GB609654A - Improvements in or relating to time switches - Google Patents

Abstract

609,654. Mercury switches. SVENSKA LASMUTTER AKTIEBOLAGET. March 19, 1946, No. 8562. Convention date, April 4, 1945. [Class 38 (v)] A thermally-operated switch in which two contacts are bridged by mercury when a heater is energized and opened automatically after a predetermined time comprises as shown in Fig. 1 a tube which may be of V-shape, having two compartments 1, 2 filled with gas and connected by a constricted passage 3 of which the width is greater than the height. When mounting the switch the tube is laid in a horizontal plane, whereby the mercury leaves a portion of the passage 3 free so that the mercury is distributed uniformly in the two compartments and the gas pressure is equalised. Dipping into the mercury are two contacts 4, 11, the latter being connected to a heating wire 9 having an external connection 10. Heat from the wire 9 may be absorbed in a body 12 having a large heat capacity, whereby the cooling period may be extended. An insulating cup 6 is situated in the compartment 2 and contains mercury 7 in contact with a terminal 5. When the wire 9 is energised the expanding gas in compartment 1 forces the mercury into compartment 2 completing the circuit between the terminals 4, 5 and breaking contact between 4 and 11. By keeping the terminal 10 in contact with a source of current the mercury makes and breaks contact between the terminals 4, 5 at regular intervals. Fig. 3 shows a modification in which a straight tube is divided by a vertical partition 18 leaving a passage 3 at the bottom of greater width than height. The Specification as open to inspection under Sect. 91 describes a modification of the construction shown in Fig. 1 in which the terminal 5 dips into the mercury at the top of cup 6, a bead threaded on the terminal wire resting on the top of the mercury to form an arcpreventing means. A circuit is also described for illuminating a number of lamps on a staircase, the lamps being automatically switchedoff after a predetermined time. Fig. 7 (Cancelled) shows an arrangement for lighting a lamp 19 for a predetermined time after a button 22 has been pressed to close the circuit through the heater 9 and lamp 19. Additional heaters 28, 29 make contact with the mercury and are connected to a potentiometer 32 in series with the supply mains. This subjectmatter does not appear in the Specification as accepted.