Electric welder output control device

Claim 1

An output control device for an electric welder, comprising (a) an adder-subtractor circuit comprising a differential type operational amplifier and having first, second and third input terminals connected to said amplifier, and an output terminal for providing an output signal S, (b) first signal generating means coupled to said first input terminal for applying thereto a signal S 1 indicating a desired output of an electric welder, (c) second signal generating means coupled to said second input terminal for continuously applying thereto a signal S 0 for setting the open-loop initial transient output of said electric welder to approximate the desired steady state operating output of said welder, (d) controller means connected to receive the output voltage S of said adder-subtractor circuit so as to control the output of said electric welder, (e) means for coupling said electric welder to said output control device, (f) means associated with said welder to provide an output signal S 2 corresponding to the actual output of said welder which is to be controlled by said device, (g) feedback means connected to feed back the signal S 2 from an output terminal of said electric welder to said third input terminal, the output S of said adder-subtractor circuit being so selected as to be S = aS 0 + b(S 1 - S 2 ), where a is the ratio of the output S of said adder-subtractor circuit to the input signal S 0 in the absence of other input signals to the adder-subtractor circuit which is applied to said second input terminal and is less than a level at which said operational amplifier is saturated and b is a ratio of said output S to the input signals S 1 and S 2 in the absence of other input singals to the adder-subtractor circuit applied to said first and third input terminals respectively, whereby the closed-loop steadystate output of said electric welder may be controlled in response to said output S of said adder-subtractor circuit and (h) switching means for initially precluding closed-loop operation of said welder and subsequently enabling said feedback means by said signals S 1 and S 2 to said first and third input terminals respectively, only when a welding arc is struck, said signal S 0 continuing to be applied to said second input terminal after the arc is struck.