Emerson Rosemount 5900C, Reference Manual

Page: 105 / 322

Grounding - F
OUNDATION
™
Fieldbus
Signal wiring of the fieldbus segment can not be grounded. Grounding out one of the
signal wires may shut down the entire fieldbus segment.
Shield wire ground
To protect the fieldbus segment from noise, grounding techniques for shield wire usually
require a single grounding point for shield wire to avoid creating a ground loop. The
ground point shall be located at the power supply.
The devices designed for “daisy-chain” connection offer an isolated shield loop-through
terminal in order to enable a continuous shield throughout the Tankbus network.
In order to avoid unintentional grounding points, the cable shield inside the terminal
compartment must be isolated.
3.4.3 Cable selection for the Tankbus
Use shielded twisted pair wiring for the Rosemount 5900C Series in order to comply with
FISCO
(4)
requirements and EMC regulations. The preferred cable is referred to as type “A”
fieldbus cable. The cables must be suitable for the supply voltage and approved for use in
hazardous areas, where applicable. In the U.S. explosion-proof conduits may be used in
the vicinity of the vessel.
Use wire rated at least 5 °C above maximum ambient temperature.
We recommend cable size 1.0 mm
2
or 18 AWG in order to facilitate wiring. However,
cables within the range 0.5 to 1.5 mm
2
or 20 to 16 AWG can be used.
The FISCO F
OUNDATION
™
Fieldbus specification requires that cables for the Tankbus comply
with the following cable parameters:
Table 3-11: FISCO Cable Parameters
Parameter
(1)
Value
Loop resistance 15 Ω/km to 150 Ω/km
Loop inductance 0.4 mH/km to 1 mH/km
Capacitance 45 nF/km to 200 nF/km
Maximum length of each spur
(2)
cable 60 m in apparatus class IIC and IIB
Maximum cable length including trunk
(3)
and
spurs
1000 m in apparatus class IIC and 1900 m in
apparatus class IIB
(1) For further information see requirements of the IEC 61158-2 standard
(2) A spur is an unterminated part of the network.
(3) A trunk is the longest cable path between two devices on the fieldbus network, and is the part of
the network which has terminations at both ends. In the Rosemount Tank Gauging system, a
trunk is typically located between the Rosemount 2410 Tank Hub and a segment coupler or the
last device in a daisy-chain configuration.
(4) See IEC 61158-2
Reference Manual Installation
00809-0100-5901 September 2019
Rosemount 5900C Radar Level Gauge 105