Petr Kaspar

Automated system for the calibration of magnetometers

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.

Low-Power Printed Circuit Board Fluxgate Sensor

A new printed circuit board flat fluxgate sensor with integrated coils and amorphous alloy core was developed and its excitation parameters optimized for low-power consumption. The power consumption achieved with 10 kHz, 300 mA p-p pulse excitation with duty cycle 12.5% was only 3.9 mW, which is three times lower than that for sinewave B excitation. The sensor sensitivity reached 94 V/T. The required excitation bridge supply voltage was only 0.47 V. The low-cost low-power sensor has a temperature offset stability of 120 nT in the -20 to +70 degC temperature range and 0.17%/degC open-loop sensitivity tempco due to the use of a new core embedding technique. The perming error due to 10 mT field shock was suppressed below 1.2 muT. The short-time offset stability was 38 nT within 3 h. Thus the developed sensor is more precise and less energy consuming than a periodically flipped anisotropic magnetoresistance (AMR) sensor. The achieved parameters are sufficient for compass with 0.1deg error

Calibration of a triaxial fluxgate magnetometer and accelerometer with an automated non-magnetic calibration system

A method, instrumentation used and results of calibration and testing of tri-axial magnetometers, accelerometers and also possibly gyroscopes are presented. The method is based on a scalar calibration technique with the use of an innovative computer controllable non-magnetic platform [1]. The speed, precision, comfort and repeatability of the measurement are superior to techniques which use hand-driven tools.

Portable fluxgate magnetometer

Abstract A low-power three-axis fluxgate magnetometer has been developed for portable applications. The instrument has 300 mW consumption from a ±6 V source and a range of ± 100 μT with 0.01% linearity. The effective resolution is 1 nT and the response time to a large field step is 4 ms. Innovative sealed ring-core fluxgate sensors made of etched rings ensure high resistance against vibrations and mechanical shocks.

Low-power PCB fluxgate sensor

New PCB (printed circuit board) technology flat fluxgate sensor with integrated coils and amorphous alloy core was developed and its excitation parameters were optimized for low-power consumption. The power consumption achieved with 10 kHz, 300 mA p-p pulse excitation with duty cycle 12.5% was only 3.9 mW, which is 3-times lower than that for sinewave flux density excitation. The sensor sensitivity reached 94 V/T. The required bridge supply voltage was only 0.47 V. The low-cost, low-power sensor has a temperature offset stability of 120 nT in the -20...+70 degC temperature range and 0.17%/degC open-loop sensitivity tempco due to the use of new core embedding technique. The perming error due to 10 mT field shock was suppressed below 1.2 muT

Compact Digital Compass with PCB Fluxgate Sensors

The new compact digital compass with PCB fluxgate sensors and accelerometers will be introduced in this contribution. Competitive low-cost, low-accuracy compasses are dedicated for measurement in horizontal plane only. The main advantage of developed compass is that it is able to determine azimuth in every position. The compass module consists of a tri axial fluxgate magnetometer and tri axial MEMS accelerometer which is used as a tilt sensor. The excitation and evaluation electronics is build directly in the compass module. Compass module is driven by two microprocessors and is equipped with digital output. The dimensions and power consumption of the compass were decreased by using miniature PCB (Printed Circuit Board) fluxgate sensors, instead of traditional large ring core fluxgates. Improved calibration techniques have been used to decrease azimuth error of the compass. The using of accurate magnetic sensors leads to the possibility of using tri axial magnetometers for calculation of total Held intensity and use it as a vector magnetometer. The resulting device is small high accurate compass with digital output that is able to be used in underwater or underground exploration or measurement.

Sampling measurements with digital hysteresisgraph

Digital hysteresisgraph can be used for the measurement of dynamic hysteresis loops up to 100 kHz. Digital feedback allows achievement of sinusoidal flux density by iterative modification of the excitation voltage waveform. This approach is used for the measurement of closed (toroidal) samples at higher frequencies.

Compact fluxgate sensor with a vector compensation of a measured magnetic field

Compact tri-axial fluxgate sensor which combines new materials, traditional ring-core topology and vector field compensation is introduced. The core support material is BNP-2. This new material provides an extremely high thermal conductivity (92.6W/m.K), which helps to eliminate thermal gradients in the core. The core is made of Vitrovac 6025X amorphous metallic ribbon. Thermally stable glass filled laminate was used to manufacture the pick-up and vector coil compensation support. The vector compensation topology has several advantages - it eliminates the cross-field effect and brings down the non-orthogonality. The presented design should outperform common tri-axial fluxgate sensors while keeping the dimensions at acceptable level. Magnetometer construction and preliminary results are discussed.

Bomb Detection in Magnetic Soils: AC versus DC Methods

We compare the performance of eddy-current metal detectors for finding small bombs and other items of unexploded ordnance (UXO) with the potencial of DC gradiometers of scalar and resonant type. Extensive database of results was collected during laboratory measurements and field trials performed by JRC. There are two main obstacles for bomb detection: false alarms caused by metal clutter and effect of magnetic soil and rocks. A number of soil samples were collected at mine fields and UXO affected areas. Magnetic properties of these soils were examined both in time and frequency domain. The results were compared with the detection depths measured both in soil and in air for various targets. In general, the most difficult soils show frequency dependent susceptibility, which creates signal similar to metal object. We show how to compensate such soils.