Stationary Calibration Research Articles

Calibration of heat flux sensors based on anisotropic thermoelements and heterogeneous metal structures using a reflected shock wave

The applicability of the calibration method for heat flux sensors based on anisotropic bismuth thermoelements and a heterogeneous copper-nickel structure using a reflected shock wave to determine the volt-watt coefficient is demonstrated. The coefficient obtained for a sensor based on anisotropic thermoelements is close to the stationary calibration data, and for a sensor based on a heterogeneous structure, to the results of numerical simulation. Keywords: heat flux, calibration, shock tube, shock wave, ghfs, hghfs.

Калибровка тепловых датчиков на анизотропных термоэлементах и гетерогенных металлических структурах с помощью отраженной ударной волны

The applicability of the calibration method for heat flux sensors based on anisotropic bismuth thermoelements and a heterogeneous copper-nickel structure using a reflected shock wave to determine the volt-watt coefficient is demonstrated. The coefficient obtained for a sensor based on anisotropic thermoelements is close to the stationary calibration data, and for a sensor based on a heterogeneous structure, to the results of numerical simulation.

Development of a dynamic pressure standard of low amplitudes and frequencies

The height of the gravitational wave is an influential magnitude in the estimation of its energy content, a very important parameter in the design of maritime structures such as piers and breakwaters; however, there are reasonable doubts among researchers regarding the quality of its measurement. The objective of the present work was to demonstrate that a stationary calibrated pressure transmitter allows the indirect calculation of the wave height with satisfactory accuracy despite the fact that it is a dynamic event as long as its frequency range is low, as is the case with the gravitational waves of the Costa Rican central Pacific Ocean: between 0.05 and 0.39 Hz. In the absence of a primary standard of periodic pressure disturbances, an alternate path was developed based on the characterization of the parameters of the differential equation characteristic of a pressure measurement system in a shock tube prototype from normal shock wave theory and subsequent verification in a periodic disturbance generator that its attenuation and delay are practically negligible at the frequency of 0.1 Hz. The effect of the different geometry of the chamber of the pressure measurement system used in the sea was evaluated pneumatically by comparison with the dynamic pressure standard in the prototype of the periodic disturbance generator, while the effect of the compressibility of the fluid was evaluated in water in the wave channel of the Laboratory of Maritime Engineering, Rivers and Estuaries of the University of Costa Rica. The results show that the pressure measured from the least-squared adjustment coefficients of an electric current transmitter obtained by stationary calibration is acceptable to estimate the climatology of the gravitational wave characteristic of the Costa Rican central Pacific Ocean with maximum errors of 136 mm in waves of height up to 1.4 m.

Multiple Inertial Measurement Units–An Empirical Study

An inertial navigation system is commonly used in various marine platforms above and below the sea surface to calculate the position, velocity and orientation of its carrier platform. Such systems contain an inertial measurement unit (IMU) to measure the specific force and angular velocity which in turn are integrated to obtain the navigation state. Due to sensor noises and other error terms, the navigation solution drifts in time. In situations of pure inertial navigation (no external aiding), multiple IMUs (MIMU) can be used to improve the performance of a single unit. In this paper, we explore the benefits of using a MIMU system for common navigation operations. To that end, a 32 MIMU architecture (192 inertial sensors) was designed and constructed for the experimental evaluations. Utilizing this system we examined the effect of the number of sensors in the architecture versus position accuracy, stationary calibration, coarse alignment and gyro free design. We derive closed form empirical expressions enabling insight to the connection between number of IMUs to the expected performance.

Measurement of Three-Dimensional Structural Displacement Using a Hybrid Inertial Vision-Based System

Accurate three-dimensional displacement measurements of bridges and other structures have received significant attention in recent years. The main challenges of such measurements include the cost and the need for a scalable array of instrumentation. This paper presents a novel Hybrid Inertial Vision-Based Displacement Measurement (HIVBDM) system that can measure three-dimensional structural displacements by using a monocular charge-coupled device (CCD) camera, a stationary calibration target, and an attached tilt sensor. The HIVBDM system does not require the camera to be stationary during the measurements, while the camera movements, i.e., rotations and translations, during the measurement process are compensated by using a stationary calibration target in the field of view (FOV) of the camera. An attached tilt sensor is further used to refine the camera movement compensation, and better infers the global three-dimensional structural displacements. This HIVBDM system is evaluated on both short-term and long-term synthetic static structural displacements, which are conducted in an indoor simulated experimental environment. In the experiments, at a 9.75 m operating distance between the monitoring camera and the structure that is being monitored, the proposed HIVBDM system achieves an average of 1.440 mm Root Mean Square Error (RMSE) on the in-plane structural translations and an average of 2.904 mm RMSE on the out-of-plane structural translations.

