VEGA VEGAFLEX 55P (Profibus PA) - Manual (Page 10)

10 VEGAFLEX 55P (Profibus PA)
Product description
1.6 Bus configuration
The type of sensor you use depends on your
process requirements and mounting condi-
tions, as well as the requirements of your
control, regulative, or process control sys-
tem.
VEGAFLEX 55P Profibus sensors are sen-
sors for use in Profibus PA environment.
Profile 3 has been implemented in the sen-
sors. A measuring system consists of one or
several sensors, one or several segment
couplers and one DP master computer, such
as e.g. a S7 PLC with Profibus interface or a
process control system with Profibus DP-
Master-Slot. The processing unit, e.g. the
PLC, evaluates the level-proportional, digital
measuring signals in a number of evaluation
routines and puts them to use process-spe-
cifically.
On the following two pages, you will see
schematic illustrations of the bus
configuration.
The automation system as Master-Class 1
takes over bus control completely. It reads
out all signals cyclically and, if necessary,
gives instructions to the participants (e.g.
sensors). Besides this, additional master
systems (e.g. visualisation systems or ad-
justment tools) can be connected to the DP
bus. These systems operate as so-called
Master-Class 2 participants. Like the Master-
Class 1 system, they can read out signals,
give instructions and operate in the acyclical
mode.
A DP bus does not allow power supply via
signal cable, whereas the PA bus does. Both,
DP and PA, require at a minimum a screened
two-wire cable. The DP bus can additionally
have up to 8 cores (screened), of which
some can be supply cables.
Each participant on the bus must have an
unambiguous address. The addressing
covers both bus levels. A Profibus DP net-
work can have max. 126 participants, includ-
ing all participants on the PA level. In
practice, each Master-Class 1 computer gets
address 1 and the Master-Class 2 comput-
ers address 10 … 20. As a rule, the slaves or
participants get the addresses 21 … 126. On
the Profibus PA level, max. 32 sensors can
be connected on one PA segment coupler.