Networks work in distributed systems
Data-acquisition applications that use Ethernet include jet-engine testing, machine monitoring, oven and freezer monitoring, and power monitoring.
By Martin Rowe, Senior Technical Editor -- Test & Measurement World, 6/1/2009 2:00:00 AM
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When you need to keep analog measurement wires short, yet your PC is located farther away from your measurement instrument than either USB or GPIB can reach, Ethernet may just fill the bill.
Data-acquisition applications that use Ethernet include jet-engine testing, machine monitoring, oven and freezer monitoring, and power monitoring. "Power monitoring is becoming more popular with concern over energy savings," said Charlie Stiernberg, product manager for remote data-acquisition products at National Instruments.
Networked data-acquisition systems often handle high channel counts. "Typical applications for our networked data-acquisition systems use 40 to 80 channels," said Sean Sullivan, VP of engineering at Data Translation. "Applications include monitoring industrial batch ovens and battery testing where long sensor wires are impractical."
Neil Fenichel, president of Microstar Laboratories, has also seen high channel counts used in conjunction with Ethernet-based instrumentation. He cited a test system for missiles that uses 40 temperature and 40 accelerometer channels where the measurement system is 1000 ft from a control room.
Distributed data-acquisition systems needn't be that far from a PC to use Ethernet, though. Steve Radecky, product marketing specialist at IOtech, has run across distributed measurement applications that were in a relatively small area, but they were too far from the PC to use USB. The customer didn’t want to run the strain-gage sensor wires back to a PC, but USB didn’t have the distance needed, so Ethernet was the best choice.
 The EX-1000A combines 48 temperature or voltage channels with an LXI Ethernet port. Courtesy of VTI Instruments. |
New LXI instruments, which use Ethernet, appear on the market regularly. Data-acquisition instruments include those for measuring temperature (see figure), strain, and voltage. LXI instruments that support IEEE 1588 let you synchronize measurements across instruments.
Although Ethernet is often the right communications bus for sending measurement data over distances that USB and GPIB can't handle, it sometimes puts engineers face-to-face with the IT staff. "Engineers want to stay away from IT," said Radecky. "IT people don’t want engineers plugging things into corporate networks for security reasons."
"Engineers and IT people speak different languages," added Stiernberg. "IT people are also concerned about wireless data acquisition, which uses Ethernet." He also noted that the security protocols used in wireless Ethernet surpass those used in wired Ethernet, so IT staff members may be more concerned with wired measurement applications.
"Engineers need to be network savvy," added Sullivan. "They need to know static IP (Internet protocol) addresses and DHCP (Dynamic Host Configuration Protocol) servers." You may need to set up a subdomain to keep instruments isolated from a corporate network.
Many measurement applications use a network separate from a corporate network. Others may use two network-interface cards on a PC, one for the corporate network and another for the measurement network. "You need a demilitarized zone between measurement networks and corporate networks," added Stiernberg. By isolating your measurement network from a company network, you may keep your IT department at bay, you won't clog the company network with data, and you won't experience delays in getting your data.
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