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Serial Connections with a Global Reach

Serial Connections with a Global Reach

| 10/24/2013 11:00:00 AM

If you happened to see a news story about the recent America’s Cup you probably noticed that they’re using tri-hulls and catamarans these days, and that even the slowest entry would run rings around Captain Jack Sparrow’s Black Pearl. But whether it’s the Pearl or a modern racing yacht, the underlying technology hasn’t changed for thousands of years, you hoist a sail and let the wind do the work.  You may not be able to outrun a 1,350 HP cigarette boat, but you’ll get where you want to go.  And you won’t have to spend a nickel on high octane marine fuel.

Like sailboats, our trusty old serial protocols will still take you where you want to go, just as they always have.  Serial may not have the best speed or bandwidth, but it’s hard to beat for cost and reliability.  So in spite of all the predictions to the contrary, the installed base of serial equipment keeps growing every day.

Serial communications, of course, predate modern Ethernet.  But there’s no reason you can’t get the best of both worlds by letting legacy protocols and equipment communicate across modern networks, and by letting your serial devices work in tandem with the latest technologies.  It’s not that hard to do.

ZlinxMixing the old with the new
Quite recently, one of my clients wanted to monitor and control a wastewater pump lift station. To make the system work as desired, my client would need to provide data connections for a broad mix of pump switches, pump current monitors, flow controllers, level sensors and float switches. It can be very cost effective to use serial equipment in an application like this, but we also wanted to establish long range, remote communications.  So how do you communicate with protocols like Modbus when your installations are nowhere near your central office?

We solved it with a mix of the old and the new.  First, we connected the various sensors to a remote I/O radio transmitter, in this case B&B Electronics’ Zlinx  Xtreme I/O radio transmitter, via the sensors’ 4-20 ma output. The Zlinx Xtreme I/O radios supported native Modbus RTU, so no conversion was necessary.  They also provided AES encryption.  Throughput wasn’t enormous, no more than 250 Kbps, but it was ample for task at hand.

The RF signals from the various I/O transmitters were collected by an RF radio modem. Thus, up to this point, we were using technology that has been around for quite some time.  The more advanced technologies began to come into play when we wanted to connect to the Internet.

Spectre3GCellular telephone networks open new wireless remote monitoring possibilities
There was no conveniently located copper or fiber Ethernet infrastructure. So, rather than string cable out to the site we used a cellular router and the cellular telephone network to connect remotely via IP.  Like the RF equipment, the cellular router was Modbus compatible and converted the Modbus RTU from the Zlinx Xtreme to Modbus TCP/IP. To ensure security we used VPN Tunneling, which let us use the cellular network much as if it were proprietary infrastructure.

Had it been needed, we could have used the Ethernet port in the cellular router to connect additional remote monitoring equipment like IP cameras. Video is already very useful on the 3G networks that are currently in place, and when the 4G LTE buildout is complete video will be amazing.  We’ll see video being used for everything from security to remote diagnostics.

By collecting different kinds of data from numerous devices, cellular routers can create a seamless connection that allows for remote monitoring and control anywhere on the planet, provided that a cellular signal is available. A cellular router that can network-enable serial equipment not only adds new capabilities to legacy installations, it lets you use serial equipment in new installations as well. In this use case we added a seamless connection from a sensor using Modbus RTU to a remote SCADA platform using Modbus TCP/IP, allowing for remote monitoring and control from anywhere in the world.

Granted, the low latency and massive bandwidth of the new 4G LTE networks will lead to an explosion of innovation, and we can expect to see many new M2M applications that take full advantage of 4G LTE’s capabilities.  But while the new 4G LTE applications will get all the headlines, don’t forget that serial can use 4G LTE, too.  And there will still be times and places where an old-fashioned serial installation can provide a cheap, reliable solution.  Serial isn’t going away, and it will still get you where you need to go.

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