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Number-of-rotations detection cycle
With this equipment, the method which measures wind velocity in the number of rotations of the window cup is adopted. Four slits are prepared for the disk to measure number of rotations. So, the change of ON-OFF occurs eight times when the disk turns in 1.
With this equipment, it is checking that it is in the same state continuously twice. îčThis is for detecting change of each pulse certainly. Since a photointerrupter is used for detection, chattering like a mechanical switch is not generated. However, when an axis rotates at a low speed, change of ON-OFF may be repeated with the edge of a slit. If the number of times of continuation detection is increased, such incorrect detection can be prevented. Moreover, incorrect detection can be prevented even if it lengthens a detection cycle.
The detectable maximum number of rotations in this method is shown below.
If an axis rotates one time, change of ON-OFF will occur 8 times. Two detection is performed to one ON-OFF detection. Therefore, detection with 16 times is done to 1 turn. When a detection time is made into one millisecond, the detection of one rotation takes 16 milliseconds. When it converts into the number of rotations for 1 second, it is 1000/16=62.5 rotations/second. This value is the maximum detectable number of rotations at the time of making a detection interval into 1 millisecond.
The time of the pulse outputted with this equipment seems to be the left figure generally. This is a value when turning a window cup with sufficient vigor by hand.
When it converts into number of rotations, it is 1000/(30*4)=8.3 rotations/second. Even when high-speed, it is about 10 rotations/second.
For above reason, I made the period of the detection 2 milliseconds. This is the cycle which can detect about 30 rotations/second in the maximum.