Chapter 5 Relay Ladder Logic Programming
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3B
Output Instructions
Set Output Instruction (Latch)
(
¿
)
A set output instruction, or Latch, turns ON an output coil (Q) or an auxiliary contact (M) when the preceding
input contact turns from OFF to ON. Once the output is ON or set, it will remain ON until it is reset using the “Reset
output” instruction. It is not necessary to retain the input contact at ON state once the output is at ON state.
Reset Output Instruction (Unlatch)
(
À
)
A reset output instruction, or Unlatch, turns OFF a previous set output coil (Q) or an auxiliary contact (M) when
the preceding input contact transitions from OFF to ON. Once the output is OFF or reset, it will remain OFF until it
be “Set” again.
Pulse Output Instruction (Flip-Flop)
(
P
)
Flip-Flop changes the ON/OFF state of the coil (Q) or an auxiliary contact (M) when the preceding input contact
turns from OFF to ON. Once the output is ON, it will remain ON until the next time the preceding input contact turns
from OFF to ON. In the example below, when Pushbutton I03 is pressed and released coil, Q04, it will turn on and
remain on. When Pushbutton I03 is pressed again, coil Q04 will turn off and remain off.
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