Specifications

28
Reference Manual
00809-0100-2460, Rev AA
Section 3: Installation
November 2014
Installation
3.5.5 Cabling for the TRL2/RS485 Bus
In a Rosemount Tank Gauging system a Rosemount 2460 System Hub communicates with a
TankMaster control room PC using the TRL2/RS485 Modbus protocol, see Section 2: Overview.
TRL2 Bus
The TRL2 bus requires twisted and shielded pair wiring with a minimum cross-sectional area of
0.50 mm
2
(AWG 20 or similar). The maximum length of the TRL2 bus is approximately 4 km
(13000 ft). The TRL2 field bus can normally use existing cables in the tank area.
Cable cross-sectional area for the TRL2 wiring should follow the recommendations in Table 3-1:
Table 3-1. Minimum cable area for the TRL2 bus
Figure 3-3. Individually shielded pair cables minimizes crosstalk
Table 3-2 shows typical cable types that can be used for connecting the TRL2 bus. Other cables
of similar type may also be used.
Table 3-2. Recommended cable standards for the TRL2 bus
RS485 Bus
The RS485 bus should meet the following requirements:
 twisted and shielded pair wiring
 characteristic impedance of 120 
 maximum cable length 1200 m / 4000 ft.
Maximum distance Cross-sectional area
Minimum Maximum
3 km 0.50 mm
2
(AWG 20) 2.5 mm
2
4 km 0.75 mm
2
(AWG 18) 2.5 mm
2
Type Manufacturing standard Core size
Signal
BS 5308 part 1, type 1 1 mm
2
Signal (armoured)
BS 5308 part 2, type 1 1 mm
2