This section was written by Senior Editor Michael Valenti		 Instrumentation and Control

Technology Focus part 2


Keeping Machine Tools on Track
Even the most advanced machine tools are subject to error over many thousands of operating cycles. Heidenhain GmbH in Traunreut, Germany, has designed its VM 182 comparator measuring system to determine the dynamic and static positioning within the linear axis of machine tools that travel in transverse distances up to 1,520 mm, and lateral distances of 1 mm, to within 1.5 micron accuracy. The new instrument is used for acceptance testing, inspection, and calibration of machine tools, and is available in North America through the Heidenhain Corp., a subsidiary that is based in Schaumburg, Ill. The system is used by manufacturing companies, including Boeing in Seattle.

The VM 182 uses light diffraction to measure the positioning of a machine tool within 1.5 micron accuracy and display it electronically.

The VM 182 system consists of a graduated steel scale that uses a two-coordinate phase grid and a noncontact scanning head located on an auxiliary carriage. The scale is clamped paraxially to the machine table and the scanning head is connected to the quill of the machine by a magnet. The auxiliary carriage is removed.

The scanning head contains a bidirectional-phased grating, similar in appearance to a chessboard where alternating squares have different depths. The grating is coated with reflective material to receive the light from the scanning head.

As the machine tool moves, the target surface moves across the grating, causing phase shifts in the wavelength of light that are proportional to the positioning of the tool. The comparator uses this diffraction to measure tool positioning. Using custom evaluation software, the operator can take linear displacement accuracy data in accordance with ISO 230 Series test standards. VM 182 data is also displayed to the machine tool's operator in a simplified form by using the Heidenhain ND 281V display unit that is incorporated into the measuring system. An RS-232 connection enables the measurement system's findings and actions to be downloaded to a personal computer.

Civilian Roles For Sonar
 Originally developed and still used as a means of detecting enemy submarines, sonar has become an important peacetime tool for research and commercial pursuits. Thomson Marconi Sonar, in Brest, France, formed by the merger of Thomson, the French manufacturer of defense electronic and acoustic systems, and its British counterpart, GEC Marconi, has drawn on military expertise to create sonar systems that serve civilian applications, including oceanography, trawling, navigation, and offshore oil exploration.

Oceanographers use the Posidonia sonar system to track remotely operated undersea vehicles from their survey ship.

For example, French Polar Institute oceanographers stationed onboard the Marion Dufresne, based in Brest, use the Seafalcon 11 deep water multibeam echosounders to perform 3-D depth measurement and profiling at depths down to 36,000 feet, and sub-bottom profiling down to 16,000 feet. The echosounders are designed to operate effectively in high seas, at speeds up to 17 knots. They can tolerate vessel rolls of 15 degrees and pitches of 10 degrees.

Another product from Thomson Marconi, the Posidonia ultrashort baseline positioning system, has been used to position remotely operated vehicles and towed vehicles in noisy undersea environments, such as those caused by the bow propeller of a ship, at depths of 19,700 feet. The positioning system tracks objects over a 26,000-foot range within a 170- degree conical angle. When operating in survey mode, the Posidonia provides several days of uninterrupted positioning over long distances. In local mode, the system uses an additional bottom transponder and provides high-accuracy positioning over small areas, typically 1,600 feet square. Posidonia systems are used aboard the Atalante, Nadir, Thalassa, and Europe vessels operated by the French Marine Research Institute in Toulon, the Marion Dufresne, and the Polarstern, operated by the Wegener Institute in Bremen, Germany.

The Thomson Marconi Cupido acoustic current profilers work in cable and pipe laying, fisheries, coastal engineering, harbor and estuary surveillance, as well as on inland waterways. One system is aboard the Marion Dufresne. The Cupido measures current profiles accurately down to 3,300 feet by transmitting and receiving wideband acoustic signals and processing the data. The long-range version of Cupido is equipped with a phased array of sonar beams. The medium- and short-range versions use four beams at 30 degrees depression angle from vertical.

Simplifying Cable Installations
The separate sets of industrial cables that control complex machines can become unwieldy, a situation aggravated when space is at a premium. Using cable tracks and conduits to route the lines adds to the complexity and costs of cabling. C&M Corp. of Wauregan, Conn., custom designs and builds podded cable packages that can combine power, signal, motor control, pneumatic, and hydraulic lines, and data transmission cables in a single package.

By combining different cables into a single package, C&M Corp.'s podded cables save space and installation costs for users of complex machines.

C&M makes the cables for an application, and extrudes jackets out of polyvinyl chloride, thermoplastic elastomer, or polyurethane. "Each cable in the package is isolated from the others. When the podded cable meets the machine, we break the cables out individually to meet their point of contact," said Robert Blake, an electrical engineer and product development engineer at C&M.

