Communication

The communication network is the backbone for any Control system and is required for various control devices to communicate with each other and to a central information centre capable of taking control actions, which could be either LAN or WAN.

Common Wired Communication:

• RS232 (One-to-One): Its a single-ended full-duplex interface is used for short distances, maximum cable length - 50 feet
• RS422 (1Tx-to-10Rx): Reducing common mode noise to enable data transmission over long distances in noisy industrial and factory automation environments, maximum cable length - 1650 feet.
• RS485 (32Tx-to-32Rx): Similar to RS422 but have multiple commanding devices (Tx) and multiple receiving devices (Rx), maximum cable length - 650 feet.

Industrial Specific Protocol:

• Serial: PROFIBUS, PROFINET, Modbus™ and CAN
• Ethernet: EtherCAT, PROFINET, Modbus™ TCP/IP, Ethernet/IP and PowerLink

Data buses like Modbus and Profibus are no longer the de facto standard for industrial communications; both have been overtaken by Ethernet. Ethernet accommodates a wide range of applications, has become universally supported by communications equipment manufacturers and counts ease of configuration and low cost among its many advantages.

However, all the wired communications modes share one significant drawback with other: Cabling.

Wireless communication technologies address the cabling drawbacks of hardwired connections and offer many new possibilities in the industry for particularly flexible and efficient automation solutions. There are many different methods of wireless communication, based on the distance between the transmitting and receiving points. For example, Bluetooth and Wi-Fi for short distances, GSM or CDMA for longer distances.

The key requirement for the use of wireless technologies in industrial applications is that the technology must be as rugged and reliable as a cable connection, even under harsh conditions. The wireless connection is subject to interference, such as electromagnetic interference fields, which can adversely affect transmission.

• ZigBee - used for simple applications with a low data rate, low power and low-cost requirements. It offers a diversity of channel selections over three bands: one in 868MHz, ten channels in 902-928MHz and sixteen available in the 2.4GHz ISM.


• Bluetooth - operates in the 2.4GHz (ISM) band. Piconet is the basic unit of networking in Bluetooth. It is an ad-hoc network with one master and up to seven active slave nodes. Ultra-wideband technology is designed for applications which require a power-efficient, high bandwidth solution. UWB offers enormous bandwidth which enables it to tackle multipath and jamming issues.


• WirelessHART and ISA100.11a protocol has become popular for communication in various types of field devices, such as flow-meter, level controllers with the PLC and Panel instruments. Both are well positioned to address the industrial needs especially because of the advanced security, channel hopping, TDMA and blacklist-based approach to guarantee real-time operations and reliability in an unprotected license-free radio spectrum.


• Industrial wireless Ethernet is suitable for integration in processes that use data or for SCADA and PLC applications. They transmit distributed Ethernet and analogue, serial or digital I/O data to IP-based networks. It can support all common IP protocols, such as Modbus TCP, PROFINET or EtherNet/IP.

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