DSAI130D 3BSE003127R1 ABB

In order to achieve complete isolation on the input and output circuits,photoelectric coupling has been widely used in control systems in recent years,and has become one of the most effective measures to prevent interference.The optocoupler has the following characteristics:firstly,because it is sealed in a tube shell,it will not be disturbed by external light;secondly,because the signal is transmitted by light,the connection of the ground wire between the circuits of each component is cut off;thirdly,the light-emitting The dynamic resistance of the diode is very small,and the internal resistance of the interference source is generally large,so the interference signal that can be transmitted to the input and output of the optocoupler becomes very small;fourth,the transmission ratio of the optocoupler is compared with the amplification factor of the transistor,Generally small,it is far less sensitive to interference signals than transistors,and the light-emitting diodes of optocouplers can only emit light when a certain current is passed.Therefore,even when the amplitude of the interference voltage is high,the light-emitting diode cannot be made to emit light due to insufficient energy,so that the interference signal can be effectively suppressed.Since the linear region of the optocoupler is generally only within a certain range,it should be ensured that the variation range of the transmitted signal is always within the linear region.In order to ensure the linear coupling,it is necessary to strictly select the optocoupler and take corresponding nonlinear correction measures,otherwise a large error will be generated.

为了实现输入输出电路上的完全隔离，近年来在控制系统中光电耦合得到广泛应用，已成为防止干扰的最有效措施之一。光电耦合器具有以下特点:首先，由于是密封在一个管壳内，不会受到外界光的干扰;其次，由于靠光传送信号，切断了各部件电路之间地线的联系;第三，发光二极管动态电阻非常小，而干扰源的内阻一般很大，能够传送到光电耦合器输入输出的干扰信号就变得很小;第四，光电耦合器的传输比和晶体管的放大倍数相比，一般很小，远不如晶体管对干扰信号那么灵敏，而光电耦合器的发光二极管只有在通过一定的电流时才能发光。因此，即使是在干扰电压幅值较高的情况下，由于没有足够的能量，仍不能使发光二极管发光，从而可以有效地抑制掉干扰信号。由于光电耦合器的线性区一般只能在某一特定的范围内，因此，应保证被传信号的变化范围始终在线性区内。为了保证线性耦合，既要严格挑选光电耦合器，又要采取相应的非线性较正措施，否则将产生较大的误差。