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Program help for plc ladder building

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pixy hazmet

Electrical
Aug 24, 2023
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AU
need help with following program any hints will be appriciacted

plcchepy_lw8kh8.png

1. Program the PLC to execute the attached Step Action Diagram.
2. When the program is first downloaded, the machine should wait for the green
button to be pressed.
3. Once the A button is pressed, the machine should start from step number 1 and
then proceed through steps 2,3,4,etc.
4. Make the program cycle through repeatedly, with a 1-second pause between each
cycle.
5. If the B button is pressed and released while the machine is running, the
machine winds down to stop at the end of the cycle.
6. If the C button is pressed while the machine is running or winding down, the
machine undergoes an emergency stop at the end of the current step.
7. If the D button is pressed during an emergency stop, as it is released the
machine gets reset and any extended cylinders are retracted in the order:
cylinder 4,
cylinder 3,
cylinder 2,
cylinder 1.
8. After being reset or wound down as described above (in points 7 and 5), if the
A button is pressed, the machine restarts from step number 1, and behaves
as described in point 3.
9. If the A button is pressed during an emergency stop, the machine returns to
the mode it was in when the emergency stop was activated and resumes from the
step it was up to.
10.Any button or combination of buttons not assigned a function, must do nothing
if pressed.
11.If on the most recent occasion that the A button was used to start the
machine from step 1, a double click (A double click is defined as the button
being pressed twice in 0.5 seconds) was used rather than a single click; steps 6,
7, 8, 9, 10, 11 and 12 are repeated twice during every cycle.
12.This continues until the machine is next restarted from step 1, as described in
points 3 and 8.
13.During the repeating steps operation, the buttons all function as described for
regular running, as described in points 3-10.
 
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I haven't spoken Boolean in a long time and I am a little rusty, but I would start with a shift register that is 4 bits wide.
I would first program the operations in step 3.
For each succeeding step I would evaluate whether to use an additional shift register or to force the outputs of the primary shift register.
For step 10, a network of nor gates may be used so that when any button is pushed, all other buttons are disabled.
Are you aware that the resulting actions of a PLC program may depend on how the PLC scans the inputs and how the PLC solves the logic?
As I mentioned, it's been a long time, I'm getting rusty and memory fades and I don't remember the exact details but I had a short demonstration program to make this point to students.
The program gave different results depending on the scanning method of the PLC.
1. The PLC scans a line of the program, solves the logic and sets the outputs.
Then it moves on to the next line.
2. The PLC scans a block of the program, solves the logic and sets the outputs.
Then it moves on to the next program block.
3. The PLC scans the entire program, solves the logic and sets the outputs.
Then it repeats from the beginning of the program.​

--------------------
Ohm's law
Not just a good idea;
It's the LAW!
 
It looks like a request for how to draw the RLL diagram rather that how to design a PLC.

Typically homework is preceded by classroom instruction of the various components required to solve the problem.

It should have included timers and loops and conditional operations, so separate out each step and work the lowest levels first and then bundle them into loops.
 
I was responding to this.
1. Program the PLC to execute the attached Step Action Diagram.
If you program ladder logic (or Boolean logic) into a PLC without knowing how the PLC scans and solves the logic, be prepared for unintended consequences that you will never see with relay logic.
The last PLC that I programmed used Boolean logic, but I have programmed several PLCs with ladder logic.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!
 
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