The counters of the built-in PLC functions are up counters. An up counter stops counting and its contact turns on when the count value reaches the setting.
1. Count processing
• The coil of the counter is turned on /off at execution the OUT C instruction and its resent value are updated and their contact turns on after execution of the END instruction.
• The counter counts on detection of the leading edge (OFF to ON) of the coil. It does not count if the coil remains on.
2. Counter resetting
• The count value is not cleared even if the coil turns off. Use the RST C instruction to clear the count value and turn off the contact.
• When the counter is reset by the RST instruction, the present value and contact of the counter are cleared at execution of the RST instruction.
The counter counts on the leading edge of the input condition of the counter imported at an input refresh.
The maximum counting speed of the counter is determined by the scan time, and the counter can count only when the ON/OFF period of the input condition is longer than the scan time.
Maximum counting speed Cmax = (n/100) x (1/ts) [times/s]
N : Duty (%)
ts : Scan time [s]