In the PLC control system,the power supply occupies an extremely important position.The power grid interference is serially connected to the PLC control system,and it is coupled in through the power supply of the PLC system(such as CPU power supply,I/O power supply,etc.),the power supply of the transmitter,and the power supply of the instrument with direct electrical connection with the PLC system.
Now,for the power supply of the PLC system,the power supply with better isolation performance is generally used,but the power supply of the transmitter and the power supply of the instrument with direct electrical connection with the PLC system have not received enough attention.Some isolation measures have been adopted,but generally they are not enough.The main reason is that the isolation transformer used has large distribution parameters and poor interference suppression capability.Common mode interference and differential mode interference are connected in series through power coupling.Therefore,for the power supply of the transmitter and the common signal instrument,the distributor with small distributed capacitance and large suppression band(such as using multiple isolation and shielding and leakage inductance technology)should be selected to reduce the interference of the PLC system.
在PLC控制系统中,电源占有极其重要的地位。电网干扰串入PLC控制系统,丰要是通过PLC系统的供电电源(如CPU电源、I/O电源等)、变送器供电电源和与PLC系统具有直接电气连接的仪表供电电源等耦合进入的。
现在,对于PLC系统供电的电源,一般都采用隔离性能较好的电源,而对于变送器供电的电源和与PLC系统有直接电气连接的仪表的供电电源,并未受到足够的重视,虽然采取了一定的隔离措施,但普遍还不够,主要是使用的隔离变压器分布参数大,抑制干扰能力差,经电源耦合而串入共模干扰、差模干扰。所以,对于变送器和共用信号仪表供电,应选择分布电容小、抑制带大(如采用多次隔离和屏蔽及漏感技术)的配电器,以减少PLC系统的干扰。
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