Optical Port Connections 9300 Series User’s Guide
Page 108 Chapter 5 - Features and Applications
Install a ¼ Watt termination resistor (RT) between the (+) and (-) terminals of the
device at each end point of a straight-line bus. The resistor should match the
nominal impedance of the RS-485 cable (typically 120 ohms – consult the
manufacturer’s documentation for the cable’s impedance value).
CAUTION
Do not connect ground to the shield at both ends of a segment. Doing so allows ground loop currents to
flow in the shield, passing noise into the communications cable.
RS-485 Connection Methods to Avoid
Any Device connection that causes a branch in the main RS-485 bus should be
avoided. This includes star and tee (T) methods. These wiring methods cause signal
reflections that may cause interference. At any connection point on the RS-485 bus,
no more than two cables should be connected. This includes connection points on
instruments, converters, and terminal strips. Following this guideline ensures that
both star and tee connections are avoided.
Refer to the “Hardware Reference” chapter for the optical port specifications.
The optical (infrared) port on the meter’s front panel is compatible with an ANSI
C12.13 Type II magnetic optical communications coupler. The optical magnetic
coupler is purchased separately. Contact your supplier for a list of recommended
opto-couplers.
The optical port can communicate real-time measurements to a laptop or similar
device via ION, Modbus RTU, or DNP 3.0 (9330 and 9350). The port can also be used
for infrared energy pulsing.
Avoid
3-way “Star”
connection point
Avoid
3-way “T”
connection point