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At least 937 records · Page 52

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NASA NTRS1971

Miniature pressure valve for on-board calibration of pressure transducers.

This paper describes the development and testing of a miniature one-pole, three-position pressure valve and actuation mechanism. This valve was designed primarily for installation with a pressure transducer directly in a wind-tunnel model, thereby reducing lag time effects resulting from long connecting tubes to the transducer. This valve provides for the in-situ calibration of the transducer during testing by providing one position for transducer zero, a second position for a known calibrate pressure, and a third position for measurement of the unknown test pressure. The valve is driven from the spring loaded test pressure position to the zero and calibrate positions by a pneumatically operated dual-piston yoke assembly. Large numbers of transducers can be simultaneously calibrated from a remote location in a matter of seconds.

Rollins, G. N.↗

NASA NTRS1975

Photometer calibration problem for extended astronomical sources

Analysis of calibration tests for the Skylab experimental T027 photometer is used to show that if an instrument is focused at infinity, the uniform extended calibration source should be positioned at distances at least equal to the hyperfocal distance and should be large enough to fill the field of view. It is noted that the field depth can be increased by focusing the optical system at the hyperfocal distance and that this method of focusing reduces the needed diameter of the calibration source to half that of a system focused at infinity. Other calibration methods discussed includes determining the radiance responsivity distance and extrapolating the curve to larger distances as well as extensive mapping of the spatial response combined with the irradiance responsivity to obtain the radiance responsivity.

Muscari, J. A.↗

NASA NTRS1975

Spectroradiometric calibration techniques in the far ultraviolet - A stable emission source for the Lyman bands of molecular hydrogen

The problems associated with making accurate spectroradiometric measurements in the far UV region are sketched briefly. The equipment and methods that were developed for providing absolute sensitivity calibration of an Apollo 17 far UV spectrometer are described. The absolute reference standards were photoelectric diodes calibrated at the National Bureau of Standards. A complete vacuum optical facility, which included a premonochromator and stable UV light sources, was developed to calibrate the Apollo 17 instrument, and it has been used for a number of other tasks. Absolute radiometric calibrations between about 1200 and 1700 A were performed with an absolute accuracy of + or - 10%. The light source, which was designed to provide a very stable light output, is a low-pressure molecular hydrogen lamp in which the pressure is stabilized by thermal control of uranium hydride powder.-

Fastie, W. G.↗

NASA NTRS1975

Absolute calibration of a hydrogen discharge lamp in the vacuum ultraviolet

A low-pressure hydrogen discharge lamp was calibrated for radiant intensity in the vacuum ultraviolet spectral region on an absolute basis and was employed as a laboratory standard source in spectrograph calibrations. This calibration was accomplished through the use of a standard photodiode detector obtained from the National Bureau of Standards together with onsite measurements of spectral properties of optical components used. The stability of the light source for use in the calibration of vacuum ultraviolet spectrographs and optical systems was investigated and found to be amenable to laboratory applications. The lamp was studied for a range of operating parameters; the results indicate that with appropriate peripheral instrumentation, the light source can be used as a secondary laboratory standard source when operated under preset controlled conditions. Absolute intensity measurements were recorded for the wavelengths 127.7, 158.0, 177.5, and 195.0 nm for a time period of over 1 month, and the measurements were found to be repeatable to within 11 percent.

Nealy, J. E.↗

NASA NTRS1975

High altitude calibration of solar cells using rockets

The use of sounding rockets for calibrating solar cells offers two principal advantages: there is no effect due to the terrestrial atmosphere and the cells are recoverable immediately after calibration. Four n/p photovoltaic cells were calibrated in space and successfully recovered from a NASA Aerobee rocket that reached a peak altitude of 251 km. Two of the cells were optically filtered with 0.6 to 0.9-micron bandpass filters. The short-circuit current agreed to within 4% of the laboratory calibration; variation of cell output due to atmospheric attenuation in the altitude range of 80 to 251 km was 0.4% for the unfiltered cells.

