Search

In this article, we present research, development, calibration, and characterization of a novel concept of a digitally compensated, low-noise magnetometer based on anisotropic magnetoresistance sensors that is suitable for space applications. The main idea of the design was to reduce the number of precise analog components while using the digital signal processing power available in a modern microcontroller. Our most recent effort targeted lowering power consumption, enhancement of radiation hardness, and overall improvement of the parameters. The principle of operation is presented in detail, along with a detailed description of the instrumentation used to characterize the real instrument, including its noise, linearity, and temperature stability in the range of −20 °C to +70°C. The results of total ionizing dose (TID) testing at a gamma-ray irradiation facility are discussed at the complete magnetometer and part levels. This is an extended version of an article presented at I2MTC 2020 that contains the results of a second radiation test done with a slightly modified design. The instrument worked well throughout the entire irradiation session (TID of 1.05 kGy over 72 h), and the stability of main parameters was very good (50 pT/Gy offset and 1 ppm/Gy sensitivity stability). [ABSTRACT FROM AUTHOR]

This paper considers the possibilities of using digital feedback for precise anisotropic magneto-resistance (AMR) magnetometers using commercial off-the-shelf (COTS) components. Requiring only a few analog parts, most of the signal processing is done digitally within an STM32 microcontroller. Because most of the precision is made by the feedback circuit, the analog-to-digital converter (ADC) can be a low-cost type. The compensation source is made with a pulsewidth modulation-driven H-bridge sourced from a voltage reference, so the cost reduction when compared to a “full-analog” design is large. The demodulation of a flipped-AMR signal is done with software after the AD conversion because it improves the offset stability and brings the reduction of the preamp’s and ADC’s LF noise. This paper presents the full characterization of a real instrument, including its noise, linearity, stability, and power consumption. [ABSTRACT FROM AUTHOR]

The article presents testing of a miniature fluxgate sensor developed and manufactured by Texas Instruments as well as an application of the sensor in a compact magnetic field probe with USB interface and LabView based software. Several basic properties of the sensor were evaluated and compared with the datasheet specifications. Offset stability measurements have indicated some possible problems for applications that require very high DC and low-frequency precision. Jumps in offset were present for some of the devices, frequency and duty of the jumps varying between individual pieces and with respect to the supply voltage. Magnetic probe for fast and handy measurements of DC and AC (up to 30 kHz) magnetic fields (up to ±1 mT) is also presented. The probe contains 24-bit analog to digital converter, microcontroller and high-speed USB interface which allows a live view of the signal in time and spectral charts. The probe proved to be very useful for the DRV425 debugging, application development, EMC measurements and magnetic field demonstrations activities. [ABSTRACT FROM AUTHOR]

A completely nonmagnetic calibration platform has been developed and constructed at DTU Space (Technical University of Denmark). It is intended for on-site scalar calibration of high-precise fluxgate magnetometers. An enhanced version of the same platform is being built at the Czech Technical University. There are three axes of rotation in this design (compared to two axes in the previous version). The addition of the third axis allows us to calibrate more complex devices. An electronic compass based on a vector fluxgate magnetometer and micro electro mechanical systems (MEMS) accelerometer is one example. The new platform can also be used to evaluate the parameters of the compass in all possible variations in azimuth, pitch, and roll. The system is based on piezoelectric motors, which are placed on a platform made of aluminum, brass, plastic, and glass. Position sensing is accomplished through custom-made optical incremental sensors. The system is controlled by a microcontroller, which executes commands from a computer. The properties of the system as well as calibration and measurement results will be presented. [ABSTRACT FROM AUTHOR]

