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Chapter 4. Ladder Diagram (LD) Programming
Examples Comparing PTCOIL and POSCOIL
PTCOIL
In the example below, the power flow into the PTCOIL alternates between OFF and ON. On the first
sweep the power flow in is OFF, on the second sweep it is ON, and so forth. Each time the power flow
into the PTCOIL changes from OFF to ON, the value of Xsition is turned ON. Therefore, on the first
sweep, the PTCOIL turns Xsition OFF, on the second sweep it turns it ON, on the third sweep it turns
it OFF, and so forth. Notice that the behavior of the PTCOIL is not affected by the presence of the
fourth rung, which also writes to Xsition. PTCOIL behaves the same way when the fourth rung is
removed.
POSCOIL
If a POSCOIL is used in place of the PTCOIL in the example below (keeping the rest of the logic
identical and same alternation of power flow into the POSCOIL), the behavior of the logic will be
different. The behavior of the POSCOIL is affected by the execution of the fourth rung, which writes
to Xsition and changes both its value and its transition bit. In this example, the POSCOIL never turns
Xsition ON. If the fourth rung is removed, POSCOIL will behave exactly as the PTCOIL behaves,
turning Xsition OFF on the first sweep, ON on the second sweep, and so forth.
Flip the value of PflowIn. If it was ON turn it OFF. If it was OFF turn it ON.
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PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual
GFK-2950C
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