Example: 30 Hz

Indicates 30 pulses per second (1,000 ms).
Therefore,
1000 ÷ 30 = Approx. 33.3 ms
33 ÷ 2 = 16.7 ms (minimum ON signal width and OFF signal width)

Description
ON/OFF Ratio
Ratio of the count input signal's ON time to OFF time.
(The Counter's maximum counting speed is specified at an ON/OFF ratio of 1:1.)