How to convert fiber optic cable to RS485

To convert a fiber optic signal to RS485, you need a fiber-to-RS485 converter, which translates optical signals into electrical RS485 signals for serial communication.

Methods of Conversion

There are two main approaches to converting fiber optic signals to RS485: 1. Level-Type Conversion: This method directly converts the RS485 electrical signal into an optical signal and vice versa without changing the data format. It is ideal for point-to-point RS485 device connections. You simply use a pair of fiber-to-RS485 converters, one at each end of the fiber link. The computer or RS485 device connects to the converter's serial port, and the data is transmitted over the fiber. This method does not require knowledge of serial parameters like baud rate or parity for the fiber link itself, making it simpler for direct device-to-device communication . 2. Protocol-Type Conversion: Also called a serial device server, this method converts RS485 data into TCP/IP packets for transmission over fiber. It allows the fiber link to be shared with other devices via network switches. However, it requires IP configuration and knowledge of RS485 serial parameters (baud rate, data bits, stop bits, parity) and is more complex to set up. The upper computer accesses the data through the device's IP address .

Equipment Options

• Phoenix Contact PSI-MOS-RS485W2/FO: Converts RS485 2-wire bus systems to fiber optic, supports multimode fiber, and includes optical diagnostics for monitoring signal quality .
• Moxa Serial-to-Fiber Converters: Industrial-grade converters that support RS232/422/485 to fiber optic conversion, suitable for reliable long-distance communication .
• CommFront RS485-to-Fiber Converters: Rugged, point-to-point converters for industrial environments, supporting multi-mode (up to 5 km) and single-mode (up to 40 km) fiber links .
• Siemens 7XV5650: Optical fiber converter for asynchronous RS485 protocols, designed for SIPROTEC devices and industrial applications .

Practical Considerations

• Distance: Fiber optic links can extend RS485 communication far beyond the typical 1.2 km limit of copper RS485. Multi-mode fiber supports shorter distances, while single-mode fiber supports tens of kilometers.
• Pairing: Level-type converters must be used in pairs, one at each end of the fiber link.
• Industrial Environment: Choose converters rated for temperature extremes and rugged conditions if used in industrial settings.
• Connectors: Ensure compatibility with fiber connectors (ST, SC, FC) and RS485 wiring standards.
• Monitoring: Some converters include optical diagnostics to detect signal degradation or fiber breaks . By selecting the appropriate converter type and following proper installation, you can reliably convert fiber optic signals to RS485 for long-distance serial communication.