Calibration of Photocon pressure transducer
Frequency response data for pressure transducers used in sonic boom evaluation
FREQUENCY RESPONSE↗
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Unsteady Pressure Sensitive Paint Camera Calibration Improvements
Data collection using unsteady pressure-sensitive paint (uPSP) has been greatly increased in recent large-scale demonstrations. With this significant increase comes challenges to process this magnitude of data. Techniques designed for several thousands of images collected in a lab do not necessarily scale to millions collected in a production-level system. Novel techniques are needed to meet the tighter requirements imposed on computation time, robustness, and accuracy. This paper outlines a number of such techniques and improvements in regards to the camera calibration process.
Camera calibration↗
Rotating pressure measurement system using an on board calibration standard
A computer-controlled multichannel pressure measurement system was developed to acquire detailed flow field measurements on board the Large Low Speed Centrifugal Compressor Research Facility at the NASA Lewis Research Center. A pneumatic slip ring seal assembly is used to transfer calibration pressures to a reference standard transducer on board the compressor rotor in order to measure very low differential pressures with the high accuracy required. A unique data acquisition system was designed and built to convert the analog signal from the reference transducer to the variable frequency required by the multichannel pressure measurement system and also to provide an output for temperature control of the reference transducer. The system also monitors changes in test cell barometric pressure and rotating seal leakage and provides an on screen warning to the operator if limits are exceeded. The methods used for the selection and testing of the the reference transducer are discussed, and the data acquisition system hardware and software design are described. The calculated and experimental data for the system measurement accuracy are also presented.
Senyitko, Richard G.↗
Simulation of liquid-hydrogen turbine-type flowmeter calibrations using high-pressure gas
Simulation of liquid-hydrogen turbine-type flow meter calibrations using high-pressure nitrogen gas at liquid-hydrogen density
FLOW METER↗
Improved pressure measurement system for calibration of the NASA LeRC 10x10 supersonic wind tunnel
This paper discusses a method used to provide a significant improvement in the accuracy of the Electronically Scanned Pressure (ESP) Measurement System by means of a fully automatic floating pressure generating system for the ESP calibration and reference pressures. This system was used to obtain test section Mach number and flow angularity measurements over the full envelope of test conditions for the 10 x 10 Supersonic Wind Tunnel. The uncertainty analysis and actual test data demonstrated that, for most test conditions, this method could reduce errors to about one-third to one-half that obtained with the standard system.
Blumenthal, Philip Z.↗
Supplementary calibration test of the tip-aerodynamics- and acoustics-test pressure transducers
A calibration test is described that was performed to supplement the normal calibration of the 188 pressure transducers used in the Tip Aerodynamics and Acoustics Test. This calibration led to the identification of 15 transducers which had a slope change of greater than 7% from the initial calibration. The calibration procedure is described and the results presented. The effect of the slope changes on the pressure distributions are described, followed by a method to compensate for these changes.
Watts, M. E.↗
Precision ozone calibration system based on vapor pressures of ozone
A precision ozone calibration system for stratospheric research has been developed and evaluated. Vapor pressures above solid ozone are mixed with a carrier gas (N2) to produce stratospheric ozone mixing ratios at total pressures of 1 to cover 20 torr. The uncertainty in the ozone mixing ratios is approximately + or - 1.5 percent, the stability of ozone is + or - 0.3 percent. Experiments to be calibrated may sample the gas mixture over a wide range of flow rates; the maximum throughput of gas with corrections of less than 1 percent to ozone is about 200 torr 1/min. A mass spectrometer system continuously monitors the purity and stability of the N2-O3 gas mixture.
Mauersberger, K.↗
Device enables calibration of microphones at high sound pressure levels
Coupling device accurately calibrates microphones at high sound pressure intensities. The system which uses a liquid as the coupling medium can operate in an automatic mode by using a standard microphone as a control sensor. Feedback from the standard microphone controls the calibration signal level.
Gillen, A.↗
Electronically scanned pressure sensor module with in SITU calibration capability
This high data rate pressure sensor module helps reduce energy consumption in wind tunnel facilities without loss of measurement accuracy. The sensor module allows for nearly a two order of magnitude increase in data rates over conventional electromechanically scanned pressure sampling techniques. The module consists of 16 solid state pressure sensor chips and signal multiplexing electronics integrally mounted to a four position pressure selector switch. One of the four positions of the pressure selector switch allows the in situ calibration of the 16 pressure sensors; the three other positions allow 48 channels (three sets of 16) pressure inputs to be measured by the sensors. The small size of the sensor module will allow mounting within many wind tunnel models, thus eliminating long tube lengths and their corresponding slow pressure response.
Gross, C.↗
Preliminary investigation of acoustic oscillations in an H2-O2 fired Hall generator
Burner pressure oscillations and interelectrode voltage oscillations measured in an open-cycle supersonic flow Hall generator are presented. The ionized gas for the channel was supplied by seeding the approximately 1 lb/sec of hydrogen-oxygen combustion products with cesium. Since both the burner and the channel were located within magnetic fields exceeding 4 Tesla during operation, an infinite probe pressure measurement technique was used to measure burner pressure oscillations. Calibration of the burner pressure transducer using a resonance tube technique is presented. Evidence is presented for the existence of the first longitudinal mode of oscillations (5000 Hz) within the burner. Interelectrode voltage oscillations were simultaneously measured at two separate axial stations. The magnitude change and the phase shift between the two signals was interpreted as a decaying magnetoacoustic wave driven by the burner that propagates at local gas plus sonic velocities. The amplitude of the electrical voltage oscillations at the start of the power producing region of the channel varied with the magnetic field. This variation is compared with the results of a simple perturbation analysis. Arguments are presented for using an unsteady model for analyzing wave processes in channels.
