FIFO with siemens S7-300 cpu's

Rverhoeven

Member
R
Join Date
Jun 2002
Posts
16
We have a priority energy system for 4 pump systems. only one pump system can be started at a specific time. The commands for starting the pumps however can be given at almost the same time. So the program has to "remember" which pump system was first. Therefor i thought i could use a FiFo, and there's the problem. i don't have a clue how a can create a FiFo in Siemens Step 7 (cpu type is S7-316)

Does anyone have an idea how to do this.....









An end is the beginning of something.......................
 
;)

If have a look in your Program Elements, you will find a library, the path is:
Libraries \ Standard Library \TI - S7 Converting Blocks \ FC85
if you highlight the FC-block and press F1 you will get some help on how to programme it

Hope this helps you out :D

fifo.jpg
 
When you say:
only one pump system can be started at a specific time
Click to expand...
do you mean the classic:
"Due to inrush concerns, no pump may be started within 10 seconds of another pump"?

If so, you don't need a FIFO, you need a Start Permissive.

Straight ladder (I don't know Step 7 specifically, but this code is pretty generic)


Step 1.  Remember the Start Command (this rung will be repeated 4 times, once per pump) 

 

   START-1              START-1

   CMMD       PUMP-1    MEMORY

----| |----+----|/|------( )

           |

   START-1 |   

   MEMORY  |

----| |----+

 

 

Step 2.  Create a one-shot of the pump starts.  

         Repeat 4 times. 

                        PUMP-1

  PUMP-1     oneshot   ONESHOT

---| |----+----|/|-------( )

          |

          |            oneshot

          +--------------( )

There are dozen different ways to do this - again, this is generic

 

 

Step 3.  Run the Permissive timer when there are no pumps starting.  

         If a pump starts, reset the timer 

    PUMP-1    PUMP-2    PUMP-3    PUMP-4     +--- TIMER ---+  TIMER

   ONESHOT   ONESHOT   ONESHOT   ONESHOT     |             |  DONE

-----|/|-------|/|-------|/|-------|/|-------|EN         DN|---( )

                                             |     10      |

    PUMP-1                                   |     SEC     |

   ONESHOT                                   |             |

-----| |-----+-------------------------------|RESET        |

             |                               |             |  

    PUMP-2   |                               +-------------+

   ONESHOT   |

-----| |-----+

             |

    PUMP-3   |

   ONESHOT   |

-----| |-----+

             |

    PUMP-1   |

   ONESHOT   |

-----| |-----|

 

 

Step 4.  The actual pump start logic (Repeat 4 times) 

  START-1   TIMER         STOP-1  

  MEMORY    DONE          CMMD     PUMP-1

----| |------| |-----+-----|/|------( )

                     |

   PUMP-1            |

----| |--------------+



Does that help?

Now this code starts the pumps in scan order, not pushbutton order like a FIFO would. But presumably you won't be getting too many pump start commands during the "blackout period" for this to be an issue.
 
Last edited:
Thanx

Steffen and Allen. thanx for the information

To Allen:
I had to use the fifo cause there was a situation i didn't mention. sorry about that.

The system is also used in case of the EPS usage during powerout. in this case i have to remember which CPU ask for the power up command for the pump. it's a little more complex than i can write down here.



To Steffen:
i didn't know before but you can use the TI - S7 conversion functions in a normal S7 program.
 

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