Calibration Rig Research Articles

Unsteady pressure measurement instrumentation using anodized-aluminium PSP applied in a transonic wind tunnel

The objective of this work is to demonstrate the feasibility of pressure measurement instrumentation using anodized-aluminium pressure-sensitive paint (or AA-PSP) for application in unsteady flows. An anodized procedure was applied to an aluminium tape that can be easily placed on a model even when it is mounted in a wind tunnel. The response time of the PSP coating is assessed using a calibration rig that generates fast pressure steps or sinusoidal pressure fluctuations up to 1 kHz. A pointwise measurement system made with a Cassegrain telescope and a photomultiplier tube was designed to collect the PSP luminescence. The spot displacement on the model surface was carried out by using a 3D moving bench. A camera is used to identify the spot position according to the model geometry. An application in a wind tunnel was performed on a forced shock wave oscillation test, generating amplitude variations up to 25 kPa. The calibration problem due to non-uniformity of the anodized properties did not allow quantitative data processing of pressure levels. Nevertheless frequency analysis demonstrates that the coating is able to follow the pressure fluctuations, as shown by comparison with standard pressure transducers.

Repeatability of gait data using a functional hip joint centre and a mean helical knee axis

Repeatability of traditional kinematic and kinetic models is affected by the ability to accurately locate anatomical landmarks (ALs) to define joint centres and anatomical coordinate systems. Numerical methods that define joint centres and axes of rotation independent of ALs may also improve the repeatability of kinematic and kinetic data. The purpose of this paper was to compare the repeatability of gait data obtained from two models, one based on ALs (AL model), and the other incorporating a functional method to define hip joint centres and a mean helical axis to define knee joint flexion/extension axes (FUN model). A foot calibration rig was also developed to define the foot segment independent of ALs. The FUN model produced slightly more repeatable hip and knee joint kinematic and kinetic data than the AL model, with the advantage of not having to accurately locate ALs. Repeatability of the models was similar comparing within-tester sessions to between-tester sessions. The FUN model may also produce more repeatable data than the AL model in subject populations where location of ALs is difficult. The foot calibration rig employed in both the AL and FUN model provided an easy alternative to define the foot segment and obtain repeatable data, without accurately locating ALs on the foot.

Technical feasibility of a three-axis force transducer for measuring pressure and friction on the model die surface — prototype development

A new transducer for measuring normal and shear stress in physical modelling was designed and tested. From many methods of contact stress measurements, a local approach based on pin load cell was chosen. The sensing element employed was a stack of piezoelectric plates which measured three components of the force directly. The design process included a study of piezoelectricity in various materials, designing a prototype transducer and choosing an appropriate electronic circuit. The piezoelectric stack and the whole transducer were tested using a calibration rig capable of applying the normal and tangential force independently. Calibration results confirmed the suitability of the adopted concept and provided guidelines for proper design of the final transducer. In particular, a new calibration procedure was proposed which took into account interactions between the measured force components.

Air-braked cycle ergometers: validity of the correction factor for barometric pressure.

Barometric pressure exerts by far the greatest influence of the three environmental factors (barometric pressure, temperature and humidity) on power outputs from air-braked ergometers. The barometric pressure correction factor for power outputs from air-braked ergometers is in widespread use but apparently has never been empirically validated. Our experiment validated this correction factor by calibrating two air-braked cycle ergometers in a hypobaric chamber using a dynamic calibration rig. The results showed that if the power output correction for changes in air resistance at barometric pressures corresponding to altitudes of 38, 600, 1,200 and 1,800 m above mean sea level were applied, then the coefficients of variation were 0.8-1.9% over the range of 160-1,597 W. The overall mean error was 3.0 % but this included up to 0.73 % for the propagated error that was associated with errors in the measurement of: a) temperature b) relative humidity c) barometric pressure d) force, distance and angular velocity by the dynamic calibration rig. The overall mean error therefore approximated the +/- 2.0% of true load that was specified by the Laboratory Standards Assistance Scheme of the Australian Sports Commission. The validity of the correction factor for barometric pressure on power output was therefore demonstrated over the altitude range of 38-1,800 m.

Dynamic calibration of mechanically, air- and electromagnetically braked cycle ergometers.

