VEGA VEGAPULS 56 Profibus PA - Manual (Page 7)

VEGAPULS 56 Profibus PA 7
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). Layers 3 … 5 have not yet been
developed as a standard, leaving Profibus
with far-reaching perspectives for the future.
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
enables power supply over the bus. Up to 32
sensors with power supply and measuring
signal can be operated on a shielded two-
wire cable that carries both power supply
and measuring signal. In Ex areas, up to ten
sensors can be connected from the PA level
to one two-wire cable (EEx ia).
Bus structure
A Profibus system with DP and PA segments
consists of up to 126 Master and Slave par-
ticipants. Data are always exchanged from
point to point, with the data traffic being ex-
clusively controlled and checked by master
devices. Communication is carried out ac-
cording 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 predetermined time interval, the Token
is passed on by the master to the next mas-
ter.
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 (instrument master file) is
provided with the VEGAPULS Profibus sen-
sor. This file is necessary to integrate the
sensor in the bus system. The GSD contains,
beside the sensor name and manufacturer,
the sensor-specific communication param-
eters which are necessary for a stable inte-
gration of the sensor in the bus.
Load the GSD belonging to the sensor into
your bus configuration program. If the GSD
is not available, it can be downloaded from
the VEGA homepage: http://www.vega.com.
Do not mistake the GSD for the EDD (Elec-
tronic Device Description), which is neces-
sary for the PDM environment and can also
be found on the VEGA homepage.