The fixed frequency sample PWM method is put forward in this paper together with the theoretical analysis about their switch strategy.

It introduces the methods of alternating current sampling for the power parameter of sing chip computer in fer- roalloys furnace.

Test methods for AC sampling equipment by using middleware technique;

Evaluation of uncertainty about indication error of AC sampling apparatus;

AC sampling anti-interference design based on inner A/D of DSP56 F807;

Research on the current sampling precision in the electric quantity gauge;

And the problem of current sampling was stressed in the software.

Considering the discrete sampling character of the digital system,the current sampling point was regulated according to the duty ration for each switching period in order to make better sampling precision.