Patent GB-591330-A (GB)
Title: Improvements in or relating to electric control systems
IPC: B23K11/24
Filed: 1945-05-25
Abstract: 591,330. Control systems for consumption apparatus. BUDD MANUFACTURING CO., E. G. May 25, 1945, No. 13137. Convention date, April 5, 1944. [Class 38 (iv)] In an electrical power circuit, subject to voltage variations, a circuit for fixing a percentage of the voltage of the power circuit and adapted to be connected thereto also includes means operative at a change in the power circuit voltage to the fixed percentage voltage, to actuate a control circuit to open the said power circuit. In the arrangement of Fig. 1, adapted to be connected to a power circuit at terminals 10, 11, closure of the main switch 14 applies the power circuit voltage across a resistor 15, the negative end of which is connected to the screen grid 21 of a gas-filled tetrode valve 18 and whereby an adjustable percentage of this voltage is applied by means of a slider 22 to the screen grid of a similar valve 19. Switches 35 and 53 which are ganged with switch 14, close and open respectively with the closure of switch 14 to complete, respectively, circuits for the relays 26, 28 from a D.C. source 25, 34 and to effect the discharge of a condenser 47 previously charged through a potential divider circuit 42 and resistor 46 from another D.C. source 40, 41. Discharge of the condenser 47 reduces the bias on grid 52, of a triode valve 49, which then becomes conducting to increase the potential on control grids 38, 39 of valves 18, 19 until valve 19 strikes to effect the energization of relay 28 to open contacts 32, 33 and terminate discharge of condenser 47. If the power circuit voltage diminishes by a percentage determined by the setting of slider 22 of resistor 15, screen grid 20 and control grid 38 of valve 18 attain the striking point at which valve 19 became conducting, thereby to energize relay 26 to energize a control circuit, connected to terminals 12, 13, for opening the power circuit. In the arrangement of Fig. 2 for a resistance spot-welding circuit, modifications of the circuit of Fig. 1, include the provision of a vacuum triode valve 103 and resistor 107 in the discharge circuit of a condenser 4, which is charged-prior to the closure of a welding switch and the discharge of which raises the potential of valve 97 to cause valve 89 to strike, whereby to increase bias on the grid of valve 103 beyond the cut-off point and terminate the condenser discharge. When valve 88 becomes conducting, the voltage drop across resistor 93 effects energization of a control circuit (not shown) to open the welding circuit. In a modification, Fig. 3, gas-filled tetrodes 123, 125 are adapted to operate directly from an A.C. source 171 instead of D.C. as in the arrangements of Figs. 1 and 2. A combination of non-linear and linear resistances 126, 127 ensures the variation of the percentage voltage, if desired, inversely as the increase of total voltage between 128 and 129. Prior to the closing and opening respectively of the ganged switches 174 and 173, adjustment of phase displacement between the A.C. source 171 and the power circuit at terminals 115, is effected by means of phaseshifting elements 165 and by reference to the meter 138. Also condenser 149 is charged from a D.C. source 176 and on the opening of switch 173 discharges through the valve 151 and resistance 152 to cause the valve 125 to strike, thereby energizing resistor 181 from an anode transformer 135, the primary of which is serially connected with that of a grid transformer 155. Subsequent diminution of voltage across resistor 127, 126 effects the striking of valve 123 and a voltage drop across resistor 136 which is utilized to actuate a control circuit to open the power circuit supplying terminals 115. Minor modifications of the circuits may be made to effect their actuation in dependence upon a voltage rise in the power circuit.