HW-7_solutions0

HW-7_solutions0 - 1 min / 000 , 18 sec / = sec / 600 , 3...

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12.12 Consider measuring a rotational speed usi ng a stroboscope. The rotational speed is higher than the flash rate of the stroboscope. The stroboscope is observed to synchronize at 10,000, 18,000, and 22,000 flashes per second. Determine the rotational speed. ω 1 = max achievable synchronization speed ω N = lowest synchronization speed N = number of synchronization speeds ( ) N N N ωω ω - - = 1 1 1 ( ) 000 , 10 000 , 22 1 3 000 , 10 000 , 22 - - × × = sec / 667 , 36 rev = (seconds is likely a typo, and would be much more realistic as minutes) A magnetic pickup is used to detect the shaft speed of an experimental high speed compressor. A gear with 12 teeth is used to excite the sensor. If the shaft is turning at 18,000 rpm, how many positive pulses will be created per second? By what number must the number of counts in a second be multiplied to produce a result in rpm? teeth of number rev pulses × × = sec 60 min 1 min / sec / teeth rev pulses 12 sec 60 min
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Unformatted text preview: 1 min / 000 , 18 sec / = sec / 600 , 3 pulses By what number must the number of counts in a second be multiplied to produce a result in rpm? min 1 sec 60 12 sec 1 = pulses rev pulse conversion 5 = conversion A strobe based tachometer is shining at a disk rotating at 2400 rpm. The disk has one circumferential mark for speed measurements. a. How many marks will you see if the strobe flashing rate is 1200 per minute? b. Repeat part (a) for flashing rates of 800, 2400, 4800, and 7200 flashes / min. Rotation Rate (rpm) Flash Rate (fpm) Rotations per Flash Marks Seen 2400 800 2400 / 800 = 3 1 2400 1200 2400 / 1200 = 2 1 2400 2400 2400 / 2400 = 1 1 2400 4800 2400 / 4800 = 1/2 2 2400 7200 2400 / 7200 = 1/3 3 Disk Rotation Rates Flash Rates (fpm) 2400 (rpm) 2400 (rpm) 2400 (rpm) 2400 (rpm) 2400 (rpm) 800 1200 2400 4800 7200...
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HW-7_solutions0 - 1 min / 000 , 18 sec / = sec / 600 , 3...

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