Phillips, B.↗
Piston manometer as an absolute standard for vacuum-gauge calibration.
Determination of total pressure in a calibration volume by measuring the force on a thin circular disk, of accurately-known area, that is freely suspended in a hole in the container wall, so that the disk is substantially flush with the wall. The disk almost fills the hole, so that there is a narrow annular gap. A continuous flow of calibrating gas, injected into the container in order to maintain a desired pressure, passes through the annular gap to a diffusion pump. The ratio of pressures on the two faces of the disk is on the order of 100:1, so that downstream pressure need be known only nominally in order to deduce the upstream pressure. Force on the disk is measured by a balance that is calibrated in situ with dead weights. In one arrangement, pressures in the range from 10 to 500 microtorr were measured with an estimated probable error of (1 microtorr + 1%).
Warshawsky, I.↗
Shock-tube calibration of a fast-response pressure transducer
The sensitivity of a miniature fast-response piezoresistive pressure transducer determined dynamically was found to be slightly higher than that determined statically. Thus, mean pressures in a turbulent or unsteady flowfield that are measured using statically-calibrated pressure transducers would be slightly above true values. Unsteady pressure measurements to obtain space-time correlations and spectra can, however, be properly performed if the slight error is acceptable. These measurements are, obviously, subjected to limitations imposed by the bandwidth and the spatial resolution of the transducer. The noise spectrum revealed that the noise is predominantly above the transducer's resonant frequency. Filtering to improve the signal-to-noise ratio is particularly necessary when using the transducers at their low range. Transducer drift increases the signal-to-noise ratio and can adversely affect mean measurements.
Chung, Kung-Ming↗
Evaluation of a volume-ratio calibration system for vacuum gages from 10-6 to 10-3 torr
Volume-ratio pressure measurement calibration system for vacuum gauges
CALIBRATION↗
Calibration improvements to electronically scanned pressure systems and preliminary statistical assessment
Orifice-to-orifice inconsistencies in data acquired with an electronically-scanned pressure system at the beginning of a wind tunnel experiment forced modifications to the standard, instrument calibration procedures. These modifications included a large increase in the number of calibration points which would allow a critical examination of the calibration curve-fit process, and a subsequent post-test reduction of the pressure data. Evaluation of these data has resulted in an improved functional representation of the pressure-voltage signature for electronically-scanned pressures sensors, which can reduce the errors due to calibration curve fit to under 0.10 percent of reading compared to the manufacturer specified 0.10 percent of full scale. Application of the improved calibration function allows a more rational selection of the calibration set-point pressures. These pressures should be adjusted to achieve a voltage output which matches the physical shape of the pressure-voltage signature of the sensor. This process is conducted in lieu of the more traditional approach where a calibration pressure is specified and the resulting sensor voltage is recorded. The fifteen calibrations acquired over the two-week duration of the wind tunnel test were further used to perform a preliminary, statistical assessment of the variation in the calibration process. The results allowed the estimation of the bias uncertainty for a single instrument calibration; and, they form the precursor for more extensive and more controlled studies in the laboratory.
Everhart, Joel L.↗
Development of a pressure and force transducer calibration procedure for the hypersonic shock tunnel, volume I Final report, May 1963 - Oct. 1966
Investigation of pressure transducers, sound pressure generation systems, pressure transducer mounting, and forced oscillation dynamic balance for application to hypersonic shock tunnel
FORCED OSCILLATION↗
Static test of an ultralight airplane
This paper describes all of the work necessary to perform the static test of an ultralight airplane. A steel reaction gantry was designed first, then all of the loading whiffletrees, the hydraulic actuation system, and instrumentation systems were designed. Loads and stress analyses were performed on the airplane and the gantry and whiffletrees. Components tested to date are: tubing samples, cables, and two-by-four whiffletrees. A hydraulic system consisting of a 3000-psi hand pump, 10,000-pound actuator, pressure gage and lines, and a Barksdale valve are described. Load cell calibration and pressure indicator calibration procedures are also described. A description of the strain and deflection measurement system is included. Preliminary data obtained to date are compared to the analytical predictions.
Smith, H. W.↗
An implantable blood pressure and flow transmitter.
A miniature totally implantable FM/FM telemetry system has been developed to simultaneously measure blood pressure and blood flow, thus providing an appreciation of the hemodynamics of the circulation to the entire body or to a particular organ. Developed for work with animal subjects, the telemetry system's transmission time is controlled by an RF signal that permits an operating life of several months. Pressure is detected by a miniature intravascular transducer and flow is detected by an extravascular interferometric ultrasonic technique. Both pressure and flow are calibrated prior to implanting. The pressure calibration can be checked after the implanting by cannulation; flow calibration can be verified only at the end of the experiment by determining the voltage output from the implanted sensing system as a function of several measured flow rates. The utility of this device has been established by its use in investigating canine renal circulation during exercise, emotional encounters, administration of drugs, and application of accelerative forces.
Rader, R. D.↗
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.↗