Monday, June 20, 2011

Scan Time of Virtual bases on 2541 PLC





Arranging “virtual” bases in the 2541 PLC Series is the similar as adding bases of “real” I/O to the system of PLC. The adding of bases of “virtual” can extensively enlarge the PLC’s scan time. Every base of “virtual” added to the system can include from 15 to 20 ms to the total scan time of PLC. This should be measured when conniving the warm backup system, particularly where scan times of PLC are important to the process.

Update time of setting the 2541 I/O
This setting identifies the quantity of time (in ms) that have to pass by before the module of 2541 logs an I/O timeout and moves control to the Standby PLC if Update of I/O is chosen as a transfer option. Characteristically, it is suggested that this worth be set a little higher than the maximum scan time of PLC projected. There are convinced procedures, for example ONLINE compiles and downloads from APT or ONLINE EDITS from TiSoft, which can considerably enlarge the scan time of PLC during the procedure. If Update of I/O is chosen as a transfer option and the Update of I/O time is place close to the PLC’s normal scan time, after that this might cause the 2541 to change control to the Standby PLC if these processes are applied to the main PLC.

It is suggested that the Update of I/O move option be disabled in the module of 2541 before doing ONLINE downloads or edits to the main PLC to avoid an unexpected control transfer to the Standby PLC.

Enable option of Checksum Match
If this alternative is ENABLED, it should be distinguished that if an edit of ladder is completed in the main PLC then the checksum of ladder match will not pass and the 2541 will consider the Standby PLC not available for transfer. The “PLC ACTIVE” LED consequent to the selected “Standby” PLC will go OFF representing that the Standby PLC is not working. Also, while changes to the main PLC RLL are not transferred automatically to the Standby PLC, any updates in RLL have to be done to every PLC separately.



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