Philips Semiconductors
Magnetoresistive sensors for
magnetic field measurement
General
Figure 7 also shows that the flipping itself is not instantaneous, because not all the permalloy strips flip at the same rate. In addition, it illustrates the hysteresis effect exhibited by the sensor. For more information on sensor flipping, see Appendix 2 of this chapter.
Effect of temperature on behaviour
Figure 8 shows that the bridge resistance increases linearly with temperature, due to the bridge resistors’ temperature dependency (i.e. the permalloy) for a typical KMZ10B sensor. The data sheets show also the spread in this variation due to manufacturing tolerances and this should be taken into account when incorporating the sensors into practical circuits.
In addition to the bridge resistance, the sensitivity also varies with temperature. This can be seen from Fig.9, which plots output voltage against transverse field ‘Hy’ for various temperatures. Figure 9 shows that sensitivity falls with increasing temperature (actual values for given for every sensor in the datasheets). The reason for this is rather complex and is related to the energy-band structure of the permalloy strips.
MBB897
3
handbook, halfpage
Rbridge (kΩ)
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Fig.8 Bridge resistance of a KMZ10B sensor as
a function of ambient temperature.
2000 Sep 06 | 7 |