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16-mm film: 8-mmfilm:
4000 V
8000
(8) (8')
For example: With a maximum film velocity, Vm*x = 70 ft/sec (Vmax = 2800 frames/sec for a 16-mm film), the average film velocity is approximately 56 ft/ sec or 2240 frames/sec, which means a total running time of 1.78 sec.
What is the average velocity of a machine part, v*, when its travel over a known distance of s inches corresponds to N frames on the film?
First, the corresponding time t, in ms, has to be determined according to equations (1) and (5). Then the average velocity is:
V* = 1000 • ; in./sec. (9)
or
83.33 • ft/sec. (9')
For example: With s = 4.8 in., and t = 25 ms, the average velocity is v* = 16 ft/sec.
Basic Tasks for Precalculation and Formulae Used
This second group of tasks comprises calculations which must be made prior
FILM VELOCITY, V, IN FRAMES/SEC
IN FEET I -USEFUL RANGE OF FILM
Fig. 2. Acceleration characteristic of film run.
to taking a picture in order to determine optimum operating conditions for the camera.
1. Time to Be Recorded
What is the time of a burst of N' shots, T', when fired with a cyclic rate of n rpm?
T' =
60 • N'
sec.
(10)
For example: A burst of 25 shots, fired at a cyclic rate of 1200 rpm, lasts 1.25 sec. Since the initial run of the camera does not give sharp pictures due to the low film velocity in the beginning (see Fig. 2), the burst and its recording is started with a certain delay after the beginning of film run by means of an electronic timing device. Assuming that a delay of 0.50 sec is necessary, the total running time of the film, T, has to be at least 1.75 sec in order to cover the whole burst. Therefore, the time to be recorded, T', prescribes a lower limit for the total running time, T, or, in other words, an upper limit for the maximum film velocity, Vmax. To select the right maximum film velocity and corresponding voltage, the acceleration characteristic of the camera and some additional data must be given.
2. Minimum Film Velocity
What is the minimum film velocity permissible for sharp pictures, vmm or
Vmin?
The image of a moving gun part on the film also moves during exposure time of the corresponding frame and brings about a blurred picture (see Fig. 3); therefore, the image travel per frame must be less than a certain limit, when sharp pictures are desired. The factors determining the image travel are:
Maximum velocity of machine part, v*: The faster the machine part is moving, the greater will be the image travel during exposure time. Here, only the projection of the velocity onto a plane
Karl W. Maier: Slide jKule for High-Speed Data
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