Reference Manual
00809-0100-4841, Rev. AA
May 2007
3-11
Rosemount 3490 Series
d) Turn the power supply off and connect the second transmitter, either at
the same terminals 1-3 as the first transmitter or at the junction box, such
that both transmitters are now connected.
e) Turn the power supply on. The 3492 will once again search for and detect
connected transmitters. After the second transmitter is found, the 3492
will automatically change the poll address from “0” to “2”. The second
transmitter will also be automatically allocated to Channel 2 of the 3492.
Note that the 3492 may also offer the user the opportunity to set the
Bottom Reference of the transmitter at this point, which may be done or
ignored by press the ESC button.
Power Connections If the 3490 Series Control Unit is powered by mains AC power, select the AC
voltage as 115V or 230V using the voltage-selector slide switch.
If the 3490 Series Control Unit is DC powered, ensure the supply is adequate
(15 - 30V dc). Do not exceed 30V dc.
A switch or circuit breaker should be installed in close proximity to the
instrument, and labelled as such.
Although the 3490 Series Control Unit meets all European standards for
surge immunity on power and signal lines, it is recommended that lightning
suppressors, such as made by Telematic Limited, are fitted if local conditions
make this advisable.
Earthing Connections The IP-rated Rosemount 3490 Series of Control Units are double insulated
and DO NOT require a mains earth.
DO NOT connect a mains earth to terminal 30.
Terminal 30 is provided for use as an Intrinsically Safe (or functional) earth
connection, which MUST be used when a transmitter is mounted in a
hazardous area and is connected to terminals 1 and 2.
Terminal 3 is to be used for connection of the shield of the twisted-pair
transmitter cable when the 3490 Series Control Unit is powering the
transmitter (as in Figure 3-4 on page 3-9). Note that this shield should be left
unconnected at the transmitter end unless there is a terminal provided for this
purpose.
On the NEMA4X-rated Control Unit, protective earth cables must be
connected to at least one of the bonding points on the inside of the enclosure.
Bonding between conduit entries is not automatic and must be provided as
part of the installation.
When connected to equipment located in a hazardous area, not meeting the
requirements of clause 6.3.12 (Isolation of circuits from earth or frame) in IEC
60079-11:2006 (EN 60079-11:2007), equipotential earthing must be ensured
between the equipment and the intrinsically safe earth. An example of
equipotential earthing is a cable with a cross sectional area greater than
4mm
2
and a resistance of less than 1ohm.
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