Turning one output off when another is turned on

Describe your system and processes, and post your config file.
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Moad
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Turning one output off when another is turned on

Post by Moad » Wed Oct 12, 2016 6:13 am

I have 2 circuits for my elements. One circuit has a 3.5kw element and powers everything else on the rig aside from the other 3 elements.

With the 3 element circuit I have a 4.5kw in the HLT and a 3.5 + 4.5 in the kettle. I want to ensure only the HLT 4.5kw OR the BK4.5kw can come on at the same time.

Reason being when I am boiling, I want to be able to start heating strike water for the next batch. If the 3 elements came on at the same time for some reason I would trip the breaker.

I know this could be done through wiring but I would prefer to do it programatically if possible. Is registers where I need to look?

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JonW
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Re: Turning one output off when another is turned on

Post by JonW » Wed Oct 12, 2016 8:53 am

Ladder logic is where you'd want to set it up.

You can control things manually, via processes and via ladder logic. Processes take precedence over manual control and ladder logic takes precedence over processes.

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oakbarn
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Re: Turning one output off when another is turned on

Post by oakbarn » Wed Oct 12, 2016 1:03 pm

You can certainly do that and while Ladder Logic may work, two States would also work. Are you trying to do in the Same process and State? I would assume that once you have reached Boil on Batch 1, you want to start the HLT for Batch 2.
Of course if you wanted to Turn on the HLT On when the BK2 was Off, Ladder Logic could do that, but if you had them under PWM Control, it might take a while for the HLT to get to Temp as it would be getting power only when the BK2 was off. It would really depend on how much power you need to maintain the Boil. Would one element work or do you need 2? If you had a Duty Cycle of 50% for BK2, then the HLT could be on for "half" the time as well.
From a safety standpoint, Wiring would be the Correct Solution as you would never want to wire a circuit with more than 80% of the rated amperage by Code. You would want to consult a Certified Electrician for that and if you have one doing the wiring, they would conform to the required code. Circuit breakers and SSRs can fail.
That being said:

Two State Method:

State 0 : Wait for Boil:
Element BK 1 On
Element BK2 On
Element HLT Off
ll_1.jpg
ll_1.jpg (73.28 KiB) Viewed 887 times
State 1: Boil
Element BK1 On
Element BK2 Off
Element HLT On
ll4.jpg
ll4.jpg (86.5 KiB) Viewed 887 times

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oakbarn
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Re: Turning one output off when another is turned on

Post by oakbarn » Wed Oct 12, 2016 1:14 pm

Ladder Logic:
State 0: As Above
State 1: Boil With Ladder Logic
Element BK1: On PWM (example 90%)
Element BK2: Duty Cycle 50% or other PWM
Element HLT: On Hysteresis PWM (but Ladder Logic only when BK2 = off).
ll0.jpg
ll0.jpg (76.27 KiB) Viewed 887 times
Ladder Logic
Output 0 = BK 2
Output 6 = HLT
Process = Boil Process
Reg 1 = State 1. You set this by Asserting Reg 1 in State 1 of the Boil Process.
ll2.jpg
ll2.jpg (50.82 KiB) Viewed 887 times
I use the Process and State (Reg) so that the HLT will not turn on unless the Process 0 and Reg 1(State 1) are asserted. If you just had it where the HLT turned on whenever the Out 0 was off, it would immediately turn the Out 6 ON even if no processes were running.
ll1.jpg
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JonW
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Re: Turning one output off when another is turned on

Post by JonW » Wed Oct 12, 2016 2:15 pm

Processes & States would work to do this if programmed correctly, but in a situation like this, you could still overdraw your current if you are in manual mode. I agree with Oakbarn that hard-wiring is really the preferred method.

Moad
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Re: Turning one output off when another is turned on

Post by Moad » Wed Oct 12, 2016 4:56 pm

Thanks guys,

I've used another process (Strike 2) to start heating the HLT with only the smaller element for now.

I am unsure how much power will be required to maintain the boil as elements are being wired up this afternoon by my (qualified) buddy.

I read that higher order processes will take preference so I could turn the larger HLT element OFF during the "ramp to boil" process and then deselect this item during boil process. Then once at boil I'll be able to turn one of the BK elements off and have both HLT elements on. If that works I can just use the original "Strike Heating" process.

Valid point about wiring and SSRs failing. I'll discuss with my mate to see whats involved.

Thanks again for the replies

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