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C-R-TuBE APPLICATIONS
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vertical plates, and by expressing its position by means of a potentiometer geared to the phototube on the horizontal axis. This type of presentation has been duplicated by slower methods, such as pen recorders.
In some cases, however, it is desirable to do this very rapidly. For example, if we have a large number of samples, it is necessary, continually, to draw these distribution curves. This may be done readily by means of the following system, which also enablesthe use of a standard sample for comparison: two samples, one the standard and the other under test, are mounted back to back and spun by means of a synchronous motor about the axis of the motor. A phototube and light source are placed at some angle arbitrarily chosen, or at 90 degrees. As the samples are rotated by the motor, the angle at which the phototube alternately views the standard and the sample changes continuously. The phototube output displayed with a synchronous sweep on a cathode-ray tube is then a graph of light reflection as a function of the angle of view. Since the samples are presented alternately, the curves appear simultaneous and superposed to the observer.
Fig. 4 is a typical example of such a recording in which the reflection from a clear sheet of glass is compared with that of a sample treated with glare-reducing material. By means of intensity modulation, using a synchronized multivibrator, 3-degree angle markers have been put on the baseline which was recorded by double exposure. This technique, as mentioned previously, should find wide application in any industry where surface specification is desired. With this type of presentation, changes of reflectance characteristic during a
Fig. 4 — Relative reflection versus angle for clear glass (tall spike) and matte-coated glass. Angle markers on baseline are 3.6 degrees apart.