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At least 1,801 records · Page 100
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NASA NTRS1973

In situ transfer standard for ultrahigh vacuum gage calibration

A compact insitu calibration assembly, for ultrahigh vacuum gauges is described. The system depends on the repeatable generation of a specific gas pressure by the dissociation of a solid solution chemical compound when subjected to a given temperature. A precise temperature measurement is related to the pressure generated within the vacuum by the properties of the solid solution compound. this accurately establishes the gas pressure which in turn is used to calibrate a vacuum gauge. Also included is a metering orifice used in the calibration system and which is made movable to facilitate the degassing bakeout required in ultrahigh vacuum devices.

Outlaw, R. A.↗
NASA NTRS1974

Tracking system analytic calibration activities for the Mariner Mars 1971 mission

This report describes the functions of the Tracking System Analytic Calibration activity for Mariner Mars 1971 (MM'71), its objectives for this and future missions, and the support provided to the MM'71 Navigation Team during operations. The support functions encompass calibration of tracking data by estimating physical parameters whose uncertainties represent limitations to navigational accuracy, and detailed analysis of the tracking data to uncover and resolve any anomalies. Separate articles treat the activities and results of producing calibrations for the various error sources: Deep Space Station Locations, timing and polar motion, charged particles, and the troposphere. Two other articles are also included dis- - cussing the effects of the media error sources on orbit determination and the merits of the smoothing technique used for DRIVID.

Facilities↗
NASA NTRS1974

The tracking system analytic calibration activity for Mariner Mars 1971: Its function and scope

The functions of the Tracking System Analytic Calibration activity for Mariner Mars 1971 (MM'71), its objectives for this and future missions, and the support provided to the MM'71 Navigation Team during operations are described. Support functions encompass calibration of tracking data by estimating physical parameters whose uncertainties represent limitations to navigational accuracy, and detailed analysis of the tracking data to uncover and resolve any anomalies. Separate articles treat the activities and results of producing calibrations for the various error sources: Deep Space Station Locations, timing and polar motion, charged particles, and the troposphere. Two other articles are also included discussing the effects of the media error sources on orbit determination and the merits of the smoothing technique used for DRIVID.

Madrid, G. A.↗
NASA NTRS1974

On-line calibration of high-response pressure transducers during jet-engine testing

Jet engine testing is reported concerned with the effect of inlet pressure and temperature distortions on engine performance and involves the use of numerous miniature pressure transducers. Despite recent improvements in the manufacture of miniature pressure transducers, they still exhibit sensitivity change and zero-shift with temperature and time. To obtain meaningful data, a calibration system is needed to determine these changes. A system has been developed which provides for computer selection of appropriate reference pressures selected from nine different sources to provide a two- or three-point calibration. Calibrations are made on command, before and sometimes after each data point. A unique no leak matrix valve design is used in the reference pressure system. Zero-shift corrections are measured and the values are automatically inserted into the data reduction program.

Armentrout, E. C.↗
NASA NTRS1974

On-line calibration of high-response pressure transducers during jet-engine testing

Current jet engine testing is concerned with the effect of inlet pressure and temperature distortions on engine performance and involves the use of numerous miniature pressure transducers. Despite recent improvements in the manufacture of miniature pressure transducers, they still exhibit sensitivity change and zero shift with temperature and time. To obtain meaningful data, a calibration system is needed to determine these changes. A system has been developed which provides for computer selection of appropriate reference pressures selected from nine different sources to provide a two- or three-point calibration. Calibrations are made on command, before and sometimes after each data point. A unique 'no leak' matrix valve design is used in the reference-pressure system. Zero-shift corrections are measured and the values are automatically inserted into the data reduction program.

Armentrout, E. C.↗
NASA NTRS1975

Calibration source for remote sensors

The source described was developed as a calibration target for the multispectral scanner (MSS) which was flown on the Earth Resources Technology Satellite A (LANDSAT 1). The wavelength region of interest covered the four (4) MSS bands extending from 0.5 to 1.1 micrometers, although the target was calibrated from 0.32 to 2.5 micrometers. The following characteristics for the target were required: (1) large aperture, sufficient to accommodate an instrument with a 9 inch (23 centimeters(cm)) aperture and 2 1/2 deg field of view (fov), (2) highly diffuse energy from target, (3) high spatial uniformity across aperture area of source, (4) spectrally calibrated in absolute units, (5) stable output over long periods of time (1-2 yrs), and (6) rugged, yet portable enough to be easily transported long distances without detrimental effects on the operational capabilities of the target. Two approaches were considered: a thirty (30) inch (76 cm) diameter integrating sphere with a twelve inch (30.5 cm) exit port, or the use of one hemisphere of a 76 cm sphere in conjunction with a Kodak ektolite screen. The screen has the property of reflecting back uniformly into a well defined area the majority of the light received. After some preliminary trials it seemed that the 76 cm sphere would give the most satisfactory results.

