GB1412016A - Electrical control circuits - Google Patents

Abstract

1412016 Automatic control of welders MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 29 Nov 1972 [30 Nov 1971 (2)] 55040/72 Heading G3R The output of an electric welder is controlled by an operational amplifier having input signals S 1 , S 2 and So corresponding respectively to a desired welder output, actual welder output and a signal that produces the desired welder output in the absence of any other signals to the amplifier. The operational amplifier calculates a signal S 1 where S = aS 0 + b(S 1 -S 2 ), that is used to control the welder output. As shown, the signal S 2 , dependent upon the welder current, is fed back to the adder-subtractor circuit 13 (including one or more operational amplifiers 14) via a smoothing circuit 19, for example a low pass filter. The output S of circuit 13 passes through a time delay 18 (e.g. a servomotor with a long time constant) to welder control means 15 which could be a variable impedance or saturable reactor. Under stable running conditions the welder output S 2 is maintained at the desired value S 1 by the signal So. Upon starting or under non-welding conditions with S 2 = 0, the welder output is maintained at approximately the desired level by signal S o until the feedback signal S 2 is produced and stable running conditions are assumed. Smoothing circuit 19 and time delay 18 can be omitted, and signals S 1 and So obtained from a common source rather than, as shown, from separate signal generators 11, 12.