Drift-Free Integration in Inductive Magnetic Field Measurements Achieved by Kalman Filtering

Sensing coils are inductive sensors commonly used to measure magnetic fields, such as those generated by electromagnets used in many kinds of industrial and scientific applications. Inductive sensors rely on integrating the output voltage at the coil’s terminals in order to obtain flux linkage, which may suffer from the magnification of low-frequency noise resulting in a drifting integrated signal. This article presents a method for the cancellation of integrator drift. The method is based on a first-order linear Kalman filter combining the data from the coil and a second sensor. Two case studies are presented. In the first one, the second sensor is a Hall probe, which senses the magnetic field directly. In a second case study, the magnet’s excitation current was used instead to provide a first-order approximation of the field. Experimental tests show that both approaches can reduce the measured field drift by three orders of magnitude. The Hall probe option guarantees, in addition, one order of magnitude better absolute accuracy than by using the excitation current.

Salinity drift prevention experiments in the Korea ocean research stations and suggestions for high quality salinity observation

The importance of salinity has been highlighted to cope with climate changes and disaster prevention. The salinity of accuracy up to 0.005 is normally required in an open ocean to understand various oceanic and climatic phenomena; however, the reliability of salinity measured on the coast and open seas around Korea was low due to the lack of a standardized observation system and post-processing of quality verification. Korea Ocean Research Stations (KORS) has been producing salinity time series since 2003 through the Aanderaa conductivity-temperature (CT) 3919 inductive sensors, which have an advantage of on-site maintenance but tend to drift toward a lower conductivity because of biological attachments to the sensor. This study applied copper taping and UV light exposure techniques to the sensors and then compared its salinity measurements with RBR CTD mooring observations and SeaBird19 CTD profiles to assess a biofouling effect on salinity observations. This experiment shows that the salinity from the CT sensor without biofouling prevention starts to drift in a week, particularly for a surface sensor. This biofouling induced the decrease of salinity up to 10 in a month. The copper taping methodology efficiently suppressed the biological attachment but disturbed an electromagnetic field around the sensor, thus resulting in unrealistic salinity values. When UV light was periodically exposed at a distance of about 5 cm away from the CT sensor, relatively stable salinity could be observed without significant drift at least in two months. Besides, the SBE37 CTD, an electrode-type sensor, seems to be relatively free from biofouling but has difficulties in sensor maintenance and a sensor calibration process. Our results underline a double installation of salinity observation equipment with UV light exposure. In addition, the pre-calibration of a CT(D) sensor and post-verification should be included in a standard procedure for high-quality salinity measurement.

Theory and Modeling of Eddy Current Type Inductive Conductivity Sensors

While transformer-type conductivity sensors are the usual type of inductive sensors, this paper describes the theory behind less used eddy current sensors. This type of sensor measures the conductivity of a liquid by inducing eddy currents and observing the effect on the sensor coil, which allows a simpler sensor design and promises a cost advantage in implementation. A novel model description is derived from the Maxwell equations and implemented by an equivalent RLC circuit. The designed model is validated by comparisons with experimental observations and FEM simulations. The result leads to a better understanding of the physical effects of the sensor and the influencing parameters for future sensor developments. The aim is to provide starting points for further sensor development of low-cost inductive conductivity sensors.

Non-Destructive Testing of the Longest Span Soil-Steel Bridge in Europe—Field Measurements and FEM Calculations

The article describes interdisciplinary and comprehensive non-destructive diagnostic tests of final bridge inspection and acceptance proposed for a soil-steel bridge made of corrugated sheets, being the European span length record holder (25.74 m). As an effect of an original concept a detailed and precise information about the structure short-term response was collected. Periodic diagnostics of bridge deformations was done one year after it was built. Load test design was based on numerical simulations performed by means of finite element method (FEM). In situ measurements were done with the aid of: inductive sensors, optical total station, and terrestrial laser scanner. The results produced by terrestrial laser scanning were used to build a precise image of structure deformation in 3D space during the tests. The accuracy of laser mapping was significantly increased using the information coming from total station and inductive sensors. These have higher accuracy and therefore can be used as reference. Thus, new quality in measurements is introduced. Good correspondence between in situ values and FEM estimations was achieved. Therefore, such a combination of testing methods can be used in non-destructive diagnostics of structures and is an interesting alternative for the standard approach, in which the measurements are done in limited number of points.