Physical Sciences

Infrared CO2 Sensor With Built-In Calibration Chambers

A proposed infrared CO2 sensor, operated in conjunction with suitable readout, data-processing, and control circuitry, could be calibrated repeatedly during operation to compensate for changes in sensor response induced by such phenomena as aging and changes in temperature. The sensor would include an infrared source, an infrared detector, and four chambers containing CO2 at various concentrations. Three of the chambers would be calibration chambers: they would be sealed and would contain CO2 at known low, intermediate, and high concentrations, respectively. The fourth chamber would be filled with the gas under test containing CO2 at a concentration to be determined. There would be optics for multiplexing infrared radiation from the source through the four chambers and demultiplexing the radiation from the chambers to the infrared detector. During an operation/calibration cycle, radiation would be directed through each chamber in turn, and the response of the detector recorded for each chamber. A three-point calibration for that cycle would be computed from the responses for the three calibration chambers. Then the concentration of CO2 in the fourth chamber would be computed by simply multiplying the detector response for that chamber by a factor calculated as part of the calibration.

Posted in: Briefs, TSP, Physical Sciences, Calibration, Sensors and actuators, Carbon dioxide


Solid-State Potentiometric CO Sensor

A solid-state sensor was developed that measures the concentrations of one or more gases of interest in a mixture of gases. This simple solid-state sensor produces a voltage signal that is sensitive to CO concentration from percent to ppm (parts per million) levels. It was intended originally for use in measuring concentrations of carbon monoxide in fuel and oxidizer gases generated on Mars in a process that would include the decomposition of atmospheric CO2 into CO and O2 In that application, the sensor would be capable of measuring high concentrations of CO expected to occur on the fuel side of the process, yet would be selective and sensitive enough to measure the low concentrations of CO in O2 expected on the oxidizer side of the process. On Earth, sensors like this one could be used to detect toxic concentrations of CO emitted in diverse processes, including refining of petroleum and combustion of hydrocarbon fuels in furnaces and automobiles.

Posted in: Briefs, Physical Sciences, Sensors and actuators, Carbon monoxide, Gases


Planetary Rover Absolute Heading Detection Using a Sun Sensor

Headings are accurate to within a few degrees. A relatively inexpensive Sun sensor for determining the absolute heading of planetary rovers to within ± 3° using a monochrome charge-coupled device (CCD) camera is presented. The Sun sensor was developed for the Field Integrated, Design and Operations (FIDO) rover. This rover is an advance technology rover that is a terrestrial prototype of the rovers that NASA/JPL plans to send to Mars in 2003. The goal of the FIDO team was to develop a Sun sensor that fills the current cost/performance gap, uses the power of sub-pixel interpolation, makes use of current hardware on the rover, and demands very little computational overhead. In addition, a great deal of emphasis was placed on robustness to calibration errors and the flexibility to make a transition to a flight rover with very little modification.

Posted in: Briefs, Physical Sciences, Navigation and guidance systems, Sensors and actuators, Sun and solar, Autonomous vehicles, Spacecraft


Multiple-Path-Length Optical Absorbance Cell

Wide dynamic range is provided for measuring widely different concentrations of CDOM. An optical absorbance cell that offers a selection of multiple optical path lengths has been developed as part of a portable spectrometric instrument that measures absorption spectra of small samples of water and that costs less than does a conventional, non-portable laboratory spectrometer. The instrument is intended, more specifically, for use in studying colored dissolved organic matter (CDOM) in seawater, especially in coastal regions. Accurate characterization of CDOM is necessary for building bio-optical mathematical models of seawater. The multiple path lengths of the absorption cell afford a wide range of sensitivity needed for measuring the optical absorbances associated with the wide range of concentrations of CDOM observed in nature.

Posted in: Briefs, Physical Sciences, Fiber optics, Spectroscopy, Waveguides, Water


Model of a Fluidized Bed Containing a Mixture of Particles

Predictions thus far are in reasonable agreement with experimental data. A mathematical model has been developed for use in analyzing the dynamics of an isothermal, non-chemically-reacting mixture of particles in a bubbling fluidized bed. Although the model has generic validity, it is intended, more specifically, to be applied to a fluidized bed that contains a mixture of sand and biomass particles, fluidized by steam. The model includes components in common with the models described in “Model of Pyrolysis of Biomass in a Fluidized-Bed Reactor” (NPO-20708), NASA Tech Briefs, Vol. 25, No. 6 (June 2001), page 59 and “Multiphase-Flow Model of Fluidized-Bed Pyrolysis of Biomass” (NPO-20789), NASA Tech Briefs, Vol. 26, No. 2 (February 2002), page 56.

Posted in: Briefs, TSP, Physical Sciences, Computational fluid dynamics, Particulate matter (PM), Soils, Biomaterials, Gases


Refractive Secondary Concentrators for Solar Thermal Systems

Concentration ratios as high as 104 and operating temperatures >2,000 K are anticipated. High-throughput, non-imaging, secondary concentrating optics that utilize refraction and total internal reflection are undergoing development for use in conjunction with advanced primary solar concentrators to provide solar thermal energy for space applications. This development is prompted by (1) a need to concentrate sunlight by factors of as much as 104 to satisfy design and operating requirements for some advanced solar thermal systems and (2) the impracticality of fabricating primary concentrators with sufficient precision to afford such high concentration ratios by themselves. Figure 1 illustrates the operation of a refractive secondary concentrator.

Posted in: Briefs, TSP, Physical Sciences, Optics, Solar energy


Cold Flow Calorimeter

This apparatus can measure a rapidly varying heat-transfer coefficient. The cold flow calorimeter is an apparatus for measuring a possibly rapidly varying heat-transfer coefficient on a surface. The cold flow calorimeter includes (1) a small strain gauge bonded to a small, thin steel shim that is placed on the surface of interest and (2) a circuit that controls the electric power supplied to the strain gauge to keep the strain-gauge grid at a constant temperature [e.g., 150 °F (≈66 °C)]. The instantaneous value of the heattransfer coefficient is deduced from the instantaneous power required to maintain the constant temperature. The heat-transfer coefficient measurable by use of this apparatus can range from values characteristic of natural convection to values as large as about 1,000 Btu/(ft·h·°R) [≈1.7 kW/(m·K).

Posted in: Briefs, Physical Sciences, Heat transfer, Test equipment and instrumentation


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