In one of our project we are working with S7 400 H PLC in PCS 7 platform.
After smooth running of the plant for more than six months we have faced a peculiar problem.
One day we found that some digital inputs like LCP/MCC signals as well as the running feedback of some pump were not updating.
Even some analog inputs were freezed/hold to the last state and were not changing with I/O updation while updatation takes place for other I/Os.
We have observed that Digital signals like Remote, Local, Emergency etc. from the LCPs’/MCCs’ were properly coming to the DI Cards and the corresponding LEDs were also glowing. But the CPU is not updating the actual I/O status.
From the library CH_DI/DO/AI/AO blocks are used for reading the I/O Status. One DI card had been replaced with new card but it did not help us.
After that, the CPU was given manually “Reset” but we did not get any result.
We have observed that after resetting the CPU manually by the reset button on the CPU, CPU started updating some more Inputs than when the problems were first noticed.
But for analog signals like level and pressure etc., the value of the process inputs were still in hold condition.
At the end, we had given the CPU complete memory erase, netpro download, hardware download, complete download of the program and started the CPU in redundant mode. After this step everything became normal and CPU started updating all the IOs.
Another thing we had observed that during the faulty condition, the CPU did not give any fault message in the diagnostic buffer. Even the communication between the CPU and RIO was showing healthy.
Can anybody suggest what is the reason behind this & how to prevent it ???
Regards.
Sunith
After smooth running of the plant for more than six months we have faced a peculiar problem.
One day we found that some digital inputs like LCP/MCC signals as well as the running feedback of some pump were not updating.
Even some analog inputs were freezed/hold to the last state and were not changing with I/O updation while updatation takes place for other I/Os.
We have observed that Digital signals like Remote, Local, Emergency etc. from the LCPs’/MCCs’ were properly coming to the DI Cards and the corresponding LEDs were also glowing. But the CPU is not updating the actual I/O status.
From the library CH_DI/DO/AI/AO blocks are used for reading the I/O Status. One DI card had been replaced with new card but it did not help us.
After that, the CPU was given manually “Reset” but we did not get any result.
We have observed that after resetting the CPU manually by the reset button on the CPU, CPU started updating some more Inputs than when the problems were first noticed.
But for analog signals like level and pressure etc., the value of the process inputs were still in hold condition.
At the end, we had given the CPU complete memory erase, netpro download, hardware download, complete download of the program and started the CPU in redundant mode. After this step everything became normal and CPU started updating all the IOs.
Another thing we had observed that during the faulty condition, the CPU did not give any fault message in the diagnostic buffer. Even the communication between the CPU and RIO was showing healthy.
Can anybody suggest what is the reason behind this & how to prevent it ???
Regards.
Sunith
