Magnetic Field Sensors
Angle Sensor KMT 31
Function principle
Magnetoresistive materials can change their resistivity in an external magnetic field. The
variation of the resistivity is determined by the rotation of magnetisation with respect to the
direction of the current flow. Permalloy
(Ni
81
Fe
19
)
is commercially used as
magnetoresistive material. The relative change of resistivity is 2-3 % for this material. The
high sensitive and small size sensor consists of a silicon chip coated with thin film
permalloy stripes. These stripes form a Wheatstone bridge whose output voltage depends
on the magnetic field.
Characteristic
Magnetic fields vertical to the chip surface have no influence on the output voltage. A
strong magnetic field H
rot
≥
50 kA/m parallel to the chip surface causes a sinusoidal output
signal which is determined by the angle between field direction and orientation of the
permalloy stripes of the Wheatstone bridge. The field H
rot
is created by a permanent
magnet which rotates over the sensor. The sensor output gives information about the
direction of the magnet. The output characteristic of an additional galvanic seperated
Wheatstone bridge is 45° phase shifted compared with the other bridge.
V
max
1
Bridge 1
0,8
Bridge 2
0,6
0,4
0,2
0
0
-0,2
Output voltage of both
Wheatstone bridges versus
angle
α
of the magnetic field
direction
-0,4
-0,6
-0,8
V
min
-1
0°
45°
90°
135°
180°
225°
270°
315°
360°
[ ]
Application
The KMT 31 allows the contactless counting of the revolutions of a rotating magnet which
is mounted on the axis of a wheel. Zero output voltages of the Wheatstone bridges are
used as trigger signals. The sense of rotation of the wheel is taken into account by
comparing the signal outputs of both Wheatstone bridges which are proportional to
sin2(
α
) or sin2(
α
+ 45° The angle can be determined by evaluating these signals.
).
Alternatively it is possible to use the voltage signals of four half bridges which are trimmed
on V
b
/2.
Sensors in thin film technology
HL-Planartechnik GmbH
Hauert 13, D - 44 227 Dortmund, Tel.: +49 (0) 231/97400, Fax.: +49 (0) 231/974020
Internet:
http://www.hlplanar.com
E-Mail: service@hlplanar.de
Magnetic Field Sensors
Angle Sensor KMT 31
Technical data
Absolute maximum ratings
Parameter
Supply voltage
Total power dissipation
Operating temperature range
Storage temperature range
Sensor chip alignment error
Symbol
V
B
P
to
T
amb
T
stg
Unit
V
mW
°
C
°
C
°
Value
5
120
-40 ... + 125
-65 ... +125
≤
2
α
e
Electrical characteristics (T
amb
= 25° H
rot
≥
25 kA/m)
C,
Parameter
Bridge resistance
Offset voltage
Half bridge symmetry
Sensitivity
Output voltage range
Zero offset angle hysteresis
Symbol
R
B
V
OFF
/V
B
(V
s
/2 - V
o
)/V
B
S
α
(|V
max
|+ |V
min
|) /V
B
Unit
kOhm
mV/V
mV/V
(mV/V)/°
mV/V
°
Value
3
±
1.0
≤ ±
2.0
≤ ±
2.0
> 0.418
≥
24
≤
1
Condition
bridge 2
bridge 1
α
=0°
α
=0°
α
=0°
α
=45°
α
=45°
α
=45°
∆α
Parameter
Temperature coefficients ( - 25 ° < T
amb
< 125 °
C
C)
of bridge 1 and 2
Symbol
T
CBR
T
CSV
T
CSI
T
COFF
Unit
%/K
%/K
%/K
(µV/V)/K
Value
0.30
±
0.05
-0.30
±
0.05
0.00
±
0.05
≤±
3
Bridge resistance
Open circuit sensitivity
(V
B
= const)
(I
B
= const)
Offset voltage
Housing of KMT31: SM-8
bridge 1:
pin 4: + V
B
pin 8: GND
pin 1: - V
0
pin 5: + V
0
bridge 2:
pin 3: + V
B
pin 7: GND
pin 2: - V
0
pin 6: + V
0
(GND)
(+ V
B
)
(+ V
0
)
(- V
0
)
(GND)
(+V
B
)
(+ V
0
)
(- V
0
)
Assembly is pining independent. Sensor mirror symmetrically built !
Sensors in thin film technology
HL-Planartechnik GmbH
Hauert 13, D - 44 227 Dortmund, Tel.: +49 (0) 231/97400, Fax.: +49 (0) 231/974020
Internet:
http://www.hlplanar.com
E-Mail: service@hlplanar.de
21.05.03, Zn
