Closed-loop Calibration Research Articles

A novel perspective to high-speed cross-hot-wire calibration methodology

A practical cross-hot-wire calibration and data reduction methodology for instantaneous measurements of mass flux and flow angle is developed for two dimensional subsonic compressible flows. Historically, data reduction for flow conditions of 0.4 < M < 1.2 is regarded as problematic, even in the simplified case of flow normal mounted wires. Thus, in comparison with the incompressible and supersonic conditions, the literature addressing these flow regimes is quite limited. The present study addresses this void by relating the wire voltages to flow conditions through renormalized, Mach and overheating independent, nondimensional quantities. Therefore, a short and robust calibration can be performed in an unheated free jet facility with applicability toward a broad range of planar flow conditions. This disposes the need for typical closed loop calibration wind tunnels which vary flow velocity, density and temperature independently to parameterize the voltage dependency in a purely empirical manner.

Research of Closed-Loop Calibration Model Based on Kalman Filtering Algorithm

The firing calibration of Artillery fire control system with closed-loop calibration manner can improve the firing accuracy significantly. The miss distance prediction is the theory core of closed-loop calibration. Whether the prediction algorithm of closed-loop calibration corrects or not is directly related to the calibration’s success or failure. Mainly for the external error sources not caused by fire control computer system, this paper established a closed-loop calibration model based on Kalman filtering algorithm, researched the specific implementation process of algorithm model, and applied the MATLAB software simulating the model. Simulation results show that the closed-loop calibration model based on Kalman filtering algorithm can significantly inhibit firing error and is a feasible algorithm and provides a good theoretical basis for forecasting error.

Measurement Technology Research on Target and Projectiles’ Miss Distance Based on Digital Image Processing

At the closed-loop calibration research of anti-aircraft weapons systems, the miss distance between target and projectiles is difficult to obtain accurately. In order to solve this problem, this paper provided using the digital image processing technology to research the miss distance measurement methods, focusing on the image filtering technology, edge detection technology and target recognition technology. According to the simulation results, the paper selected the adaptive median filtering to remove image noise, adopted the edge detection method based on the iterative threshold to obtain target edge and used template matching technology to identify the target in the image. Finally, according to the principle of image measurement technique, using centroid tracking measurement technology to achieve the miss distance measurement. The application of digital image processing technology makes the miss distance measurement become simple, effective and convenient. This measurement method enables to save money, improve accuracy, get results in real time and have a high research value.

Integrated Kinematic Calibration for All the Parameters of a Planar 2DOF Redundantly Actuated Parallel Manipulator

In this paper, the kinematic calibration of a planar two-degree-of-freedom redundantly actuated parallel manipulator is studied without any assumption on parameters. A cost function based on closed-loop constraint equations is first formulated. Using plane geometry theory, we analyze the pose transformations that bring infinite solutions and present a kinematic calibration integrated of closed-loop and open-loop methods. In the integrated method, the closed-loop calibration solves all the solutions that fit the constraint equations, and the open-loop calibration guarantees the uniqueness of the solution. In the experiments, differential evolution is applied to compute the solution set, for its advantages in computing multi-optima. Experimental results show that all the parameters involved are calibrated with high accuracy.

Limit-Cycle Oscillations Based Auto-Tuning System for Digitally Controlled DC–DC Power Supplies

This paper introduces a new method and system for parameter extraction and automated controller adjustment, suitable for low power digitally controlled DC-DC switch-mode power supplies (SMPS). The system allows closed-loop calibration throughout regular converter operation. During a short-lasting test phase, SMPS parameters, such as output capacitance and load, are estimated by examining the amplitude and frequency of intentionally introduced limit cycle oscillations in duty ratio control variable as well as from its steady state value. Accordingly, a digital compensator is automatically constructed to provide fast dynamic response and good output voltage regulation. In addition, the load estimation data are used for improving efficiency of a converter having segmented transistors. It is performed through a selection of driving sequence resulting in minimized sum of switching and conduction losses. The effectiveness of the system is demonstrated on an experimental 400 kHz, 9 V-to-3.3 V, 10 W, digitally controlled synchronous buck converter.

Digital self-learning calibration system for smart sensors

Design and realization of a digitally controlled closed loop calibration system for smart sensors, capable of self-learning, is reported. Closed loop design enables analysis of sensor properties and optimization of calibration procedure. Dedicated software was developed, enabling control of acquired data and calibration procedure. Resulting statistical data provide closed loop feedback variable for failure analysis. Calibration system enables digital temperature compensation by acquisition of calibration points, calculation of sensor polynomial coefficients and storing the calculated data in the sensor memory. Due to the proposed digital temperature compensation method, temperature output error of pressure sensors was significantly reduced (typically from 0.15% FSO/°C to 0.05% FSO/°C, based on calibration of 29482 manifold absolute pressure sensors). Modular approach results in reduction of calibration time (typically down to 42 s/sensor), thus enabling mass calibration.

