Abstract: System for protection against remote access to digital equipment (1) emitting stray electromagnetic radiation (2) and operating with digital signals under clock control and being based on the representation of a given set of characters, comprising means (18, 19) for emitting protective electromagnetic radiation covering the frequency spectrum of said stray radiation. A store (14) for a character set comprises at least some of the characters in said given set of characters, and means (13) are included for selecting characters in random order from the store (14). The selected characters are applied to drive means (15, 16, 18) which are adapted to generate digital signals corresponding to the selected characters and modulated in a manner corresponding to the digital signals of the equipment (1) so as to be of substantially the same nature as these.

Abstract: A method and inlet control system for controlling a gas flow sample to an evacuated chamber such as found in a mass spectrometer, is disclosed. The system utilizes a short inlet passage having an effective opening determined by a tapered diamond or steel tip needle adjacent to the inlet passage. The needle is positionally adjusted with respect to the inlet passage by being mounted on a piezoelectric crystal which is flexed by coupling thereto an electric potential derived by sensing the ions at the ionization chamber of a mass spectrometer, for example, and developing therefrom an electric signal indicative of the total pressure within the ionization chamber. The signal coupled to the piezoelectric crystal is preferably a pulse-width modulated signal with the needle maintaining the inlet passage closed except during the time that the piezoelectric crystal is flexed due to a received pulse.