Abstract: A control system for resistance welders of the type in which welding current is supplied to a workpiece through a transformer. The system assures weld quality by monitoring the change in resistance across the weld during the welding operation without the need for auxillary leads or separate sensing transducers at or near the workpiece and automatically terminates the welding current when a quality weld is made as determined by resistivity characteristics of the weld. The system monitors discrete changes in the characteristics of the current in the primary of the welding transformer which occur as a result of changes in weld resistance. The system compares the monitored current characteristics of the welding current with a plurality of parameters indicative of a quality weld and terminates the welding current when a selected number of monitored characteristics are within selected parameters.

Abstract: An automatic voltage compensation control for a microprocessor controlled resistance welder system includes a digital voltmeter for measuring the line voltage cycle by cycle and associated circuitry to compensate the welding current in response to the measured line voltage in a manner which tends to hold the welding current constant and independent of line voltage variations. The digital voltmeter consists of a voltage-to-frequency converter coupled to a counter. The output of the voltage-to-frequency converter which is proportional to the line voltage is accumulated for the period of one cycle of the line frequency. This produces in the counter at the end of each measurement interval, a number of counts proportional to the average line voltage. The microprocessor using the count obtained adjusts the welding current by altering the timing of the firing points of the SCR contactors used to control the welding current.

Abstract: A digital welder control system for controlling a portable gun welder of the type used in the automotive industry on an assembly line. An 8 bit microprocessor is the main control element of the system. The known cycle time of the microprocessor is used to generate a real time delay which in turn is used to generate a digital phase shift heat control. RAM locations in the microprocessor are used to store medium constants of the welding sequence which were previously stored, in prior art controls, in the position of tap switches or thumbwheel switches. The controller provides diagnostics for six common problems often encountered by welder control systems such as override timeout, half cycling, transformer temperature rises, a low water flow, a shorted SCR, and a change in the heat settings. The controller also provides a maintenance interval counter and compensator control having a four-step stepper.