High-Speed DAQ Expands Its Influence

Manufacturers are producing plug-in data acquisition (DAQ) boards, data recorders, and software capable of handling data rates in excess of 10,000 readings per second. This data is becoming accessible over the web. Who needs this type of speed? Well, your customers do, for starters. And in ever-increasing numbers, machine builders do, too.

Machine builders are embedding the means to capture performance data in order to support the move toward after-sales service and support contracts. As end users turn to machine builders for service and maintenance support, OEMs need to gather this information to find faults, perform preventive maintenance, keep customers' machines running, and make a profit on their service contracts.

End users have high-speed DAQ for quality control, asset management, testing, maintenance, and other purposes. In some cases, it's necessary to acquire a great deal of data to capture information for testing and research (Figure 1), inspect material that is moving quickly on a web or through a continuous process, spot "blips" in processes, or find transient faults in process equipment.

Historically, end users did all this themselves. But, as end users lose their in-house engineering support, they'll begin to expect OEMs to build in the capability for them.

The need for speed is reflected in data compiled by Keithley Instruments (http://www.keithley.com), which conducts a measurement trends survey every year. According to Keithley vice president David Patricy, engineers have asked for faster measurement speeds (more than than 10,000 readings/sec.) and higher resolution (19+ bits) every year since 1998. "High speed and high-resolution measurements are critical," he says. This year, 19% of survey respondents say they want at least 10,000 readings/sec., up from 12% in 2000.

Engineers also want more accuracy. For the past three years, Keithley's studies show a steady increase in accuracy requirements. The latest survey says 30% of engineers require readings with 0.10% FS accuracy.

"The consistent yearly increase in accuracy mirrors what we see from our customers in both development labs and on the production floor," says Patricy. "As devices miniaturize and manufacturing indices continue to be pressured, our customers increasingly incorporate high-precision instrumentation into their test systems."

Keithley's 2001 survey showed customers seem to be happy with Ethernet connections, since it had the highest score in user satisfaction out of 12 communications protocols listed; and the 2002 survey says 29% of the respondents use Ethernet. Serial port and GPIB use dropped.

In a white paper, "Instrument-Grade DAQ via Ethernet," Keithley points out that Ethernet systems are much less expensive than any other interface, are easy to connect to PCs, are fast enough for high-speed DAQ, and work over long distances. The white paper compares Ethernet performance favorably to other high-speed industrial networking systems such as Universal Serial Bus (USB) and FireWire (IEEE-1394).

Keithley feels confident that its customers are now ready for the next step: web-based DAQ. It recently announced a new DAQ system, which combines 22-bit resolution, 10/100BaseTX Fast Ethernet, and a web server. The system can scan data at 500 channels/sec., transmit over Ethernet, make data compatible with Excel spreadsheets, and let users view data and diagnostics over a web browser.

Bently Nevada also has a high-speed DAQ system in the works that will transmit data via Ethernet and the web. Such devices should interest machine builders because of the increasing need for remote monitoring of equipment under service contracts.

Builders of packaged process equipment, turbomachinery, power generating equipment, and similar systems need these data-collection capabilities, whether they supply it to customers for internal use or embed it for themselves, to facilitate after-sales troubleshooting. High-speed data acquisition (Figure 2) finds all kinds of process problems early on, before they can grow into big problems.

"Recently, we've started to emphasize collecting not just machinery data, but also the surrounding process data so it can be correlated with changes in a machine's mechanical behavior," says Steve Sabin, marketing manager at Bently Nevada (http://www.bently.com).

A good example of that would be a blip in a process that would cause a compressor surge, leading to characteristic vibration and other after-effects. "The ability to capture machine and process parameters at high speeds can often yield important insights into cause-and-effect relationships," Sabin explains. "Did the machine behave badly because of a mechanical malfunction, causing process problems? Or did process anomalies cause the machine to malfunction?"