The interference sources that affect the DCS control system are the same as the interference sources that generally affect the power control equipment.Most of them are generated in the parts where the current or voltage changes drastically.The parts where the charges move violently are the noise sources,that is,the interference sources.The types of interference are usually divided into common mode interference and differential mode interference according to different noise interference modes.Common mode interference and differential mode interference are a more commonly used classification method.Common mode interference is the potential difference between the signal and the ground,which is mainly formed by the power grid in series,the ground potential difference and the common mode(same direction)voltage induced on the signal line by the ground potential difference and space electromagnetic radiation.The common mode voltage can be converted into a differential mode voltage through an asymmetric circuit,which directly affects the measurement and control signals and causes damage to components(this is the main reason for the high damage rate of some system I/O modules).This common mode interference can be DC,can also be used for communication.Differential mode interference refers to the interference voltage acting between the two poles of the signal.It is mainly caused by the coupling induction of the space electromagnetic field between the signals and the voltage formed by the unbalanced circuit converting the common mode interference.They are directly superimposed on the signal and directly affect the measurement and control accuracy.
影响DCS控制系统的干扰源与一般影响电力控制设备的干扰源一样，大都产生在电流或电压剧烈变化的部位，这些电荷剧烈移动的部位就是噪声源，即干扰源。干扰类型通常按噪声干扰模式不同，分为共模干扰和差模干扰。共模干扰和差模干扰是一种比较常用的分类方法。共模干扰是信号对地的电位差，主要由电网串入，地电位差及空间电磁辐射在信号线上感应的共态（同方向）电压叠加所形成。共模电压通过不对称电路可转换成差模电压，直接影响测控信号，造成元器件损坏（这就是一些系统I/O模件损坏率较高的主要原因），这种共模干扰可为直流，亦可为交流。差模干扰是指作用于信号两极间的干扰电压，主要由空间电磁场在信号间耦合感应及由不平衡电路转换共模干扰所形成的电压，它们直接叠加在信号上，直接影响测量与控制精度。
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