Page 219 - Understanding Automotive Electronics

2735 | CH 6 Page 206 Tuesday, March 10, 1998 1:10 PM

6 SENSORS AND ACTUATORS

and +0.8 V for the low level. Used as pulses, the signals provide time-
referenced pulses that can be signal processed easily with digital integrated
circuits.
One of the problems with optical sensors is that they must be protected
from dirt and oil; otherwise, they will not work properly. They have the
advantages that they can sense position without the engine running and that
the pulse amplitude is constant with variation in speed.

THROTTLE ANGLE SENSOR
Still another variable that must be measured for electronic engine
control is the throttle plate angular position. As explained in Chapter 1, the
throttle plate is linked mechanically to the accelerator pedal. When the driver
depresses the accelerator pedal, this linkage causes the throttle plate angle to
increase, allowing more air to enter the engine and thereby increasing engine
power.
Measurement of the instantaneous throttle angle is important for control
purposes, as will be explained in Chapter 7. Most throttle angle sensors are
essentially potentiometers. A potentiometer consists of a resistor with a movable
contact, as illustrated in Figure 6.15.

Figure 6.15
Throttle Angle
Sensor: A
Potentiometer

FPO

206 UNDERSTANDING AUTOMOTIVE ELECTRONICS