Sensaphone Sentinel Pro, Инструкция по установке и настройке, Страница: 36 / 44

36
Sentinel Pro Installation and Setup Guide
suggested Cable type:
The table below gives suggested specifications for the cable used to connect the Sentinel Pro to other
Modbus RS-485 devices. The closer the cable you choose matches these specs, the more likely it is that
your Sentinel Pro will be able to communicate to other modbus devices without error. Please note the
though the ground connector is not required by the RS-485 standard, it is strongly recommended that it
be used in your network.
Type
Shielded twisted pair with an additional
ground conductor
Wire Gauge 18-24 AWG
Characteristic Impedance (Twisted Pair) 120 Ohm
Shunt Capacitance 16 pF/feet or below
Propagation Velocity 66% or greater
Sentinel Pro (Master)
Modbus Slave
Modbus Slave
D+ D– GND
D+ D– GND
D+
D–
GND
Modbus Slave
D+
D–
GND
The image to the left represents the basic lay-
out of a properly wired RS-485 network. Your
RS-485 network should consist of a single main
cable “trunk.” Never run multiple long runs to
each modbus slave device. Termination resistors
should be placed between the two communica-
tion conductors at each end of the main run, but
nowhere else. The value of the termination resis-
tors should match the characteristic impedance
of the cable you are using. If your Sentinel Pro
is at one end of the run, its internal termination
resistor can be used by setting the “Bus Term.”
Switch next to the RS-485 terminal block to the
“In” position. If your Sentinel is not at the end
of the main run then set this switch to the “Out”
position. If the devices at the ends of the main
run do not have an internal termination resistor,
an external one must be used. A standard 1/4W,
5% resistor is adequate.
Many times, it may not be possible to have all
devices along the main run and a short cable
stub must be spliced into the main run to attach
a device. Make every effort to make the stub
runs as short as possible. If this stub length is greater than approximately 22 feet (6.7m), the main cable
should be re-routed so as to make the stub shorter. It’s always better to have a longer main run and
shorter stub lengths. Also, make sure that all devices connected to the main run, whether via a stub or
directly, are adequately spaced apart along the cable. Make sure there is at least 18 inches (0.5m) of cable
between all devices and splices on the data bus. If necessary, make the main run longer to meet this
requirement.