Mitsubishi Electric MELSEC-L02SCPU User Manual page 229

(1) Required settings
(a) Rotation speed movement averaging processing count
The rotation speed measurement function performs moving average processing to reduce the unevenness
among the measured rotation speed. The setting range is 1 to 100. When "1" is set, the processing is not
performed.
(b) Rotation speed measurement unit time setting
Select a pulse measurement unit time to calculate rotation speeds from 0.01s, 0.1s, and 1s. The rotation
speeds are calculated using the following formula.
Rotation speed (r/min)
When the count per time unit is 0, the rotation speed becomes 0. When counting down, the frequency becomes
a negative value.
(c) Number of pulses per rotation (pulse)
Set the number of pulses per rotation when a rotation speed is measured.
• Setting range 1 to 200000 (pulse)
(2) Relationship between rotation speed measurement unit time and rotation
speed
Rotation speed is calculated from the count value per time unit ( Page 227, Section 8.6 (1) (b)). The following
table shows the unit of pulse speed for each rotation speed measurement unit time setting when the rotation
speed movement averaging processing count is set to "1". Select an appropriate unit time according to the time
and rotation speed to be measured.
Rotation speed measurement unit time
(3) Rotation speed error
Rotation speed error (maximum) can be calculated using the following formula.
Error (maximum) = Actual rotation speed
(r/min) (r/min)
Setting larger values for the following items helps reduce error and unevenness among the measured rotation
speeds.
• Rotation speed measurement unit time
• Rotation speed movement averaging processing count
• Number of pulses per rotation (pulse)
=
Rotation speed measurement unit time setting (S)
1s
0.1s
0.01s
60(ppm)
+
rotation speed
1000000
measurement unit time (s)
CHAPTER 8 HIGH-SPEED COUNTER FUNCTION
60 count value per unit time
number of pulses per revolution(pulse)
Unit of pulse speed
1 pulse/s
10 pulse/s
100 pulse/s
60
number of rotation speed
moving averages
8
number of pulses per
revolution (pulse)
227