Multiple temp probes per output?

[microbusbrew]

I'm still in the process of building my HERMS but I think I ran into a problem. I have an HLT (5 gallon cooler) with an element and a temp probe. I also have a HEX (2 gallon cooler) with an element and a temp probe. I have a third temp probe on my HXE outlet. My original plan was to have a state for system startup that would include heating the water in the HLT as well as pre-heating the water in the HXE. The temp probes in each would be used to control the heating (the temp probe on the HXE outlet wouldn't be used until I start mashing). Once I start the mash (and thus recirculating) I want the HXE element to be controlled by the temp prob on the outlet rather than by the temp prob in the HXE itself. So during startup output1 would be assigned to temp1 and during the mash output1 would be assigned to Temp2. The problem appears to be that each output can only be assigned to one temp probe. Am I understanding this correctly?

Assuming I am, can anyone think of a way around this? I was thinking I might be able to wire the temp probes into a DPCO type toggle switch. So during system startup the switch would be in position 1 and reading from the probe in the HXE. Then when I start the mash the switch would be in positon 3 (position 2 would be off) and therefore reading from the HXE outlet. Does that sound doable? Am I overthinking this and/or is there another way around my problem? I'm aslo wondering if the resistance in the switch is going to cause problems with reading the temperature. Any input would be greatly appreciated.

***Update - looking at a wiki on switches, it also looks like a SPDT toggle switch might work. I'm thinking I basically need something to work as a changeover switch.

[np0x]

Wire two different outs from the bcs to the ssr controlling the element and associate them to different temperature probes. You can then control the element from either output(and differently associated temperature probe) as your process desires if I understand your question correctly.

[microbusbrew]

Duh, I should have thought of that. See, I figured I was probably over-complicating it. I don't see any reason why that wouldn't work and it's more simple and more automated than manually flipping a switch. Thanks for the suggestion!

[ECC]

Wire two different outs from the bcs to the ssr controlling the element and associate them to different temperature probes.

If you have one bcs output driving 5V, and another one driving 0V, and they're both connected to the same terminal of the SSR, you'll get a short which is not recommended.

You are correct, changing temp probe association on a state-by-state basis isn't allowed, they are considered static system setup. The output control types that need a temperature probe association are Differential and PID, but you could create a process that does the same thing using exit conditions, so you wouldn't need to be associated to the correct probe.

Preheat Hex Process
State0: HEX Heat direct ON
Exit: If Hex Temp >= setpoint+swing/2, goto State1
State1: HEX Heat direct OFF
Exit: If Hex Temp <= setpoint-swing/2, goto State0

And if you want to preheat the HLT using the same process, just add control for that in both states using differential or PID. The HLT will transition seamlessly since it has the correct association.

Your switch idea would also work. The resistance of the switch won't be a problem. You could even use a relay instead of a switch, controlled by the BCS . Many solutions, just pick the one that you like best.

[np0x]

Yeah, so in order to do what I said you would need two seperate ssr's. Then it could work, Right?

[ECC]

Yeah, so in order to do what I said you would need two seperate ssr's. Then it could work, Right?

Yeah, that would work. Probably the cleanest solution if there are spare outputs. If they are guaranteed to not be on at the same time, you wouldn't have to worry about phase differences (although maybe that's not a problem).

[microbusbrew]

Good point about the short, I hadn't thought of that. I saw some relays for around five bucks at radioshack. I like that idea because it still keeps things automated rather than using a manual switch. Thanks guys, when I make up my mind I'll post an update.

[microbusbrew]

I ended up taking the simple approach by switching the probe between two fittings. So during system startup the probe is inserted into the heat exchanger. Then before I start recirculating the mash, I move the temp probe to the output of the heat exchanger. I brewed my first batch last Saturday and this setup seemed to work fine. I'm planning on fully documenting my setup as well as a full brew session on my blog, but in the meantime I have a few assorted pics if anyone wants to check them out, http://microbusbrewery.blogspot.com/

[np0x]

are you switching 220 in that configuration?

[microbusbrew]

No, both the HEX and HLT use 1500 watt 110v water heater elements. On the brew stand I essentially have three outlets each controlled by an SSR; one for the pump, one for the HLT, and one for the HEX. Likewise I have three outlets on my patio, one existing 110v 15amp line, and two dedicated 110v 20 amp lines that I was able to run before I finished my basement.

On the brewstand, the pump outlet is just a basic 15amp 110v while the HEX and HLT use outlets rated for 220v, but I wired them for 110. The pump outlet is connected (via the SSR) to the existing 15 amp GFCI outlet on my patio. The HLT and HEX are each connected (via SSR's) to one of the dedicated 110v 20amp GFCI outlets on my patio. Hopefully that makes sense. I used the 220 volt outlets on my brewstand for safety just in case I have a helper that accidentally tries to plug the HLT or HEX into the 15amp outlet for the pump. Since the plugs are different on the HLT and HEX compared to the pump, they can only be plugged into their respective outlets on the brew stand. Likewise, the pump can only be plugged into it's outlet on the brew stand.

Oh I probably also should mention I have my BCS-460 mounted remotely in the basement. I ran some cat-6 to the back patio to control the SSR's on the brewstand and to connect to the temp probes.