Siemens S7-400PLC can set a fixed scan time - Database & Sql Blog Articles

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1. You can set and find the CPU properties you are using. Look for 'Scancycletime' to see the current scan cycle.

2. How to check the scan time:

a. Online monitoring: Connect your PC to the 400 system and open the 'Hardware' section. Go online, then double-click the CPU to open the 'Module Information' dialog box. Select 'Scancycletime' to view the current scan cycle.

b. Through programming: In OB1, there are three temporary variables related to the scan cycle: 'OB1_PREV_CYCLE' (the time of the previous scan cycle), 'OB1_MIN_CYCLE', and 'OB1_MAX_CYCLE' (the minimum and maximum scan cycles during operation). These values can be observed by moving them into a memory area or DB storage using the MOVE instruction.

Additionally, it's important to understand that the scan cycle affects the overall performance and responsiveness of the system. Monitoring these values helps in optimizing the program execution and ensuring stable operation. If any anomalies are detected, such as unusually high or low scan times, further investigation into the program logic or hardware configuration may be necessary.