이름 : Juli
이메일 : juli.wisewould@laposte.net
연락처 :
예식일 : The Rs485 Cable Cover Up
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A challenge is that Laureate meters use RJ11 jacks, while Laureate LT series transmitters use screw-clamp connectors for three discrete wires. RS485 is specified for multi-point communicates where multiples devices have their own address on the same communication line, while RS232 is only specified for point-to-point communications. The RS485 interface allows the creation of multi-point networks. The RS485 employs a set of 120 Ohm termination resistors located at each end of the line. Can I mix Laureate LT transmitters and meters on the same RS485 line? Laureate meter and LT series transmitters support the Modbus RTU protocol and Laurel’s simpler ASCII character based Custom ASCII protocol. Set the PC to N81 for the Custom ASCII protocol, or to N82 or E81 for the Modbus RTU protocol. A single analog input meter or transmitter can stream readings to a PC at up to 60 readings per second and the Custom ASCII protocol set to continuous (or streaming) model. See page 7 of the Laurel digital panel meter manual, page 7 of the Laurel counter manual, page 8 of the Laurel scale meter manual, or page 8 of the Custom ASCII protocol manual.

If multiple analog input meters or transmitters are digitally addressed in command mode on an RS485 line using the Modbus RTU protocol or the Custom ASCII protocol, the rate becomes about 2 readings per second. What are setup steps for RS485? The presence of a new board and the type of board are automatically sensed by the meter’s firmware or by Instrument Setup (IS) software. The board with dual RJ11 jacks is the more popular since is can use commercial straight-through, non-reversing, 6-wire data cables with RJ11 connectors. This MJ20-PRG module clicks in the PLC and provides one RJ11 socket for serial communications with a PC. PCs are normally not equipped with an RJ11 socket for serial RS232 communications. With this boards, a CBL03 lines with RJ11 connectors can branch out to support an RS485 line consisting of three discrete wires. If on the other hand each terminal can accept only a single cable, a proper branch must be created using three auxiliary terminals for each instrument to be connected. In some countries, inserting two cables into the same screw terminal is permitted. 24 AWG solid wires, which are typically used in Cat 5 cables, can break easily when connected to a screw terminal block, which does not provide any strain relief.

Grounds between buildings may vary by a small voltage, but with very low impedance and hence the possibility of catastrophic currents - enough to melt signal cables, PCB traces, and transceiver devices. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. According to the EIA there is a maximum of 32 Unit Loads on one cable segment. The cable shield must be earthed only in one point. The diagram below shows a basic RS485 cable for use with the RJ11 socket on Unitronics PLCs. Therefore the pin assignment is a little bit different from the default pin assignment on the RJ11 socket. This cable provides a USB type A connector for the PC end and an RJ11 connector for the meter end. The main cable must be no longer than 700 m! In order to avoid signal reflections, a 120 Ohm termination resistance must be fitted on each end of the main cable. Therefore for RS485 communications no crossover cable is used. Transmission speed refers to the rate at which data is transferred between devices using the RS485 cable.

This has led to the development of enhanced shielding techniques and improved cable designs to minimize signal loss and maintain signal integrity over longer distances. In order to increase the extent of the Modbus network, repeaters can be used; and signal amplifying and regenerating devices provided with two communication ports that transfer to each what they receive from the other. The cabling of the industrial communication systems (Modbus RS485) is different in some ways from the cabling used for power cabling and the electrician may experience some difficulties if he is not an expert in Modbus communication networks. These cables allow the dual RJ11 jacks of the RS485 option board of Laureate meters (digital interface ordering option 2) to be daisy chained and to be addressed digitally with no need for a hub. Laureate meters are modular with a middle slot reserved for a communication board, as illustrated in our Laureates Overview web page. These cables are commonly used in industrial automation, building automation, and other applications where reliable and robust communication is necessary. Both protocols (or communication languages) are built into the instrument’s firmware and are user selectable.