The control of this series of welding machine adopts PID automatic thermostatic control with high control accuracy and low temperature fluctuation; speed control adopts PWM automatic voltage and speed regulation circuit, driven by DC servo motor, with great output torque and the operating is stable. It can maintain a constant speed on the condition of creeping, vertical creeping and variable road load. Also this series of welding machine is stable in performance despite of external temperature and voltage variation.  http://www.china-buttwelder.com/