Single PID, Two Sensors (switchable?)

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Single PID, Two Sensors (switchable?)

Postby thedrayman » Mon Sep 28, 2015 07:34

I'd like to be able to use a single PID to control my HLT and then, when needed, control the temperature of the sparge water from the HLT using a sensor in the sparge arm feed on the MT to control the temperature at that point (using the same PID, as it will be regulating the temperature of the sparge water).

Would it be possible to fit a switch in-place to switch between sensors, or would it affect the accuracy of the temperature reading?

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Re: Single PID, Two Sensors (switchable?)

Postby Hairybiker » Mon Sep 28, 2015 10:31

Should be possible but you would need a multi pole switch, e.g. for a pt-100 you would need 3 poles switched.
You could just install a plug/socket and plug the other sensor in in-place of the hlt one. much easier.

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Re: Single PID, Two Sensors (switchable?)

Postby rpt » Tue Sep 29, 2015 16:51

If the PID learns how to do one job will it fail to do the other one effectively?

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Re: Single PID, Two Sensors (switchable?)

Postby ockelford » Tue Sep 29, 2015 20:21

rpt wrote:If the PID learns how to do one job will it fail to do the other one effectively?


rpt is spot on...

The pid needs setting up or autotuning for each whole process, including sensor calibration and pid settings... Having played with pids for hours, i would say it would be more fun to set up an arduino with a double relay for each process and two sensors... If you're computer savvy, then this would be very economical option, otherwise buy 2 pids... I think what you' save on a pid would cost you in ruin beers and lost hair in the meantime!!

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Re: Single PID, Two Sensors (switchable?)

Postby Hairybiker » Wed Sep 30, 2015 14:17

Since it is the SAME HLT in use, the heat calibration would be the same across both sensors. If using PT-100's they should be virtually the same anyway, unlike NTC's etc.

Suck it and see would be my way, if it is way off then add another pid you already have the sensor plug ready.

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