Real‐time compensation of magnetic data acquired by a single‐rotor unmanned aircraft system

ABSTRACTTwo methods for low‐altitude calibration of a single‐rotor unmanned aircraft system using a real‐time compensator are tested: (1) a stationary calibration where the unmanned aircraft system executes manoeuvres while hovering in order to minimize ambient field changes due to the local geology; and (2) an adapted box calibration flown in four orthogonal directions. Both methods use two compensator‐specific limits derived from established methods for manned airborne calibration: the lowest frequency used by the compensator for the calibration algorithm and the maximum variation of the ambient magnetic intensity experienced by the unmanned aircraft system during calibration. Prior to flying, the unmanned aircraft system was magnetically characterized using the heading error and fourth difference. Magnetic interference was mitigated by extending the magnetometer‐unmanned aircraft system separation distance to 1.7 m, shielding, and demagnetization. The stationary calibration yielded an improvement ratio of 8.595 and a standard deviation of the compensated total magnetic intensity of 0.075 nT (estimated Figure‐of‐Merit of 3.8 nT). The box calibration also yielded an improvement ratio of 3.989 and a standard deviation of the compensated total magnetic intensity of 0.083 nT (estimated Figure‐of‐Merit of 4.2 nT). The stationary and box calibration solutions were robust with low cross‐correlation indexes (1.090 and 1.048, respectively) when applied to a non‐native data set.

Dynamic Full Range Input Shaping of Injection Parameters for Reduction of Transient NOx Emissions

For modern passenger car Diesel engines strong limitations on emissions, due to legislation, require large efforts in combustion and aftertreatment control. This control problem is mainly approached by an intensive stationary calibration process and dynamic compensation techniques. However, large differences in combustion conditions between steady state, as used for calibration, and real transient maneuvers, such as tip-ins, can lead to undesired emission peaks. Against this background, the present work adapts a previously introduced input shaping strategy for injection parameters, such that it is applicable in the full engine operation range. Different to the former approach, the shape of the correction profile is determined directly from identified local models of the selected injection parameters to the NOx response. By using local linear models it is possible to consider variations in the system dynamics and parameterize the input shapers in an automated fashion. Additionally this approach can be applied together with a state of the art engine control, since it does not need a change in the base calibration. The improved strategy is evaluated on a passenger car Diesel engine and it is shown that a reduction of the undesired NOx overshoot can be achieved without impacting other performance indicators.

Improvement and field testing of a combined horizontal penetrometer for on-the-go measurement of soil water content and mechanical resistance

Soil water content has a significant effect on penetrometer resistance, so simultaneous on-the-go measurement of both these parameters can provide useful information on within-field spatial variations in soil compaction. In this study we improved and refined the electronic circuitry and mechanical construction of an existing sensor and evaluated it as a combined horizontal penetrometer in the field. This paper concentrates on its ability to determine soil water content (volumetric basis) in the field. Stationary calibration was first performed in the laboratory on remoulded loam soil (gleyic Cambisol) at gravimetric water content 0–0.28gg−1 and wet bulk density 1.4–1.8gcm−3. A quadratic relationship was found between sensor output and volumetric water content. Simulations of the sensor fringe field using a finite element model showed that at a dielectric constant of 5 (dry soil) the zone of influence of the sensor (i.e. the distance from the centre of the sensor) was approximately 70mm, whilst at a dielectric constant of 30 (an estimate of wet soil) it was 40mm. The dielectric sensor was then implemented together with a load cell on a tine for field measurement of water content and penetrometer resistance, and a series of transect measurements were conducted to assess its accuracy over a range of natural soil water contents in the field. Within the volumetric water content range 0.30–0.40cm3cm−3, a linear relationship fitted the sensor output versus water content data, which was in close agreement with the laboratory calibration. Additional studies on the effect of travelling speed on dielectric sensor performance showed no clear trends, but further investigations are needed. A significant negative correlation was observed between penetrometer resistance and water content. The developed combined horizontal penetrometer can be a promising useful instrument for future studies in soil compaction and precision agriculture.

