変調電極付きBayard-Alpert型電離真空計の負電圧変調特性

概要

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One of the disadvantages of the modulation technique by a modulated Bayard-Alpert type ionization gauge is the pressure variation with long time constant observed after the switching of modulator potential (Vm). This phenomenon is supposed to be caused by desorption and adsorption of molecules on the surface of modulator due to the change of the electron current to the modulator when Vm is kept higher than the filament potential (Vf). Therefore, the pressure variation is supposed to be much reduced if Vm is always kept lower than Vf. In order to check the possibility to use the modulation technique maintaining Vm lower than Vf for pressure measurements, the modulation factor and the sensitivity of the modulation technique were measured over wide ranges of Vm, pressure and electron current of the gauge. As a suitable mode of modulation, the change of Vm from OV to-150V is proposed. The mode has the modulation factor of ca. 0.4 and the sensitivity of ca. 5. The mode was applied to measured the pressure of oxygen.