Rosemount 3491, Справочное руководство, Страница: 27 / 152

Reference Manual
00809-0100-4841, Rev. AA
May 2007
3-9
Rosemount 3490 Series
Transmitter Connections
and Cabling
Connection of a transmitter to the control unit does not confer Intrinsic Safety
on the transmitter. It is the responsibility of the user to ensure any transmitter
installed in a hazardous area is suitable for use and certified accordingly. The
installation should be in accordance with a recognised code of practice.
Check the parameters of the installed system of control unit, transmitter, any
loop-powered devices, and interconnecting cable to ensure compliance with
the product certificates and technical data (Appendix A and Appendix B).
Particular attention must be given to the cable and the transmitter to ensure
that the total capacitance and inductance limits stated in the technical data in
Appendix B are not exceeded.
Cable joins are allowable in cabling the transmitter, provided that the joint is
made within an IP20/NEMA 3 (minimum) enclosure suitable for the
environment, and that wiring withstands a test voltage of 500V r.m.s. to earth.
The maximum length of cable permissible between the transmitter and control
unit is determined by limits imposed by the Intrinsic Safety certificates of the
instruments and Control Drawings.
No other outputs from the control unit must be routed through a hazardous
area unless protected by an additional I.S. Barrier (not supplied).
It is the responsibility of the user to ensure that any transmitter is installed in
accordance with the manufacturer’s instructions supplied with the transmitter.
Cable between the 3490 Series Control Unit and the transmitter should be
shielded twisted-pair with the shield connected to terminal 3 (marked with
earth symbol) on the 3490 Series Control Unit. The shield should be left
unconnected at the transmitter
unless there is a terminal specifically provided
for this purpose.
Cable runs should be separate from any high voltage or mains cables to avoid
crosstalk or interference.
Multi-core cable may be used, provided that other cores carry only low
voltage (24V dc nominal) signals and each pair of cores is individually
shielded.
Loop-powered transmitters must be connected to terminals 1 - 3 (Figure 3-4).
Figure 3-4.
Loop-powered transmitter
connections to 3490 Series
Control Unit
The 3490 Series Control Unit is able to provide 24V dc to a transmitter with a
max load of 25mA. Separately powered transmitters must be connected to
terminals 2 - 3 as shown in Figure 3-5
30 I.S. Earth (Earth symbol)
31
(2)
Negative -
32
(2)
Positive +
(1) Mains powered control unit only.
(2) DC powered control unit only.
Terminal Function Layout
1
2
3
24V
Iin
(Control Unit)
(Transmitter)