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SENSORS AND ACTUATORS 6

Optical Crankshaft Position Sensor

In the optical crankshaft In a sufficiently clean environment a shaft position can also be sensed
position sensor, a disk using optical techniques. Figure 6.14 illustrates such a system. Again, as with
coupled to the crank- the magnetic system, a disk is directly coupled to the crankshaft. This time,
shaft has holes to pass the disk has holes in it that correspond to the number of tabs on the disks of
light between the LED the magnetic systems. Mounted on each side of the disk are fiber-optic light
and the phototransistor. pipes. The hole in the disk allows transmission of light through the light
An output pulse is gen- pipes from the light-emitting diode (LED) source to the phototransistor
erated as each hole used as a light sensor. Light would not be transmitted from source to sensor
passes the LED. when there is no hole because the solid disk blocks the light. As shown in
Figure 6.14, the pulse of light is detected by the phototransistor and coupled
to an amplifier to obtain a satisfactory signal level. The output pulse level
can very easily be standard transistor logic levels of +2.4 V for the high level

Figure 6.14
Optical Position
Sensor

FPO

UNDERSTANDING AUTOMOTIVE ELECTRONICS 205