1 .IGBT module and Inverting technologies of First generation been used; 2 .Simple structure and light weight and easy for maintenance; 3. Simple to operate, A few minutes is enough to learn it; 4. Simple to install, Installation can be done by unprofessional person very easily; 5 .Advantages of the model with timer: the power and the operating time of the heating period and the retain period can be preset respectively, to realize a simple heating curve, this model is suggested to use for batch production to improve the repeatability; 6 .The separated models are designed to fit the dirty surrounding of some cases