VEGA VEGAPULS 41 Profibus PA - Manual (Page 7)

VEGAPULS 41 – Profibus PA 7
27292-EN-041227
Product description
1.3 Profibus output signal
PRO PRO PRO PRO PROcess FI FI FI FI FIeld BUS BUS BUS BUS BUS (PROFIBUS) is the re-
sult of a joint project of thirteen companies
and five universities. The companies Bosch,
Klöckner-Möller and Siemens played a deci-
sive role. The specifications of the bus are
described in the protocol layers 1, 2 and 7 of
the ISO/OSI reference model and are avail-
able from the PNO (Profibus user organisa-
tion). Since layers 3 … 5 have not yet been
developed as a standard, Profibus still has a
lot of far-reaching potential.
Today approx. 600 companies make use of
Profibus technology and belong to the PNO.
Profibus FMS
FMS FMS FMS FMS stands for Fieldbus Messaging
Specification, Profibus DP DP DP DP DP for Decentralised
Periphery and Profibus P P P P PA A A A A for Process Auto-
mation.
As a process automation bus, Profibus PA
also enables power supply over the bus. Up
to 32 sensors can be operated on a shielded
two-wire cable that carries both power sup-
ply and measurement signal. In Ex areas, up
to ten sensors can be connected from the PA
level to one two-wire cable (EEx ia).
Bus structure
The Profibus DP and PA network consists of
up to 126 master and slave participants.
Data are always exchanged from point to
point, with the data traffic being exclusively
controlled and checked by master devices.
Communication is carried out acc. to the
Token-Passing procedure. This means that
the master holding the Token can contact the
slaves, give instructions, enquire data and
cause the slaves to receive and transmit
data. After the work is done or after a prede-
termined time interval, the Token is passed
on by the master to the next master.
Master-Class 1
is the actual automation system, i.e. the proc-
ess control computer or the PLC that en-
quires and processes all measured values.
Master-Class 2
One or several Master-Class 2 can operate in
a Profibus network. As a rule, Master-Class 2
devices are engineering, adjustment or visu-
alisation stations. The VEGA adjustment soft-
ware VVO (VEGA Visual Operating) operates
as Master-Class 2 participant on the DP bus
and can work on an engineering PC, on an
adjustment PC or on the process control
computer and can access any VEGA sensor
on the PA level.
Instrument master file
A so-called GSD file is delivered with every
VEGAPULS Profibus sensor. This file is re-
quired to integrate the sensor into the bus
system. The GSD (instrument master file)
contains, beside the sensor name and the
manufacturer, the sensor-specific communi-
cation parameters which are necessary for a
stable integration of the sensor in the bus.
Load the GSD file belonging to the sensor
into your bus configuration program. If the
GSD file is not available, it can be
downloaded from the VEGA homepage: http:/
/www.vega.com.
Do not confuse the GSD file with the EDD
(Electronic Device Description), a file which is
necessary for the PDM environment (this can
be also found on the VEGA homepage).