pump change over

vinuvinod · Feb 15, 2004

Dear plc friends,
i am new to plc programming.my company have s7 200/300 plcs used contol a process in which there are two pumps working as duty standby.
i have to develop a program by which the pump operation should alternate between each start ups.can any one help me?inputs available are start and stop signals from push buttons.

randylud · Feb 15, 2004

Sounds like a Flip-Flop

When you start pump "A", set a latch bit that will be the permissive for pump "B" when you are ready to run it. When you run pump "B", then reset the latch when you stop pump "B" and you will be ready for pump "A" again. There are probably 100 variations on this theme so any one should work ok. Try it out and let us know how you do. There are several people who frequent this site that are S7 speakers but I am not. Been a long time AB guy and have not programmed any TIs since the old 5TI. Of course that was back when TI was in the PLC business and before Seimens bought them out.

elevmike · Feb 15, 2004

This code assumes the following:

1) The start and stop buttons are momentary.
2) The Start button has normally open contacts that close when the button is pushed.
2) The stop button has normally closed contacts that open when the button is pushed.





  Start

  Button    Latch 1     pump b   STOP

---||-------|/|---------|/|------||----+---(pump A) Pump output

                    |                  +---(PD A) one shot 

  pump A            |                   

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



       PD A 

--------||-----------(SET) Latch 1               

                  



  Start

  Button    Latch 1     pump A    STOP

---||-------| |---------|/|------||----+---(pump B) Pump output

                    |                  +---(PD B) one shot 

  pump B            |                   

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



   PD B 

---||-----------------(RST) Latch 1

P.S. Credit to Randy, as this is what he described.

Have fun!

Pierre · Feb 15, 2004

One simple way to do this is to ADD a value of 1 to a register every time you start a pump.

You then use the LSB in serie with the starting run. One with a NO and one with NC.

So in only one single rung you have all the logic to do this task.

randylud · Feb 16, 2004

If you are using LogixPro or want to download it from www.thelearningpit.com, you can use the program I posted on the file storage site. The link to it is here, down at or near the bottom fo the page. It is titled motor starter.rsl. I based it on the two compressor sim which comes with the LogixPro software. Seems to work pretty well and between this one and the one elevmike put up for the S7, you ought to be able to make something happen.

p.s. Mike, thanks for the idea credit.

pump change over

vinuvinod

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elevmike

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Pierre

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randylud

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