3-32 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
WIRING CHAPTER 3: INSTALLATION
3
manner without exceeding driver capability. For larger systems, additional serial channels must be added. It is also
possible to use commercially available repeaters to have more than 32 relays on a single channel. Avoid star or stub
connections entirely.
Lightning strikes and ground surge currents can cause large momentary voltage differences between remote ends of the
communication link. For this reason, surge protection devices are provided internally at both communication ports. An
isolated power supply with an optocoupled data interface also acts to reduce noise coupling. To ensure maximum
reliability, ensure that all equipment has similar transient protection devices installed.
Terminate both ends of the RS485 circuit with an impedance as shown in the figure.
Figure 3-29: RS485 serial connection
3.3.9.3 100Base-FX fiber optic ports
The fiber optic communication ports allow for fast and efficient communications between relays at 100 Mbps. Optical fiber
can be connected to the relay supporting a wavelength of 1310 nm in multimode.
Ensure that the dust covers are installed when the fiber is not in use. Dirty or scratched connectors can lead to high losses
on a fiber link.
3.3.10 IRIG-B
IRIG-B is a standard time code format that allows stamping of events to be synchronized among connected devices. The
IRIG-B code allows time accuracies of up to 100 ns. Using the IRIG-B input, the L90 operates an internal oscillator with 1 µs
resolution and accuracy. The IRIG time code formats are serial, pulse width-modulated codes that can be either DC level
shifted or amplitude modulated (AM). The GE MultiSync 100 1588 GPS Clock as well as third-party equipment are available
for generating the IRIG-B signal; this equipment can use a global positioning system (GPS) satellite system to obtain the
time reference so that devices at different geographic locations can be synchronized.
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