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Retransmission Rate High PreAlert limit
Retransmission rate = Re-transmissions/Total pass token requests from LAS over the
last month. Default is 0.1 % (approximately 1 retransmission per hour).
The Retransmission Rate provides an excellent indicator for the quality of fieldbus
segment communications. To provide an accurate Retransmission Rate, a large sample
of Pass Token message replies needs to be monitored. To provide useful data at all
times - even just after power is connected to the F809F-Plus, or after the
retransmission counter is reset - the device calculates the retransmission rate in three
phases.
a) To avoid the risk of nuisance alarms during the initial phase from 1 to 5,000 Pass
Tokens (typically 6 hours when 8 segments are being monitored), the displayed value
will approach the actual value from below.
b) During the averaging phase from 5,000 to 100,000 Pass Tokens (typically 6 days
when 8 segments are being monitored) the accuracy of the displayed value increases.
c) In normal operation, with greater than 100,000 Pass Tokens monitored, the
F809F-Plus displays a moving average retransmission rate that avoids nuisance alarms
from typical events whilst providing good response to changes in fieldbus
communications performance.
8.4.3.
Wizard in the device node
Wizards are software functions executed inside the F809F itself. The device node contains
s
this device to Zero, and consequent
