JUST LIKE BEAUTY, data acquisition (DAQ) is in the eye of the beholder. This means its usefulness is judged subjectively based on the needs of its users and the decisions it enables, rather than on the technology used to gather it. And, anyway, appearances can be deceiving—especially these days.
“There are 100 different types of devices from DCSs to PLCs to PCs that can perform DAQ functions, but there are still a few aspects of DAQ that remain fixed,” says Steve Byrum, DAQ product manager at Yokogawa Corp. of America’s Network Solutions division. “Despite all the recent changes, DAQ is still all about measuring and recording a signal.
“And, while measurement hardware hasn’t changed much, what has changed radically in the past 10 years—and improved the lives of those who need plant data—is the connectivity of those measurements to the PC environment. This has happened mostly via Ethernet networking, which has enabled standardization on more readily available platforms including OPC. It’s far easier to implement a DAQ recording system now and merge plant data with a PC platform due to the ease of the networking. These days, if your instrumentation device doesn’t have an Ethernet port and/or a USB interface, then you’re odd man out.”
John Alvey, owner/engineer at Automation Troubleshooters, a system integrator in Placentia, Calif., adds, “Some people in oil production need to see their data constantly updated. Others only need to see their data if it moves out of tolerance. But either way you need hardware to collect the data and record the jumps, and you need software to further gather the information, run it thorough a dynamic data exchange function and then usually move it to a Windows-based system.” (See Figure 1 below)
FIGURE 1: PC-BASED DAQ
In its most basic form, DAQ involves gathering measurement signals and digitizing them for analysis on a PC. Source: National Instruments.
While any sensor/actuator combination can respond to immediate status changes, DAQ is distinguished by that fact that it’s based on gathering multiple snapshots or slices of time, analyzing them together and usually spotting and being able to act on otherwise unseen trends. Still, the old days of data recorders, HMI/SCADA software or even PCI boards always looking the same and always performing a traditional well-defined set of functions are long gone. DAQ devices and systems are taking on as many new functions and forms as the industrial PCs and software in whose technological gravity well they’re being pulled along.
“The main DAQ trends have been from custom-designed, proprietary systems to off-the-shelf, open, PC-based architectures, and users adapting to this new flexibility,” says Brian Betts, National Instruments’ DAQ product manager.
What cosmic force is driving this diversification? Economics, of course, and the hunger of more and smaller end users and manufacturers for faster and better information to help them compete.
“DAQ systems were originally used in refineries and other large applications that needed centralized control and the ability to check intricate processes. Now, DAQ’s a lot less expensive, so it can be used in smaller applications to provide accurate day-by-day trend information, and help those companies operate more efficiently,” says Alvey. “A lot of smaller-scale, 24/7 facilities are running multiple lines and knocking out parts, and they need to keep tabs hour by hour or even minute by minute because they’re getting beaten up by Asian competitors. They can’t wait until the end of the day to find out how bad a shift was because they can loose their shirt in one day.
“So, we can set up a real-time clock that shows cycles or parts per minute and write a micro PLC program in ASCII to gather and display a couple of digital or analog signals on LED signs or wherever they’re needed. This can let an operator know that his process is sucking mud and needs maintenance by 8 a.m., when he wouldn’t have noticed it otherwise.”
|FIGURE 2: SUBWAY POWER|
New York City’s Metropolitan Transit Authority recently used Logic Beach’s DAQ equipment to monitor increased, system-wide electrical current draw more closely when it was running added subway trains in the wake of 9/11. Source: 2004 Metropolitan Transportation Authority.
Alvey adds that having two DAQ system in place can be even more useful because each can collect different data about the same application. For example, one DAQ can gather basic, real-time production data, such as units, produced, scrapped, and downtime, while the other DAQ checks more diagnostic data and the time frames associated with it; for example, jamming incidents plotted over a week, which could show a bigger picture of proactive maintenance needed that wouldn’t be visible at the hourly level.
“Many facilities also have ancillary equipment, such as compressors or chillers, which no one usually thinks to monitor or visit,” he says. “However, these also can be tied to micro-PLCs to show data from simple signals, such as pressure or temperature, which can indicate how well they’re operating or if they might have a problem.”