Installation is inherently less costly because expensive cable-carrying systems and routing labor are not required. The reduced profile of podded cable permits cables as large as 2.5 inches in the x axis and 1 inch in the y axis. Round cables are combined, thereby creating low-profile cables for higher-flex products in smaller vertical spaces.

For example, C&M is designing a podded cable to replace three 0.4-inch-round cables attached to 89 components on a CAT scan machine. The scanner's manufacturer found that space constraints prevented the installation of tracking needed to guide the cables as the scanner moved over a patient's body. "We are supplying a single, 0.4 x 1.2-inch podded cable for this project," said Blake.
Measuring Transients 100 Times Faster
 Nicolet Technologies Inc. of Madison, Wis., is marketing an OD-200 acquisition card, designed to provide transient capture speeds 100 times greater than its predecessor, the Nicolet Odyssey acquisition card.

Nicolet's new OD-200 cards let computers analyze automotive system transients 100 times faster than the company's older cards could.

The high acquisition speed of each OD-200 card is derived from four independent 14-bit, 10 million-Hz channels that offer greater signal fidelity than the previous model. Transient memory of up to 8 million samples per second per channel completely records any signal of interest.

According to Nicolet, the OD-200 cards have flexible capture features to ensure transient capture. For example, once registering a transient, the card will rearm instantly, without dead time. If a second transient event is encountered during the collection of a first transient, the triggered segment of the card's memory automatically extends to record the second event. All events are recorded as disk access permits, freeing up transient memory for future events, even during new recording.

The U.S. Naval Air Warfare Center in China Lake, Calif., is using the OD-200 cards in its Aircraft Survivability Test Range. The cards are also used in automotive crash and airbag testing, and high-voltage impulse and switch-gear testing by the power industry.

High Capacity Comes in Small Packages
One area that would benefit from microelectromechanical systems, or MEMS, technology is relaying electrical power. The small size and low power consumption of micro-relays would open up new design options for engineers in the telecommunications, automated test equipment, and automotive arenas, for example, by integrating the relay directly with other semiconductor components, such as capacitors, to create a control package with more functions than a switch. In time, sensors could be integrated with micro-relays to create a smart switch. MCNC of Research Triangle Park, N.C., developed a micro-relay with that idea in mind.

Despite their small size, the MCNC micro-relays are designed to carry up to 300 mA in telecommunications and automated testing applications.

The new device measures 1.5 mm x 1 mm x 600 microns. The thermally actuated micro-relay consists of nickel surface components with gold contacts for high conductivity. The instrument has carried up to 300 mA of current in communications tests.

The U.S. Naval Surface Warfare Center's Indian Head division in Carderock, Md., tested the micro- relay's endurance under tough conditions during the last quarter of 1998. The center's engineers cycled the micro-relay 20 times between -65°F and 160°F, at 10-minute intervals at each extreme and found no change in performance. Nor did 60 gravity shock pulses, lasting 8 to 10 milliseconds each, affect the micro-relay.

According to MCNC, beta testing has indicated that the micro-relay meets requirements for automated testing and micro-instrumentation applications. The company said it hopes to develop its micro-relay to perform faster and consume less power for applications that include probe card reconfiguration in automatic test equipment. The beta version of the micro-relay is housed in a ceramic package; future production is expected to include packaging in injection molded plastic.

Oxygen Analyzers Clean Up Power Plant
Managers of a major power plant approached AC Controls of Charlotte, N.C., in January to get analyzers to monitor the oxygen level in boiler combustion fuel gases. The information would guide plant operators in adjusting fuel/air ratios for maximum combustion efficiency and in reducing nitrogen oxide emissions. Combustion tests had found that stratification of different mixtures exists in the large flue gas ducts, requiring 16 analyzers to average out the variations in flue gas. AC Controls is incorporating World Class 3000 oxygen analyzers made by Rosemount Analytical Inc.'s process analytical division in Orrville, Ohio, to do the job.

The World Class 3000 contains a heat sensing cell made of zirconium oxide that becomes an electrolytic conductor when there is a difference between the oxygen level in the flue gas and the reference standard of ambient air, which is 20.95 percent. When there is a difference, the cell generates a small voltage that is received by porous platinum electrodes deposited on both sides of the cell. Microprocessor-based electronics condition and amplify this small signal, and send it into an automatic control system that modulates the main burner fans to control oxygen value.

Rosemount designed the oxygen analyzer so that it can be diagnosed and calibrated from the control room while providing readings with 0.75 percent accuracy.


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