In the early 1970s,some people replaced the original centrally installed analog instrument control with a small computer such as the PDP/1124.There are many cables connected to the central control room.For example,a minicomputer is used as a controller,and the CRT connected to the minicomputer is used as a display device(ie,a human-machine interface).A small computer needs to receive signals from thousands of transmitters or other sensors to complete the calculation of hundreds of loops.Clearly the danger is somewhat concentrated.There are as many cables connected as the analog gauges,and once the minicomputer goes down,the controls and displays are gone.The digital control did not serve the intended purpose.
70年代初，有人用如PDP/1124这样的小型机代替原来的集中安装的模拟仪表控制。连接到中央控制室的电缆很多。如用小型机既作为控制器、同时把连接小型机的CRT又作为显示设备（即人机界面）。一台小型机需接收几千台变送器或别的传感器来的信号，完成几百个回路的运算。很显然其危险有点集中。和模拟仪表连接的电缆一样多，并且一旦小型机坏了，控制和显示都没有了。数字控制没有达到预期的目的。
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