Both ends of armature voltage of DC motor are used as feedback terminal. The Siemens $7-200 PLC is used as controller. The PID loop control instruction is used to make calculation. The PWM wave is output and the DC motor speed regulation is implemented.%以直流电机电枢两端电压作为反馈，采用西门子S7-200PLC作为控制器，利用其PID回路控制指令进行计算，然后输出PWM波，达到对直流电机转速进行调节的目的。
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