Wiring 2 temp probes to one PID. Possible?

I have my wiring figured out with the help of P-J's wiring digrams and many other comments/ideas from the forum. A simple gravity system (i.e. no pumps) with 5500w elements in the HLT and BK. The PID will control the SSR for the HLT, but I would like to also use the same PID/SSR for the BK. I only need to reach 220F (100C) to boil in the BK, but don't want to just turn on the element and boil crazy. Would like to control it to a simple rolling boil and not have the element at full all the time.

Can I put a temp probe in the BK and switch it between the HLT and BK? Woudl a probe be of any help if it is set for 220 deg? Or is there a better way?

(Also thinking of a PWM circuit, but looking for the cheapest/easiest solution. aka, short on $)

It is possible to set up 2 probes but that will not help you for what you are trying to do. Once you reach the boiling point the temperature is the same on a gentle boil and a raging boil.

What PID do you have? If it is the Auber Instrument SYL-2352 or SYL-2362, you are in business without any issue. That PID has a manual mode that delivers percent of power to the element. You just need to set up the configuration for manual mode and then you are there with a push of a button.

How can I help you?

P-J

Just to further clarify, you don't even need a probe in the BK in this situation. You can use a single SSR driven off a single PID but the high current side would have to be switched between the HLT and BK via a high current double throw switch or contactor. You could also use two SSRs and use a low current double throw switch to send the PID control signal to the correct SSR (not as safe).

When you switch a PID into manual mode to control duty cycle to the boil kettle element, it doesn't care what the temp probe is sensing.

Bobby_M said:

Just to further clarify, you don't even need a probe in the BK in this situation. You can use a single SSR driven off a single PID but the high current side would have to be switched between the HLT and BK via a high current double throw switch or contactor. You could also use two SSRs and use a low current double throw switch to send the PID control signal to the correct SSR (not as safe).

When you switch a PID into manual mode to control duty cycle to the boil kettle element, it doesn't care what the temp probe is sensing.

Click to expand...

Agreed. There is no reason for multiple temp probes. However, if you want to have multiple temp probes setup to one pid the simplest option may be to purchase multiple probes from auberins and install a temp probe in each kettle, tun, etc. Then just switch the sensor cable connected to the pid (since it has a disconnect) b/w each temp probe.

Hopefully that makes sense. It should be noted, each sensor often has a little bit of variation that needs to be adjusted so your readings may be slightly off.

I actually just did something similar to this for my build. I used a 3 pole2throw switch and can toggle between two temp probes on the BK and the HLT. Both are on one PID.

As others have mentioned, you can really only have one accurate temp reading unless your temp probes have exactly the same error in reading for calibration (unlikely). So I set the accurate temp probe reading to the HLT and not there is a couple degrees of difference between the real and actual in the BK.

I like to use the temp probe like this for the BK so I can read the temp quickly and estimate when my boil start is getting close, as well as where I am in the chilling process.

This is a little different than your question, but the other guys already aptly answered the PID boil control functionality questions.

As a side note I set my control box up to toggle between the HLT and BK with two contactors as bobby suggested. Based on this I don't have to plug in or unplug anything through the brew session.

I have 2 thermocouples and 2 dual SSRs connected to my PID through a 3 pole DT switch. See this post for schematic and other details. I've used it for about 50 batches, so I can confirm it works well

BTW, it is a very good idea to be able to see the temp in your boil kettle if you are chilling in there. I don't understand why this is overlooked so often.

P-J said:

... the Auber Instrument SYL-2352 or SYL-2362, ... has a manual mode that delivers percent of power to the element. You just need to set up the configuration for manual mode and then you are there with a push of a button.

Click to expand...

Thanks P-J. That's what I didn't know.

CidahMastah said:

I like to use the temp probe... so I can ... estimate when my boil start is getting close, as well as where I am in the chilling process.

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Thanks CidaMastah. I hadn't even thought of the chilling process. Now I know I need the probe!

And thanks Bobby M, rsklhm10, and passedpawn. Your comments gave me more useful help for my next steps.

But one more question: I read that a K type probe should not be switched. Do you all agree? Is it better to use an RTD probe if it is to be switched?

KEG99 said:

...
But one more question: I read that a K type probe should not be switched. Do you all agree? Is it better to use an RTD probe if it is to be switched?

Click to expand...

You are far better off with the RTD temp probe for many reasons.

p-j said:

you are far better off with the rtd temp probe for many reasons.

Click to expand...

+1.

+1 to PJ's comment - my probes are rtd

Definitely go with rtd probes.