In this study we measured the accuracy of the following types of cycle ergometer against the criterion of a dynamic calibration rig (DCR): 35 friction-braked (Monark), 5 research-grade air-braked (Repco) and 5 electromagnetically braked (2 Siemens, 1 Elema-Schonander, 1 Ergoline, 1 Warren E. Collins). Monark ergometer power outputs over the range 58.9-353.2 W significantly (P < 0.001) underestimated those registered by the DCR with mean accuracies of 91.7-97.8%. The least accurate individual reading for each of the six up-scale (0-353.2 W) power outputs ranged from 81.6 to 91.6%; corresponding down-scale (353.2-0 W) accuracies were 85.1-92.5%. A hysteresis effect was furthermore evident for this ergometer in that up-scale measurements were significantly (P < 0.05) greater than down-scale ones. In addition, when the oldest [mean (SD): 11.3 (2.3) years old] and newest [1.4 (0.8) years old] eight ergometers were compared, the latter were significantly (P < 0.05) more accurate over the range 117.7-294.3 W. Apart from the two lowest power outputs of 47 W (62.2-96.0% accuracy) and 127 W (88.0-97.7% accuracy), the individual up-scale and down-scale accuracies of the Repco ergometers ranged from 98.0 to 104.2% for power outputs of 272.7-1137.8 W and the means were not significantly different from those of the DCR. There was also no evidence of hysteresis. Except for the initial power output of 50 W (40 rev/min: 83.8-99.2% accuracy; 60 rev/min: 93.2-122.6% accuracy), the individual accuracies of the electromagnetically braked ergometers ranged from 89.3 to 101.4% over the up-scale range of 100-400 W, and none of the means were significantly different from those of the DCR. The variability of individual errors for the preceding data emphasises that all cycle ergometers should be validated against the criterion of a DCR if accurate power outputs are required.

A macro-driven Excel template for determining the anaerobic capacity using an air-braked ergometer.

This paper describes a microcomputer system for automating the process of data collection, calculation and display of anaerobic capacity tests on an air-braked ergometer. The use of the spreadsheet Excel and associated 'Dalog' program represents an advance on current software which estimates the anaerobic capacity from work performed alone. Numerous calculations are required when air-braked, rather than friction-braked erogometers are used. Each 1 s power output collected during an all-out sprint on the ergometer is corrected against the criterion of a dynamic calibration rig and adjusted for differences in barometric pressure, ambient temperature and humidity. The Excel template features a series of macros invoked by buttons imbedded in the spreadsheet. Their selection displays various dialogue boxes which request input related to the calculation of oxygen deficit and related variables. Selecting the final macro prints a summary table and charts which include: power output, fatigue index, mechanical work performed, % aerobic contribution to work, oxygen demand, oxygen consumption and anaerobic capacity as determined by the maximal accumulated oxygen deficit.

The use of critical flow venturi nozzles with saturated wet steam

This paper describes the results of an investigation into the use of critical flow venturi nozzle flowmeters with wet saturated steam. The real-gas flow coefficient has been calculated using the equations of state for steam, which show the steam behaviour to be far from ideal along the saturation line. The nozzle was calibrated using superheated steam and the mass flow rate measured using a condensate weightank was seen to agree with the flow rate measured by the nozzle to within ±2%, although up to half of this uncertainty may be due to the uncertainty in the calibration rig and in the measured parameters used in the nozzle equation. The nozzle was then calibrated in saturated steam with dryness fractions down to 84%. The nozzle can still be used by including a wet steam correction factor in the flow rate calculation, or a more practical approach might be to precede the nozzle by an efficient steam/water separator, assume the steam then to be dry saturated and accept an uncertainty in the mass flow of 3%.

The dynamic calibration of cycle ergometers.

The components of our rig, which is used for the dynamic calibration of cycle ergometers, were purchased for $4,080 (USA); interfacing the instrument with a computer and printer increased the cost by an additional $2,550 (USA). The rig is essentially a torque balance and was therefore validated against the primary measurements of: angular velocity (rev.min-1), distance (m) and mass (kg). Summing the inaccuracies associated with these 3 measurements yields a worst case error of only 0.3%. The coefficients of variation for a dynamic calibration rig and mechanically braked Monark cycle ergometer assembly ranged from 0.6 to 3.2% for 6 trials at each of the following power outputs: 117.7, 176.6, 235.4, 294.3 and 353.2 W. The instrument therefore has a high degree of precision.

