Conception and realisation of a sensor

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 10 | Oct-2014, Available @ http://www.ijret.org 268
CONCEPTION AND REALISATION OF A SENSOR
ELECTROMAGNETIC FORCE-DISPLACEMENT
Z.Ezzouine1
, A. Nakheli2
, Z. Abbassi3
, A. Benabdellah4
1
LASMAR, Faculty of Sciences, Moulay Ismail University, Meknes, Morocco
2
Electrical Engineering Departments, ESTM, Moulay Ismail University, Meknes, Morocco
3
4
Abstract
The experimental device that we propose is an electromagnetic sensor permits the measures of force and displacement. her
principle of working rests on the phenomenon of influence by magnetic induction between two flat spools, in the same way
diameter and including the same number of spires, situated to a certain distance, x, one of the other, on a same axis passing by
their centers. The sensor is constituted of two converters, the first is the spring (converter force-displacement), and the second is a
magnetic circuit permitting the conversion of the displacement in tension (converter displacement - tension) via the electronic
circuit of conditioning.
Keywords: Sensor electromagnetic, converter force-voltage, converter force-displacement
--------------------------------------------------------------------***----------------------------------------------------------------------
1. INTRODUCTION
In the field of physical instrumentation, there are many
sensor measuring force and displacement; they are generally
electrodynamics sensors Piezoelectric, or using strain
gauges [1-9].
The electromagnetic sensor of force-displacement we
propose is similar to the spring balance (of which one
usually measures the elongation using a ruler moving on a
graduated scale), to which we associated a converter
distortion- voltage. The given measures are strengths that
can be convert them by the displacements, knowing the
characteristic of the spring, k=2mg/µm and the relation x =
m /k.
2. DESCRIPTION OF THE SENSOR
ELECTROMAGNETIC
The operating principle of the sensor is based on the
magnetic induction created by the fixed coil, gives rise to an
electromotive force at the terminals of the voice coil, that
depends on the distance x between the coils. When asked on
a mass tare spring lengthens, the cylinder moves downward,
and the distance between the coils x decreases. This results
in an increase in the voltage across the moving coil. The
spring plays the role of a converter force- displacement. The
conceived device is an electromagnetic force sensor, and can
also be considered as a displacement sensor.
The sensor of forces that we propose consists of a spring R,
two flat coils of 30 coils each, and of 2 cm radius, and a flat
coil is mounted on a support around a hole (transmitting
coil), it is supplied by a sinusoidal signal from a Low
Frequency Generator .The second coil receiving platform
BM is wound on an insulating cylinder of 2cm radius and
5.3 cm height, The latter is suspended by a hook at the lower
end of a spring whose upper end is fixed on a support
through a hook Fig -1.
Fig -1: The sensor for electromagnetic forces
The spring assembly, cylinder and port are well aligned
vertically in a manner that the cylinder passes through the
hole virtually without friction. The two receiving coils and
issuing are linked to the conditioning circuit through the
wires of connections. A hook is fixed on the lower part of
the cylinder and is used to suspend the masses. The two
coils are still parallel, remote X one of the other, X being the
variable distance between coils.
dt
d
e

 (1)

_______________________________________________________________________________________
The fixed coil is supplied by an low frequency generator of
a frequency f0 = 16 KHz whose phase conditions and
amplification are satisfactory, and therefore it is traversed by
a sinusoidal current which creates a sinusoidal magnetic flux
density along its axis, the latter creates through the moving
coil a variable flow Φ and induced sinusoidal electromotive
force measurable, The maximum value of this Electrometric
Force induced depends on the distance x between the two
coils, and the flux Φ is proportional to the magnetic
induction B, whose variation, as a function of x, is given by
the following relationship [9-10] :
2/322
2
0
)(*2
***
)(
XR
RIN
xB



