VEGA VEGASON 54P…56P Profibus PA - Manual (Page 33)

VEGASON 54P … 56P 33
Electrical connection
3.6 Bus configuration
The type of ultrasonic sensor you use de-
pends on the process requirements and
mounting conditions, as well as on the re-
quirements of your control, regulative, or
process control system.
VEGASON 54 … 56 Profibus sensors are
sensors 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 four pages you will see
schematic illustrations of the bus configura-
tion.
The automation system as Master-Class 1
takes over the complete bus control. It reads
out all signals cyclically and, if necessary,
gives instructions to the participants (e.g.
sensors). Additional master systems (e.g.
visualisation systems or adjustment tools)
can also 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 least one screened
two-wire cable. The DP bus can additionally
have up to 8 cores (screened), some of
which can be supply cables (see also "Instal-
lation Guides PA + DP" of the Profibus User
Organisation (PNO).
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 network segment, a max. of
32 sensors can be connected on one PA
segment coupler.
Ex environment
In Ex environment, intrinsically safe (EEx ia)
PA sensors are used with Ex segment cou-
plers. Generally, the number of PA sensors
on a segment coupler (Ex or non Ex) de-
pends on the current requirement of the
sensors and on the current supplied by the
segment coupler. Segment couplers for
EEx ia environment provide 90 … 110 mA.
The number of sensors results from the sum
of:
- the basic current intake of all sensors
- plus 9 mA communication signal
- plus the leakage currents of all sensors
- plus a recommended current reserve
(approx. 10 mA)