Sensors and Actuators A 105 (2003) 132–136
Spin-valve current sensor for industrial applications
J. Pelegrí a,∗ , J.B. Ejea b , D. Ramírez b , P.P. Freitas c
a
EPSG-Polytechnic University of Valencia, C/Nazaret-Oliva s/n, 46730 Grao de Gandia, Valencia, Spain
b University of Valencia, C/Doctor Moliner 50, 46100 Burjassot, Valencia, Spain
c Instituto de Engenharia de Sistemas e Computadores, R. Alvés Redol 9-1, 1000 Lisbon, Portugal
Received 28 March 2003; received in revised form 28 March 2003; accepted 28 March 2003
Abstract
This work presents an industrial application of a new spin-valve current sensor based on the giant magnetoresistance effect (GMR) and
provides a comparison between this sensor and the typical sensor used in these applications, the hall sensor. Experimental results derived
from the application of this two sensors in a power application (a bi-directional three-phase rectifier) are shown.
© 2003 Elsevier Science B.V. All rights reserved.
Keywords: Magnetic field measurement; GMR; Spin-valve sensor; Current sensing; Three-phase rectifier; Conductance control; Hall sensor
1. Introduction
The measurement of the magnetic field constitutes a good
method to measure and control some quantities related with
it, as for example, the electric current. Three techniques have
commonly been used to sense the current: shunt resistor, current transformer and Hall effect sensor [1–3]. The first one
is based on Ohm’s law and the other two ones are based on
Ampere’s law. Recent introduction of sensors based on the
giant magnetoresistance effect (GMR) have permitted measurements of the magnetic field in very different situations
[4–6].
The GMR sensor with spin-valve technology has been
obtained after a easy process of microelectronic fabrication.
The sensor has been used inside a feedback loop of the system to monitor the current in a high-frequency bi-directional
three-phase rectifier [7]. Experimental results corresponding to the frequency response of the power system with this
sensor and a Hall sensor have been compared.
2. Sensor description and characteristics
The sensor is a spin-valve sensor based on a GMR. It
has been implemented at the Instituto de Engenharia de Sistemas e Computadores (INESC) and has a sandwich structure with a non-magnetic middle layer and two magnetic
∗ Corresponding author. Tel.: +34-96-2849404; fax: +34-96-2849309.
E-mail address: jpelegri@eln.upv.es (J. Pelegrí).
extreme layers (see Fig. 1). Referring to the magnetization
vector of these last two layers, one of this is pinned and
the other is free [8,9]. The resistivity of the one spin-valve
element, ρsv , is described in Eq. (1)
ρsv = ρ(1 − 21 MR cos(θfree − θpinned ))
(1)
where ρ is the intrinsic resistivity, MR the magnetoresistive
value and θpinned and θfree are the angles of the magnetization
vectors of the magnetic layers.
A Wheatstone bridge topology with four active spin-valve
elements named R1 , R2 , R3 and R4 has been employed
where R1 = R4 and R2 = R3 [10]. This connection provides an inherent linearity, with a high sensitivity and better
interference and drift compensation. Moreover, Wheatstone
circuit allows to make differential measurements easily [11].
The instrumentation system used for the process of characterization can be found in [12]. Basics characteristics of
the sensor are: high precision (better than 1% at full scale),
intrinsic galvanic isolation, high bandwidth, high level of the
output signal (1.2 Vpp for a power supply of 10 mA), very
small size (1.4 mm × 1.4 mm), low cost, simple design for
multiple ranges of current: 0–250 mA, 0–1.5 A and 0–10 A
(see Fig. 2). A very important characteristic for a robust
GMR sensor is the thermostability [13]: temperature coefficient of the output voltage is TCVo = ±0.2 up to 150 ◦ C,
temperature coefficient of the bridge sensor resistance is
TCR = ±0.11 ◦ C. Fig. 3 shows the output signal of the sensor versus the magnetic induction for different temperatures.
With this features, the sensor can be compared to any sensor
that is nowadays employed in industrial environments.
0924-4247/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0924-4247(03)00091-8
J. Pelegrí et al. / Sensors and Actuators A 105 (2003) 132–136
133
the particles is related with the current that circulate across
the magnet system (inductive load).
For the correct operation of the control loops, the small
signal model of the converter with inductive load has been
used in order to use an average current control or conductance control [14] using a GMR sensor [2].
Fig. 5 shows that with the spin-valve current sensor the
system with the inner current loop behaves as a current
source up to 1 kHz due to its flat frequency response for the
magnitude of the closed current loop frequency response.
These results are agree with the theoretical design.
Fig. 1. Sensor’s structure.
