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Alarm systems: Rs485 cables in alarm systems help transfer alarm signals and information from alarm devices to the control center. This ensures that all security-related information and incidents are transmitted quickly and with high reliability. Unlike what happens in many energy distribution systems, the manner in which the devices are connected in parallel is important. Each device has a communication port with two terminals, which are indicated for the sake of convenience as A and B. In these two terminals the communication cable is connected so that all the devices that take part in the communication are connected in parallel. Rs485 is low impedance balanced , so twisting the pair helps with noise immunity as well as reducing the attenuation effect of higher baud rates due to the parallel capacitance of the wires in the cable jacket over the long lengths. High noise immunity. We employ transient suppression and 3KV galvanic isolation. To prevent noise to interfere with the communications, often twisted pair cable is used. Rs485 cable is essentially a signal cable with a twisted pair structure, additionally shielded with 2 layers of noise protection used in industrial communication. Industrial automation systems: In the industrial automation sector, rs485 signal cables play a vital role in connecting and remotely controlling motors.

Access control systems: Rs485 cables are mainly used to connect and transmit data between access control devices such as security gates, RFID cards, or time attendance machines and the control center. Control and monitoring systems: A single pair of rs485 signal cable can connect up to 32 devices, with a signal transmission distance of up to 1200m. Therefore, using rs485 cables is an ideal choice for industrial control and monitoring systems, especially those with large-scale and high dispersion. 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. Henceforth, we shall consider Slave devices to be measuring instruments with serial communication, even if the cabling is similar for all Modbus devices. Interoperability of even similar devices from different manufacturers is not assured by compliance with the signal levels alone. Longer branches could cause signal reflections and generate disturbances and consequent errors in the reception of data. The branches must be no longer than 1200 m!

The main cable must be no longer than 700 m! Using a repeater, the main cable is divided into different segments, each of which can be up to 700 m in length and connect 32 devices (this number includes the repeaters). The maximum number of repeaters that should be serially connected is 3. A higher number introduces excessive delays in the communication system. Rs485 cables not only vary in the structure of the core but also in the number of twisted pairs. This ensures maximum protection for the inner core. Kits for board as pictured with all headers, $13.50 to US addresses, includes padded envelope shipping via USPS & paypal fee. Assembled boards with straight male headers $4 7. Add USPS shipping & paypal fee. Add USPS shipping & paypal fee. 3 boards daisychained. Connect signals from 1st to 2nd to 3rd, add power & Gnd to each. Standalone board controlled by shift register from any Arduino, easy to daisychain, shown pictured with barrel jacks for power. Uno shield, shift register controlled by any 3 pins. Mega shield, relays driver by D22-D29.

Relay Board with '1284, RS232, USB, directly driven relays. Pricier than e-bay modules, easier to use - shift in a 1, relay contacts close. The diagram below shows a basic RS485 cable for use with the RJ11 socket on Unitronics PLCs. It seems if there is a lot of RFI in the installation, shielded twisted cable can be justified. Now there was certain instances I used STP wire for rs485 because I had a lot of devices connected in a long run chain (DMX512 lighting fixtures). In order to avoid errors when many devices are connected, cables of the same colour should be used for all the connections to the terminals A and cables of the same colour should be used for all the connections to the terminals B of the various devices (e.g. white for A and blue for B). The shielding may be braided (be formed by a mesh of thin conducting wires) or be a foil (consisting of a sheet of metal wound around the conductors): the two types are equivalent. The outer layer of aluminum foil covers the entire conductive core, serving to counteract high-frequency interference.