EXPLOSIONS MAKE TUBES SENSITIVE
Photo Electric Cells
Sunday, August 9, 1931
One of the delicate operations in the process of making photo-electric tubes is the explosion of several little caesium pills within the tube and Dr. E. D. Wilson, research engineer of the Westinghouse Electric and Manufacturing Company, explains that it is this detail which makes the tubes sensitive to light.
Equipment required for the creation of this interesting device includes a liquid air bottle, a mercury vacuum gauge, two mercury diffusion pumps, and electric heater, an oil pump and its motor, and electric over, a 100-watt lamp, together with necessary auxiliary equipment and a seasoning table.
The gauge, shown at the left, determines the proper degree of vacuum in the tube. The heater boils the mercury in the pumps, seen between the gauge and the oven, and the rising vapor sweeps the gases out of the tube through glass tubes to the oil pump where they are dispelled by motor driven equipment.
The oven is pulled down over the tube and bakes gaseous impurities out of the glass bulb and the metal part inside. These are carried off by the pumps until a very high vacuum is produced.
Meantime the liquid air bottle, slipped over the pump tubing, freezes out the mercury vapor and harmful impurities.
Heat created by special radio waves causes the caesium pills within the tube to explode into vapor which condenses on the inside surfaces of the tube.
Oven heat then distills this deposit over to the metal part and makes it light sensitive.
That is, it will pass electric current when illuminated by the 100-watt light in Wilson's hand.
This current is metered and, when adequate, the photo-electric tube
is ready for 100 continuous hours of seasoning, followed by actual
industrial use as a light relay in traffic light controls or in any
one of numerous industrial and practical applications.
Original Caption by Science Service