Niraj Haria, Data Communications Senior Sales Engineer at Amplicon explores the advances in industrial communication. Serial communications (RS232/422/485) have traditionally been used in industrial automation to connect various instruments such as sensors, data loggers to standalone monitoring stations like computers. The limitations of serial communications, such as distance, accessibility, the amount of data transferred at any one time and speed has led to a demand for a more flexible means of communicating.
Although slow to catch up with IT infrastructure in commercial environments, Ethernet is increasingly regarded as the defacto standard of communications in industrial markets. However, the sheer volume of serial based products already in existence and the low cost and ease of integration of these ‘legacy’ protocols means that serial communication is alive and well in many areas of industry.
Due to the minimal processing power required, the ruggedness and reliability of connectors, even relatively new products such as GPS receivers continue to adopt RS232 and RS485.
RS485 has been the physical layer protocol for industrial networks since Modbus was launched by Modicon in the 1970’s. Other PLC manufacturers followed suit and used protocols such as Profibus DP and Interbus. The more modern PLC systems are Ethernet based, to allow individual ‘islands of automation’ to share data captured throughout the plant and the company, ‘top floor to shop floor’ and in some cases, even the world.
To enable legacy serial based hardware to take advantage of Ethernet, Serial to Ethernet device servers were born.
Advantages of serial to Ethernet:
The life time of expensive serial based equipment can be extended with serial to Ethernet devices. It allows low cost remote maintenance, reducing system downtime and labour cost. Control and management intelligence, enables more efficient business decisions. It also delivers the security features Ethernet affords into previously vulnerable systems.
A Serial to Ethernet device server is intelligent, with a processor, memory, operating system and a TCP/IP stack built in. It also comes equipped with the required hardware interface such as RS232, RS422 and RS485. This type of device server can transfer and even process data between the serial and Ethernet interfaces to carry out pre-defined tasks.
There are various ways in which a Serial to Ethernet device server can be used, dependent on the need of the application. For example, some may require that the serial device initiates transmission, with the host (PC) applications waiting for incoming data. For others it could be visa versa.
By supplying software drivers that work with the most popular operating systems, the device server establishes a transparent connection between the host and device by mapping the IP address and port number to a local COM port on the host computer or server. The benefits of this, are that it enables the upgrade of applications to Ethernet without modifying the source code.
When the device server is set as TCP Server mode, it acts like a server. It waits for the host to contact it. Once the host makes contact, it can send and receive data to and from the serial device. This mode also allows multiple hosts to communicate with the same serial device, at the same time or not as the case may be. It also allows more than one host to share the device server
More traditional Serial to Ethernet device servers operate without data encryption, leaving data vulnerable. Secure Socket Layer (SSL) is now used to provide secure end to end data transfer.
Port Buffering enables the device server to act as a serial port buffer if the network connection is lost. Buffer sizes can be increased by using SD Cards in some instances.
Device servers are now available with support for PoE (802.3af). This reduces cabling and facilitates ease of installation, saving time and money.
Ring redundancy has become common practice in industrial networks, increasing the availability of serial based devices. It also saves cost in not having to employ an additional Ethernet switch.
Serial to Ethernet device servers now support any data rate up to 1Mbp, which is useful for specialist devices.
Integration of digital and analogue signals to the Ethernet network assist Supervisory Control and Data Acquisition (SCADA). Distributed I/O traditionally using RS485 can now be connected to a Serial to Ethernet device server. These I/O Modules can use Simple Network Management Protocol (SNMP) traps, allowing information about the status of digital or analogue devices to be easily integrated into existing SNMP deployments (company infrastructure for example).
Serial to Ethernet is the natural next step, allowing simple, cost effective systems integration into existing infrastructure. By centralising monitoring of these systems, it enables business decisions to be made more efficiently and ultimately reducing complexity and cost.
