glycol safety feature

Describe your system and processes, and post your config file.
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jward
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glycol safety feature

Post by jward » Sat Jan 21, 2017 6:14 pm

I am finally back to building a glycol chiller and am working out how to add a float switch to disable the AC unit and pumps if the glycol level is too low. My first best answer was simple ladder logic, no float switch no power. The problem is this could lead to short cycling the AC and pumps since activating the pump lowers the glycol level which rises again when the pump turns off. How do you implement this kind of protection or what would you do? As I type this, I'm thinking configuring the floatswitch as a "one-shot" might work.

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Re: glycol safety feature

Post by jward » Sat Jan 21, 2017 8:09 pm

Wiring up a switch and leds for bench testing shows the ladder logic is not a good choice for the safety. Well, at least not with having the rest of the control logic in processes. I had the wrong idea that output would only be effected when the input was raised instead of the correct understanding that it is set according to whatever the input and logic dictate.

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Re: glycol safety feature

Post by jward » Sun Jan 22, 2017 2:15 pm

New approach. Created a "glycol" process set to run at start with 2 states. The entry state is "glycol normal" which has hysteresis control of the AC unit. Ladder logic is used to always run the pump when the AC is on. (I may put them on the same power source and not worry about this.) The exit condition is the glycol level float switch. The next state is "glycol low". It turns off the AC, chiller pump, and fermentation pump, no exit condition. I'll manually reset after I fix the glycol leak.

The email alert doesn't seem to work when "glycol normal" exits into "glycol low". Is there some trick to getting the email to work?

I was thinking of a separate process for managing the fermentation. This would also turn on and off the fermentation pump potentially in conflict with the glycol process, glycol low state. How do conflicting processes get worked out? If the glycol is low it would be better to have all pumps off even if other processes want to turn them on.

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JonW
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Re: glycol safety feature

Post by JonW » Sun Jan 22, 2017 6:08 pm

Why are you using a float switch on the glycol? It should be a closed system that would never get to a low glycol level. You have the volume in your conical jacket (or coil) plus the reservoir volume. Why would the level ever drop?

I would keep the pump and chiller on separate circuits. You need to pump to kick in when fermenter cooling is called for, but the chiller may not need to run at that time if the bath is sufficiently cool.

E-mail alerts are being handled with a commercial e-mail provider in the next firmware update since HostGator keeps screwing with the current setup.

In relation to your question on conflicting processes - everything is handled by a precedence order. Process control takes precedence over manual control. Higher number processes take precedence over lower numbered processes. Ladder logic takes precedence over any processes (or manual control).

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Re: glycol safety feature

Post by jward » Sun Jan 22, 2017 6:43 pm

JonW wrote:Why are you using a float switch on the glycol? It should be a closed system that would never get to a low glycol level. You have the volume in your conical jacket (or coil) plus the reservoir volume. Why would the level ever drop?
A leak in the system probably with a host or fitting.
I would keep the pump and chiller on separate circuits. You need to pump to kick in when fermenter cooling is called for, but the chiller may not need to run at that time if the bath is sufficiently cool.
I probably didn't explain the cooling part of the chiller. I'll try to post a photo. There are 2 pumps in my system. One pushes water past the AC coils. The AC coils are in a PVC pipe and not in the ice that holds the glycol. That pump needs to run when the AC runs. The second pump is for moving glycol to the fermentor which is on a separate circuit.
E-mail alerts are being handled with a commercial e-mail provider in the next firmware update since HostGator keeps screwing with the current setup.
UCI blocks parts of HostGator. They are populated with a lot of spammers. I look forward to it working.
In relation to your question on conflicting processes - everything is handled by a precedence order. Process control takes precedence over manual control. Higher number processes take precedence over lower numbered processes. Ladder logic takes precedence over any processes (or manual control).
Excellent, then I can move that process to the highest numbered process. Thanks.

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