Russ McKenna

Schema - multiple uses of a single coil or set?

3 posts in this topic

I have heard "Don't use SET or duplicate coils". I kind of agree, so how do you handle it?

Do you use logic to control coil A1 and other logic to control coil A2. Then coil A is controlled by either A1 or A2.

Do you use logic to SET or RST A and other logic to SET or RST A.

Please realize the logic is not as simple as stated above. not simply condition 1 or condition 2 then out A.

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@Russ McKenna Yes, You should not use duplicate coils for my program I have to use memory bit to buffer data for input/output


I need to use X0 to On Y0

normal program are


If you need to create other program to control Y0 you need to parallel sequence before Y0 such as



Then I have use Memory bit to solve this







That you can use any condition to control Y0 by use output at M data then parallel at output sequence and you can use M0 M1 for HMI control too.

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it is not JUST "coils"....

"do not duplicate" mantra applies to ANY instruction that modifies state of an output.
the more instructions write to an output, the harder is to troubleshoot. 
two is the minimum number of instructions that would cause duplication. 
and that is already considered too much and frawned upon.
some products have built in check for duplicates and 
in some cases will force you to prevent use of dupplicates. 
typically this would only look for bit-level instructions and 
word level instructions for exaample would still get free pass...

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