Rockwell Automation 1404-M4_M5_M6_M8 Powermonitor 3000 User Manual, Firmware rev. 3.0 or LATER - Manual (Page 97)

Publication 1404-UM001F-EN-P - November 2009 97
Communication Chapter 4
Polled I/O messaging can automatically provide fresh data at update
rates as fast as 100 ms. The power monitor supports both Every Scan
and Background polled messaging. You select the poll type and
polling rate by using RSNetworx for DeviceNet software.
•
Every Scan: Polls the power monitor once per scan. Set the
Interscan Delay to at least 100 ms. An Interscan Delay of less
than 100 ms slows the power monitor’s delivery of metering
information.
•
Background: Polls the power monitor at intervals you specify by
using the Foreground to Background Poll Ratio. So long as the
power monitor is polled no more frequently than every 100 ms,
it operates and communicate at its optimal rate. You may
calculate the total scan time with this formula.
Change of State I/O messaging (COS) reports data only when the
content of the I/O table changes. COS messaging can be more
efficient for discrete applications because it tends to reduce the
network traffic. If you have configured the input message table to
include metering data, however, COS may reduce the network
efficiency because the data constantly changes.
Cyclic I/O messaging reports data periodically according to a time
increment you configure.
COS and Cyclic messaging typically reduce the network bandwidth
loading compared with Polled messaging. To optimize explicit
messaging performance, use a Background Polled I/O connection
with a high foreground to background poll ratio.
To help obtain optimal network operation, verify the following
settings by using RSNetworx for DeviceNet software, looking at the
scanner Properties dialog:
•
For Polled I/O messaging, verify that the effective polling rate
(or scan time) is less than the expected packet rate (EPR) to
prevent time-out errors. You may find the EPR on the Module by
clicking Advanced.
•
For COS or Cyclic I/O messaging, verify that the COS/Cyclic
Inhibit Time is less than the EPR and that the ACK time out is set
appropriately. You may find these parameters on the Scanlist by
clicking Edit I/O Parameters.
Total Scan Time 1 R + ( ) D • =
Where:
R = Foreground to Background Poll Ratio
D = Interscan Delay