GB673893A - Improvements in control arrangements incorporating contact-making indicating instruments - Google Patents

Abstract

673,893. Contact-making ammeters and voltmeters. METROPOLITAN - VICKERS ELECTRICAL CO., Ltd. March 24, 1950 [June 20, 1949], No. 16368/49. Class 37. [Also in Groups XIX and XL (c)] When the predetermined value or particular reading is attained the instrument contacts IC close (for example the instrument pointer meets a stationary contact) to apply striking potential to the grid of a cold cathode discharge tube CCT, Fig. 1. The resulting ionization and anode current operates an alarm or other device either directly or through a relay R. The potentiometer P across the A.C. or D.C. supply S has a mid-point tapping for connection to the grid through IC. In Fig. 3 (not shown), the instrument contacts IC are in the upper half of the potentiometer. The potentiometer P may be omitted and the grid of CCT connected through a resistance to the anode connection to the supply S. If the instrument has " high " and " low " contacts IC1 and IC2, Fig. 2, two cold cathode discharge tubes CCT1, CCT2 are employed with a common potentiometer P across the supply tapped as in Fig. 1. Closure of relay contacts R1, R2 may initiate the operation of control apparatus to reinstate conditions to take the instrument pointer away from the " high " or low " contacts.