Mitsubishi Electric MELSEC iQ-F FX5 User Manual page 133

Pulse density
Pulse density is stored in the special register for each channel.
For details concerning specials registers for high-speed counters, refer to Page 155 Special registers list.
Precautions
■Count direction switch during measurement
The pulse density measurement mode calculates pulse density based on difference in measuring unit time of the current
value of high-speed counters. 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.
Ex.
When pulse density is measured, 14 pulses are input within measuring unit time, but the current value of the high-speed
counter remains "0", as shown in the following figure. As a result, pulse density is "0" for this measuring unit time.
Measurement
intervals
Direction
switching
Count input
Current value
10
9
8
7
6
5
4
3
2
1
0
■Operation when counting in the minus direction
Pulse density 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
Pulse density measurement can continue even when current value of high-speed counter overflows during measurement.
■Relationship with the SPD/DSPD instruction
If pulse density measurement has already been started by the HIOEN/DHIOEN instruction, the SPD/DSPD instruction cannot
be used for the same channel.
If pulse density is currently being measured by the SPD/DSPD instruction, pulse density measurement cannot be started for
the same channel.
For details on the SPD/DSPD instruction, refer to MELSEC iQ-F FX5 Programming Manual (Instructions, Standard
Functions/Function Blocks).
■Other precautions
There are common precautions when using high-speed counters. For details, refer to Page 176 Precautions when using
high-speed counters.
19 HIGH-SPEED INPUT/OUTPUT FUNCTION
19.1 High-speed Counter Function
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