Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
New LaserVec from TSI
Keywords Lasers, Optical sensors, Control systems
The Laservec Diode Velocimeter is designed around a unique new optical head that combines both transmitter and receiver in a single unit (see Plate 2). The use of diode laser technology results in a compact, robust velocimeter system that does not need water cooling or special power supply capabilities. With 50 mW of power in the visible beam, this diode laser package delivers more power to the measuring region than other systems, especially those using He-Ne lasers.
Plate 2 The LaserVec Diode Velocimeter
Laservec systems incorporate diode laser design techniques developed for process control systems that must operate reliably in harsh environments, and so depend on the stable operation of the diode laser. Laservec systems contain the latest advancements, including a unique approach to compensate automatically for potential variations in laser performance over its lifetime.
The unique optical package includes frequency shifted beams with carefully matched beam paths. The effect of the Bragg cell on diode laser beam quality was carefully analyzed to arrive at the optimum optical arrangement. The configuration selected assures the best fringe uniformity in the measuring volume. The scattered light collected in backscatter is focused onto a photodiode (see Plate 3).
Plate 3 LaserVec Systems contain the latest advancements
The ergonomically-shaped head is compact and can be mounted on a tripod for flow measurements. For automatic flow-field mapping, the optical head could also be mounted on a traverse system.
Signal processor (model IFA 600)
The IFA 600 is a compact unit that provides electrical power to the optical head and performs all control and signal processing functions. It contains a digital signal processor that extracts the instantaneous velocity values from the photodiode output. The IFA 600 is entirely software controlled. With no external knobs, no adjustments or calibrations other than those performed by software are required to operate the system.
Over the years, TSI has developed a variety of signal processors using FFT and auto-correlation techniques. The IFA 600 design harnesses elements of both to create an easy-to-use, compact, cost effective, yet highly accurate signal processing system. Through a novel SNR-based burst detection technique, the processor identifies the presence of true velocity signals. The burst detector centers the burst so that the best portion of the signal is processed to derive the velocity information. These patented signal processing techniques ensure accurate velocity measurements from the IFA 600 Digital Burst Processor.
Data analysis and display
Windows®-based data collection and analysis software and a plug-in interface card are supplied as part of the Laservec system. The interface card provides DMA data transfer from the IFA 600 processor to the computer. True real-time data displays make system optimization, including seeding, easy and straightforward.
A real-time time history of the velocity at the measuring point permits an on-line display of flow turbulence. Statistical properties of the flow, such as mean, standard deviation, skewness, and flatness are calculated and displayed. In addition to real-time displays, the software provides traverse control, power spectrum, and time history of the flow, and advanced graphics capabilities.
Application areas where the TSI LaserVec system has generated considerable interest include air and water flows. For example, LaserVec systems are used to look at internal flows in computer chassis as well as flows in water flumes for looking at pollutant dispersal. The system has also been used to look at fans and a typical application is shown in Plate 3. The system can be externally triggered to cope with the blade passage frequency.
BIRAL are manufacturers and suppliers of a wide range of scientific instruments for environmental research and industrial applications.
Further information is available from Bristol Industrial & Research Associates Limited, PO Box 2, Portishead, Bristol BS20 7JB. Tel: +44 (0) 1275 847787; Fax: +44 (0) 1275 847303; E-mail: firstname.lastname@example.org