Bradley Smoker PLC-5 user manual Maximizing System Performance, Using This Chapter Program Scan

Appendix C

Using This Chapter

Program Scan

Maximizing System Performance

For Information About	Go to Page
Program scan	C-1
Calculating throughput	C-5
Input and output modules delay	C-6
I/O backplane transfer	C-6
Remote I/O scan time	C-6
Controller time	C-11
Example calculation	C-12
Performance effects of online operations	C-12
Inserting ladder rungs at the 56K-word limit	C-13
Using program control instructions	C-14

For information about the time that it takes the controller to execute a specific instruction, see Appendix D.

Since the program scan is comprised of the logic scan and housekeeping, any event that impacts the time of one segment affects the program scan.

You can monitor the scan time by using the controller status screen in your programming software.

If no change in input status occurs and the controller continues to execute the same ladder logic instructions, the program scan cycle is consistent. In real systems, however, the program scan cycle fluctuates due to the following factors:

•false logic executes faster than true logic

•different instructions execute at different rates

•different input states cause different sections of logic to be executed

•interrupt programs affect program scan times

•editing programs while online affects housekeeping times

Publication 1785-UM012D-EN-P - July 2005