Pyromation T82 - Manual (Page 15)

T82 Wiring
15
*
*
1
2
3
4
2- 1+
2-
1+
A0008284
å 6 Connecting the signal cable and power supply - left: installed in field housing, right: installed in terminal head
A Terminals for HART ® -protocol and power supply
B Internal ground terminal
C External ground terminal
D Shielded signal cable (recommended for HART ® protocol)
• The terminals for connecting the signal cable (1+ and 2-) are protected against reverse
polarity.
• Conductor cross-section:
– Max. 2.5 mm 2 for screw terminals
– Max. 1.5 mm 2 for spring terminals
5.4 Shielding and grounding
Optimum electromagnetic compatibility (EMC) 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 optimum EMC protective effect when communicating with HART
® , 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, three different types of shielding are possible when
communicating with HART
® :
• Shielding at both ends
• Shielding at one end on the feed side with capacitance termination at 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 termination at 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! Where there are large differences in potential between the
individual grounding points, only one point of the shielding is connected directly with the
reference ground. In systems without potential equalization, therefore, cable shielding of fieldbus
systems should only be grounded on one side, for example at the supply unit or at safety barriers.