VEGA VEGAPULS 41 Profibus PA - Manual (Page 33)

VEGAPULS 41 – Profibus PA 33
27292-EN-041227
3.5 Bus configuration
The type of radar sensor you use depends
on your process requirements and mounting
conditions, as well as on the requirements of
your control, regulative, or process manage-
ment system.
VEGAPULS 42, 44 and 45 Profibus radar
sensors are sensors for use in Profibus PA
environment. Profile 3 has been implemented
in the sensors. A measuring system consists
of one or several sensors, one or several
segment couplers and one DP master com-
puter, such as e.g. an S7 PLC with Profibus
interface or a process management system
with Profibus DP-Master-Slot. The processing
unit (e.g. the PLC) evaluates the level-propor-
tional, digital measuring signals in a number
of evaluation routines and puts them to use
process-specifically.
On the following four pages you will see
schematic illustrations of the bus configura-
tion.
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). Beside this, additional master sys-
tems (e.g. visualisation systems or adjust-
ment 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 in-
structions 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 (see also „Instal-
lation Guides PA + DP“ of the Profibus User
Organisation (PNO).
Each participant on the bus mast have a
unique address. The addressing covers
both bus levels. A Profibus DP network can
have max. 126 participants on the PA level. In
practice, each Master-Class 1 computer gets
address 1 and the Master-Class 2 computer
address 10 … 20. As a rule, the slaves or
participants get the addresses 21 … 126. On
the Profibus PA network segment, max. 32
sensors can be connected on one PA seg-
ment 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)
The min. basic current has been set at 10 mA
according to the Profibus specification.
VEGA Profibus radar sensors constantly
consume a basic current of 10 mA and oper-
ate without leakage current requirements, so
that in Ex environment, up to max. ten VEGA
sensors can be operated on one segment
coupler.
Types and versions