Electronic safety device, esp. for resistance welding machines - where control circuit precludes excessive welding times, used esp. when welding motor car bodies

摘要

The device is located between a low voltage circuit (a), and a power circuit (b) which provides the machine with a.c. during a period (T) through switches formed by ignitrons, thyristors or triacs. The device includes two optoelectronic couplers (OEC), of which the diodes are connected to the terminals of circuit (b) and to the switches. The transistors of the OEC are in circuit (a). In circuit (a) is a first logic circuit (a1) providing a signal which remains unchanged during the entire welding operation; and a second logic circuit (a2) with an output signal changing with each fraction of period (T). The two signals are fed to a display and to a deductor or subtractor which switches off the power (b) if the welding time is exceeded. Control of welding parameters in mass prodn. resistance or spot welding.