VEGA VEGAFLEX 52P (Profibus PA) - Manual (Page 11)

VEGAFLEX 51P and 52P 11
1.6 Bus configuration
The type of sensor you use depends on the
process requirements and mounting condi-
tions, as well as on the requirements of your
control, regulative, or process control sys-
tem.
VEGAFLEX 51P and 52P Profibus sensors
are sensors for use in Profibus PA environ-
ment. Profile 3 has been implemented in the
sensors. A measuring system consists of
one or several sensors, one or several seg-
ment 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 find a
schematic of the bus configuration.
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). In addition, further master systems
(e.g. visualisation systems or adjustment
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 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.
Each participant on the bus must have an
address. The addressing covers both bus
levels. A Profibus DP system can have max.
126 participants, including all participants on
the PA level. In practice, each Master-Class 1
computer gets address 1 and the Master-
Class 2 computers address 10 … 20. As a
rule, the slaves or participants get the ad-
dresses 21 … 126. On the Profibus PA level,
max. 32 sensors are possible 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)
The min. basic current has been set at 10 mA
according to the Profibus specification.
VEGA Profibus sensors constantly consume
a basic current of 10 mA and operate without
leakage current requirement, so that in Ex
environment, up to ten VEGA sensors can be
operated on one segment coupler.
Product description