3. Industrial application
4. Comparison with a Hall sensor
The new sensor is used to measure the current in an application that needs an inner current loop. The sensor is
mounted on a sensed current track of a printed circuit board
of a high-frequency bi-directional three-phase rectifier (see
Fig. 4) [7]. Space vector modulation technique and average
current control has been used in this topology to obtain a sinusoidal average input current in phase with the main input
voltage and to regulate the output voltage in a wide range of
variation. Experimental results derived from the application
of these two sensors have been obtained. The bi-directional
rectifier has been tested in collaboration of the European
Laboratory for Particle Physics (CERN) to be used in accelerator applications obtaining excellent results. In these applications, it is important to control the output current with
very high precision because the applied magnetic field to
For the current sensing and control, it is frequently used a
Hall effect current transducer that is able to measure dc, ac
and complex current waveforms providing a galvanic isolation (that is necessary in this application). A common Hall
effect current transducer is the LEM module LA 55-PS/P1
[14]. Its output provides very good results in applications
with a noisy environment. In the application, the solid state
sensor based in a spin-valve sensor has been used with a differential amplifier for conditioning the output signal. This
output signal has been compared with the one of the LEM
module. The results are shown in Fig. 6, where can be seen
various advantage: first the solid state sensor is the better
response in the beginning of the current waveform (see the
square in Fig. 6), better rejection common mode. Second
the spin-valve sensor have better rejection noise (the noise
Fig. 2. Sensor’s output signals under low and high current level excitation.
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Fig. 3. Thermostability of the spin-valve sensor.
Fig. 4. High-frequency bi-directional three-phase rectifier and its control.
Fig. 5. Conductance (inner) closed loop frequency response.
Fig. 6. Comparison of the output signals of the spin-valve sensor (Ch1)
with the one of a current probe AM503A (Ch3) and the one of LEM
module (Ch2).
J. Pelegrí et al. / Sensors and Actuators A 105 (2003) 132–136
Fig. 7. Size comparison of the LEM sensor with the SV sensor.
of commutation in minor). Third the simple structure of the
sensor, a Wheatstone bridge, front to the hall sensor that
need a magnetic core. Therefore, spin-valve sensor can be
used instead of the LEM module with success. Fig. 7 shows
the comparison of the size of the LEM module is 25 times
greater of the spin-valve bridge sensor.
5. Conclusions
A current regulated high-frequency bi-directional
three-phase rectifier using a new spin-valve current sensor
has been verified with very satisfactory results. A very high
power density could be achieved with this kind of current
sensor instead of using magnetic cores together with Hall
effect sensors (to achieve dc+ac sensing) as the LEM transducer. A comparison between this two current sensors has
been made. The spin-valve sensor also provides galvanic
isolation in an 1.4 mm × 1.4 mm area, a very important
characteristic for safety reasons and for current sensing
al lines with potentials different of zero. The spin-valve
transducer is a robust element for high temperatures (good
temperature coefficient) of magnetosensitivity.
Acknowledgements
This work has been supported by the Ministerio de
Medio Ambiente (AMB99-0504-C02-02 project), Plan
Nacional I + D (1FD1997-0508-C03-02 project) and the
Oficina de ciencia y tecnologia of Generalitat valenciana (CTDIA/2002/50 project) from Spain and by the
PRAXIS-Agencia de Inovac,ao (P014-P31B-9/96 project)
and PRAXIS (TPAR/2066/95 project) from Portugal.
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Biographies
José Pelegrí Sebastiá received his MSc degree in physics in 1994 and
electronic engineering degree in 1998 and PhD degree in 2002 from
University of Valencia, Spain. His thesis topic involved the study of GMR
sensors and its applications. He is currently a associate professor at the
Electronic Engineering Department in the EPSG-Polytechnic University
of Valencia, Spain. His research interests include instrumentation systems,
characterization sensors in special magnetic sensors and its industrial
applications.
Juan B. Ejea Martí was born in Spain on June 27, 1969. He received the
BS and the PhD degrees in electronics engineering from the University of
Valencia, Spain in 1993and 2000, respectively. He joined the Department
of Electronics Engineering in 1993, where he is presently an associate
professor. His research interests include power converters design and
modeling.
Diego Ramírez Muñoz received the MSc degree in 1986 and PhD degree
in 1995 from University of Valencia, Spain. He is currently professor in
electronic instrumentation and measurement systems in the Electronic Engineering Department of the same University. His interests are focused in
instrumentation systems, sensors and their characterization and industrial
projects related with electronic instrumentation.
Paulo Jorge Peixeiro de Freitas received his PhD degree in solid state
physics from Carnegie Mellon University in 1986. His thesis topic involved the study of magnetoresistance in CoFe thin films. Between 1986
and 1987, he was a post-doctoral fellow at IBM, Yorktown Heights where
he work on magnetic thin films and high TC superconductors. Since
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1990, he has been at the Instituto Superior Tecnico, where he is an associate professor in the Physics Department. He is presently the Director of
INESC Microsystems and Nanotechnologies and the responsible for the
magnetic recording technology research group. His current research inter-
ests include GMR heads for ultra-high density recording, spin-dependent
tunneling junctions, non-volatile memories, magnetic multilayers and
thin films, micromagnetism, transport phenomena, GMR sensors and
bioelectronics.