Thomas, N. L.↗

NASA NTRS1976

Development of dynamic calibration methods for POGO pressure transducers

Two dynamic pressure sources are described for the calibration of pogo pressure transducers used to measure oscillatory pressures generated in the propulsion system of the space shuttle. Rotation of a mercury-filled tube in a vertical plane at frequencies below 5 Hz generates sinusoidal pressures up to 48 kPa, peak-to-peak; vibrating the same mercury-filled tube sinusoidally in the vertical plane extends the frequency response from 5 Hz to 100 Hz at pressures up to 140 kPa, peak-to-peak. The sinusoidal pressure fluctuations can be generated by both methods in the presence of high pressures (bias) up to 55 MPa. Calibration procedures are given in detail for the use of both sources. The dynamic performance of selected transducers was evaluated using these procedures; the results of these calibrations are presented. Calibrations made with the two sources near 5 Hz agree to within 3% of each other.

Hilten, J. S.↗

NASA NTRS1977

Calibration of Viking imaging system pointing, image extraction, and optical navigation measure

Pointing control and knowledge accuracy of Viking Orbiter science instruments is controlled by the scan platform. Calibration of the scan platform and the imaging system was accomplished through mathematical models. The calibration procedure and results obtained for the two Viking spacecraft are described. Included are both ground and in-flight scan platform calibrations, and the additional calibrations unique to optical navigation.

Breckenridge, W. G.↗

NASA NTRS1977

Radiance calibration of the High Altitude Observatory white-light coronagraph on Skylab

The processing of over 35,000 photographs of the solar corona obtained by the white-light coronograph on Skylab is described. Calibration of the vast amount of data was complicated by temporal effects of radiation fog and latent image loss. These effects were compensated by imaging a calibration step wedge on each data frame. Absolute calibration of the wedge was accomplished through comparison with a set of previously calibrated glass opal filters. Analysis employed average characteristic curves derived from measurements of step wedges from many frames within a given camera half-load. The net absolute accuracy of a given radiance measurement is estimated to be 20%.

Poland, A. I.↗

NASA NTRS1977

Absolute flux density calibrations of radio sources: 2.3 GHz

A detailed description of a NASA/JPL Deep Space Network program to improve S-band gain calibrations of large aperture antennas is reported. The program is considered unique in at least three ways; first, absolute gain calibrations of high quality suppressed-sidelobe dual mode horns first provide a high accuracy foundation to the foundation to the program. Second, a very careful transfer calibration technique using an artificial far-field coherent-wave source was used to accurately obtain the gain of one large (26 m) aperture. Third, using the calibrated large aperture directly, the absolute flux density of five selected galactic and extragalactic natural radio sources was determined with an absolute accuracy better than 2 percent, now quoted at the familiar 1 sigma confidence level. The follow-on considerations to apply these results to an operational network of ground antennas are discussed. It is concluded that absolute gain accuracies within + or - 0.30 to 0.40 db are possible, depending primarily on the repeatability (scatter) in the field data from Deep Space Network user stations.

Freiley, A. J.↗

NASA NTRS1978

A small gas inlet system for orbital mass-spectrometer calibrations

A gas inlet system is described for generating precise gas pressures that are to be used as calibration references for the mass spectrometers aboard the dual air density Explorer satellites. This gas inlet system was developed as an inflight calibration technique in which a known amount of onboard gas is released in the satellite cavity and is detected by the mass spectrometer. Although several flight mass spectrometer experiments have been proposed, none make use of the inflight calibration technique described in this report. Laboratory measurements and calibration of the metering leak technique for the gas inlet systems are discussed. The systems tested have metering leak rates between 2 and 4 microliters/sec at 298 K for argon-40, and they produce molecular flow up to 100 torr, which is the highest test pressure in this experiment. Test data show that metering leak rates are reproducible within 1 percent of established means for helium-3, helium-4, and argon-40.

Smith, A.↗

NASA NTRS1977

Calibration analysis for a multi-channel infrared scanning radiometer

A procedure for calibrating an infrared scanning spectroradiometer by a computerized parametric error analysis technique was developed. The uncertainties in the radiometric measurements of scene radiance and (for the case of a blackbody scene) temperature due to possible uncertainties in the calibration target temperature, calibration target emissivity, and instrument temperature were calculated for a range of uncertainty levels in the parameters, as well as for a gamut of scent temperatures corresponding to a given spectral channel. This technique is applicable to the radiometric calibration of any infrared radiometer. It was applied specifically to the Cloud-Top Scanning (C.T.S) Radiometer, a three-channel instrument designed for aircraftborne cloud radiance measurements in the 6.75 and 11.5 micron thermal emission spectral regions.

