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P R O F I B U S P
O W E R
The PA cycle time T
•
the number n of nodes on a channel
•
the effective data length L
The effective data length L is a unitless variable calculated as the sum
of input and output effective data quantity (in bytes) of all devices.
The cycle time is calculated approximately as follows:
Nonredundant system:
T
Cycle_PA_Channel
Redundant system:
T
Cycle_PA_Channel
Cycle time discrepancy in real application
•
This is the basic cycle time for ideal conditions. In reality acyclic commu-
nication, retries and diagnosis data can increase the cycle time so an ad-
ditional safety margin has to be added. For the calculation of a overall
Attention
cycle time (Change of a measured signal until reaction of an Actuator)
additional parameters like the measurement cycle time of the PROFIBUS
PA devices and IO Processing cycle of the controller must be considered.
5.2.4
Additional Information on Adjusting Retry
If the coupling from DP to PA is designed redundantly and the DP bus
uses optical fiber as a communication medium, Pepperl+Fuchs recom-
mends increasing the retry limit of the DP master.
Recommended retry limits corresponding to various baudrates:
5.3
DTM Software Installation and Commissioning
System requirements for installation, commissioning and operation of
the DP/PA Gateway DTM:
•
Hardware requirements based on your frame FDT
•
FDT frame application (FDT specification 1.2)
•
Latest version of HD2-GTR-4PA-DTM
Subject to reasonable modifications due to technical advances.
Pepperl+Fuchs Group • Tel.: Germany +49 621 776-0 • USA +1 330 4253555 • Singapore +65 67799091 • Internet http://www.pepperl-fuchs.com
H
S
U B
E G M E N T
Cycle_PA_Channel
= (0.256 ms * L) + (n * 12 ms) + 40 ms
= (0.256 ms * L) + (n * 12 ms) + 100 ms
Baudrate
45.45 kBd
93.75 kBd
187.5 kBd
1.5 MBd
3 MBd
6 MBd
12 MBd
C
O U P L E R
PROFIBUS Commissioning
depends on:
Retry limit
2
2
2
2
4
6
7
Copyright Pepperl+Fuchs, Printed in Germany
35
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