【正文】 But the radiation of the network, is introduced and interfered by the reaction of the munication line while municating to PLC. Radiation is interfered with the onthespot equipment assigning and size of electric magnetic field that the equipment produce , especially frequency have something to do with, generally through set up shielding cable and PLC some shielding and high pressure discharge ponent protect.2) Interference from lead wire outside the systemIntroduce through the power and signal line mainly, is usually called and conducted interfering. This kind of interference is relatively serious at the industrial scene of our country.3) Interference from powerPractice has proved , interference introduced because of the power causes situations of PLC control system trouble a lot of, I meet in debugging in some project, is it isolate performance high PLC power to change, the problem is solved .Normal power supply power, PLC of system supply power by the electric wire netting. Because the electric wire netting is widely covered, it will be interfered the voltage of reaction and circuit on the circuit electromagnetically by all space. Change of electric wire netting, enter switch operate wave well up, largescale electric equipment is it park, is it is it move in harmony wave, electric wire netting that device cause short out the attitude is bludgeoned into etc. temporarily to spread direct to pay to get up especially, it is through it is the original since transmission line of electricity last power. PLC power usually adopts and isolates the power, but its organization and manufacturing engineering factor make its isolating unsatisfactory. In fact, because of distributing the existence of the parameter especially distribution capacity, it is impossible to isolate definitely.4) Come from the interference that the signal thread introducesAll kinds of signal transmission lines connected with PLC control sy。s voltage of difference, influence the signal of observing and controlling directly altogether, cause the ponents and parts to be damaged (this is some systematic I/O moulds a main reason of higher spoilage), this kind mould can interfere for direct current, can for exchange also altogether. The difference mould interferes referring to acting on the voltage of interference between the two poles of the signal, coupling reaction change voltage that mould39。 Different according to the wave form, nature of the noise, divided into a lasting noise, accidental noiseless.。 systematic antiinterference ability is the key to concerning the whole system and running reliably. All kinds of PLC used in the automated system, some install concentrated in the control room , some install in production scene and every electrical machinery equipment, they in strong electric circuit and strong electric abominable electromagnetic environment that equipment form mostly. Should improve PLC dependability of control systems, on one hand require PLC manufacturer to improve the antiinterference ability of the equipment。s M. Depenblock proposes the direct torque control technique（DTC） for the first time，The direct torque control technique analyzes the motor mathematical model directly under the stator coordinate system. Uses the stator magnetic field direction detection but not to need the solution lotus root electric current，directly control the electric motor flux linkage and torque, enable the torque to obtain the fast response, in order to obtain the highly effective control performance.Direct torque control technique is another kind of new、high performance alternating frequency conversion velocity modulation technique after vector control technique in the nearly 10 years, this kind of control technique is insensitive to the electrical machinery parameter, not influence by the rotor parameter, easy and feasible, it has the broad development and the application prospect.4) PWM (pulse width modulation) Control TechniqueIn1964, Germany39。s only then just started Embarks from this reality, frequency conversion technology remain have the very big development space, we should plete the promoted application work doggedly.And with the constant development of control technique and control avenue, frequency variation speed controlled has developed the vector controlled frequency variation velocity modulation, by controlling the AC motor inside act for shunt DC motor field coper’s flux, to enhance the permanent torque output scope and static and dynamic character, make the AC motor frequency variation speed controlled system superior to DC motor voltage variation speed controlled system. For simplifying the control system, reducing the fault rate, there has developed a vector controlled frequency variation speed control without speed sensor which based on the vector controlled frequency variation speed control. In some application which have low require , vector controlled frequency variation speed control without speed sensor could pletely pare with the vector controlled frequency variation speed control that have speed sensor. The vector control has the epochmaking significance to the AC current motor velocity modulation.Frequency variation speed control is the best way in the motor speed modulation, it is the perfect gear in the pany’s technical reform and product renewal, it is the essential position in the industrial automatic system, it is the assumption of realizing the automatic of product proceed and management, it is also the precondition in the development of informationization. In our country’s traditional estate, using the DC motor speed control actuation account about 85%~90% in the speed controlled system, but the AC speed controlled system account about 10%~15%. Low efficiency, bad quality, large cost, high fault rate have already been the bottleneck that restrain the development of the pany. So, we must promote the advanced AC frequency variation speed control technique posi