Walden, H.↗

NASA NTRS1978

Meteorological radar calibration

A meteorological radar calibration technique is developed. It is found that the integrated, range corrected, received power saturates under intense rain conditions in a manner analogous to that encountered for the radiometric path temperature. Furthermore, it is found that this saturation condition establishes a bound which may be used to determine an absolution radar calibration for the case of radars operating at attenuating wavelengths. In the case of less intense rainfall or for radars at nonattenuating wavelengths, the relationship for direct calibration in terms of an independent measurement of radiometric path temperature is developed. This approach offers the advantage that the calibration is in terms of an independent measurement of the rainfall through the same elevated region as that viewed by the radar.

Hodge, D. B.↗

NASA NTRS1977

Strain gage calibration of a complex wing

Modern complex structural arrangements have complicated the task of measuring flight loads with calibrated strain gages. This paper examines the use of a relatively simple structural model to characterize the load responses of strain gages located on various spars of a delta wing. Strains measured during a laboratory load calibration of a wing structure are compared with calculations obtained from a simplified NASA structural analysis (NASTRAN) model. Calculated and measured influence coefficient plots that show the shear, bending, and torsion characteristics of typical strain-gage bridges are presented. Typical influence coefficient plots are given for several load equations to illustrate the derivation of the equations from the component strain-gage bridges. A relatively simple structural model was found to be effective in predicting the general nature of strain distributions and influence coefficient plots. The analytical processes are shown to be useful in obtaining a good load calibration. The analytical processes cannot, however, be used in lieu of an actual load calibration of an aircraft wing.

Jenkins, J. M.↗

NASA NTRS1978

An unconventional approach to imaging radar calibration

An unconventional approach to imaging radar calibration was considered for the entire system, including the imaging processing as a measurement instrument. The technique made use of a calibrated aircraft scatterometer as a secondary standard to measure the backscatter (sigma zero) of large units of constant roughness. These measured roughness units when viewed by an imaging radar system can be used to provide gray scale level, corresponding to known degrees of roughness. To obtain a calibrated aircraft scatterometer, a homogeneous smooth surface was measured by both the aircraft scatterometer and a sphere calibrated ground system. This provided a measure of the precision and accuracy of the aircraft system. The aircraft system was then used to measure large roughness units in the Death Valley, California area. Transfer of the measured roughness units to radar imagery was demonstrated.

Fenner, R. G.↗

NASA NTRS1979

FTS maintenance and calibration at DSS 42/43

An FTS maintenance and calibration task was conducted at DSS 42/43 during August 1978. The objectives of this effort were (1) the routine maintenance and calibration of hydrogen masers, (2) installation and calibration of cesium standards, (3) installation of test equipment for frequency measurement, (4) CRG testing, (5) cabling inspection and repair, (6) check thermal and magnetic environment of H-maser/cesium room, and (7) calibration of frequency and timing subsystem.

Dachel, P. R.↗

NASA NTRS1979

Voyager high gain antenna calibration and pointing

A mathematical description of the data reduction technique used in analyzing Voyager calibration data is presented. To achieve the required telecommunication link performance, highly accurate pointing of the Voyager high gain antenna boresight relative to earth is necessary. To provide the optimum pointing, in-flight calibrations of the high gain antenna pointing mechanism are regularly made, and the design of the calibration and the antenna error models is delineated. It is shown that due to the use of wide angle sun sensors for celestial attitude control, the Voyager antenna error model differs from those of previous missions. Results of the in-flight calibrations and their implementation in improving the antenna pointing are also presented.

Jahanshahi, M. H.↗

NASA NTRS1981

Fast calibration of gas flowmeters

Digital unit automates calibration sequence using calculator IC and programmable read-only memory to solve calibration equations. Infrared sensors start and stop calibration sequence. Instrument calibrates mass flowmeters or rotameters where flow measurement is based on mass or volume. This automatic control reduces operator time by 80 percent. Solid-state components are very reliable, and digital character allows system accuracy to be determined primarily by accuracy of transducers.

Lisle, R. V.↗

NASA NTRS1980

Low-speed airspeed calibration data for a single-engine research-support aircraft

A standard service airspeed system on a single engine research support airplane was calibrated by the trailing anemometer method. The effects of flaps, power, sideslip, and lag were evaluated. The factory supplied airspeed calibrations were not sufficiently accurate for high accuracy flight research applications. The trailing anemometer airspeed calibration was conducted to provide the capability to use the research support airplane to perform pace aircraft airspeed calibrations.

Holmes, B. J.↗