GE PACSystems RX7i, Руководство пользователя

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Chapter 5. Ethernet Global Data
76 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q
Configurable Producer Period for an EGD Exchange
The Producer period for an EGD exchange can be 2 milliseconds to one hour. In the PLC, the Ethernet Interface
attempts to produce the data at this interval. As explained above, the exchange production may vary from the
configured interval by up to one production period or one producer CPU sweep period, whichever is smaller.
Producer period is configurable in increments of 2 milliseconds. If the Producer Period is set to zero, production
is scheduled every scan or every 2ms, whichever is slower. In a PLC with rapid scan times, scheduling a
produced exchange at zero results in a very high load on the network and on the Ethernet Interface, which can
degrade overall Ethernet performance. Scheduling multiple exchanges for a zero period in a PLC with a low
scan time can result in the Ethernet Interface being unable to produce all the required data, and will also
degrade SRTP communication.
Consumer Update Timeout Period
For each consumed exchange, an Update Timeout period can be configured. It determines how long the
Ethernet Interface will wait for the starting or subsequent packet of data in the exchange before declaring a
refresh error. The update timeout period for the consumer should be set to at least twice the producer period.
At very small producer periods, the update timeout should also allow for network transfer variation. Otherwise,
the PLC may occasionally falsely report refresh faults. Use zero for the update timeout period of a consumed
exchange to disable timeout detection.
Producer Period Guidelines for PLCs
Do not produce and consume data faster than is required by your application. This reduces the load on the
network and on the devices, providing capacity for other transfers.
The following illustrations show the relationship among the PLC output scan time, the produced exchange
timer, and data samples on the network.
Timing Example 1
Only one sample is produced on the network per producer period expiration. The time between samples can
vary up to the producer CPU sweep time.
Producer Period = 1.5 Times CPU Sweep
Producer PLC Output Scan
Ethernet Global Data
Production Timer Expires
Sample on Network
Figure 38: EGB Timing Example #1