3-30
The second method is used where the value of A
B becomes progressively smaller. The A reading
is obtained as in the previous example (for the sake of easier computation, suppose that the A reading is
still 4,000 rpm). Then obtain another submultiple reading for B, keeping in mind the number of times a
stationary single image was observed. If a stationary single image was observed seven different times and
the final B reading was 2,000 rpm, the calculation would become as follows:
At speeds lower than the lowest range of the stroboscope, multiple images will be observed. For
example, assume a dial reading of 900 rpm was obtained when two stationary images were observed.
Then dividing the rpm by the number of images will give the unknown shaft speed, as shown below:
