Cable Specification For Fieldbus (Profibus- Pa ® ); Cable Type - Endress+Hauser iTEMP PA TMT184 Bedienungsanleitung

TMT184
!
Endress+Hauser
In order to stop these low frequency compensation currents it is therefore suggested that in plants
without potential compensation systems the cable screen should only be connected to the basic
ground (e.g. ground cable) at one end and to connect all further ground points using capacitors.
Note!
It is recommended to screen the sensor connection cable on remote installation in high EMC endan-
gered areas!
4.3.3 Cable specification for Fieldbus (PROFIBUS-PA

Cable type

It is recommended that a twin core cable be used when connecting the measuring device to the
fieldbus. In combination with the IEC 61158-2 four different cables types (A, B, C, D) can be used,
however, only cable types A and B are screened.
• It is recommended that cable types A and B should always be used on new installations. These
are screened and therefore guarantee enough protection against electromagnetic interference and
will then guarantee the highest possible reliability of data transmission. Using multi twisted pair
cables (type B) more than one fieldbus (of the same type) can be connected using one cable. Other
forms of circuits are forbidden.
• Practical experience has shown that due to the missing screening cables, types C and D should
not be used. This is also due to the fact that the interference security is not sufficient for the
requirements described in the standards.
The electrical data of the fieldbus cables are not fixed, but some important conditions such as length,
number of users and electromagnetic compatibility etc assist in the final selection during the plan-
ning stage.
Cable construction
Core section
Loop resistance (DC)
Ripple resistance at 31.25
kHz
Ripple damping at
39 kHz
Capacitive unsymmetry
Group delay distortion
(7.9 to 39 kHz)
Screen covering
Max. cable length (incl.
spurs >1 m)
1. not specified
Type A
Twisted cable pairs, screened
0.8 mm (AWG 18)
²
44 Ω/km
100 Ω ± 20%
3 dB/km
2 nF/km
1.7 µs/km
90%
1900 m
4 Wiring
®
)
Type B
single or multi twisted cable pairs, total
screened
0.32 mm² (AWG 22)
112 Ω/km
100 Ω ± 30%
5 dB/km
2 nF/km
1
a
1200 m
51