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handbook of modern sensors

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272 7 Position, Displacement, and Level<br />

too powerful or the sensor passes too close to the magnet, the output signal will be<br />

drastically different.<br />

Suppose the sensor is initially on the transverse axis <strong>of</strong> the magnet (x = 0). H y<br />

will be zero and H x will be at its maximum value (> H x ). Thus, the sensor will<br />

be oriented in the +x direction and the output voltage will vary as in Fig. 7.19E.<br />

With the sensor’s movement in the +x direction, H y and V 0 increase, and H x falls to<br />

zero and then increases negatively until H y exceeds −H x . At this point, the sensor<br />

characteristic flips and the output voltage reverses, moving from A to B in Fig. 7.19E.<br />

A further increase in x causes the sensor voltage to move along BE. If the sensor is<br />

moved in the opposite direction, however, H x increases until it exceeds +H x and V 0<br />

moves from B to C. At this point, the sensor characteristic again flips and V 0 moves<br />

from C to D. Then, under these conditions, the sensor characteristic will trace the<br />

hysteresis loop ABCD and a similar loop in the −x direction. Figure 7.19E is an<br />

idealized case, because the reversals are never as abrupt as shown.<br />

Figure 7.20A shows how KMZ10B and KM110B magnetoresistive <strong>sensors</strong> may<br />

be used to make position measurements <strong>of</strong> a metal object. The sensor is located<br />

between the plate and a permanent magnet, which is oriented with its magnetic axis<br />

(A)<br />

(B)<br />

Fig. 7.20. One point measurement with the KMZ10. (A) The sensor is located between the<br />

permanent magnet and the metal plate; (B) Output signals for two distances between the magnet<br />

and the plate.

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