Mclean, J. T.↗
NASA NTRS1975

Results of the 1973 NASA/JPL balloon flight solar cell calibration program

High altitude balloon flights carried 37 standard solar cells for calibration above 99.5 percent of the earth's atmosphere. The cells were assembled into standard modules with appropriate resistors to load each cell at short circuit current. Each standardized module was mounted at the apex of the balloon on a sun tracker which automatically maintained normal incidence to the sun within 1.0 deg. The balloons were launched to reach a float altitude of approximately 36.6 km two hours before solar noon and remain at float altitude for two hours beyond solar noon. Telemetered calibration data on each standard solar cell was collected and recorded on magnetic tape. At the end of each float period the solar cell payload was separated from the balloon by radio command and descended via parachute to a ground recovery crew. Standard solar cells calibrated and recovered in this manner are used as primary intensity reference standards in solar simulators and in terrestrial sunlight for evaluating the performance of other solar cells and solar arrays with similar spectral response characteristics.

Yasui, R. K.↗
NASA NTRS1976

An automated secondary standard for calibrating liquid flowmeters

A secondary working standard of flow calibration has been developed to be used in place of a primary weight-time standard, and which can thereby effect a 75 percent reduction in calibration time while maintaining acceptable accuracies. The secondary standard uses six previously calibrated turbine-type flowmeters built into two manifold systems containing automatically switched flow valves. The pair of systems is capable of covering the flow range of 0.0004 to 19 l/s (0.007 to 300 gpm) with the uncertainty in volume flow rate not exceeding + or - 0.25 percent over the range of 0.06 to 19 l/s and not exceeding + or - 0.5 percent over the range 0.0004 to 0.06 1/s. Data reduction and plotting of results are by computer.

Hobart, H. F.↗
NASA NTRS1976

A dynamic pressure source for the calibration of pressure transducers

A dynamic pressure source is described for producing sinusoidally varying pressures of up to 34 kPa zero to peak, over the frequency range of approximately 50 Hz to 2 kHz. The source is intended for the dynamic calibration of pressure transducers. The transducer to be calibrated is mounted near the base of the thick walled aluminum tube forming the vessel so that the pressure sensitive element is in contact with the liquid in the tube. A section of the tube is filled with small steel balls to damp the motion of the 10-St dimethyl siloxane working fluid in order to extend the useful frquency range to higher frequencies than would be provided by an undamped system. The dynamic response of six transducers provided by the sponsor was evaluated using the pressure sources; the results of these calibrations are given.

Vezzetti, C. F.↗
NASA NTRS1976

Trailing anemometer for low airspeed calibration

A propeller-type trailing airspeed anemometer system is described for low airspeed (M not exceeding 0.2) calibration which has improved accuracy and is easy to implement as compared to most methods currently in use. The trailing anemometer system consists of the trailing anemometer itself, a deployment mechanism, and an operator's control box. The trailing anemometer is a small low-drag brass body provided with tail fins for self-alignment with the airstream. The rotational speed of a small six-bladed low-inertia propeller is sensed with a miniature self-generating tachometer inside the anemometer. A very satisfactory airspeed calibration can be made with this device in which true airspeed can be measured to within 1 knot. Results from flight calibration of an aircraft and trail-back characteristics of the anemometer and cable are included. The operating speed range of the designed cable-anemometer combination is 7 to 165 knots.

Fisher, B. D.↗
NASA NTRS1978

Improved dewpoint-probe calibration

Relatively-simple pressure-control apparatus calibrates dewpoint probes considerably faster than conventional methods, with no loss of accuracy. Technique requires only pressure measurement at each calibration point and single absolute-humidity measurement at beginning of run. Several probes can be calibrated simultaneously and points can be checked above room temperature.

