Internet PLC Forum
General => Technical support => Topic started by: prginocx on September 13, 2006, 01:21:38 PM
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In my ladder rungs I want to latch two different relays at two different
times, but they will activate the same output a different way. This is to generate two fault messages. One blinking light, one solid light ON.
Program won't allow me to do this. In fact I can't operate them in the manual mode, either "monitoring mode".
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In ladder logic all the COILS cannot only be triggered at a single rung. So normally you use two different relays at two different rung and bring their contact to another circuit and the two parallel contacts are then used to drive a single output coil.
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I'm not quite sure I understand. Are you saying I can't have a rung with RLY1 turning on Output 1 via the .5mS special relay blinking..
And then another rung with RLY2 turning on Output 1 solid ON.
So there is NO way to utilize the light blinking for one purpose, then solid ON for another purpose ?
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This is actually a fundamental Ladder Logic principle. You have to make use of internal relays for such purpose.
E.g.
1) some logic rung turns on and off RLY 1 - blinking
2) Some other logic rungs turns on RLY 2 - SOLID
RLY1 OUT1
|---||-------------------(OUT)
| RLY2 |
|---||-----
This way, the same output can be controlled differently by either the RLY1 or RLY2. Note that if RLY2 is ON then the OUT1 will be solid ON regardless of the pulsing of the RLY1.
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So really what you are saying is I have a Fundamental Mis-Understanding of ladder logic ? That is entirely possible, likely even...
No wonder I couldn't figure it out. I will do your solution and see how it works. Thank you very much.