Example Calculation; Performance Effects Of Online Operations - Allen-Bradley PLC-5 User Manual

C-12 Maximizing System Performance

Example Calculation

Performance Effects of
Online Operations
Publication 1785-UM012D-EN-P - July 2005
The worst-case controller time is:
Variable
periodic input buffer update from remote I/O
buffer
one program scan to guarantee inputs received xx ms
one program scan to guarantee outputs received xx ms
0.18 ms times number of racks
total
For a 3-rack system with a 20 ms program scan, the worst-case controller time
is: 10 + 20 + 20 + (0.18 3) = 50.54 ms.
Based on the results of each throughput component calculation presented
within the chapter, an example of a worst-case update time calculation is:
Variable
input card delay
I/O backplane
worst-case remote I/O scan time
worst-case controller time
worst-case remote I/O scan time
I/O backplane
output card delay
total
The performance of the PLC-5 controller is affected when you perform online
operations via a DH+ link to your program files while in Run mode. Affected
activities are:
DH+ messages
serial port messages
channel 3A messages
remote block-transfers
Value
10 ms
xx ms
Value
10 ms typical
1 ms
30 ms
50.54 ms
30 ms
1 ms
1 ms typical
123.54 ms