For the design of AC spot welder control system, on the one hand, we should consider meeting the control requirements of AC spot welder, on the other hand, we should consider the safety of AC spot welder control system to prevent equipment damage or personal injury caused by misoperation or other accidents.
（1）After the AC spot welder power supply and controller power supply, the system is automatically reset, each control parameter is initialized, the cylinder moves to the initial position, the electrode is high, each operating condition is detected, the equipment system is judged to be operating normally, and the control system displays abnormal warning (the control system displays abnormal information through the man-machine interface).
（2）The welding program of the AC spot welder can only run when both start buttons are pressed with both hands; only one start button cannot start the welding program. This avoids pressing the start button incorrectly and damaging the workpiece or equipment, or even personal injury. As long as the program does not enter the welding cycle, release one or two buttons to stop operating the welding program, the welding gun, but if the program enters the welding cycle, you should ensure that the welding goes smoothly, even if you release the start button can not stop the welding, ensure that the welding process to maintain a certain pressure, if the discharge process pressure is not enough, the conductive block and the top plate contact is poor, it is likely to damage the conductive block and top plate.
（3）After the electrode is lowered, the travel block releases the travel switch SW2 to generate an analog pressure signal, open the pressure switch and input the pressure signal I0.4. If the fault reset and emergency stop switch are not pressed, the SCR temperature is normal and the start button is not released, the welding program of the AC spot welder will be entered. First is the pre-pressure time, then the pressurization time, preheating time, welding time, maintenance time and end time. After the welding of the AC spot welder is finished, the electrode rises automatically. The second welding can only be done after the start button is released and the start button is pressed again.
（4） After the failure of AC spot welder, in order to restore the machine to normal operation, press the reset button, at which time the PLC initializes the control parameters in the control program, such as each status marker bit, timer, etc., and raises the electrode to the high position. After resetting, press the start button to start the welding program again.
（5）If there is an abnormality in the welding process of AC spot welder, you can press the emergency stop switch to prevent further welding (stop discharging when discharging), the electrode rises and loosen the workpiece.