2 PIDs controlling one Honeywell?

[ptmahoney]

I'm in the process of building a 3 keggle single tier HERMS setup, based off the Brutus designs. So here's my basic question: is it possible to control one Honeywell valve with 2 separate PIDs? I'd like to have one thermocouple monitoring the temp at the HERMS coil output and have it control the burner under the HLT during mash recirculation. Once the mash is complete I'd like to switch over to a PID with a thermocouple monitoring the HLT temp to control fly sparging temps.

Is anyone or has anyone seen anyone running a setup like this (and have any wiring diagrams/photos)? Thanks in advance for any advice!

 

[itsme6582]

You can do this. You'll need a spdt relay/contactor on the input side of your honeywell and a maintained switch to go from one PID to the other.

Contactor - I think you need a 24v 30a for the honeywell. Just pick one that matches the input power.
http://www.auberins.com/index.php?main_page=index&cPath=2_31


Switch
http://www.auberins.com/index.php?main_page=product_info&cPath=7_32&products_id=349

 

[dantodd]

Wouldn't it be easier and less expensive to just switch thermocouples going into one PID?

 

[schematix]

Wouldn't it be easier and less expensive to just switch thermocouples going into one PID?

Switching TCs is bad. If you do this you have to have special switches with the right kinds of metals in them or you'll get a measurement offset.

Also if your 2 systems have significantly different behaviors in each mode you'll need different gains for each system, which can be a huge hassle to deal with in the middle of a brew.

Lots of ways to do this but i'd look to using some switches, 2 TCs and 2 PIDs....

 

[dantodd]

Switching TCs is bad. If you do this you have to have special switches with the right kinds of metals in them or you'll get a measurement offset.

Also if your 2 systems have significantly different behaviors in each mode you'll need different gains for each system, which can be a huge hassle to deal with in the middle of a brew.

Lots of ways to do this but i'd look to using some switches, 2 TCs and 2 PIDs....

I hadn't thought about the PID tuning issues.

 

[ptmahoney]

Switching TCs is bad. If you do this you have to have special switches with the right kinds of metals in them or you'll get a measurement offset.

Also if your 2 systems have significantly different behaviors in each mode you'll need different gains for each system, which can be a huge hassle to deal with in the middle of a brew.

Lots of ways to do this but i'd look to using some switches, 2 TCs and 2 PIDs....

Would this be as simple as using a SPDT switch (on-off-on) downstream from the PIDs before the power enters the 24v transformer?

 

[beernutz]

I'm in the process of building a 3 keggle single tier HERMS setup, based off the Brutus designs. So here's my basic question: is it possible to control one Honeywell valve with 2 separate PIDs? I'd like to have one thermocouple monitoring the temp at the HERMS coil output and have it control the burner under the HLT during mash recirculation. Once the mash is complete I'd like to switch over to a PID with a thermocouple monitoring the HLT temp to control fly sparging temps.

Is anyone or has anyone seen anyone running a setup like this (and have any wiring diagrams/photos)? Thanks in advance for any advice!

Why not use only 1 PID and 1 TC and just move the TC as needed? I ask because that is exactly what I do and it works fine.

 

[schematix]

Why not use only 1 PID and 1 TC and just move the TC as needed? I ask because that is exactly what I do and it works fine.

This very likely is the easiest way to do it and what i'd do first.

As I mentioned before the only downside here is if your 2 systems need very different gains its going to either be a PITA to change during brewing, or just deal with less than optimal settings for one or both. But it might work just fine. Won't know for sure until its tested.

One benefit of a PID controller though is that it is stable over a wide range of gains and systems, even if its not controlling perfectly, it'll still 'work'.

 

[ptmahoney]

This very likely is the easiest way to do it and what i'd do first.

As I mentioned before the only downside here is if your 2 systems need very different gains its going to either be a PITA to change during brewing, or just deal with less than optimal settings for one or both. But it might work just fine. Won't know for sure until its tested.

One benefit of a PID controller though is that it is stable over a wide range of gains and systems, even if its not controlling perfectly, it'll still 'work'.

I thought about doing this as well, the only thing stopping me is my own ambition. I just want to see if there is a way to pull this off without having to move sensors around.

 

[ptmahoney]

So here's a quick update for anyone who might be interested.

I spoke to the folks at Auberins about their thoughts on this, and they were able to recommend a switch to select between to RTD sensors (I decided to move towards RTDs rather than TCs because there are plenty of options out there that include 3 pin connectors so that the wiring can be easily removed from the kettle without taking out the probes. A couple of weldless fittings and I shouldn't have to worry about thermowells).

I'm going to move forward with my two RDT / single PID plan and see how it works. I figure that if there are significant problems, I can purchase another PID and build the system up from there.

I'll try to keep updates on the results coming, just in case anyone is interested. Cheers!

 

[ptmahoney]

Why not use only 1 PID and 1 TC and just move the TC as needed? I ask because that is exactly what I do and it works fine.

Just for my own knowledge, what kind of thermowells/TCs are you using? I ask because most of the TCs I have seen have some smaller diameter threads and aren't compatible with the common 1/2 NPT fittings on thermowells. That was really my biggest concern - not having a reliable transfer of heat between the TC and thermowell.

 

[schematix]

I had a disgustingly awful experience with Auber. I would highly recommend not buying anything from them. Worst customer service experience of my life by far.

 

[beernutz]

Just for my own knowledge, what kind of thermowells/TCs are you using? I ask because most of the TCs I have seen have some smaller diameter threads and aren't compatible with the common 1/2 NPT fittings on thermowells. That was really my biggest concern - not having a reliable transfer of heat between the TC and thermowell.

I don't use a thermowell. I use an Auber Liquid tight RTD sensor, 2 in, 1/4" NPT and an Auber SLY-2362 PID. I bought a SS 1/2" T-fitting which I screw the RTD sensor into using a 1/4" to 1/2" SS NPT connector. I screwed quick disconnects into the other two openings on the T-fitting to attach it to hoses or to my HERMS coil. Liquid flows from one opening of the T out another and past the RTD sensor which is kept immersed. Because of the quick disconnects I can move the TC wherever it is needed.

 

[dantodd]

This might help.

https://www.homebrewtalk.com/showthread.php?t=477980