Internet PLC Forum
General => Technical support => Topic started by: ssali on January 29, 2009, 12:09:34 PM
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Hi.
I am very new to PLCs
I am trying to use a sequencer to be able to start and stop a motor. i understand that the sequencer needs to go from on to off to increment. i tried using 1.0 s clock, which runs each sequence for 1.0 second. My problem is that i want to run sequence 1 for 30 sec seq 2 for 5 sec and seq 3 for 30 sec..and so on. does anyone have any idea on how to do it?
I would really appreciate any help.
Thanks :)
sara.
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You can't drive it with a fixed clock since the sequence timing is different from one step to another.
You can use step 1 (e.g. Seq1:1) of the sequencer to trigger a timer for 30 sec. When the timer times out it advance the sequencer by 1 step to Seq1:2. Now trigger another timer for 5 second. When the 5 second timer times out advance the sequencer by one more step to Seq1:3. e.g. At each step of the sequencer you can also control the ON/OFF of any I/Os or run a custom function etc.
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Hey,
Thank you so much for the help.
I got it done. I really appreciate it.
I have one more question. I am trying to run a dc motor.
It needs to reverse directions. is it possible to do that in ladder?
Thanks,
Sara.
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Reverse DC current flow requires a H-bridge design which comprises of 4 contacts. You could construct a H-bridge using 4 external relays driven by two outputs. Your ladder circuit must interlock to prevent both outputs to be on at the same time which can cause short circuit.
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yeh..thats what i thought...Hbridge...just wanted to see if there was other ways..
ill look into Hbridge design and all ..dont know too much about it...but i did come across some good links on the web.
Thanks alot once again.
I appreciate all your help and quick replies.
tc.
Sara.