Section 1,
Typical ModBUS Network Topography
(FIGURE 1-1).
As part of the CSA certification, it was verified that the modbus
communication functions of this gas detection instrument do not
adversely affect the gas detection operation and functions of the
instrument. This Certification, however, does not include or imply
certification of the modbus communication function of this gas
instrument.
Sensors
• A network can consist of up to 31 monitors.
• Each monitor can support up to three sensors.
• Total number of sensors is 93.
Wiring
Power
• Maximum power cable length depends on sensor configuration and
wire gauge (TABLES 1-1, 1-2 and 1-3).
RS485 Communications
• Three-wire cable, 22 AWG is labeled:
• A = Transmit + / Receive +
• B = Transmit - / Receive -
• C = Common
• Typical Communications Wiring Scheme
(see FIGURE 1-2)
• Maximum RS-485 communications cable length:
• Trunk: 3000 feet
• Branch: 60 feet
• Use line termination devices to match communication line
characteristics (typically 120 Ohms).
Transmitter Sensor Distance (FIGURE 1-3)
• Maximum transmitter-sensor distance is normally 100 feet.
• The distance is extended to 3000 feet if the signal boost option is
installed.
• This option requires the sensor to be locally powered.
• It is possible to selectively use this feature on a per-sensor
basis.
1-2
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