Siemens SIMATIC NET PROFIBUS manual Reaction time, Redundancy, Reference potential, Segment

Glossary

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.

PROFIBUS Networks SIMATIC NET	Glossary-5
6GK1970-5CA20-0AA1 Release 2 05/2000