IO module replacement advice: Consider legacy connections, Ethernet, peer-to-peer
I/O wiring can be among the most challenging (and perhaps feared) of upgrades. When replacing input/output connections, what are key considerations? Daniel Liu, business development manager, data acquisition and control, Moxa Technologies Inc., offered answers to some key questions.
The history of I/O wiring can be divided into three phases.
In the first phase when remote I/O products were not available, all I/O contacts needed to homerun all wires back to where the controller was located. As running cables can be costly and troublesome, PLC or controller manufacturers began to use different vendor-defined protocols, or fieldbus networks, to develop remote I/O technology. In this way, less cabling infrastructure was required since only one set of wires (such as Ethernet or serial) was required to homerun to the controller, as compared to multiple wires from each I/O contact in a traditional I/O deployment.
A more recent development in remote I/O technology corresponds to the advent of Ethernet in automation applications. Running a fieldbus protocol over Ethernet makes it more convenient to build just one Ethernet infrastructure and use Ethernet switches to extend the reach of the remote I/O (as compared to serial-to-Ethernet infrastructure). This use of Ethernet infrastructure provides a substantial benefit, reducing cabling costs.
As Ethernet becomes more of a standard in the remote automation space, new I/O installations will need to be integrated with older systems that may still be using serial-based remote I/O technology, or are running hard wiring from the I/O contacts to the I/O controller (an extremely traditional deployment of I/O). To upgrade the older system and reduce cabling infrastructure, one technique is to use TCP/IP, so the operator can enable peer-to-peer communications between two remote I/O connections to replicate the I/O signal over an IP-based network.
For example, Moxa’s ioLogik E1200 series modules are designed to be used as a remote I/O as well as the cable replacement solution. The modules enable the capture of digital and analog signals and then translate those signals into TCP/IP packets. They then send the TCP/IP packet through the network and reproduce the digital and analog signal at the other end.
This gives I/O module replacement a tremendous advantage in that now the I/O signal can run through any type of IP-based network, including wireless. (Despite wireless applications for remote I/O, this technology is still considered premature as IEEE 802.11 technologies used for simple data acquisition applications are considered an alternative to wired remote I/O solutions.) In conclusion, peer-to-peer communication provides the operator with the ability to seamlessly integrate I/O connections to the Ethernet network, thereby saving time and money. Building unnecessary cabling infrastructure becomes a practice of the past.
Moxa provides additional help on cable replacement in remote I/O applications. http://www.moxa.com/Event/Net/2010/Peer-to-Peer_Remote_IO/index.htm
- Daniel Liu is business development manager, data acquisition and control, Moxa Technologies Inc. Edited by Mark T. Hoske, CFE Media, Control Engineering, www.controleng.com.
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