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42817Re: PID Controller

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  • GGB
    Nov 22, 2012
      > Cool, great info. I am actually using it for a barley mash process. So if I understand correctly, an SSR performs the same functions as a PID, but better?

      No, they're completely different things. The PID is a logic "brain" that attempts according to the parameters you program in to shoot for a particular temperature. It determines how long the element is "on" or "off" and makes adjustments according to results.

      SSR stands for Solid State Relay. It's really just an electronic switch - it has no moving parts. It is the equivalent of the contactor but because the contactor has moving parts it is not capable of switching power off and on to the element frequently without destroying itself.

      Your PID itself is able to switch loads of up to 3 amps, but this is well short of 2000 Watts. Remember that Watts = Voltage x Amps. Re-arrange this formula to get W/V = A, and depending on what your voltage is this will tell you how many Amps capability you need.

      So you employ a contactor, or SSR, to do the heavy-duty switching because these are capable of handling many more amps.

      There is one thing to remember with a SSR, and that is if they fail they switch, as far as I understand, to full on and will not turn off. The SSR has its own connection to voltage mains. So, as with all setups like this, you should always supervise operation.

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