PLC operation program item change detection method

The embodiment of the invention provides a PLC running program item change detection method, which comprises the following steps of: inserting a function FC and a data block DB in a PLC running program item, establishing a verification result variable through the data block DB, periodically reading system states of the function FC and the data block DB, and storing state words. The status words of two adjacent periods are verified, the verification result is stored in the verification result variable, if the verification result variable is changed, it can be confirmed that the PLC operation program item is changed, the requirement that the PLC operation program item is strictly prohibited from being changed at will is met, and even if the operation program item is not changed according to the program change process, detection and discovery can be conducted in time. 本申请实施例提供一种PLC运行程序项目变更的检测方法，在PLC运行程序项目中插入功能FC和数据块DB，通过数据块DB建立校验结果变量，周期性读取功能FC和数据块DB的系统状态并存储状态字，校验两个相邻周期的状态字并将校验结果存储在校验结果变量中，如果校验结果变量变更则可确认PLC运行程序项目