Applications

· magnetic field sensors - GMRŠ Air Force Academy Košice and EDIS, Ltd. Košice,SR

A relax type wide range field sensor using Finemet (presented at 4^th EMSA 2002, Athens;

extended version appeared in Sensors and Actuators A 106 (2003), 22-25.)

P.Butvin^a, D.Praslička^b, J.Blažek^b, B.Butvinová^a

a - Institute of Physics, SASc, 84228 Bratislava, Slovakia

b - Airforce Academy of M.R.Štefánik, 04121 Košice, Slovakia

Let's consider a magnetic core which is magnetized to its saturation and then left to relax the surplus energy down to the level corresponding to the core's energy in an ambient field. If the ambient field changes, the relaxed energy changes proportionally. So the relaxed energy carries an unambiguous information about the ambient field. A sensor using this principle is often called 'relax type'. Proper circuitry [1] enables precise measurement of the relaxed energy by converting it to the time interval t_r , during which the load current linearly falls to zero at a constant voltage maintained by a voltage limiter (a diode). The quantity t_r is then ready to A-D conversion in a 16 or 24-bit counter provided that there are proper conditions for comparators to start and stop the counter. Based on this concept, the magnetometer series VEMA with an online laptop (optimized software inclusive) is produced and also exploited with great success for mostly environmental measurements by an affiliate company. The most frequently used magnetometer type shows the basic range of 0.1 mT with resolution of 2 nT (averaging improves this figure by ~2 orders) and bandwidth of dc to 500 Hz. The sensors used so far exploit a Co-based metallic glass straight-strip probe. To improve the above parameters, several compositions of FeNbCuBSi nanocrystalline series (Finemet) have been tried for such a probe. The relative brittleness of Finemet proved not to be a real challenge unless extremely rough handling should be tolerated. Higher saturation induction B_s enables alternatively: to double the dynamic range, to spread the bandwidth, to speed-up the data processing by omitting/reducing non-linearity corrections. Probes with Finemet withstand higher continuous duty and storage temperature in non-aggressive environment. Special attention has been paid to Barkhausen noise immunity although the sensor principle avoids most of the risk. Some high B_s members of the FeNbCuBSi series showed also intolerable coercivity, non-linearity and unfavorable approach to saturation. Besides slightly higher demands to probe construction to respect the larger magnetostriction, the use of Finemet with ~13 at.% of Si is found a real progress. Some circuitry improvements are briefly commented too.

[1] J.Blažek, J.Hudák, D.Praslička; Sensors and Actuators A 59 (1997) 287.

A multiprobe box of the field sensor located below the conveyer belt transporting just excavated coal in a surface mine.

· precise electrometric current transformers - FEI STU, Bratislava, SR

Typical toroidal cores used at the magnetic measurements. Some of the cores (annealed to nanocrystallize the material) are those used for the electrometric current transformers.