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4.3.4
Transition Coils
PACSystems controllers provide four transition coils: PTCOIL, NTCOIL, POSCOIL, and NEGCOIL.
POSCOIL and NEGCOIL are updated every time they are called.
PTCOIL and NTCOIL are updated once per CPU scan.
For examples showing the differences in the operation of the two types of transition coils, see
Examples Comparing PTCOIL and POSCOIL
POSCOIL and NEGCOIL
Positive Transition Coil (POSCOIL)
If:
the transition bit is OFF, and
■
the input power flow is ON,
■
the POSCOIL sets the reference bit of its
associated variable ON until the coil is executed
again. When the coil is executed again, it sets its
reference bit OFF.
Note: When the Positive Transition Coil sets its
reference bit ON, it also sets its transition
bit to ON. The next time the Positive
Transition coil executes, it finds its
transition bit set to ON and sets its
reference bit to OFF.
GFK-2950C
These transition coil instructions should not be used in
■
a parameterized block or user-defined function block
(UDFB) with a parameter or member. In these cases, an
R_TRIG or F_TRIG should be used instead.
Do not override a transition coil by putting a force on
■
its reference bit. If a transition coil is overridden, the
coil has no effect on the bit, and if the override is then
removed, the coil might be set ON for one sweep. . This
can cause unexpected behavior in the Controller logic
and in field devices attached to the Controller.
Do not write to the reference bit of a transition coil
■
using any other instruction or from an external device.
Doing so will destroy the coil's one-shot nature and the
coil may not behave as described.
Do not use a transition contact with the same
■
reference address used on a transition coil because the
value of the transition bit, which stores the power flow
value into the coil, will be affected.
February 2018
Chapter 4. Ladder Diagram (LD) Programming
Warning
Negative Transition Coil (NEGCOIL)
If:
the transition bit is OFF, and
■
the input power flow input is OFF,
■
the NEGCOIL sets the reference bit of its
associated variable ON until the coil is executed
again. When the coil is executed again, it sets its
reference bit OFF.
Note: When the Negative Transition Coil sets its
reference bit ON, it also sets its transition
bit to ON. The next time the Negative
Transition Coil executes, it finds the
transition bit set to ON and sets its
reference bit to OFF.
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