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Old July 25th, 2010, 10:21 PM   #1
shapcrook
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convert flowchart to ladder diagram

hello,
im a litle bit confused how to convert flowchart to ladder diagram..lets say the flow chart like attach pic,

may anyone help me..

thanks
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File Type: jpg tank filter system.jpg (20.0 KB, 141 views)
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Old July 25th, 2010, 11:12 PM   #2
Honga
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Diamonds are if statements... or in ladder XIC/XIO, rectangles are bit sets, or assignments.
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Old July 25th, 2010, 11:14 PM   #3
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Give me a yell if you need more info, though I suggest trying it first.
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Old July 26th, 2010, 08:20 AM   #4
mordred
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Flow charts are merely a series of steps to accomplish a task look at each step seperately. Work out how to program each step individually but keep in mind the assigned I/O points.
step 1) open outlet valve and close inlet valve
step 2) if start button pressed open inlet valve close outlet valve.
step 3) input level sensor
step 4) if tank is full or stop button pushed open outlet valve and close inlet valve

how to program each step will depend on which PLC make and model your using which you did not specify.
Also hopefully this is merely an assignment and not an actual machine if its an actual machine you will want margin levels on your tank full logic to keep the vavle outputs from stuttering (coming on and off too often)
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Old July 26th, 2010, 02:08 PM   #5
shooter
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make it with SFC or with CFC in your head:
ladder rung 1 is step 1
if conditions are good step 2 is activated and step 1 is off.
and so on.
you can even step over with this ladder.
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Old July 26th, 2010, 02:48 PM   #6
TConnolly
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Greetings Shapcrook.
This appears to be a homework problem. While we don't provide the final solutions for homework problems, we do provide help in solving them. If its not a homework problem then this will hopefully still be helpful.


You have two states.

In state 0 the outlet valve is open, the inlet valve is closed.

In state 1 the outlet valve is closed, the inlet valve is open.

Pressing the start button transitions you from state 0 to state 1. Pressing the stop button or having the tank full transitions your from state 1 back to state 0.

Since its a tank filling, lets call the state Filling. When Filling = 0 we are not filling the tank, and when it is 1 we are filling the tank.

If we create a truth table for this we get

Filling | Inlet_Valve | Outlet_Valve
--------+-------------+--------------
0 | 0 | 1
--------+-------------+--------------
1 | 1 | 0




Looking at the table we see that

Outlet_valve = NOT Filling

and

Inlet_Valve = Filling.

Now all we need to define now is the logic for the state, or Filling, which can be 0 or 1. In plain language, when we push the start button we want FILLING to change to a 1 and we want it to remain a 1 until the stop button is pushed or the tank is full. If we write that statement as a boolean equation we get

FILLING = (Start_Button OR FILLING) AND NOT Stop_button and not Tank_Full.

From here you should be able to construct three rungs of ladder logic that implement the flow chart.


Extra Credit: Reduce this to two rungs and eliminate the need for a bit to define the state (Hint: Outlet_Valve = Not Inlet_Valve and Inlet_Valve = Filling)
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Last edited by TConnolly; July 26th, 2010 at 03:00 PM.
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Old July 26th, 2010, 03:00 PM   #7
Archie
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Here is something that could be food for thought in pointing you to one method of going from a flow chart (SFC) to ladder:

http://www.youtube.com/watch?v=rCa_U6YATTA
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