(2)
With I the current flowing through the coils, R their radius,
N their number of spire, and x the distance between the two
coils. For x = 0, the previous formula becomes simple, and
thus:
R
IN
B
2
**
)0( 0
 3
When a mass suspended on the hook on the bottom of the
cylinder, the latter moves down by extending the spring, and
the distance x between the two coils is reduced and as a
result the voltage induced across the receiver moving coil
increases. The induced voltage is sinusoidal and its
amplitude is low, so it has been necessary to introduce
circuits for amplification, rectification and filtering to make
this voltage usable, the corresponding sensor output signal
conditioning circuit is as follows [11]:
Fig-2: Conditioning circuit
The conditioning circuitry is powered by a stabilized supply
symmetrical ±15 (Fig -3).
Fig -3: supply to the electronic circuit card conditioning
3. PERFORMANCE OF THE
ELECTROMAGNETIC SENSOR
3.1 Sensor Drift
When we turn the sensor on, the output voltage decreases
exponentially and after 30 to 60 minutes of operation, this
voltage stabilizes at a characteristic constant of the
experimental device.
3.2 Sensitivity
The sensitivity of the sensor depends on the spring constant
of the spring used and conditioning circuit (particularly the
gain of the amplifier stages), we achieved a sensitivity of
S=200 mg/mV, at the beginning (before suspending
masses). However, the electromagnetic unit consisting of
transmitter and receiver coil may be modified to increase the
sensor sensitivity. In general, inductive sensors were first
used for historical reasons, but are still interesting because
of their accuracy and robustness. In addition, the coils are
cheap and easy to produce industrially, at least within
reasonable dimensions. The induction of a coil is directly
related to its number of turns, its diameter and thus its size;
the small coils generally have a lower sensitivity. However,
advanced techniques now allow the production of coils of
small size with high sensitivity, with complex shapes or a
larger number of turns. The frequency domain for an
inductive sensor depends strongly of its impedance.
3.3. Measuring Range
From 0g to 10 g, it’s related to the mechanical properties of
the spring. The sensor is designed to work in a range of 0 to
10g.
3.4 Accuracy
The sensor accuracy depends on the specific elements of the
experimental device (coils, cylinder, friction, distance
between coils, spring, and the signal conditioning circuit),
and on the quality of the measuring instrument used. In our
case we used a digital multimeter whose accuracy is 0.1
mV. The voltages delivered by the sensor are measured with

_______________________________________________________________________________________
an error of 0.05 mV, and the accuracy of the measured
masses is estimated to Δm = 10 mg at the origin. So we can
say that all measure masses between 0 and 10 g, Δm is equal
or less than Δm = 10 mg. This is related to the sensor
sensitivity which is variable and depends on the distance
between coils, this sensitivity changes from 200 mg/mV to
80 g/mV , so the precision of the sensor of force and
displacement :
8mg ≤ ∆m ≤ 20g ; 4µm ≤ ∆x ≤ 10 µm.
3.5 Hysteresis
We have made measurement on the sensor by hooking
increasingly masses of 0g to 10 g per 1g in steps of 1g, and
then we note the output voltage values by removing masses
in steps of 1g. The results are perfectly reversible and there
was no hysteresis cycle due to the mechanical properties of
the spring which acts as a force-displacement converter. We
were limited to a maximum weight of 10g, and beyond,
there is a small deformation appearing. The choice of a good
spring (perfectly elastic) is important. The spring constant of
the spring used is k=2mg/µm.
4. CALIBRATION OF THE SENSOR OF FORCE
The characteristic curve of the sensor shown in Fig-3 is
obtained by hooking high-precision masses from 0g to 10g
in steps of 1g (Table -1), and we note the voltage values
corresponding to each mass with a voltmeter of precision
0.1 mV. The curve response is not linear; it is rather
parabolic in relation with the sensor sensitivity as a function
of the distance between coils.
Table -1: Sensor Electromagnetic of Force Calibration
m(g) 0 1 2 3 4 5
V(mv) 9.85 15.25 21.05 27.25 34.05 41.25
m(g) 6 7 8 9 10
V(mv) 49.15 57.65 67.15 77.75 88.75
Chart -1: Sensor response from 0 g to 10 g: m = f (V)
We used a polynomial fit of order 5 which is characterized
by a standard deviation commensurate with the experimental
sensor accuracy. The polynomial fit of the mass as a
function of the voltage (m= f (V)) shown below will be most
useful for determining the mass of any unknown by
knowing its corresponding voltage delivered by the sensor.
The corresponding polynomial adjustment is given by:
i
ii
vam 

5
0
The polynomial adjustment of the mass as a function of the
voltage corresponding to the experimental accuracy of our
sensor is as follows:
5443
2
*10*84615.3*00956.0*06976.0
*41911.0*96455.487028.9)(
VVV
VVgm



