Test & Measurement

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.

Posted in: Test & Measurement, Briefs, TSP

Read More >>

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.

Posted in: Test & Measurement, Briefs, TSP

Read More >>

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.

Posted in: Test & Measurement, Briefs, TSP

Read More >>

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.

Posted in: Test & Measurement, Briefs

Read More >>

Thrust Stand Measures Thrusts of

This device measures thrusts produced by miniature cold-gas thrusters in vacuum and air. The development of miniature, cold- gas thrusters for on-orbit propulsion of such small devices as remotely piloted cameras and for inclusion in astronaut propulsion backpacks gave rise to a need to measure thrusts ranging from 0.04 to 0.8 lb (0.2 to 3.6 N). In addition, there was a need to measure thrust in a vacuum environment as well as in air at a pressure of 1 atmosphere (0.1 MPa), and over a wide range of propellant inlet pressures. The primary obstacle to be overcome for such measurements was to solve the problem of delivering the cold-gas propellant (compressed nitrogen gas) to the thruster without affecting thrust measurements, particularly those below 1/4 lb (1 N).

Posted in: Test & Measurement, Briefs, TSP

Read More >>

Mechanism for Adjusting and Measuring Tension in a Cable

Where measurement is necessary, this mechanism could be preferable to a turnbuckle. The figure illustrates a simple mechanism designed for anchoring one end of a cable on a structure and for adjusting the tension in the cable. Unlike turnbuckles and other conventional cable-tensioning mechanisms, this mechanism also facilitates direct measurement of the tension in the cable. Several of these mechanisms are used in concert in order to suspend a structure for thermal isolation.

Posted in: Test & Measurement, Briefs, TSP

Read More >>

Electromechanical Testing of Microelectromechanical Devices

Devices would be probed at the wafer level before dicing and packaging. A method of electromechanical testing has been proposed for general diagnosis, evaluation of performance, and burn-in (accelerated life testing) of microelectromechanical devices. The tests would ordinarily be performed at the wafer level; that is, after the devices have been fabricated on wafers but before the wafers have been diced and the dies packaged. Alternatively or in addition, the tests could be performed at other stages of the fabrication process.

Posted in: Test & Measurement, Briefs, TSP

Read More >>