There is a common misunderstanding on the scene: after getting on the ring network, you want to replace the 485 bus altogether. In fact, the acquisition bus on the instrument and protection device side will not disappear in the short term. The problem is how to make it safely pass through the Ethernet ring network and reach the control layer.

First distinguish the roles of the two networks

RS485 and RS422 are responsible for the bottom layer collection, the speed is not high but real-time and stable requirements are required; Industrial Ethernet is responsible for the upper layer aggregation and return transmission, and the two cannot replace each other. There are three ways to transmit bus signals across the ring network: protocol gateway conversion, serial port server packetization, and optical transceiver transparent transmission. In the transformation project, the amount of transparent transmission changes was small, and the original polling logic did not need to be changed; forcibly replacing 485 with Ethernet would create an additional layer of protocol conversion failure points. The number of stations on the bus and the longest distance determine whether relay segments are needed. These two things need to be clarified during the planning stage.

Specific connection methods for transparent transmission

Place one on each end of the bus2-way bidirectional RS485 data optical terminal, move the differential signals to the optical fiber, the ring network only bears Ethernet traffic, and is still the same 485 bus logically; the optical transceiver does not analyze the protocol, but only carries the signal, and the program on the host computer side basically does not need to be changed. Optional workstations that need to transmit switches or network signals at the same timeThree-in-one data optical transceiver, one link carries away multiple signals.

There are a few pitfalls that are easy to fall into after receiving it.

• There are no 120 Ω terminal resistors at the beginning and end of the bus, so the bit error rate increases as the distance increases.
• The optical transceiver and the instrument share the same ground to form a ground loop, and use isolated power supply or single-point grounding instead.
• The polling cycle is set too short, the serial port bandwidth is full, and the response of the slave station is obviously slow.
• Optical fibers and differential lines run in the same trunking but are not marked, making it easy to connect them in the wrong direction during maintenance.

EB-LINK can provide connection suggestions based on the length of the fieldbus and the number of stations. Tel: 0755-83179002.