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Old April 4th, 2021, 11:00 PM   #1
Aintbad
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Logixpro Dual Compressor

Hi folks, i'm pretty much new on this topic and i need some help with
the dual compressor part 3 and 4, currently working on part 3 i cant make it to do this, When at 50% loading, the compressors should alternate with each taking a turn. At 100% loading, both compressors should engage once it is detected that the pressure is continuing to drop.
Any help will be so appreciated.
i attached a jpg of what ive done so far..
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File Type: jpg LadderRungs.jpg (80.7 KB, 86 views)
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Old April 5th, 2021, 06:44 AM   #2
drbitboy
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I am not sure we know enough about the process
  • Can you provide a schematic and a summary of inputs (pressure switches, momentary push buttons, switches, etc., and outputs)?
  • Logix 5000? (whoops, never mind, LogixPro in your title).
  • Is this bang-bang control i.e. both compressors off when there is adequate pressure (I:1/2 is 0), and 1 or 2 compressors on when there is inadequate pressure (I:1/2 is 1)?
  • How is it determined that 2 compressors need to be on?
    • Is there a second pressure switch with a lower setpoint? (whoops, never mind, yes cf. here).
Not that I am sure they are correct in the first place*, but the current logic in Rungs 001 and 002 can be replaced by a single rung: [XIC O:1/2 XIO I:1/2 OTE B3:0/2]. That being the case, the logic on the left side of Rung 003 can be replaced ... oh bugger ... here, see second image below.


* On further reflection, I think they are not correct.


I am still looking at Rungs 004 and 005. It appears that Rung 005 is supposed to be a flip-flop that triggers on the rising edge of I:1/2 (pressure sw mtr 1); a flip-flop is a simpler circuit than that see the first image below (from here); although that is the same number of instructions, it is still cleaner than your version.

Okay, the behavior we want to see is:
  • Motor 1 is on if lamp is on AND pressure is low AND either
    • 1 motor is required and the alternating bit is 1
    • OR
    • both motors are required
  • Motor 2 is on if lamp is on AND pressure is low AND either
    • 1 motor is required and the alternating bit is 0
    • OR
    • both motors are required





LadderRungs.jpg

Last edited by drbitboy; April 5th, 2021 at 07:43 AM.
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Old April 5th, 2021, 08:03 AM   #3
drbitboy
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Quote:
Originally Posted by drbitboy View Post
...the behavior we want to see is:
  • Motor 1 is on IF lamp is on AND pressure is low AND either
    • 1 motor is required (PE1 is 1) AND the alternating bit is 1
    • OR
    • both motors are required
  • Motor 2 is on IF lamp is on AND pressure is low AND either
    • 1 motor is required (PE1 is 1) AND the alternating bit is 0
    • OR
    • both motors are required
...

What I am pointing out there is that the behavior of the motors is essentially identical; the only difference is the state of the alternating bit. So there will be one rung for Motor 1, and a nearly identical rung for Motor 2. I assume you know how to code ANDs and ORs in ladder, so that should make coding the motor behaviors above straightforward; if you do not know about ANDs and ORs, feel free to ask.


What is left is to set a bit that says [both motors are required]. The behavior of that bit is that
  • [both motors] bit
    • is 1 when PE2 becomes 1 (pressure drops below 98),
    • is 0 when PE2 becomes 0 (pressure rises above 120).
Hmmph, I just re-read the exercise and got that, so that is trivial; I thought we were going to need a start/stop circuit because PE2 would return to 0 well below 120, so PE2=1 would be the start and PE1=0 would be the stop.


P.S. Welcome to the forum

Last edited by drbitboy; April 5th, 2021 at 08:08 AM.
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Old April 5th, 2021, 02:15 PM   #4
MikeyN
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It looks like you are close. I am looking at your original post, and not including the changes that drbitboy has suggested since I don't know if you have used those yet or not.

I would imagine that what you are seeing is that compressor 1 is always turning on regardless of the state of your alternator. Compressor 2 may be the one working with your alternator. So when PE1 is off, but PE2 is still on, either Compressor 1 is running by itself, or both compressors are running. Both compressors run when both PE 1 and PE2 are off. Am I close?

Do you really want I:1/2 to control compressor 1 when it is controlling your alternator (rung 3)?
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Old April 5th, 2021, 03:32 PM   #5
drbitboy
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Quote:
Originally Posted by MikeyN View Post
I am looking at your original post, and not including the changes that drbitboy has suggested since I don't know if you have used those yet or not.



