A novel eddy current speed sensor is developed to measure the rotational speed of conductive objects. The sensor consists of one excitation coil and two pick-up coils around a rotating cylinder or rod. The sensor does not use magnetic yoke. For the analysis and experimental verification, we used 30 mm diameter non-magnetic aluminum and also magnetic solid iron cylinders. The calculated and measured speed ranges are up to 1200 r/min. A 2-D analytical method is developed to calculate sensor performance. A 2-D finite element is also used for simulations to compare results with the 2-D analytical method. A 3-D finite-element analysis is required to take into account significant 3-D effects due to the air coil configuration. The experimental results are presented at different steady-state speeds. The calculation results are compared with measurements to validate theoretical models and sensor performance. The eddy current speed sensor shows high linearity even at low speeds. For ferromagnetic rods, we suggest a novel double-layer configuration: non-magnetic conductive ring or shell on top of the iron rod minimizes the influence of the permeability changes. The main advantage of the novel sensor is that it has neither mechanical nor electrical contact to the rotating rod.

This paper describes a novel method for calibrating dc-precise magnetometers in the low field range (± 100 μT), 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.

Novel eddy current speed sensor with axisymmetric coils and solid iron rod as moving part is presented. The analysis is performed for both dc and ac coil currents and for variable iron rod translational speed. The coil inductance and induced voltage results using the analytical method and finite-element method calculation are compared with the measured values. Two different coil configurations are used for simulations and measurement.

Novel rectangular yokeless current transducer with the range 400 A using 16 microfluxgate sensors around the busbar conductor is presented in this paper. Compared to yokeless transducers utilizing the differential pair of magnetic sensors, our solution has much better suppression of the external currents (lower crosstalk). Compared to industrial transducers with yoke, the new transducer has 15-times lower noise, 7-times better temperature stability, and same crosstalk. Sensor design and design of current monitoring system is presented together with the results of long-term field tests. Crosstalk error is examined in dependence on the number of the operating sensors and external current position.

This paper presents the design and optimization of a novel eddy current speed sensor for rotating rods and cylindrical shafts. The sensor consists of one excitation coil and two pick-up coils. All coils are stationary; we consider air coils, and we also use a magnetic yoke. We utilize a copper coating on an iron rod to increase the sensitivity, and we compare the performance with the performance achieved for an uncoated iron rod. 3D FEM is utilized for analyzing and for optimizing the design of the proposed sensor. The main advantages of the novel sensors are their simplicity, their low cost and their robust configuration. A linearity error of 0.5% has been achieved. The level of accuracy is limited by mechanical factors. A 1D analytical model has also been developed for rapid analysis and optimization of the sensor. An aluminum rod was also used in the measurements for a comparison with the results achieved with the iron rod.

Yokeless busbar current transducers with circular sensor array achieve high precision when replacing Hall sensors by microfluxgate. Limited field range of fluxgate can be compensated by inverse design with sensors inside the busbar. In this paper, we present a novel scheme how to improve the immunity of such sensor against external field and field gradient. We also examine crosstalk error for external currents close to the transducer. Using five microfluxgate sensors, we designed a 400 A current transducer which has a suppression of 93,000 for currents in 40 cm vicinity.