A dielectric-based combined horizontal sensor for on-the-go measurement of soil water content and mechanical resistance

Precision agriculture is drawing widespread attention and increasing interest in the use of on-the-go sensors to extract soil and plant information. This new trend is evident from an increased number of (tillage) studies concerning the development of sensors for measuring physical soil properties. In this study, a new dielectric-based horizontal sensor was designed and stationary calibrated in pots for measurement of volumetric soil water content. Subsequently, the sensor was combined with a load cell and installed on a tine with thickness of 25 mm, and its dynamic performance was assessed. The load cell behind the tine measures horizontal soil mechanical resistance. In order to evaluate the on-the-go performance of this combined sensor, two experiments were carried out in a soil bin, with the purpose of (i) measuring soil water content along a transect of longitudinally variable water contents, (ii) investigating the difference in horizontal resistance force measured by either the combined (horizontal force and water content) or a single sensor (horizontal force only). The stationary calibration results showed that quadratic equations with coefficients of determination ( R 2) of 0.989 and 0.918 could be fitted to the data points obtained from measurements in soil bulk densities of 1.5 and 1.2 g cm −3, respectively. The results of the soil bin experiments indicated that the response of the dielectric sensor to soil water content variations was reasonable, but that the output voltage of the sensor should be amplified for a better sensitivity and resolution. The presented combined sensor can provide useful information on soil physical properties towards site specific applications in soils.

The Effect of Transponder Motion on the Accuracy of the Calypso Electromagnetic Localization System

To determine position and velocity-dependent effects in the overall accuracy of the Calypso Electromagnetic localization system, under conditions that emulate transponder motion during normal free breathing. Three localization transponders were mounted on a remote-controlled turntable that could move the transponders along a circular trajectory at speeds up to 3 cm/s. A stationary calibration established the coordinates of multiple points on each transponder's circular path. Position measurements taken while the transponders were in motion at a constant speed were then compared with the stationary coordinates. No statistically significant changes in the transponder positions in (x,y,z) were detected when the transponders were in motion. The accuracy of the localization system is unaffected by transponder motion.

The Effect of Transponder Motion on the Accuracy of the Calypso Electromagnetic Localization System

The Calypso localization system remotely detects miniature electromagnetic transponders implanted in a patient. The system is capable of continuously measuring the position of a treatment site during radiotherapy. If the site is moving during respiration then the system can be used for dynamic tracking of the target. With this application in mind we have made measurements to see if there is any change in localization accuracy due to transponder position or motion. Three localization transponders were mounted on a remote-controlled turntable that could move the transponders along a circular trajectory at speeds up to 3 cm/sec. A stationary calibration established the coordinates of six points on each transponder's circular path. We then compared position measurements taken while the transponders were in motion at a constant speed to the stationary coordinates. To synchronize the position of the moving transponders to a known point on the circular path we injected an RF noise pulse into the Calypso readout antenna when the turntable passed 0°. This produced outliers on the arc of moving transponder positions that could be used to compare the transponder positions in the direction of motion to the calibrated stationary positions. The stationary localization uncertainty varied from 0.02 to 0.06 cm per axis in the (x,y) plane, which is consistent with the observations of other researchers. We detected a small systematic trend in the stationary uncertainty as a function of transponder position along an arc 11 cm long. Lung tumors do not move more than about 3 cm in the most extreme cases. Therefore the Calypso system will have less than 0.02 cm systematic change in localization accuracy over the full range of tumor position. There was no statistically significant change in the transponder positions in either the radial or tangential direction when the transponders were in motion. If the Calypso system is used for real-time respiratory motion tracking, then tracking accuracy will be unaffected by transponder motion, at least for the velocity and position range that will be encountered in clinical applications. If the transponder is moving, its reported location corresponds precisely to its position at the midpoint of the readout interval, regardless of speed.