Rockwell-automation Ethernet Design Considerations Reference Manual Bedienungsanleitung PDF herunterladen (Seite 87)

Rockwell Automation Publication ENET-RM002C-EN-P - May 2013 87

Predict System Performance Chapter 5

Use this table to count the total packets/second sent for each EtherNet/IP

communication module in the example system shown on page 84

In addition to the configurable RPI parameter, you control system includes the

Actual Packet Interval (API). The API is the actual time that requested data is

delivered.

The relationship between the RPI and API in your system depends on the

controller initiating the communication. In general, these controller types

calculate the API as follows:

• ControlLogix: API = RPI

• 1768 CompactLogix: API = RPI

• CompactLogix 5370 controllers, SoftLogix™: API = RPI

• 1769-L23Ex, 1769-L3xE: API = 2

(where 2

is a value that is a power of

2, for example, 2, 4, or 8, that is equal to or faster than the RPI you

configured)

Communication

Module

Connection Type Packets/Second

Local 1756-EN2T

communication module

Produced tag between

controllers

(1 + 1)/20ms = 100

Rack-optimized connections (2 x 1)/20ms = 100

Direct connections (2 x 2)/50ms = 80

Module total packets/second = 280

(1)

(1) A 1756-EN2T/ A module, firmware revision 2.003 has a packet rate capacity = 10000 packets/second. When sending 280

packets/second, the module in the example system uses approximately 3% of its packet rate capacity, well below the recommended

maximum of 90% of the module’s packet rate capacity.

Remote 1756-EN2T

communication module

Consumed tag between

controllers

2/20ms = 100

Rack-optimized connections (2 x 1)/20ms = 100

Direct connections (2 x 2)/50ms = 80

Module total packets/second = 280

(1)

IMPORTANT

In most cases, you can get data faster than the RPI you configured. This

increased data transmission rate can increase the number of packets to be

more than you expected based on the RPI.

Therefore, the percentage of the EtherNet/IP communication module’s packet

rate capacity used can be slightly higher than expected.

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