999.02
r And 043.0
2
r : Correlation coefficient
 : Residual sum of squares
5. CONVERSION THE MASS IN
DISPLACEMENT
The curve of Determination of the displacement X obtained
by conversion the masses in displacement while using the
characteristic for spring K (with K= 2g/mm).
Table -2: Sensor Electromagnetic of Displacement
Calibration
d(mm) 0 0.5 1 1.5 2 2.5
V(mv) 9.85 15.25 21.05 27.25 34.05 41.25
d(mm) 3 3.5 4 4.5 5
V(mv) 49.15 57.65 67.15 77.75 88.75
Chart -2: Sensor response from 0 mm to 5mm: d = f (V)
The polynomial adjustment of the mass as a function of the
voltage corresponding to the experimental accuracy of our
sensor is as follows:
543
2
*012311.0*15291.0*55804.0
*67646.1*92909.987028.9)(
VVV
VVmmd



_______________________________________________________________________________________
12
r And 24913.0
2
r : Correlation coefficient
 : Residual sum of squares
6. CONCLUSIONS
The electromagnetic sensor of force-displacement is
characterized in that is characterized in that it comprises the
diameter of the spools, the number of spires of every spool,
and the section of the thread that can be modified. The
choice of the constant k of the spring permits to fix the
extended of measure and the range of use.
The proposed electromagnetic sensor of force-displacement,
composed of a spring which allows the displacement in
conversion of the forces, at which we have associated a
magnetic circuit for converting the displacements into
electrical voltages via a conditioning circuit, this voltage is
displayed by a digital voltmeter precision 0.1mV. The
calibration of the electromagnetic balance, using precision
masses of from 0g to 10 g, into a field of gravity given
constant, allows us to make use of weighing with high
accuracy.
The range of use of this scale is between 0 g and 10 g, with
an accuracy Δm = 0.33 mg and up to 0.1 mg. The
measurements are reproducible and deformations of the
spring are perfectly reversible within this range of measures.
In the best conditions of working, the precisions of these
sensors become: 4mg ≤ ∆m ≤ 10mg and 2µm ≤ ∆x ≤ 5 µm.
Finally, some improvements could be brought to this sensor,
to make the more effective and promising to numerous
industrial applications.
REFERENCES
[1] Georges Asch, Les capteurs en instrumentation
industrielle, Dunod,(ISBN 2100057774)
[2] P.Poulichet Etude des capteurs magnétiques
(www.incertitudes.fr/robot/capteurs-
magnetique.pdf)
[3] Sensor One AE-801 Micro Force Sensor,
http://sensorone.com/AE801 Home.
[4] T. Itoh, T. Suga, Self-excited force-sensing
microcantilevers with piezoelectric thin films for
dynamic scanning force microscopy, Sens.
Actuators A: Phys.54(June(1–3))(1996)477–481.
[5] Beroulle, V.; Bertrand, Y.; Latorre, L.; Nouet, P.
Monolithic Piezoresistive CMOS magnetic field
sensors. Sens. Actuators A 2003, 103, 23-32
[6] Herrera-May, A.L.; García-Ramírez, P.J.; Aguilera-
Cortés, L.A.; Martínez-Castillo, J.; Sauceda-
Carvajal, A.; García-González, L.; Figueras-Costa,
E. A resonant magnetic field microsensor with high
quality factor at atmospheric pressure. J.
Micromech. Microeng. 2009, 19, 015016
[7] [18] J. K. Spong, V. S. Speriosa, R. E. Fontana, Jr.,
M. M. Dovek, and T. L. Hylton, “Giant
Magnetoresistive Spin Valve Bridge Sensor,” IEEE
Trans. Magn., vol. 32, 366-371 (1996).
[8] J. Daughton, J. Brown, R. Beech, A. Pohm, and W.
Kude, “Magnetic Field Sensors Using GMR
Multilayer,” IEEE Trans. Magn., vol. 30, 4608-
4610,(1994).
[9] J.E. Lenz, G.F.Rouse, L.K. Strandjord, B.B.Pant,
A.Metze, H.B.French, E.T.Benser, D.R.Krahn, “A
Highly Sensitive Magnetoresistive Sensors”, Solid
State Sensors and Actuator Workshop, 1992.
[10] D.Cordier- Cours de physique, électromagnétisme,
1.Electrostatique et magnétostatique - Editions
Dunod.22 juillet 2004.
[11] National Semiconductor, Application note 31: Op
amp circuit collection,
http://www.national.com/an/AN/AN-31.pdf,
September, 2002.

Conception and realisation of a sensor

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