The Use of Allan Variation in the Study of the Random Errors of Angular Rate Sensors

This paper describes the use of Allan variation in the study of the random errors of angular rate sensors. The results of the study are presented: Allan diagram, Angle Random Walk, Bias Instability.

The results of laboratory tests underwater navigation system for environmental monitoring devices

An urgent task facing the developers of unmanned underwater vehicles (UUVs) (autonomous underwater vehicles, remotely operated underwater vehicles) is to improve the accuracy of determining the output navigation parameters: orientation angles, linear velocities and location coordinates. The systems for determining the course and attitude position (Attitude and Heading Reference Systems – AHRS) and spatial positioning systems, which are supposed to equip the UUV, should not be expensive, but technologically suitable for mass production with acceptable coordinate determination accuracy. At the first stage of the research, a prototype of the navigation platform with software for it was developed and manufactured, on which experimental data from the measuring channels were obtained in laboratory conditions, and then their preliminary processing was carried out. The analysis of existing methods for increasing the accuracy of determining the output navigation parameters of unmanned underwater vehicles showed that, despite their dynamic development and constant improvement, the error in calculating coordinates when using MEMS sensors remains high and unstable. The use of an additional hydrostatic tilt unit in the navigation platform will make it possible to compensate for the errors of MEMS sensors, which require constant correction during their stable operation, unfortunately, only for a short period of time. The analysis of typical errors of MEMS sensors is carried out. The deterministic part of the error of these sensors can be eliminated by calibration, and to estimate the stochastic errors, we used the Allan variation. The obtained error values will be used in the future to form the Kalman filter of the resulting system.

Analysis of Inertial Sensors for the Requirement to Control a Small Unmanned Airplane

The article deals with the analysis of angular velocity sensors, for the control of a small unmanned airplane. In the paper, the authors discuss the process of creating an angular velocity sensor error model for the analysis of the interfering component size of the useful signal. The built-in error model of the inertial sensor will be implemented in a small, unmanned airplane model, in order to increase the stability and controllability of the airplane. Allan variation will be used to analyze stochastic processes of inertial sensors.

Simultaneous Measurements of CO and CO2 Employing Wavelength Modulation Spectroscopy Using a Signal Averaging Technique at 1.578 μm

A resolved line pair was selected for simultaneous measurement of carbon monoxide (CO) and carbon dioxide (CO2) in the near-infrared (NIR) region. The spectral lines of CO and CO2 at 1.578 µm were measured by wavelength modulation spectroscopy (WMS)-2 f and the absorption was enhanced with a multipass absorption cell. The white noise was further reduced by averaging technology. The detection sensitivity (1σ) for the system is estimated at 2.63 × 10−7 cm−1 for direct absorption spectroscopy. The ultimate detection limits of CO2 and CO mixed with pure N2 at 75 Torr are 29 parts per million (ppm) and 47 ppm, respectively. It is demonstrated that the signal is highly linear with the concentration in the range of 100–800 ppm. Based on an Allan variation analysis, the minimum detectable limit of CO2 and CO is 7.5 and 14 ppm, respectively. The response time of the system is about 30 s and a relationship of temperature dependence was obtained. As an example, an in situ measurement of exhaust of alkane combustion emission is presented.

Pressure-Dependent Detection of Carbon Monoxide Employing Wavelength Modulation Spectroscopy Using a Herriott-Type Cell

Wavelength modulation spectroscopy (WMS) combined with a multipass absorption cell has been used to measure a weak absorption line of carbon monoxide (CO) at 1.578 µm. A 0.95m Herriott-type cell provides an effective absorption path length of 55.1 m. The WMS signals from the first and second harmonic output of a lock-in amplifier (WMS-1 f and 2 f, respectively) agree with the Beer–Lambert law, especially at low concentrations. After boxcar averaging, the minimum detection limit achieved is 4.3 ppm for a measurement time of 0.125 s. The corresponding normalized detection limit is 84 ppm m Hz–1/2. If the integrated time is increased to 88 s, the minimum detectable limit of CO can reach to 0.29 ppm based on an Allan variation analysis. The pressure-dependent relationship is validated after accounting for the pressure factor in data processing. Finally, a linear correlation between the WMS-2 f amplitudes and gas concentrations is obtained at concentration ratios less than 15.5%, and the accuracy is better than 92% at total pressure less than 62.7 Torr.

CHARACTERIZING THE MASS/FORCE MEASUREMENT CAPABILITY OF A MICROBALANCE

Specifying and reducing the uncertainty is very important to all kinds of measurements. In order to have a better understanding of the noise mechanism responsible for lowering the quality of mass/force measurements, the Allan variation method is applied to investigate the noise performance of a commercial ultra-microbalance installed on different noise reduction platforms. It turns out that the marble table provides a better noise isolation environment for mass measurements than an optical table. The optimal integration time is found to be 100 sec ~ 200 sec, with a lowest deviation of 0.07 μg. A different data treatment simulating the ABA load/unload cycle is also applied with or without a delay time for signal integration. The consistency between Allan deviation and the ABA simulation plots points out that the optimal integration time is applicable either in single or cyclic mass measurements.