Nation projector carbons (1935)

National Projector Carbons smooth, firm contact of full area is maintained. Defective1 contact between carbons and holders is a frequent cause of spindling. It is likewise essential that feed rollers on high intensity condenser and high intensity reflector lamps be kept clean and in good condition to insure steady and accurate rotation of the positive carbon, maintain a symmetrical crater, and prevent possibility of jamming. Carbons should always be operated within the recommended current range. If operated at a current lower than that recommended, the efficiency is greatly reduced for reasons that have been explained in detail in preceding chapters. Currents above the recommended range cause spindling, short life and unsteady burning, with very little advantage in the form of increased volume of projection light. Carbons must be kept in proper alignment. Poorly formed craters and lowered efficiency of light production are invariably encountered when the correct alignment of the carbons is not maintained. If the allowance for movement of the carbon holders is insufficient to establish exact alignment, the desired results can usually be obtained by the use of shims. Particular attention should be given to the lateral alignment of the carbons. It is equally important, in attaining full efficiency of light production, that the crater of the positive carbon be kept in the correct position relative to the optical system. Modern lamps are equipped with gauge pins or with means for projecting the arc image on a chart at the side of the lamp housing which indicates the correct location of the positive crater. The feed of the positive carbon should be regulated to maintain the crater as near as possible to this position throughout the burning period. The feed of the negative carbon should also be adjusted to maintain correct and uniform arc length during 92