Development of a measuring system for segmented ship models

The use of segmented ship models to test and study various ship responses in model scale poses a challenge to instrumentation and test engineers. In recent years, the authors have developed a segmented ship model to study and trace ice loads acting on the ship hull. The model contains three segments at the bow. Each segment is supported at multiple points which enable the resolution of the location, magnitude, and direction of the external loads. The typical segment support system consists of four vertical, two transverse, and one longitudinal support points with uniaxial compression pression transducers. Stabilization of the segment is achieved by using three specially designed tension links acting in the vertical, transverse and longitudinal directions, respectively. The system is subjected to several levels of calibration which include individual transducer calibration, calibration using internal loading applied by the tension links, external calibration using a specially designed and built calibration rig capable of exerting normal and inclined loads, and calibration of the effects of buoyancy changes in a floating model. The results of calibration and ice-breaking tests indicate that position prediction of the external load can be made within 20 mm. The normal load of less than 100 Newtons can be determined within a few percentage points but the frictional load magnitude and direction are found to be subject to greater errors particularly for low friction factors of the order of 0.1.

A remote-controlled calibration device for displacement transducers

A remote-controlled calibration device for displacement transducers has been developed for use in a shielded facility. The system consists of a piezoelectric translator including a microprocessor-based controller in a calibration rig. In this rig two transducers can be verified simultaneously. The equipment has been integrated into a computer-controlled data acquisition system to provide for the required data processing and analysis. A description is given of the displacement calibration system and its peripherals as well as the calibration procedure. The system has been proved to function satisfactorily and reliably, showing high resolution and accuracy; it is also easy to operate remotely.

Flow Calibration Rig

Flow Calibration Rig

A five‐component strain gauge wind tunnel dynamometer

The design, construction and calibration of a five‐component dynamometer is described. The dynamometer was constructed primarily for the testing of ship control surfaces including, in particular, skeg rudders; it has facilities for the independent adjustment of angle of attack, and the derivation of the forces and moments, on both rudder and skeg.An outline of the specialised design requirements is given. The basic design concept is described together with the reasons for the choice of shear flexures and their dimensions, strain gauges, circuits, bridge voltages and instrumentation. Following a brief description of the calibration rig and programme, the calibration results and origins of interactions are described and discussed.It is concluded that the relatively small size of the interaction corrections and overall measuring accuracy of the dynamometer confirm the choice of the overall design concept and design details.

On the measurement of transverse sensitivity of strain gauges

The influence of the transverse sensitivity factor n on errors in the measurement of strain are discussed and it is concluded that, providing the factor n is within £0015, its effect may be disregarded in all normal applications. The determination of n on a gauge factor calibration rig is considered and an analysis made of the degree of accuracy attainable.

Investigation on the Nonconstant Behavior of a Vortex Flow Meter with Narrow Gauge Pipe via Conducting Measurements and Numerical Simulations

Vortex shedding flowmeters can be used for a wide range of flow measurement applications with various kinds of fluids. The critical point in applying this method comes from the assumption that the Strouhal number is constant for the given Reynolds number range. In some cases – typically regarding flowmeters with narrow gauge pipes –, this assumption is only partially met, thus limiting the widespread use of these instruments in certain industrial appliances. The paper presents a diagnostic investigation on the effects of this nonconstant behavior. The method elaborated in this report can be applied to vortex flowmeters with narrow gauge pipes. In these instruments – usually due to the narrow cross-sections of the gauge pipe – measurement possibilities are limited, thus it is not possible for the user to determine the effects of the nonconstant behavior. To conduct these investigations, a calibration rig was designed and assembled. The presented diagnostic method combines measurements and numerical simulations. The results of the investigations can be used in the data processing phase, in order to reduce the uncertainty of the volume flow rate measured by vortex flowmeters.

Pivoted-Pad Journal Gas Bearing Performance in Exploratory Operation of Brayton Cycle Turbocompressor

This paper describes findings obtained to date in the area of journal gas bearings from an experimental study of a Brayton cycle turbocompressor designed for the requirements of a two-shaft 10-kw space power system. The journal bearing design utilizes three pads pivoted on conforming balls and sockets. Two of the pivots are rigidly mounted to the frame, and the third pivot is mounted to the frame through a low-spring-rate diaphragm. This paper describes the salient package and bearing design features and then presents the principal results obtained from testing the package in both a spin calibration rig and operation at design temperature conditions with an inert gas. The results discussed include (a) the successful use of a pneumatic loading device to vary pad load during operation, (b) the operating characteristics of the bearings as obtained over a range of pad loads and ambient conditions, (c) structural and dynamic behavior of the bearing-support system during design temperature operation and (d) a discussion of the wear characteristics of the conforming ball-and-socket pivot as obtained from the tests made to date.