Rockwell Automation 1788-CN2FF ControlNet to Foundation Fieldbus H1 Linking Device Installation Instructions - Manual (Page 8)

8 ControlNet-to-Foundation Fieldbus H1 Linking Device
Publication 1788-IN051D-EN-P - February 2004
Power Conditioning
You must use a power conditioner between your Fieldbus power supply and the Fieldbus
network. You can use a power supply designed for Foundation Fieldbus operation which has
the proper power conditioning elements. If you are using an ordinary power supply, a separate
power conditioner must also be used. If an ordinary power supply is connected directly to the
Fieldbus, the power supply would absorb signals on the cable because it would try to maintain
a constant voltage level. The power conditioner puts an inductor between the power supply
and the Fieldbus wiring. The inductor connects the DC power to the Fieldbus wiring but
prevents signals from going into the power supply.
In practice, a real inductor is not used in the power conditioner but an electronic equivalent.
The electronic inductor circuit has the added advantage of limiting the current provided to
the network segment if the cable is shorted.
The voltage supplied to the Fieldbus cable can be as high as 32 V. The voltage at any device
can be as low as 9 V for the device to operate correctly. A typical Fieldbus device takes about
20 mA of current from the cable. The Fieldbus is configured so that one of the wires has a
(+) voltage, the other wire has a (-) voltage and the shield is grounded.
A cable with the orange wire as plus and the blue wire as minus is shown above. This type of
cable is available from Fieldbus cable manufacturers. Other cables or existing plant wiring
conventions may be different. Regardless of the color convention, keep the sense of Fieldbus
polarity consistent throughout the plant.
(1)
Be sure to follow the wiring and installation requirements in the Foundation Fieldbus
publications listed in the section Additional Information on page 3.
IMPORTANT
We suggest that you not use White/Black or White/Red pairs since
they may be mistaken for 115 volt power wiring.
(1) RELCOM inc., Fieldbus Wiring Design and Installation Guide (2221 Yew Street, Forest Grove, OR 97116) p. 5. Reprinted by
permission.