open. So now, same question. If I put a contactor after the SSR and switched the load wire to the coils of each contactor, would I wear out the RIMS contactor? I assume the BK contactor won't be firing on and off as often, but would I potentially wear that out as well?
Or does using a PID in manual mode operate in such a way that it won't be firing the contactor on and off if I dial down the boil?
Cheers.
This is a bit complicated, but the switching rate of the PID is going to be quite high. You can not connect a PID to a contactor - It's just too fast. The contactor should be hooked up to a switch to simply turn it on and off.
Anything the PID controls with PWM needs to be through an SSR.
Remember how a PWM circuit works:
If your PID PWM frequency is 1 second, for instance, every second your contactor will change state twice, regardless of power setting.
If you set 50% power, it's on for .5 seconds and off for .5 seconds.
If you set 75% power, it's on for .75 seconds and off for .25 seconds, repeating over and over.
This is why you have to use SSR's for throttled loads - The SSR can handle that switching rate.
Since you want to be able to throttle both the RIMs and the BK elements, both need SSR's. The RIMs will be PID operated with a thermocouple and PWM controlled by the PID. The BK will be manually operated with PWM from the PID.
So these are really 2 different functions:
Contactors are the safety - Enabling you to have positive control of the voltage at the element - On and off. This is manual, and is a safety in case you need to feel safe while cleaning, or in case your SSR fails. Because SSR's usually fail "Closed" or "On". Bad.
The SSR's are what actually control the "heat" applied by the element by switching it on and off really fast.
These are 2 separate functions, and each function has an appropriate device.