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Old 06-17-2011, 08:02 PM   #1
njbabs
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Oct 2009
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I am wondering if it is possible (and how) to wire a system in which you can switch between two different PIDs to control a single element (my planned system is a two vessel no sparge HERMS, one PID to Kettle w/ element, the other to the MLT). The goal would be a selector switch to choose whether the MLT PID or the Kettle PID was controlling the element in the Kettle.

I am planning to use 1 SSR and 1 DPDT Relay to a 240V/5500W element.

I would like to use one 3 position switch at the DPDT relay (since there would be a switch there anyway), but am not sure if this is possible or how to wire it (without another SSR & relay).

Otherwise, would something like this work?


Thanks for any help.



 
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Old 06-19-2011, 08:58 PM   #2
Rondacker
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I think you have it right.
How are you going to handle two sensors? If that's the plan.


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Old 06-19-2011, 09:34 PM   #3
conpewter
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I'm confused on why you would want two PIDs for one element. Couldn't you just change the PID settings depending on if you are boiling or mashing?
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Old 06-20-2011, 12:34 AM   #4
njbabs
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I was hoping to have the ability (as long as I had two PIDs anyway) to select which PID was controlling the element in the Kettle/HLT, since each would be measuring temp at a different point (one in the kettle, one in the MLT).

I thought the flexibility to control temp during a HERMS recirculation based on either probe might prove useful as I dialed in my process/system (particularly if it was simple to wire the option).

In summary: The PID wired to the MLT or the PID wired to the Kettle could control the the kettle element (particuarly during HERMS recirculation).

...for all I know using the MLT PID and tempt probe would just lead to a bunch of overshooting.

 
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Old 06-20-2011, 03:58 AM   #5
thelorax121
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Just use the one PID, and switch it to manual output (around 60% for my system) to achieve a good rolling boil

 
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Old 06-20-2011, 12:16 PM   #6
njbabs
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I apppreciate the thought, but I'll have 2 PIDs regardless even if one is only reading temp. from the MLT. AND since I'll have two, and two possible temp probe readings to use as control points for a PID, I was wondering if switching between them was possible.

Regardless the kettle PID will run in manual during the boil. This switch would (might) only be use during mash/HERMS.



 
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