Chapter 4 Relay Ladder Logic Programming 45
Timers and Timer Status Bits (T Memory Type)
Timer status bits provide the relationship between the current value and the preset value of a
selected timer. The timer status bit will be on when the current value is equal or greater than the
preset value of a selected timer. In this example, when input I3 turns on, timer T1 will start. When the
timer reaches the preset of 5 seconds timer status contact T1 turns on. When T1 turns on, output
Q4 turns on. Turning off I3 will reset the timer.
Counters and Counter Status Bits (C Memory Type)
Counter status bits provide the relationship between the current value and the preset value of a
selected counter. The counter status bit will be on when the current value is equal to or greater than
the preset value of a selected counter. In this example, each time the input contact I4 transitions from
off to on, the counter (C1) increments by one. When the counter reaches the preset of 2 counts, the
counter status contact C1 turns on. When C1 turns on, output Q5 turns on. When M2 turns on
counter C1 will reset. If M9 is turned on, the counter will change from a count-up counter to a
count-down counter.
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