Honeywell XNX-AM Series, Техническое руководство

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XNX Universal Transmitter
Installation and Operation 58
Cable Length
Most installations are well within the 10,000 ft. (3,000 m)
theoretical limit for HART communication. However, the electrical
characteristics of the cable (mostly capacitance) and the
combination of connected devices can affect the maximum
allowable cable length of a HART network. The table below
shows the effect of cable capacitance and the number of
network devices on cable length. The table is based on typical
installations of HART devices in non-IS environments, i.e., no
miscellaneous series impedance.
More information for determining the maximum cable length
for any HART network configuration can be found in the HART
Physical Layer Specifications .
Cable Capacitance – pf/ft (pf/m)
Allowable Cable Lengths for 18 AWG (1.0 mm
2
) Shielded Twisted Pair Cable
Number of Network
Devices
20 pf/ft
(65 pf/m)
30 pf/ft
(95 pf/m)
50 pf/ft
(160 pf/m)
70 pf/ft
(225 pf/m)
1
9,000 ft
(2,743 m)
6,500 ft
(1,981 m)
4,200 ft
(1,280 m)
3,200 ft
(975 m)
2
8,750 ft
(2,667 m)
6,350 ft
(1,935 m)
4,075 ft
(1,242 m)
3,125 ft
(953 m)
3
8,500 ft
(2,590 m)
6,200 ft
(1,890 m)
3,950 ft
(1,205 m)
3,050 ft
(930 m)
4
8,250 ft
(2,515 m)
6,050 ft
(1,845 m)
3,825 ft
(1,165 m)
2,975 ft
(905 m)
5
8,000 ft
(2,440 m)
5,900 ft
(1,800 m)
3,700 ft
(1,130 m)
2,900 ft
(884 m)
6
7,800 ft
(2,380 m)
5,760 ft
(1,755 m)
3,620 ft
(1,105 m)
2,820 ft
(860 m)
7
7,600 ft
(2,317 m)
5,620 ft
(1,713 m)
3,540 ft
(1,080 m)
2,740 ft
(835 m)
8
7,400 ft
(2,255 m)
5,480 ft
(1,670 m)
3,460 ft
(1,055 m)
2,660 ft
(810 m)
Relays
The relay option (XNX-Relay) provides 3 form “C” SPCO contacts
for alarm and fault indication. A remote reset is provided to
silence alarms.
The remote reset switch (designated TB-4 and labeled “Remote
Reset SW”) is located on the relay option board. It provides
a remote hardware-based reset of faults and alarms to the
transmitter. In the event that direct access to the local user and
HART interfaces is not possible, alarms and faults from an XNX
transmitter can be reset remotely using a switch.
The transmitter can be reset by activating a momentary switch.
This will momentarily close the circuit between the two pins of
TB4, providing the same functionality as a Reset Alarms & Faults
command performed from the main screen of the local user or
the HART interfaces.
Note:
This option is not available when the Modbus or FOUNDATION Fieldbus options
are installed.
NOTE
!
Wiring for the relays is through an available cable/conduit port to a
pluggable terminal block. See Figure 33 for the terminal block
legend.
The transmitter has three relays: relay 1 is for alarm level 1, relay 2
is for alarm level 2, and relay 3 is for faults and special states. All
special states are indicated by the fault relay.
Honeywell Analytics recommends that the fault relay be used in all
installations to maintain safe operation. See
Set Alarm Values for
more information.
The relay state is refreshed every 2 seconds. The fault relay is