Siemens SIMATIC NET PROFIBUS, Owner'S Manual

Page: 485 / 490

Glossary
Glossary-5
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
PROFIBUS-DP
PROFIBUS bus system with the DP protocol. DP stands for distributed periphe-
ral I/Os.
The main task of PROFIBUS-DP is the fast, cyclic data exchange between the
central DP master and the peripheral devices.
PROFIBUS-FMS
PROFIBUS bus system with the FMS protocol. FMS stands for Fieldbus Mes-
sage Specification.
Reaction time
The reaction time is the average time that elapses between the change at an
input and the corresponding change at an output.
Redundancy
This means that standby equipment exists that is not required for the basic func-
tioning of a system. If equipment fails, the standby can take over its function.
Example:
Medium redundancy
An additional link closes the bus to form a ring. If there is a failure on part of the
bus, the redundant link is activated to maintain the functionality of the network.
Reference potential
The voltages of circuits are considered and/or measured relative to this potential.
RS-485 repeater
Device for amplifying bus signals and coupling
³
segments over large distances.
Segment
The LAN cable between two terminating resistors forms a segment. A segment
can contain a maximum of 32 bus attachments (–>nodes, –>RS-485 repeaters
–>OLMs, ...). Segments can be interconnected by
³
RS-485 repeaters.
Shield impedance
Resistance to alternating current of the cable shield. Shield impedance is a cha-
racteristic of the cable used and is normally specified by the manufacturer.
Signal propagation time
The time required by a data packet on its way through the network.