| 摘要 |
<p>1528395 Automatic control of welding STK GES FœR SCHWEISSTECHNISCHE KONSTRUKTIONEN mbH 27 Nov 1975 [28 Nov 1974 8 Oct 1975] 48880/75 Heading G3R [Also in Division H2] In an arc welding apparatus in which power is supplied to the welding electrode via a three phase transformer 10 and thyristors SCR1-SCR3, a circuit for controlling the firing points of the thyristors enables regulation of the welding current or voltage. The potential at the welding electrode is applied via trimming resistors R5, R6 to a potentiometer R4, the setting of which determines the firing point of the thyristors and therefore also the power supplied to the welding electrode. Three control circuits, each including a transistor T1, a uni-junction transistor T2 and a trigger transformer TR are supplied with D.C. from respective bridge rectifiers GL connected to the secondary windings of a three phase control transformer (not shown). The setting of the potentiometer R4 controls the conduction of the transistor T1 which controls the rate of charging of a capacitor C. When the capacitor voltage is sufficient to break-down the transistor T2, a firing pulse is supplied by the transformer TR to the thyristor. If the welding voltage increases, the conduction of the transistor T1 is increased and the potential at point P is reduced. The capacitor C charges more slowly thereby retarding the instant in the half cycle that the transistor T2 beaks down. The thyristors SCR1-SCR3 are consequently fired later in the half cycles to reduce the voltage. The circuit may be modified to regulate the welding current by using transducers, current transformers or opto-electrical couplers.</p> |
