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Fiber-Optic Sensors for Measuring Oxygen Dissolved in Water

Colors of immobilized metal complexes change in the presence of dissolved oxygen. Fiber-optic sensors for measuring concentrations of oxygen dissolved in water are undergoing development. In comparison with electrochemical dissolved-oxygen sensors, the fiber-optic sensors are expected to be easier to use and maintain. Also, unlike electrochemical dissolved-oxygen sensors, the fiber-optic dissolved-oxygen sensors are amendable to connection into networks for taking measurements at multiple sites.

Posted in: Test & Measurement, Briefs

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Helium Leak Detector With Improved Sample-Delivery System

The pressure at the inlet of a mass spectrometer is regulated. The figure schematically depicts a portable helium leak detector that includes an improved sample-delivery system. This instrumentation is designed for detecting leaks in the fuel and oxidizer systems of the space shuttle main engines. In a helium leak test, helium is used as a tracer gas in place of the hazardous fuel or oxidizer: The fuel or oxidizer plumbing of interest is pressurized with helium. The aft section of the space shuttle (which section contains the plumbing) is purged with air, and the portable helium leak detector is used to monitor for any increase in helium content of the purge exhaust at concentrations down to the part-per-million level. The portable helium leak detector can also be used to perform tests to detect very small leaks in systems other than the space shuttle main engines.

Posted in: Test & Measurement, Briefs, TSP

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Personal Cabin Pressure Alarm

Aircraft crewmembers would be alerted to prevent hypoxia.Compact instruments, similar in appearance to common personal pagers, have been proposed for warning aircraft crewmembers that cabin air pressure has decreased to a potentially dangerous level. An instrument of this type, called a "personal cabin pressure monitor and warning system" (PCPMWS), implements a warning protocol consistent with Federal Aviation Administration (FAA) requirements for commercial flight crews to (1) use supplemental oxygen after a 30-minute exposure to a cabin pressure altitude between 10,000 and 12,000 ft (about 3,050 and 3,660 m), or (2) immediately when the cabin pressure altitude exceeds 12,000 ft. The PCPMWS would provide both 10,000- and 12,000-ft warnings. The elapsed time between these two warning altitudes could also serve as an indication of the rate of decompression, and thus of the urgency of the situation.

Posted in: Test & Measurement, Briefs, TSP

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Room-Temperature Infrared Instrument Detects Trace Gases

Times for measuring concentrations of gases can be as short as a few seconds.A compact, portable, mid-infrared, laser-based instrument that operates at room temperature has been developed for use in detecting trace concentrations of CO or any of several other gases in air. The instrument utilizes infrared absorption spectroscopy in a sample cell which either holds an air sample or is exposed to an airflow. The laser beam that interrogates the cell is formed by difference-frequency generation (DFG) in a bulk nonlinear optical medium excited by two laser beams.

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Miniature Birefringence-Measuring System

Advantages over older systems include compactness, light weight, low power consumption, and greater sensitivity. A miniature birefringence-measuring system has been developed for use in investigating extensional flows of non-Newtonian polymers in microgravity. The system could also be used on Earth to perform general optical-retardation and dichroism measurements, to measure stresses with high sensitivity, to characterize polymers, and to measure orientation angles of molecular chains. The system includes a dual-crystal transverse electro-optical phase modulator that makes it possible to measure small (of the order of 10 -9) changes in the birefringence of a material under test as the material is subjected to extensional deformation or shear stress.

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Algorithm for Calibrating an Imaging Interferometer

Conventional "flat-field" calibration is obviated and systematic noise is reduced. An algorithm has been devised to greatly simplify and improve the calibration and the reduction of systematic noise of an imaging interferometer or other similar interferometric instrument. Prior to the advent of this algorithm, such calibration was achieved by means of a conventional "flat-field" correction method that requires uniform illumination of all pixels in the image detector of the instrument. To achieve uniform illumination, it is often necessary to disassemble the instrument to separate the image detector from the instrument optics, taking care to keep all optical and electronic components clean and to restore the original optical alignment upon reassembly.

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Software for Designing Model Rockets for Base-Heating Tests

This program eliminates a week or more of manual calculations for each configuration. The Impulse Combustion Excel (ICE) computer program was developed to facilitate and accelerate the design and analysis of subscale rocket engines for use in base-heating tests. Such tests are performed on the ground to obtain data for estimating the heating effects of hot exhaust plumes on the aft regions of full-scale rockets during ascent. The computer program is so named because typically, a base-heating test involves impulse combustion — short-duration (of the order of 100 ms long) hot firing using flight propellants. Heretofore, the design of the subscale engines and base-heating tests has been a difficult, time-consuming, iterative process. ICE can be expected to reduce the testing times and costs and to yield improved designs. ICE can be used to design models to be tested in both wind tunnels and vacuum tanks.

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