HIMA F8628X 984862865 黑马 PLC模拟输入模件控制模块

HIMA F8628X 984862865 黑马 PLC模拟输入模件控制模块

HIMA F8628X 984862865 黑马 PLC模拟输入模件控制模块

当PLC运行时，是通过执行反映控制要求的用户程序来完成控制任务的，需要执行众多的操作，但CPU不可能同时去执行多个操作，它只能按分时操作（串行工作）方式，每一次执行一个操作，按顺序逐个执行。由于CPU的运算处理速度很快，所以从宏观上来看，PLC外部出现的结果似乎是同时（并行）完成的。这种串行工作过程称为PLC的扫描工作方式。

用扫描工作方式执行用户程序时，扫描是从第一条程序开始，在无中断或跳转控制的情况下，按程序存储顺序的先后，逐条执行用户程序，直到程序结束。然后再从头开始扫描执行，周而复始重复运行。

PLC的扫描工作方式与电器控制的工作原理明显不同。电器控制装置采用硬逻辑的并行工作方式，如果某个继电器的线圈通电或断电，那么该继电器的所有常开和常闭触点不论处在控制线路的哪个位置上，都会立即同时动作；而PLC采用扫描工作方式（串行工作方式），如果某个软继电器的线圈被接通或断开，其所有的触点不会立即动作，必须等扫描到该时才会动作。但由于PLC的扫描速度快，通常PLC与电器控制装置在I/O的处理结果上并没有什么差别。

HIMA F8628X 984862865 黑马 PLC模拟输入模件控制模块

When the PLC runs, it is through the execution of the user program to reflect the control requirements to complete the control task, the need to perform many operations, but the CPU can not perform multiple operations at the same time, it can only be a time-sharing operation (serial work), each time to perform an operation, in order to execute one by one. Because the CPU's computing processing speed is very fast, so from a macro point of view, the results that appear outside the PLC seem to be done at the same time (parallel). This serial working process is called the PLC scanning working mode.

When the user program is executed in the scanning mode, the scan starts from the first program and executes the user program one by one until the end of the program without interruption or jump control. Then the scan is executed from the beginning, and the cycle is repeated.

The scanning mode of PLC is obviously different from the working principle of electrical control. The electrical control device adopts the parallel working mode of hard logic, if the coil of a relay is powered on or off, then all the normally open and normally closed contacts of the relay will immediately and simultaneously operate no matter where they are in the control line; The PLC adopts scanning working mode (serial working mode), if the coil of a soft relay is connected or disconnected, all its contacts will not act immediately, and must wait for the scan to the action. However, due to the fast scanning speed of PLC, there is usually no difference between PLC and electrical control devices in the processing results of I/O.