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Basic Issue with ladder program

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Hello All,


Very new at programming PLCs so please forgive me if this is a very basic question/issue. I'm in the middle of writing a program and have gotten to a point where it is beginning to work well.  My issue is however I am having a problem with a set of contacts not activating the output when another set that are connected parallel do activate the contacts. I don't understand why one set are working and not the other. Big believer in a picture telling a million words so please see attached images. If someone can point out what I'm doing wrong I would be most appreciative.



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Hello Easy700,

The issue you are describing is probably caused from trying to activate a coil more than once in you application (O0, O1 or both).

The whole principle of PLC ladder programming will not allow this.

However, if you are willing to activate a coil from more than one place in your application, you are free to use the Set/Reset coils however you like.

Please note that this is not a bug nor a phenomenon related to Unitronics products.

For further information, you can look up "Double Coil Syndrome", or look in this post: http://www.plctalk.net/qanda/showthread.php?t=4365

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Or you can use M-contacts and OR them to the coil later in the program. When you use it your way, it is always the last used network that decide the coilstaus.




M3001  |          O2

-||--------|---------( )-


As UniGuru say, this is general to all PLC-manufacturers

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Hello Flex 700


I don’t agree that your problem is related to a double assignment from output coils O0 and O1 in the program because the logic seems to work when the manual bit is on.
To test this you could use two spare MB,s or XB,s instead of O0 an O1.

Although power seems to flow through these two compare boxes you will know then if the problem is related at that point. According to the help file if you want to start this action for example at Friday from 6:00 AM to 6:10 AM  MI10=600HEX(1536 DEC) and MI11=610 HEX(1552DEC) and at the second box Friday should be highlighted as already is in your example.
Anyway assigning spare MB,s or XB,s instead of the outputs or add an extra network with the same two time compare boxes and use a spare MB or XB as output and you will know where the problem is.

Kind regards

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