An instrument that utilizes the principles of radio amplification for inspection purposes is described and the experience that led to its development is recounted. It measures the finish polish on metal pieces by light from a microscopic lamp reflected from the surface upon a photoelectric cell, or amplifying bulb, that responds instantaneously to minute variations of light intensity and is connected in a suitable amplifying circuit to a milliammeter. The elements comprising the instrument are enumerated and the circuit diagram used is explained.
As the instrument provides a method primarily of comparison, a standard value of the light reflected from a surface of the desired finish is established and the finish of parts to be compared is read from deflections of the milliammeter needle above or below this standard.
The purpose of the instrument is to supplant by an accurate mechanical means the uncertain judgment of an inspector who relies upon the physical sense of vision. The uncertainty of inspection by the physical senses presents the most difficult problem of the inspection service and one that is present constantly.
Many experiments with photomicrographs up to 100 magnifications gave inconclusive results but revealed that a high degree of surface polish produces a narrow, sharply defined band of light, whereas a lesser degree of polish produces a wide, diffused band. This led by successive stages to the development of the new instrument, which has been very successful in application. The author and his associates are convinced that this type of instrument will become highly useful for many other purposes and can be used to advantage in other branches of industry than the automotive field.


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