GB664911A - Improvements in or relating to circuits and relays for gas-filled discharge tubes - Google Patents

Abstract

664,911. Electromagnetic interrupters. PHILIPS ELECTRICAL, Ltd. Jan. 10, 1948. [Jan. 14, 1947] No. 820/48. Class 38 (v). [Also in Group XXXV] A vibratory electro-magnetic switch for starting an A.C. or D.C. operated discharge lamp (see Group XXXV) and comprising a coil 10, shunted by the switch contacts 6, 7 when energised, is constructed and adapted in the circuit arrangement to provide in the case of D.C. operation a contact period from 3 to 50 milliseconds and more than 35 per cent or even 60 per cent of the vibration period whereas for A.C. operation a vibration period from 0.5 to 1.5 of a cycle and a contact period between 0.2 and 1.0 of a cycle, to afford adequate heating of the lamp electrodes. The magnetic circuit comprises a constant air gap bounded at one end by an apertured yoke 3 to permit the armature 4 secured to a flexible contact carrying strip 5 to pass through. The stop for the moving contact strip 5 preferably constitutes a flexible wire 9 to afford simple adjustment. The electro-magnetic period of contact closure which follows the electromechanical period is preferably arranged to form at least 50 per cent of the total contact period and may be deduced from the expression L/R log e P where L and R are, respectively, the inductance and resistance of the circuit including the coil and closed contacts, and P the ratio of pull-in to release values of the coil currents. To reduce the remanent-magnetic contact period and obtain a suitable release current value shims 13 of non-magnetic material may be included between the core 1 and armature 4. To prevent contact welding the condenser for arc suppression is connected across the contacts through a resistance which may constitute the lamp electrodes.