Chapter 9
176
Logic programming – Function blocks
Determine the time between signal changes for the speed limit:
Signal frequency for release = 0.25 Hz × 4 teeth/revolution = 1 Hz
Max. input pattern period = 1/1 Hz × 185°/360° = 514 ms
Time between signal changes = 514 ms + 10 ms = 524 ms
Min. time between signal changes = 530 ms (rounded up to multiples of 10 ms)
Example 2: 1/3 gap 180° phase shift
8 teeth per revolution
Switching tolerances +/–2° teeth 118° to 122° (corresponds to t
low
, t
high
); signal
change 118° to 122° (corresponds to t
1
to t
4
)
Maximum shaft speed = 120 rpm = 2 Hz
Shaft speed for release = 12 rpm = 0.2 Hz
Logic execution time = 16 ms
Check the maximum signal frequency for incremental signals:
Max. signal frequency = 2 Hz × 8 teeth/revolution = 16 Hz
Smallest t
low
= 1/16 Hz × 118°/360° = 20.5 ms
greater than the logic execution time
Smallest t
high
= 1/16 Hz × 238°/360° = 41.3 ms
greater than the logic execution time
Determine the time between signal changes for the speed limit:
Signal frequency for release = 0.2 Hz × 8 teeth/revolution = 1.6 Hz
Max. input pattern period = 1/1.6 Hz × 122°/360° = 212 ms
Time between signal changes = 212 ms + 10 ms = 222 ms
Min. time between signal changes = 230 ms (rounded up to multiples of 10 ms)
Example 3: Zero pulse 10°
1 tooth per revolution
Switching tolerances +/–1° teeth 9° to 11° (corresponds to t
low
, t
high
); signal
change 349° to 351° (corresponds to t
1
to t
4
)
Maximum shaft speed = 300 rpm = 5 Hz
Shaft speed for release = 3 rpm = 0.05 Hz
Logic execution time = 4 ms
Check the maximum signal frequency for incremental signals:
Max. signal frequency = 5 Hz × 1 tooth/revolution = 5 Hz
Smallest t
low
= 1/5 Hz × 9°/360° = 5 ms
greater than the logic execution time
Smallest t
high
= 1/5 Hz × 351°/360° = 195 ms
greater than the logic execution time
Determine the time between signal changes for the speed limit:
Signal frequency for release = 0.05 Hz × 1 tooth/revolution = 0.05 Hz
Max. input pattern period = 1/0.05 Hz × 11°/360° = 611 ms
Time between signal changes = 611 ms + 10 ms = 621 ms
Min. time between signal changes = 630 ms (rounded up to multiples of 10 ms)
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