Wiring TMT84
16 Endress+Hauser
4.3.2 Maximum overall cable length
The maximum network expansion depends on the type of protection and the cable specifications.
The overall cable length combines the length of the main cable and the length of all spurs (>1 m/
3 ft). Note the following points:
• The maximum permissible overall cable length depends on the cable type used.
• If repeaters are used, the maximum permissible cable length is doubled. A maximum of three re-
peaters are permitted between user and master.
4.3.3 Maximum spur length
The line between the distribution box and field device is described as a spur.
In the case of non-Ex applications, the max. length of a spur depends on the number of spurs
(>1 m/3 ft):
4.3.4 Number of field devices
The line length is limited to a maximum of 1000m (3280ft) in systems corresponding to FISCO with
Ex ia types of protection. A maximum of 32 users per segment are permitted in the non-hazardous
area or 10 users in the hazardous area (Ex ia IIC). The actual number of users must be specified
during configuration.
4.3.5 Shielding and grounding
Optimum electromagnetic compatibility (EMC) of the fieldbus system can only be guaranteed if the
system components and, in particular, the lines are shielded and the shield forms as complete a
cover as possible. A shield coverage of 90% is ideal.
• To ensure an EMC protective effect, connect the shield as often as possible to the reference
ground.
• For reasons of explosion protection, you should refrain from grounding however.
To comply with both requirements, the fieldbus system basically allows three different types of
shielding:
• Shielding at both ends
• Shielding at one end on the feed side with capacitance connection to the field device
• Shielding at one end on the feed side
Experience shows that the best results with regard to EMC are achieved in most cases in
installations with one-sided shielding on the feed side (without capacitance connection to the field
device). Appropriate measures with regard to input wiring must be taken to allow unrestricted
operation when EMC interference is present. These measures have been taken into account for this
device. Operation in the event of disturbance variables as per NAMUR NE21 is thus guaranteed.
Where applicable, national installation regulations and guidelines must be observed during the
installation!
Type A 1900m 6200ft
Type B 1200m 4000ft
Number of spurs 1 to 12 13 to 14 15 to 18 19 to 24 25 to 32
Max. length per
spur
m 120 90 60 30 1
ft 400 300 200 100 3
To Next Page
Loading...
