Publication 1766-RM001A-EN-P - October 2008
550 MicroLogix 1400 Memory Usage and Instruction Execution Time
MicroLogix 1400
Scan Time Calculation
The following is an example of how to calculate a typical scan time for a
ladder program. In this example, a program scan time of 15.0 ms is
assumed. The program scan time includes the system overhead time.
Communication Channels Inactive
Program scan time: 15 ms
System overhead: 3.35 ms (typically 20% of program scan time)
Ladder logic execution time:
program scan time - system overhead = 15 - 3.35 = 11.65 ms
One Or More Communication Channels Active
When any of the channels are active, the following typical overheads
should be taken into account:
• Channel 0 overhead: 0.8 ms
• Channel 1 overhead: 0.4 ms
• Channel 2 overhead: 0.7 ms
If Channel 1 is active and the other two channels are inactive, total
program scan time is:
Program scan time (when no communication channels active) +
Channel 1 overhead = 15 ms + 0.4 ms = 15.4 ms
If all Channels are active, total program scan time is:
Program scan time (when no communication channels active) +
Channel 0 overhead + Channel 1 overhead + Channel 2 overhead =
15 ms + 0.8 ms + 0.4 ms + 0.7 ms= 16.9 ms
efesotomasyon.com - Allen Bradley,Rockwell,plc,servo,drive
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