VEGA VEGASON 54P…56P Profibus PA - Manual (Page 26)

26 VEGASON 54P … 56P
Electrical connection
3 Electrical connection
3.1 Connection
Safety information – Qualified person-
nel
Instruments which are not operated with
protective low voltage or DC voltage must
only be connected by qualified personnel.
This also applies to the configuration of
measuring systems planned for Ex environ-
ment.
As a rule, do all connecting work in the com-
plete absence of line voltage. Always switch
off the power supply before you carry out
connecting work on the ultrasonic sensors.
Protect yourself and the instruments.
Note, important for connection to an EP
card
If VEGASON 54P … 56P sensors are oper-
ated on Profibus input cards (EP cards) in
the VEGALOG 571 processing system, each
card must be powered individually with an
own power supply unit. For power supply of
an EP card, use the power supply unit "ASI-
Interface SLA 3.100" from Puls which is avail-
able from VEGA.
By this measure, the signal circuits are gal-
vanically separated. This avoids possible
crosstalks between the EP cards.
3.2 Connection cables and bus con-
figuration
Note the Profibus specification. The connec-
tion cables must be specified for the ex-
pected operating temperatures in the plant
and must have an outer diameter of
6 … 12 mm, to ensure the seal effect of the
cable entry on the sensor.
For power supply and bus communication, a
two-wire cable acc. to the Profibus specifica-
tion (up to max. 2.5 mm
2 cross-section area
of conductor) is used. The electrical connec-
tion on the sensor is made by spring-loaded
terminals.
In a laboratory setup, a Profibus system will
also work with standard, unshielded two-wire
cable. In practice however, an automation
network and bus system can only be pro-
tected reliably against electromagnetic inter-
ference with screened cable. Acc. to the
Profibus specification (IEC 1158-2),
screened and twisted cables are prescribed.
All participants are connected in one line
(serially). At the beginning and end of the
bus segment, the bus is terminated by an
active bus termination. On the DP bus level,
most participants already have a bus termi-
nation implemented. With more than 32 par-
ticipants on the DP level, a so-called repeater
must be used to open and combine another
DP level with a max. of 32 additional partici-
pants. On the PA bus branch of the segment
coupler, the PA ultrasonic sensors also work
with a maximum of 32 participants (Ex max.
10 participants).
A PA sensor can work only in conjunction with
a Profibus DP system, to which a Profibus PA
subsystem is connected. A PA Profibus par-
ticipant must consume min. 10 mA supply
current.