VEGA VEGAPULS 56 Profibus PA - Manual (Page 36)

36 VEGAPULS 56 Profibus PA
Electrical connection
4 Electrical connection
4.1 Connection – Connection cable
– Screening
Safety information – Qualified person-
nel
Instruments which are not operated with
protective low voltage or DC voltage must be
connected only by qualified personnel. This
also applies to the configuration of measuring
systems planned for Ex environment.
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 radar sensors. Pro-
tect yourself and the instruments.
Connection cables and bus
configuration
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 sealing 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 pre-
scribed.
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 radar sensors work also with
max. 32 participants (Ex max. 10 partici-
pants).
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.
Connection cable and cable length
Connection cables must correspond to the
Profibus specification and the FISCO model.
The sensor cable must be in conformity with
the values of the reference cable acc. to
IEC 1158-2:
0.8 mm
2 ; R
DCmax.
= 44
Ω
/km;
Z
31.25kHz
= 80 … 120
Ω
; damping = 3 dB/km;
C
asymmetric
= 2 nF/km.
The max. cable length first of all depends on
the transmission speed:
up to 32 kbit/s: 1900 m Pr
up to 32 kbit/s: 1900 m Pr up to 32 kbit/s: 1900 m Pr up to 32 kbit/s: 1900 m Pr up to 32 kbit/s: 1900 m Profibus P ofibus P ofibus P ofibus P ofibus PA A A A A
up to 94 kbit/s: 1200 m Profibus DP
up to 188 kbit/s: 1000 m Profibus DP
up to 500 kbit/s: 500 m Profibus DP
up to 1500 kbit/s: 200 m Profibus DP
up to 12000 kbit/s: 100 m Profibus DP
The distributed resistance of the cable, in