Siemens Simatic ET 200S Operating Instructions Manual page 324

Glossary
Real time
Real time means that a system processes external events within a defined time.
Determinism means that a system responds in a predictable (deterministic) manner.
Both requirements are important for industrial networks. PROFINET satisfies these
requirements. Thus, as a deterministic real-time network, PROFINET is designed as follows:
• The transfer of time-critical data between different nodes via a network is guaranteed
• To this end, PROFINET has an optimized communication channel for real time
• The time of transfer can be accurately determined.(forecast).
• This ensures that unimpeded communication can take place via other standard protocols
Reference potential
Potential from which the voltages of the circuits involved can be observed and/or measured.
Reversing starter
A reversing starter is a → motor starter which defines the rotary direction of a motor. It
consists of a circuit breaker and two contactors.
Segment
The bus line between two terminating resistors forms a segment. A segment contains 0 to 32
→ bus nodes Segments can be coupled via RS 485 repeaters.
SELV
Protective Extra Low Voltage = extra low voltage with safe isolation
Slave
A slave may only exchange data with a → master if called upon to do so by the latter. Slaves
are, for example all DP slaves such as ET 200X, ET 200M, ET 200S etc.
SNMP
SNMP (Simple Network Management Protocol) is the standardized protocol, for diagnosing
and also configuring the Ethernet network infrastructure.
In the office setting and in automation engineering, devices from many different
manufacturers support SNMP on the Ethernet.
SNMP-based applications can be operated on the same network in parallel to applications
with PROFINET.
The scope of the supported functions differs depending on the device type. For example, a
switch has more functions than a CP 1616.
Glossary-8
within a defined interval of time.
communication: Real time
in the same network, e.g. industrial communication for PD/PC.
Operating Instructions, 12/2005, A5E00515771-03
ET 200S