485 Module Rate Optical Coupler Requirements
For an isolated RS-485 solution, three optocouplers are required, two high-speed and one low-speed, along with additional Schmitt buffers for stronger drive to the optocoupler LED and to clean up any noise on low-speed optocoupler transistor output transition, biasing. The RS-485 bus standard is one of the most widely used physical layer bus designs. Although no maximum cable length is specified, lengths of 4000 meters are possible. Figure 1 and Figure 2 show typical circuits for isolating an RS-485 and CAN transceiver using optocouplers to achieve galvanic isolation. It uses a balanced pair of wires to send signals and can communicate at high speeds over distances up to 1200 meters. The RS 485-IS Coupler converts PROFIBUS-DP to PROFIBUS RS 485-IS with intrinsic safety (intrinsic safety ignition type i).
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