I have encountered a problem with a S7-300 (315-2DP) where the Output of the PLC "flutters" when I am monitoring the Network where the output is generated.

This problem occurs when I am monitoring the exact network where the output is generated. I have tried both the Profibus and MPI ports and also different PGs. The PLC program is quite big, occupies 77% of the Work Memory, but only 26% of the Load Memory (512MB MMC). The cycle time of the CPU is round 40ms ave. The PLC program makes use of a 50ms interrupt-OB (OB35), Ethernet CP343 and has a Profibus network of 3 x ET200s field stations. My concern is the High Cycle Time and the interruption of the outputs with "Online Monitoring" of the respective Block networks (seems to have less impact with online connection over Ethernet). The online view also seems to be affected with some of the FBD element's status not displayed. If anyone out there has encountered this before please reply (this problem could affect my sanity).

 

Does the real world output "flutter" or is it just the monitor indication in Step 7?