Wiring TMT84
18 Endress+Hauser
4.4 Fieldbus connection
Devices can be connected to the fieldbus system in two ways:
• Connection via conventional cable gland Chap. 4.4.1
• Connection via fieldbus connector (optional, can be purchased as an accessory) Chap. 4.4.2
"
Caution!
• Switch off power supply before installing or connecting the head transmitter. Failure to observe
this may result in destruction of parts of the electronics.
• Grounding via one of the grounding screws (terminal head, field housing) is recommended.
• Risk of damaging the fieldbus cable!
– If the shielding of the fieldbus cable is grounded at more than one point in systems without
additional potential matching, power supply frequency equalizing currents can occur that
damage the cable or the shielding. In such cases the shielding of the fieldbus cable is to be
grounded on only one side, i.e. it must not be connected to the ground terminal of the housing
(terminal head, field housing). The shield that is not connected should be insulated!
– We recommend that the fieldbus not be looped using conventional cable glands. If you later
replace even just one device, the bus communication will have to be interrupted.
4.4.1 Cable glands or entries
!
Note!
Please also observe the general procedure on ä 13.
a0008284
Fig. 8: Connection to the fieldbus cable - installed in the field housing on the left, and in the terminal head on the right
A Fieldbus terminals - fieldbus communication and power supply
B Inner ground terminal
C Outer ground terminal
D Shielded fieldbus cable
!
Note!
• The terminals for the fieldbus connection (1+ and 2-) are not polarity sensitive.
• Conductor cross-section:
– Max. 2.5 mm
2
(16 AWG) for screw terminals
– Max. 1.5 mm
2
(14 AWG) for spring terminals
• A shielded cable must be used for the connection.
4.4.2 Fieldbus connector
The connection technology of PROFIBUS
®
PA allows devices to be connected to the fieldbus via
uniform mechanical connections such as T-boxes, junction boxes, etc.
This connection technology using prefabricated distribution modules and plug-in connectors offers
substantial advantages over conventional wiring:
• Field devices can be removed, replaced or added at any time during normal operation.
Communication is not interrupted.
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