03.01.2015 Views

handbook of modern sensors

handbook of modern sensors

handbook of modern sensors

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

7.4 Inductive and Magnetic Sensors 273<br />

Fig. 7.21. Angular measurement with the<br />

KMZ10 sensor.<br />

(A)<br />

(B)<br />

Fig. 7.22. (A) Optimum operating position <strong>of</strong> a magnetoresistive module. Note a permanent<br />

magnet positioned behind the sensor. (B) Block diagram <strong>of</strong> the module circuit.<br />

normal to the axis <strong>of</strong> the metal plate. A discontinuity in the plate’s structure, such as a<br />

hole or a region <strong>of</strong> nonmagnetic material, will disturb the magnetic field and produce<br />

a variation in the output signal from the sensor. Figure 7.20B shows the output signal<br />

for two values <strong>of</strong> spacing d. At the point where the hole and the sensor are precisely<br />

aligned, the output is zero regardless <strong>of</strong> the distance d or surrounding temperature.<br />

Figure 7.21 shows another setup which is useful for measuring angular displacement.<br />

The sensor itself is located in the magnetic field produced by two RES190<br />

permanent magnets fixed to a rotable frame. The output <strong>of</strong> the sensor will then be a<br />

measure <strong>of</strong> the rotation <strong>of</strong> the frame.<br />

Figure 7.22A depicts the use <strong>of</strong> a single KM110 sensor for detecting rotation and<br />

direction <strong>of</strong> a toothed wheel. The method <strong>of</strong> direction detection is based on a separate<br />

signal processing for the sensor’s two half-bridge outputs.<br />

The sensor operates like a magnetic Wheatstone bridge measuring nonsymmetrical<br />

magnetic conditions such as when the teeth or pins move in front <strong>of</strong> the sensor. The<br />

mounting <strong>of</strong> the sensor and the magnet is critical, so the angle between the sensor’s<br />

symmetry axis and that <strong>of</strong> the toothed wheel must be kept near zero. Further, both<br />

axes (the sensor’s and the wheel’s) must coincide. The circuit (Fig. 7.22B) connects<br />

both bridge outputs to the corresponding amplifiers and, subsequently, to the low-pass<br />

filters and Schmitt triggers to form the rectangular output signals. A phase difference<br />

between both outputs (Figs. 7.23A and 7.23B) is an indication <strong>of</strong> a rotation direction.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!