Ladder Logic Problem

austinjjcm · Apr 7, 2006

First time on this site.
I am writing a program on a GE Fanuc 90/30 PLC. I can do the basics, but have run into a problem.
Pump control. Have 2 product pumps to be started from eight spots. Pump 1 to start with the first call and pump 2 starts with the third call. Pump 2 needs to shut down when calls drop to two.
What is available in logic to solve this problem?
Thanks,
John in Maine.

Steve Bailey · Apr 8, 2006

Assuming that the eight "calls" remain on as long as there is a need for product: Have each off-to-on transition of a call increment a counter. Have each on-to-off transition decrement the same counter. When the counter's accumulated value is 1 or two, turn on pump 1 only, when it's 3 or greater, turn on both pumps, when it's zero, turn both pumps off.

austinjjcm · Apr 8, 2006

That sounds like it will do the job. How? If I have 8 inputs how do they connect to a single counter?

Money4Nothing · Apr 8, 2006

Program them in parallel in your logic.

$

Steve Bailey · Apr 8, 2006

Here's how to do it for two calls. Note that I left out the reset line for the up counter and down counters. The two counters should be addressed to the same %R address. The 'P' coil is a positive displacement coil (On-going one shot). The 'N' coil is a negative displacement coile (Off-going one shot). This could get out of whack if two calls ever happen at exactly the same time.



Call1             Call1_On

--] [----------------(P)-

 

Call1            Call1_Off

--] [----------------(N)-

 

Call2            Call2_On

--] [----------------(P)-

 

Call2            Call2_Off

--] [----------------(N)-

 

Call1_On          _____

--] [----+-------|UPCTR|

         |       |     |

Call2_On |       |     |

--] [----+       |_____|

 

Call1_Off         _____

--] [----+-------|DNCTR|

         |       |     |

Call2_Off|       |     |

--] [----+       |_____|

austinjjcm · Apr 14, 2006

Steve,
Thanks for the help. Your idea worked great.
John in Maine

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