Abstract: To check the presence of operating vacuum in vacuum switches, high voltage can be applied between the contacts at a given contact spacing and the dielectric strength can be tested. According to the invention, the procedure for vacuum monitoring is that a contact spacing (h) below the nominal stroke of the vacuum switch is selected and that the X-radiation generated at this contact spacing (h) and high voltage (U) in vacuum due to the field electron emission between the contacts by the contact surfaces acting as anode is acquired and evaluated as proof of the presence of operating vacuum inside the switching tube. This method can preferably be applied to encapsulated vacuum switching tubes, in particular to SF.sub.6 -insulated switching facilities.

Abstract: A device for measuring the internal pressure of an operationally built-in vacuum switch which comprises a vacuum switching tube having a switching chamber and switch contacts as well as an associated drive for the contacts. For the measurement of the pressure, a cold-cathode discharge (so-called Penning effect) having crossed electric and magnetic fields is used, wherein the electric field is applied, for instance, between at least one of the switch contacts and a metallic wall of the switching chamber or a condensation shield disposed in the chamber and permanent magnets are used for generating the magnetic field. The permanent magnets are realized in the form of rods and have pole pieces formed such that the pole pieces encircle the switching chamber. A magnetic field is formed which is applied directly in the longitudinal direction to a circumferential section of the cylindrical switching chamber.