To obtain a Pirani gauge acting with rapid response as well as high sensitivity, the author constructed a Pirani gauge, the filament of which was automatically kept at a constant temperature by means of phototube and galvanometer system.
The method is this. The filament constitutes a Wheatstone bridge with the other three resistors, and is heated by the plate current of a vacuum tube. The deflection of a reflecting galvanometer caused by the change of the filament temperature, is detected by two phototubes, which are placed to receive the light reflected by the mirror of the galvanometer and to act differentially. The difference of the photoelectric currents cf the two tubes is sent to the grid impedance of the vacuum tube and controls the heating current. When the gas pressure in the gauge increases, the filament temperature drops, which causes the increase of the heating current, consequently the filament temperature is prevented from dropping and kept nearly constant. The pressure is known from the heating current. In order to stabilize the action of the system, it is effective to adjust the damping resistance of the galvanometer. The time of response of the pirani gauge thus constructed was about 5 seconds, which is about one-10th of that of the Pirani gauge used in usual method. It could measure the pressure from 1 × 10
-5 to 5 ×10
-2 mmHg. The relation between the square of the heating current and the pressure was nearly linear.
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