GB665294A - Control for electric circuit - Google Patents

Abstract

665,294. Glow discharge indicators. WAYGOOD-OTIS, Ltd. Jan. 21, 1949. [June 5, 1948] No. 1721/49. Addition to 610,407. Class 40 (i). [Also in Groups XVIII and XL (c)] In a control such as is used for operating an electric lift as described in the parent Specification, in which a cold cathode gas-filled valve has a source of current for its anode-cathode circuit and a source of alternating current connected between the anode-cathode circuit and earth the control being manually operable by a person touching it who completes a firing circuit from earth via his body insulating means are provided extending around and projecting beyond the face of the button for protecting it against accidental touching. Fig. 6 shows the electrical connections to two cold cathode valves used as the "up" and "down" controls in a lift control system. A D.C. voltage is applied across lines L1 and L2 which has a value between the sustaining and breakdown voltage for the valves so that a valve once fired will remain conducting even when the person operating the firing circuit has removed his finger from the control button. An A.C. voltage is applied across lines L3, L4 so that when a person touches the insulated front of either button 47 or 62 which are backed by a conductive portion joined to that part of the valve envelope which is adjacent to the anode, a capacitor is formed and a voltage is applied between the envelope and anode of the valve which causes it to fire. The light from the valve when fired is transmitted through a translucent arrow shaped portion of the button, Fig. 2 (not shown) to indicate that the call has been registered. An A.C. supply may be connected across lines L1, L2 instead of a D.C. source in which case the valve fires only whilst the control is touched. Shields 55, 65 associated with each valve are connected to a point in the anode-cathode circuit of each tube so as to prevent the valves from firing by stray capacitive effects to earth: Fig. 4 shows a sectional view of one of the controls. The top 54 of the valve envelope 13 is coated with a transparent conductive material such as that having the Trade Name "Nesa" or a translucent conductive material such as that having the Registered Trade Mark "Aquadag" and is connected via a spring 53 to the conductive portion 47 at the back of the control button 45. The front 46 of the button which is to be touched is formed of an insulating material of high dielectric constant such as phenol formaldehyde and the button is mounted in an arrow shaped surrounding 40 which is made of translucent material such as lucite and which projects round the button to prevent inadvertent operation of the control. The button and its surrounding members extend through the face plate 36 and can be removed in conjunction with the face plate, Fig. 1 (not shown) to give access to the valves. The face plate is normally held in position by spring latches, Fig. 5 (not shown).