WECON Technology Co., Ltd.
5
5.2 Double Coil Designation
Double or dual coiling is not a recommended practice. Using multiple output coils of
thesame device can cause the program operation to become unreliable. The example
program shown opposite identifies a double coil situation; there are two Y3 outputs.
The following sequence of events will occur when inputs X1 = ON and X2 = OFF;
1.The first Y3 tuns ON because X1 is ON. The contacts associated with Y3 also
energize when the coil of output Y3 energizes. Hence,output Y4 turns ON.
2.The last and most important line in this program looks at the status of input X2.
If this is NOT ON then the second Y3 coil does NOT activate. Therefore the status of
the Y3 coil updates to reflect this new situation, i.e. it turns OFF. The final outputs are
then Y3 = OFF and Y4 = ON.
Use of dual coils:
• Always check programs for incidents of dual coiling. If there are dual coils the
program will not operate as expected - possibly resulting in unforeseen physical
The last coil effect:
• In a dual coil designation, the coil operation designated last is the effective coil. That
is, it is the status of the previous coil that dictates the behavior at the current point in
the program.
6. And, And Inverse
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