Magnetic field sensors based on anisotropic magnetoresistance (AMR) are widely used in many scientific and industrial applications. The AMR sensor sensitivity is superior to Hall probes and size and power consumption is superior to fluxgates. However, the noise properties and the temperature stability of AMR sensors are typically worse than for fluxgates. These properties define the typical applications—less precise vectorial or gradient measurements of the magnetic field within less than ±1 mT range. AMR sensors are typically calibrated for sensitivity, offset, and orthogonality errors. However, there is another important source of error—sensitivity to the magnetic field applied in the perpendicular direction to the measurement axis. This so-called cross-field error is inherent to AMR sensors and can influence the measurements significantly. Flipping (set/reset pulses) and closed-loop operation of the sensor can reduce the cross-field error. In this paper, we present a novel approach using full vectorial compensation of the measured magnetic field resulting in a complete elimination of the cross-field effect. The vectorial compensation provided superior results over alternative approaches that were also evaluated. [ABSTRACT FROM PUBLISHER]

Vector feedback is a concept which can significantly improve linearity and stability of a magnetic field sensor. The feedback coils effectively cancel the measured magnetic field in the inner volume of the triaxial sensor. Thus, in case of fluxgates, it suppresses one possible source of nonlinearity—cross-field sensitivity error. The triaxial sensor axes orthogonality should be primarily defined by the orientation of the feedback coils, while the sensitivities are defined by feedback coil constants. The influence of the homogeneity of the feedback field and the influence of the sensor inner layout on calibration parameters of a vectorially compensated triaxial fluxgate magnetometer are presented. [ABSTRACT FROM PUBLISHER]

This paper describes a novel method for calibrating dc-precise magnetometers in the low field range ($\pm 100~\mu \text{T}$), which gives acceptable results even in laboratory conditions with significant magnetic interference. By introducing a closely mounted reference magnetometer and a specific calibration procedure, it is possible to compensate for the external magnetic field disturbances caused, e.g., by the local transportation operated with dc power supplies. The field compensation occurs only shortly after the calibrating coils are energized. In this case, the leakage of the coil’s magnetic flux to the reference sensor due to the cancelation of the time-varying compensating field was negligible. When using 60 cm coils and reference sensor in 2.5 m distance, we were able to calculate magnetometer gains with a standard deviation of 91 ppm. We show that an overall uncertainty of 0.1% can be achieved. [ABSTRACT FROM AUTHOR]

DC/AC yokeless galvanically insulated electric current sensors are required for applications, e.g., in automotive and aerospace engineering, where size, weight, and/or price are strictly limited. A busbar current sensor with differential fluxgate in the hole has 1000 A range and 10 mA resolution. Using an asymmetric shape, we achieved a frequency error below ±3% up to 1 kHz, while keeping high temperature stability and low sensitivity to mechanical misalignments. The 2.5 mA/°C maximum dc drift is four times better than when using an AMR sensor and 1000 times better than when using a Hall sensor. The sensor linearity error is below 0.1%. [ABSTRACT FROM PUBLISHER]

Large dc and ac electric currents are often measured by open-loop sensors without a magnetic yoke. A widely used configuration uses a differential magnetic sensor inserted into a hole in a flat busbar. The use of a differential sensor offers the advantage of partial suppression of fields coming from external currents. Hall sensors and AMR sensors are currently used in this application. In this paper, we present a current sensor of this type that uses novel integrated fluxgate sensors, which offer a greater range than magnetoresistors and better stability than Hall sensors. The frequency response of this type of current sensor is limited due to the eddy currents in the solid busbar. We present a novel amphitheater geometry of the hole in the busbar of the sensor, which reduces the frequency dependence from 15% error at 1 kHz to 9%. [ABSTRACT FROM PUBLISHER]

METGLAS 2714AZ material has been stress annealed without any applied magnetic field to obtain suitable magnetic properties for use as low-noise fluxgate sensor core. During the development of magnetic cores, we observed an unusual change of the anisotropy direction on Co-based amorphous alloy of METGLAS 2714 AZ. The anisotropy direction moves from its original direction along the ribbon axis to the transverse direction as expected but for short annealing times the process is not monotonous. This occurs when annealing is performed above the Curie temperature. We explain it as a mixture of different anisotropies, which are built and released during the annealing process, since the 2714AZ ribbon has manufacturer-induced anisotropy in ribbon axis. The effect of ribbon cooling on the ribbon properties is also shown as annealing in the radiation furnace was done in different ways. [ABSTRACT FROM AUTHOR]