Siemens SIMATIC ET 200iSP Operating Instructions Manual page 369

Prewiring
Wiring the terminal modules before the electronic modules are inserted.
Process image
The process image is a component of the system memory of the DP master. At the start of the
cyclic program, the signal states of the input modules are transferred to the process image of
the inputs (PII). At the end of the cyclic program, the process image of the outputs (POI) is
transferred to the DP slave as a signal state.
PROFIBUS
PROcess FIeld BUS. This is an international process and fieldbus standard as defined in
IEC 61784-1:2002 Ed1 CP 3/1. It specifies the functional, electrical and mechanical
characteristics of a bit-serial field bus system.
PROFIBUS is a bus system that connects PROFIBUS compatible automation systems and
field devices on a cell and field level.
PROFIBUS is available with the protocols DP (= distributed peripherals, that is, distributed or
remote I/O), FMS (= field bus message specification), PA (= process automation), or TF (=
technology functions).
PROFIBUS address
Each bus node must have a PROFIBUS address to identify it uniquely on the PROFIBUS.
The PC/programming device has PROFIBUS address "0".
PROFIBUS addresses 1 to 125 are permitted for the ET 200iSP distributed I/O station.
Pulse stretching
Function used to extend the duration of a digital input signal. It extends the signal at a digital
input by a set value.
Reference potential
The potential from which the voltages of the electrical circuits are evaluated and/or measured.
RTD
Measuring temperatures with resistive thermometers (RTD = resistance temperature
detection.)
Segment
The bus cable between two terminating resistors forms a segment. An RS 485 IS segment (on
RS 485-IS coupler) contains between 31 bus nodes.
ET 200iSP
Operating Instructions, 11/2017, A5E00247483-07
Glossary
369