Based on investigating the theory of the model of the synchronous motor and vector control, this thesis designed the measuring device for detecting current crossing zero, the commutating logic circuit without circumfluence, the digital pulse flip-flop circuit.

The wire control circuit is composed by pulse trigger circuit,voltage of armature feedback circuit and chopped wave circuit.

The detail analyses are given of the electric circuit principle in respects such as magnetic control sputter, trigger pulse, self adaptive regulator and the current cut off accompanied with negative feedback.

In accordance with the change of voltage phase on the positive pole of thyristor, this method, which the accurate trigger pulse outputs at the appropriate moment,is called the synchronous or locating phase.

This paper supplied a practical analysis method for us on judging the open-close situation of a thyristor(SCR)under a trigger pulse after analysing a practical pulse,measuring,calculating some important parameters and completing a commision to a control system successfully.

The triggering pulse of thynstor can be controlledprecisely by the CAM locked function and the inner clockfunction or timer T2 which are extended in 80C 196KCmicrocomputer． This controlling method is simple andpractical． Also， the corresponding program realizing thisfunction is resented

The efferent circuit of digital trigger impulse which is made up MCS-51 serial single chips can easily export many kinds of signals.