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PLC logic flow

I spent hours and trees on paper sketches, and I could not stumble on anything to make me pass this problem. I can switch between the two motors, but I cannot figure out how to turn off the engines when switching between them, but still following the criteria below.

Using ladder logic: Use only one stop station, consisting of only one NC contact and one NO contact, two motor starters and three control relays create the next cycle. (No timers or counters)

  • When you press the start button, engine 1 starts and starts to stop by pressing the stop button.
  • When the start button is pressed again, engine 2 will run until it stops by pressing the stop button.
  • When you press the start button, engines 1 and 2 will run to a stop by pressing the stop button. Pressing the start button again will start the cycle.

Any help is greatly appreciated.

thank

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2 answers
Ira Baxter is right. You must use a state machine. I have the setting below. Normally you would draw such a finite state machine using circles and arrows, but this time I think ...

Although you are talking about 3 different steps (states), I actually see 6 states:

State0: Both motors are switched off (If start button pressed goto state 1) 
State1: Motor 1 running (If stop button pressed goto state 2)
State2: Both motors are switched off (If start button pressed goto state 3)
State3: Motor 2 running (If stop button pressed goto state 4)
State4: Both motors are switched off (If start button pressed goto state 5)
State5: Both motors are running (If stop button pressed goto state 0)

What you have to do is to have one block that determines the state (0..5) and the lock of the engine control unit react to this state.

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, . . , , - + reset. , , :

START - NO, STOP - NC. M1 + M2 F1 + F2

START  M1   M2   F1  F2   M1
-|P|--|/|--|/|--|/|--|/|--(S)

STOP   M1   M2   M1  F1
-|N|--| |--|/|--(R)--(S)

START  M1   M2   F1  F2   M2
-|P|--|/|--|/|--| |--|/|--(S)

STOP   M1   M2   M1   F2   F1
-|N|--|/|--| |--(R)--(S)--(R)

START  M1   M2   F1  F2   M1   M2   F2
-|P|--|/|--|/|--|/|--| |--(S)--(S)--(R)

STOP   M1   M2   M1   M2
-|N|--| |--| |--(R)--(R)-
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