Patent GB-420522-A (GB)
Title: Apparatus for detecting the movements of objects
IPC: G08B13/26
Filed: 1933-04-29
Abstract: 420,522. Discharge apparatus; valve circuits. SPANNER, H. J., 6, Maubachstrasse, Kladow, and KRAMOLIN, L. L. DE, 53, Nassauischestrasse, Wilmersdorf, both in Berlin. April 29, 1933, No. 12550. Convention date, April 29, 1932. [Classes 39 (i) and 40 (v)] Relates to apparatus for detecting the movement of objects or persons, comprising a discharge tube 1 energized with a voltage sufficient normally to initiate a discharge and an electrode 5 at such a distance from the tube 1 and so energized, as by the transformer 11, that its electrostatic field just suppresses the discharge by inducing a charge on the wall 2 of the tube 1, disturbances of the field due to the approach of an object, starting the discharge and operating a lamp or relay &c. 6. The tube 1 is now so dimensioned that the wall 2 is spaced from the medial discharge path by a distance less than the distance between the cathode 12 and the anode 15 and not less than one tenth of this distance. A sensitive control is thus obtained without neutralization of the wall charge by the ions of the discharge. The wall 2 may be thinly coated internally as by sputtering a " getter " or spraying metal from the cathode or may be coated externally or both internally and externally. To adjust the timeconstant of the circuit of the coating to agree with the greatest speed of movement of objects, a leak resistance chosen according to the capacity of the coating is inserted between the coating and the cathode 12. This resistance may comprise the conductive glass part 4 of the tube 1 and sputtered films on the glass near the electrode leads causing variations in this resistance are avoided by mica screens 3. The coating may be replaced by a ring around the tube 1 and the ring or coating may be connected to a wire extending parallel to the conductor 5. The cathode 12 may be indirectly heated and the tube 1 may contain argon at 6-10 mms. pressure. The Specification as open to inspection under Sect. 91 comprises also the following modifications. The wall of the tube is spaced from the medial discharge path by a distance not more than twice the anode-cathode distance. The tube 1 has a cold cathode activated with alkali or alkaline earth metal and is filled with rare gas or metal vapour such as mercury or mixtures. The tube 1 is of the vacuum type. The tube 1 is resistance coupled to a second tube and a single envelope may contain both tubes which may then have a common gas space. The tube 1 has a control electrode separated from the main electrodes by a distance less than the mean free path of ions. If the tube 1 is very narrow, the charge on the wall is separated from the discharge by a chimney. The discharge is controlled by a grid covered with insulation instead of by a wall charge. The wall has an inwardly extending groove which may contain an external electrode. A pulsating supply is used or the tube 1 generates critical oscillations the frequency of which varies with the movements of objects. The distance of objects from the tube may be measured and movements thereof traced by the discharge current. The relay 6 has a large condenser across its coils or comprises a glowing tungsten filament operating a contact in vacuo. The voltage of the electrode 5 is varied by a potentiometer. The connection to the electrode 5 contains a high or variable resistance or a variable condenser. This subject-matter does not appear in the Specification as accepted.