Improved ultra-low range sidelobe pulse compression waveform design

A continuous nonlinear FM waveform design capable of achieving range sidelobe levels of better than −70 dB, suitable for use with a satellite-borne precipitation radar, is presented. The waveform shows good Doppler tolerance. It is shown that slowly-varying phase and amplitude errors in the transmitter and receiver have relatively little effect, but rapidly-varying errors result in paired echo sidelobes, the level of which can be significant. A closed-loop calibration system will undoubtedly be required to remove such errors.

The Calibration Index and Taxonomy for Robot Kinematic Calibration Methods

The major approaches toward kinematic calibration are unified by considering an end-point measurement system as forming a joint and closing the kinematic loop. A calibration index is in troduced, based on the mobility equation, that considers sensed and unsensed joints and single and multiple loops and ex presses the surplus of measurements over degrees of freedom at each pose. Past work using open-loop calibration, closed-loop calibration, and screw axis measurement is classified according to this calibration index. Numerical issues are surveyed, in cluding task variable scaling, parameter variable scaling, rank determination, pose selection, and input noise handling.

Calibration of High Pressure Polyurethane Metering Units with a Computer Controlled Closed Loop Calibration Unit

Calibration of High Pressure Polyurethane Metering Units with a Computer Controlled Closed Loop Calibration Unit

Calibration of MIRAN Gas Analyzers: Extent of Vapor Loss Within a Closed Loop Calibration System

The use of a Closed Loop Calibration System (CLCS) for calibration of several portable models of MIRAN infrared gas analyzers has been recommended by the manufacturer. The purpose of this study was to determine the extent of organic vapor loss due to wall adsorption that may result in erroneous light absorbance data. Two MIRAN-1A gas analyzers that had passed the performance and wavelength accuracy tests were connected in series to a bellows pump to form a CLCS. Fourteen organic solvents, with vapor pressure: 0.43-350 mm Hg (at 25°C), were used in the study. Increments (0.5-5 µL) of high purity solvents were introduced into the CLCS via a septum. Simultaneous gas chromatographic (G.C.) analyses were performed on aliquots of gas mixture drawn between consecutive injections of solvent liquid to determine the actual concentrations of organic vapors within the CLCS. Absorbance data were recorded separately for each gas analyzer. Two regression lines were established for each organic vapor: (i) between expecte...

Calibration of MIRAN Gas Analyzers: Extent of Vapor Loss Within a Closed Loop Calibration System

The use of a Closed Loop Calibration System (CLCS) for calibration of several portable models of MIRAN infrared gas analyzers has been recommended by the manufacturer. The purpose of this study was to determine the extent of organic vapor loss due to wall adsorption that may result in erroneous light absorbance data. Two MIRAN-1A gas analyzers that had passed the performance and wavelength accuracy tests were connected in series to a bellows pump to form a CLCS. Fourteen organic solvents, with vapor pressure: 0.43-350 mm Hg (at 25°C), were used in the study. Increments (0.5-5 µL) of high purity solvents were introduced into the CLCS via a septum. Simultaneous gas chromatographic (G.C.) analyses were performed on aliquots of gas mixture drawn between consecutive injections of solvent liquid to determine the actual concentrations of organic vapors within the CLCS. Absorbance data were recorded separately for each gas analyzer. Two regression lines were established for each organic vapor: (i) between expected (calculated) concentration vs. absorbance, and (ii) between actual concentration (determined by G.C.) and absorbance. The two regression lines were compared statistically. The differences in absorbance values between the two lines at 1/2, 1, and 2 times the OSHA Permissible Exposure Level (PEL) were insignificant for nine organic solvents with vapor pressure: 15-350 mm Hg (at 25°C). However, the absorbance values from the two lines at the above mentioned concentrations were significantly different for five organic solvents with vapor pressure: 0.43-8.3 mm Hg (25°C). In the latter group, the slopes of the lines: i and ii were almost equal; however, there were significant differences between the intercepts. In the absence of leaks from the CLCS, the unidirectional differences between the intercepts (bii>bi) resulted from the vapor loss due to wall adsorption. There was a significant correlation between the degree of wall loss within the CLCS and the decline in vapor pressure. The extent of errors (overestimation of concentration) caused by using calibration curves established by CLCS were between 4.2 to 29.3% at OSHA PEL. It was concluded that even though, from the control standpoint, such reading errors would not cause any harm to (if not benefit) the workers, the use of CLCS would not be recommended for solvents with vapor pressure lower than 15 mm Hg (at 25°C) if maximum accuracy in measurement is aimed.