SUBMULTIPLE SPEED MEASUREMENTS.

2.8.2 SUBMULTIPLE SPEED MEASUREMENTS.

If the Type 1531 Strobotac is set to flash at an integral submultiple

of the fundamental speed of a rotating object, a single image will be ob -

served, just as it will at the fundamental speed. At flashing rates between

these submultiple, multiple images will be observed. Table 2-2, for

example, shows the number of images that will be obtained at various

stroboscope flashing rates (below the fundamental speed) of a device

rotating at exactly 1800 rpm.

Note the numerical relationship between the numerator of the sub-

multiple fraction and the corresponding number of images seen. This

relationship will always hold true, regardless of the speeds involved.

Table 2-2 lists only a few of the more useful submultiple speeds and

corresponding images; many other multiple images are possible (for

example, five images will be seen at 5/7, 5/8, etc.).

Submultiple flashing is necessaryo to observe or measure the speed

of objects moving at rates above 25,000 rpm. Refer to paragraph 2.8.3

for the method of determining the fundamental speed when submultiple

operation is necessary.

Table 2-2

SUBMULTIPLE SPEED/lMAGE RELATIONSHIP

Sumbmultiples of

Fundamental

Number 0f

RPM Dial

Speed (1800 rpm)

images Seen*

Setting

1800

5/6

1500

4/5

1440

3/4

1350

2/3

1200

1080

3/5

900

1/2

720

2/5

600

1/3

l/4

450

360

1/5

300

l/6

*At dial settings above fundamental speed, multiple images

always occur. Refer to Table 4-1.

2.8.3 MEASUREMENT OF SPEEDS ABOVE 25.000 RPM.

Speeds up to about 250,000 rpm can be accurately determined by

calculations based on submultiple measurements. The procedure is as

follows :