Multiple Processes Controlling One Output

Describe your system and processes, and post your config file.
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Minnino
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Multiple Processes Controlling One Output

Post by Minnino »

I am looking to find a way to have multiple processes control a single output. I have a temperature probe on the output of my mash tun, and one on the output of my HERMS coil (inside my HLT). I am trying to have my BCS turn on and off my gas burner below my HLT in order to maintain my mash temperature. How I was thinking of having this setup was to have the BCS turn on/off the HLT burner based off of 2 temperatures probes. So if I wanted my mash at 155F, in theory my temperature probes at both the output of the mash tun, and the output of the HLT should both be 155F, and if it is below that the HLT burner should kick on, and if its equal to or above, the burner should be off. Am I correct in thinking this way? Is there an easier way of going about this?

A problem that I am running into is after doing some research I think that the BCS processes can only control one output (the HLT burner) at a time, and the higher number process takes precedence. So if process 1 is reading the HERMS output probe, and is reading 155F it will turn the HLT burner off, but if process 2 is reading the mash tun output probe, and its reading 152F is will continue to have the burner off, since this process is lower in the food chain.

Am I just way off in this or am I on the right track? Is there an easier way of doing this? Sorry for all the questions, this is my first time trying to setup the BCS and though it seems quite straight forward for the simple tasks im trying to perform, its still confusing to me.
clearwaterbrewer
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Re: Multiple Processes Controlling One Output

Post by clearwaterbrewer »

Short answer - you only want one process, but multiple outputs controlled within that process..


You want your single process to have one controlled output control the HLT be kept at the desired temp, and another controlled output in that same single process to turn on the pump if the mash temp is too low (but why not have mash pump on all the time for continuous vorlauf?)


This design of system has a couple inherent issues, delay vs. overshoot, and no flow if mash too warm....

I would suggest a simple setting of the HLT to 160 or so, and a valve(s) to either bypass or flow through the HERMS coil... ( a proportional 3-way valve would be ideal for this, but requires analog output, something that is not happening anytime soon in the BCS)

You can be confident that you are not inventing the wheel with your setup, there are plenty of gas fired herms systems on here for you to read about and learn from their trials!
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oakbarn
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Re: Multiple Processes Controlling One Output

Post by oakbarn »

I tried doing what you want to do:

I have a MLT TEE In which measures the WORT coming from my HERMS back to the MLT.
I have a MLT TEE Out which measures the WORT going to my HERMS back from the MLT.

I also have a Small Electric HLT HERMS System ( Iactually use a Chinzilla as a HERMS but that requires 2 pumps).

While not a burner, the theory was the same. Heat the Wort based upon the MLT Tee In and Oots. It did not work very well. I found it was "chasing" the Setpoint.

I was going the burner route but thought I would have much finer control with an electric element for the HERMS.

I now just maintain a Temp on the Small HLT using the Temp Probe in that vessel.

I have found that the MLT Tee Out can read low at first, but after a while both In and Out are at my Setopint.

I have found that if I want 152 degree WORT, I set my HLT at 154. It keeps the WORT at 152. This is basically what Clearwater said as well. The delta between the WORT and the HLT is something you will have to find on your setup.

As a side note: It is easy to lower the WORT Temeperature but impossible to raise the temp of the WORT in any meaniful time using HERMS. (At least on my system)
Minnino
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Re: Multiple Processes Controlling One Output

Post by Minnino »

Thanks so much for all the info guys, sorry it took me a bit to get back to this. The over all goal is to have both pumps running for the entire mash process, one recirculating hot water in the HLT to keep a consistent temperature, and the other to pump wort through the HERMS coil. I was originally looking to go all electric, but unfortunately am unable to get reliable power on that scale to my brewing area. Im glad to hear i am semi on the right track to getting things tuned in a bit better. I appreciate all the help, ill keep you posted on progress.
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oakbarn
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Re: Multiple Processes Controlling One Output

Post by oakbarn »

My HERMS electric heater is only 1500w and 110v so a regular household circuit works as long as nothing else is on it. I have it in a Stout 9 gal BK with the Electrical Setup. I bought my electric cover from Brewers Hardware which is much better than the one that came with the pot. It takes about 45 minutes to heat about 6 gallons but the BCS maintains the Temp excellently. That pot is dedicated for HERMS water although I do use the water for rinsing after cleaning. I am in the process of finding a way to turn on my burners. I got a plate ignitor and it works well. I have a 12vdc gas valve on the way. I have also a small flame detector that I hope to incorporate as a "safety".
Minnino
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Re: Multiple Processes Controlling One Output

Post by Minnino »

I have a SSR that controls my gas valves, and have a 'safety' in place. So far that has been working very well, but I am having a problem trying to get the programming right to keep a constant temperature. I know nothing will be perfect, but i have the BCS set so that there is a 0.1 degree (F) variable, and I have the temperature value set 0.5 degrees above my target temperature. So if my target temp was 155 I have the BCS reading the the temperature probe on my HERMS output, and if it drops to 155.4 it will kick the burner on until that same temp probe reads 155.5 (or higher). But I also set it up so that if the probe on the MLT OUT is below 155.5 it will kick on the HLT burner. I think this might have caused some of my problem, as the liquid coming out of the MLT became colder than my target temp, it would heat up the what was coming out of the HERMS coil and eventually it would be above my target temp. Doing this has caused a constant game of 'catch up' then 'over shoot' then 'under shoot' and back to 'catch up'. I think just using the HERMS output temperature probe for what controls the BCS, and keeping the logic in there to try and shoot for 0.5 degrees above my target with a 0.1 variable might keep my temp within a full degree (154.5 - 155.5). Can I set a value of 0.0 for the BCS so that it will try to constantly keep the temp at 155.5 or maybe even 155.2 with a little buffer room? Guess Ill have to get out there and see what kind of a temperature swing that may cause.
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