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2000 Sep 06 20
Philips Semiconductors
Magnetoresistive sensors for
magnetic field measurement
General
Fig.23 Sensor output ‘V
o
’ as a function of the transverse field H
y
.
handbook, full pagewidth
MLC132
0
24681012
O
(mV)
H (kA/m)
y
H =
4 kA/m
x
2 kA/m
1 kA/m
0
V
100
150
50
A Safe Operating ARea (SOAR) can be determined for
magnetoresistive sensors, within which the sensor will not
flip, depending on a number of factors. The higher the
auxiliary field, the more tolerant the sensor becomes to
external disturbing fields (H
d
) and with an H
x
of 3 kA/m or
greater, the sensor is stabilized for all disturbing fields as
long as it does not irreversibly demagnetize the sensor. If
Hd is negative and much larger than the stabilising field H
x
,
the sensor will flip. This effect is reversible, with the sensor
returning to the normal operating mode if H
d
again
becomes negligible (see Fig 24). However the higher H
x
,
the greater the reduction in sensor sensitivity and so it is
generally recommended to have a minimum auxiliary field
that ensures stable operation, generally around 1 kA/m.
The SOAR can also be extended for low values of H
x
as
long as the transverse field is less than 1 kA/m. It is also
recommended to apply a large positive auxiliary field
before first using the sensor, which erases any residual
hysteresis
Fig.24 SOAR of a KMZ10B sensor as a function of
auxiliary field ‘H
x
’ (MLC133).
handbook, halfpage
012 4
12
0
4
8
MLC133
3
H
d
(kA/m)
H (kA/m)
x
I
II
SOAR