Stephenson, J. G.↗
NASA NTRS1977

The use of a simplified structural model as an aid in the strain gage calibration of a complex wing

The use of a relatively simple structural model to characterize the load responses of strain gages located on various spars of a delta wing is examined. Strains measured during a laboratory load calibration of a wing structure are compared with calculations obtained from a simplified structural analysis 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 shown 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 an aid 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 NTRS1977

A study of the effect of radical load distributions on calibrated strain gage load equations

For several decades, calibrated strain gages have been used to measure loads on airplanes. The accuracy of the equations used to relate the strain gage measurements to the applied loads has been based primarily on the results of the load calibration. An approach is presented for studying the effect of widely varying load distributions on strain gage load equations. The computational procedure provides a link between the load calibration and the load to be measured in flight. A matrix approach to equation selection is presented, which is based on equation standard error, load distribution, and influence coefficient plots of the strain gage equations, and is applied to a complex, delta-wing structure.

Jenkins, J. M.↗
NASA NTRS1976

An automated secondary standard for calibrating liquid flowmeters

A secondary working standard of flow calibration has been developed to be used in place of a primary weight-time standard, and which can thereby effect a 75 percent reduction in calibration time while maintaining acceptable accuracies. The secondary standard uses six previously calibrated turbine-type flowmeters built into two manifold systems containing automatically switched flow valves. The pair of systems is capable of covering the flow range of 0.0004 to 19 1/s (0.007 to 300 gpm) with the uncertainty in volume flow rate not exceeding plus or minus 0.25 percent over the range 0.06 to 19 1/s and not exceeding plus or minus 0.5 percent over the range 0.0004 to 0.06 1/s. Data reduction and plotting of results are by computer.

Hobart, H. F.↗
NASA NTRS1977

US terrestrial solar cell calibration and measurement procedures

A workshop was held in the fall of 1976, to evaluate and revise interim terrestrial solar cell calibration and measurement procedures. The revisions made to the interim testing procedures are described. The calibration of reference cells and the design of their holders are covered. Considerations include view angle and optical and thermal matching. Atmospheric factors which affect the calibration and performance of solar cells are discussed. The most critical atmospheric parameter appears to be water vapor. Techniques for matching reference cells to cells or arrays under test are described. Data showing errors in performance under artificial sunlight simulators due to mismatch of reference and test cells are presented. Finally, measurement procedures and data transformations needed to obtain the performance of solar cells and arrays in outdoor natural sunlight are described.

Brandhorst, H. W., Jr.↗
NASA NTRS1978

A flight evaluation of a trailing anemometer for low-speed calibrations of airspeed systems on research aircraft

Research airspeed systems on three low-speed general aviation airplanes were calibrated by the trailing anemometer method. Each airplane was fitted with an NASA pitot-static pressure tube mounted on either a nose or wing boom. The uncalibrated airspeed systems contained residual static-pressure position errors which were too large for high-accuracy flight research applications. The trailing anemometer calibration was in agreement with the tower flyby calibration for the one aircraft for which the comparison was made. The continuous deceleration technique for the trailing anemometer method offers reduced test time with no appreciable loss of accuracy for airspeed systems with pitot-static system lag characteristics similar to those described.

Fisher, B. D.↗
NASA NTRS1978

Frequency selection and calibration of a water vapor radiometer

The calibration coefficients of existing water vapor radiometers are dependent upon meteorology profiles. This is shown to be due mainly to incorrect frequency pairs. By properly selecting an optimum frequency pair, the dependency can be reduced to a relatively small amount which can be handily adjusted by surface measurement alone. Hence, a universal calibration equation is applicable to all environmental conditions - site, seasonal and diurnal variations. Optimum frequency pairs are systematically searched. Error analysis indicates that calibration for the water vapor phase delay accurate to less than 2 cm is possible at all elevation angles greater than 15 degrees.

Wu, S. C.↗
NASA NTRS1978

S-band radar calibration test of the Lightning Detection and Ranging system (LDAR)

A calibration and an accuracy assessment of the Lightning Detection and Ranging System (LDAR) were attempted through a simultaneous track of an S Band radar transponder and a lightning simulator carried by the NASA 6 airplane on a test flight. Included in the report are the results of the calibration test, error analyses of the radar, and the LDAR systems, and recommendations for future calibration tests.

Poehler, H. A.↗

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