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a timing mark would appear motionless for integer multiples of the actual rotational speed and for
integral submultiples, as illustrated in Figure 12.18b–e.
The synchronization of images at flashing rates other than the actual speed requires some
practical approaches to ensuring the accurate determination of speed. Spurious images can easily
result for symmetrical objects, and some asymmetric marking is necessary to prevent misinterpretation of stroboscopic data. To distinguish the actual speed from a submultiple, the flashing
Figure 12.17 Stroboscope. (Courtesy of Mill
Devices Co., a division of A. B. Carter Inc.)
(a)
( b)
( c)
( d)
( e)
1800 fpm
1200 fpm
900 fpm
720 fpm
600 fpm
3600/n fpm
3600 rpm
3600 rpm
3600 rpm
3600 fpm
3600 rpm
3600 rpm
7200 fpm
2400 fpm
1440 fpm
10,800 fpm
5400 fpm
2700 fpm
2160 fpm
14,400 fpm
4800 fpm
2880 fpm
Figure 12.18 Images resulting from harmonic and subharmonic flashing rates for stroboscopic angular speed
measurement. (Courtesy of Mill Devices Co., a division of A.B. Carter Inc.)
12.2 Sensors 523