Just to be clear, the changes I made were only made to consolidate, and remove redundant, logic. They would not change the behavior of the program. So it does not matter if OP makes those changes or not, @MikeyN's analysis and predictions for how OP's program will run are correct either way.
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Old April 6th, 2021, 09:59 AM   #6
Aintbad
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Okay, so basically what i've done there is exercise two of the logixpro compressor where motor 1 feeds air until it reaches the desired PSI then once it goes down to 100PSI the second motor turns on, alternating between the first one and second one, which some how it did worked as i have it in the attached jpg Now what i want it to do is if %flow is at 50% i want it to work just like that alternating, plus if i switch the %flow to 100 like there's more air leaving the compressor motor 1 wont be able to keep up with the demand so motor two will help once it goes down to 98PSI. But i'm still stuck with that...
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Old April 6th, 2021, 10:55 AM   #7
Aintbad
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Also i forgot to mention, in the image i attached there's remains of the exercise 2 where i was only using PE1 to alternate between motor 1 and 2 now for this PART 3 i have to use both PE1 and PE2
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Old April 6th, 2021, 01:22 PM   #8
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Which of the following statements are true?
  1. If B3:0/2 is 1, then at least one compressor should be running.
  2. If I:1/2 is 1 and O:0/2 is 1, then at least one compressor should be running.
  3. If I:1/3 is 1, then both compressors should be running.
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Old April 6th, 2021, 02:45 PM   #9
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Quote:
Originally Posted by drbitboy View Post
Which of the following statements are true?
  1. If B3:0/2 is 1, then at least one compressor should be running.
  2. If I:1/2 is 1 and O:0/2 is 1, then at least one compressor should be running.
  3. If I:1/3 is 1, then both compressors should be running.

whoops, 3. should be "If I:1/3 is 1 and O:0/2 is 1, then both compressors should be running.
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Old April 6th, 2021, 04:44 PM   #10
PLCnovice61
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Aintbad, since you are getting someone else to do the exercise, you could just download the completed exercise from the download section.
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Old April 6th, 2021, 05:35 PM   #11
Aintbad
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Quote:
Originally Posted by PLCnovice61 View Post
Aintbad, since you are getting someone else to do the exercise, you could just download the completed exercise from the download section.
I did look for it, but its funny how everyone does what they think its right without reading the exercise carefully so there nothing close to what i need if you find one please let me know just wanna take a look to understand waht they've done.
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Old April 6th, 2021, 05:47 PM   #12
Aintbad
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Quote:
Originally Posted by drbitboy View Post
Which of the following statements are true?
  1. If B3:0/2 is 1, then at least one compressor should be running.
  2. If I:1/2 is 1 and O:0/2 is 1, then at least one compressor should be running.
  3. If I:1/3 is 1, then both compressors should be running.
the 3rd one cuz that's when both have to work to raise the PSI to the desired level meaning that the %flow is high enough for only one to raise the PSI.
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Old April 6th, 2021, 07:07 PM   #13
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Quote:
Originally Posted by Aintbad View Post
the 3rd one cuz that's when both have to work to raise the PSI to the desired level meaning that the %flow is high enough for only one to raise the PSI.



Three is definitely true.


Are you saying that 1 and 2 are not also true?


(whoops: when the pressure is over 120, is I:1/2 a 1 or a 0? If it's a 1, then 2. should say "If I:1/2 is 0 and O:0/2 is 1, then at least one compressor should be running")


I am trying to get you to think like the PLC. Learning to program is basically learning to think.

Last edited by drbitboy; April 6th, 2021 at 07:31 PM.
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Old April 6th, 2021, 08:20 PM   #14
Aintbad
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Quote:
Originally Posted by drbitboy View Post
Three is definitely true.


Are you saying that 1 and 2 are not also true?


(whoops: when the pressure is over 120, is I:1/2 a 1 or a 0? If it's a 1, then 2. should say "If I:1/2 is 0 and O:0/2 is 1, then at least one compressor should be running")


I am trying to get you to think like the PLC. Learning to program is basically learning to think.
ty i really appreciate its just that i'm having a hard time with this two last parts, its just that i dont understand how to implement it.
When the pressure is over 120 I:1/2 is a 0 so the I:1/3 right?
its only on when pressure drops down to 110.
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Old April 6th, 2021, 08:54 PM   #15
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Quote:
Originally Posted by Aintbad View Post
When the pressure is over 120 I:1/2 is a 0 so the I:1/3 right?

Why are you asking me? you have access to the simulation, I don't so I don't know.


Based on your Case 2 code, rungs 003 and 004, either compressor can only run if B3:0/2 is 1, and neither can run if B3:0/2 is a 0.


So that suggests
  • B3:0/2 will be a 0 when the compressors do not need to run
    • I.e. B3:0/2 will be 0 and the compressors will not run either
      • when the pressure is either above the maximum (120), or
      • when the pressure is decreasing from the maximum to the bottom of the span (100 = 120 - 20).
  • B3:0/2 is a 1 when trying to increase the pressure, and
    • That suggest that, once the pressure drops below the bottom of the span (100),
      • B3:0/2 should become a 1, and
      • At least one of the compressors should come on

On rung 001 your code latches a 1 into B3:0/2 if I:1/2 is a 0, and rung 002 latches a 0 into B3:0/2 if I:1/2 is a 1.


So
  • if B3:0/2=1 is one compressor on, then I:1/2=0 must be low pressure, and
  • if B3:0/2=0 is compressors off, then I:1/2=1 must be high pressure.


Is that consistent with what you see the simulation doing?
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