Book Analog Interfacing to Embedded Microprocessors
placing the sensor near the gear teeth (Figure 3.25). As each gear tooth moves
past the sensor, it affects the magnetic field between the magnet and the Hall
effect sensor, causing an output pulse to be generated.
Clarostat makes a Hall effect potentiometer. This device produces an
output voltage that is proportional to the amount of rotation of the shaft. It
is ideal for applications where a control knob is required, but where the
reliability of a resistive potentiometer is inadequate.
LVDT
The LVDT (linear variable differential transformer) consists of an excitation
coil, two pickup coils, and a movable, magnetic core (Figure 3.26). The core
provides coupling between the coils. The two pickup coils are connected in
series opposed such that their fields oppose each other. When an AC signal
84 Analog Interfacing to Embedded Microprocessors
Figure 3.26
LVDT.
is applied to the excitation coil, voltages are induced in the other two coils.
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