VEGA VEGASON 51P…53P Profibus PA - Manual (Page 13)

VEGASON 51P … 53P 13
2.2 Bus configuration
The type of ultrasonic sensor you use de-
pends on the process requirements and the
mounting conditions, as well as on the re-
quirements of your control, regulative, or
process management system.
VEGASON 51P … 53P Profibus ultrasonic
sensors are instruments for use in the Profi-
bus PA environment. Profile 3 has been im-
plemented in the sensors. 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 sys-
tem 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-specifically.
On the following two pages, you will find a
schematic diagram of the bus configuration.
The automation system as Master-Class 1
takes complete control of the bus. 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 the acyclical mode.
A DP bus does not allow power supply via
the 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),
through which supply cables can also be led.
Types and Profibus configuration
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 supplied by the sen-
sors and from the current offered 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 power consumption of all sen-
sors
- 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 draw a constant
basic current of 10 mA and operate without
leakage current requirement. This allows up
to 10 VEGA sensors in Ex environment to be
operated on one segment coupler.