Mitsubishi Electronics FX5 ユーザーズマニュアル

19  BUILT-IN I/O FUNCTION

19.1  High-speed Counter Function

Precautions

■Count direction switch during measurement

The rotational speed measurement mode calculates rotational speed based on current value difference of high-speed 
counters in the measuring unit time. You should therefore note that the input number of pulses may differ from the 
measurement value when count direction of a high-speed counter is switched within the same measuring unit time.

■Operation when counting in the minus direction

Rotational speed can also be measured when pulses are input in the direction whereby current value of high-speed counter is 
reduced.

■Operation at overflow of high-speed counter current value

Rotational speed measurement can continue even when current value of high-speed counter overflows during measurement.

■Relationship with the SPD instruction

Measurement time specified by operand of the SPD instruction is written in the special register for measuring unit time used 
by the rotational speed measurement function. Measurement results of the SPD instruction are also stored in the special 
register of measurement results.
If rotational speed measurement has already been started by the HIOEN instruction, the SPD instruction cannot be used for 
the same channel.
Inversely, if pulse density is currently being measured by the SPD instruction, rotational speed measurement cannot be 
started for the same channel.

■Other precautions

There are common precautions when using high-speed counters. For details, refer to Page 163 Precautions when using 
high-speed counters.