RKI Instruments 71-0533, Руководство оператора, Страница: 58 / 61

58 • T3A Transmitter
Proper Connection
The distance of the Modbus connection from the gas detection device to the controller cannot
exceed 4,000 feet. In the instance of daisy-chained devices, this applies to the last sensor
connected on the line. Connection distances of 100 feet, or less, require 22 to 24 gauge wire.
Connection distances that range more than 100 feet require 18 to 20 gauge wire.
For more information on properly wiring a daisy chain network of devices for Modbus,
consult the following diagram.
The signal wire of each unit is run to the signal terminal of the neighboring sensor. With each
device connected to the previous device via the signal wire, a “chain” is created, with the first
device in the chain directly connected to the controller.
(*) Terminating resistor may be required for the last device in the daisy-chain.
RS-485 Modbus Connection Distances for Electrical Wiring
Distance Length Gauge
Size
Twisted Pairs
Short < 100 Feet 22 to 24
Gauge
Shielded, in areas of
high noise
Medium 101 Feet to
1,000 Feet
18 to 20
Gauge
Shielded, in areas of
high noise
Long* 1,000 Feet to
4,000 Feet
18 to 20
Gauge
Shielded, in areas of
high noise