Flowserve MX FOUNDATION Fieldbus Field Unit - Manual (Page 15)

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MX/QX FOUNdaTION Fieldbus Field Unit FCd LMENIM2330-01 – 08/11
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Power Conditioners are power supply impedance matching networks and are required. For additional
details see FOUNDATION Fieldbus Wiring and Installation 31.25 kbits/s, Voltage Mode, Wire Medium
AG-140, available on the web at www.fieldbus.org.
2.4 Cable Shielding and Grounding
For best performance, Fieldbus cables should be shielded. When using shielded cable, connect each
spur’s shield to the trunk shield, and connect the overall shield to ground at one point.
For most networks the ground point can be anywhere. In Figure 2.5 the grounding point has been
chosen as the junction of the field instruments.
Figure 2.5 – Use of Shielded Cable
2.5 Fieldbus Power Supply
The MX/QX FF board requires 9-32 VDC and 20 mA per MX/QX FF board on the bus. The 9-32 VDC
power can come from a separate power supply, usually located at the host end of the cable, or from
the Fieldbus interface.
NOTE: If power is lost to the unit, the FF board is still active and will still generate alarms..
Figure 2.6 shows a typical Fieldbus power supply arrangement.
FOUNDATION
Fieldbus
Interface
Shielded Wire Pair
Connect Shield
to Ground at one
place only
T T
Field
Device
Field
Device
Field
Device