Page 65 - Understanding Automotive Electronics

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2 THE SYSTEMS APPROACH TO CONTROL AND INSTRUMENTATION

Figure 2.17
Sensor Transfer
Characteristics

FPO

Sometimes a nonlinear sensor may provide satisfactory operation without
linearization if it is operated in a particular “nearly” linear region of its transfer
characteristic (Figure 2.17b).
Sensors are subject to Random errors in electronic sensors are caused primarily by internal
random errors such as electrical noise. Internal electrical noise can be caused by molecular vibrations
heat, electrical noise, due to heat (thermal noise) or random electron movement in semiconductors
and vibrations. (shot noise). In certain cases, a sensor may respond to quantities other than the
quantity being measured. For example, the output of a sensor that is measuring
pressure may also change as a result of temperature changes. An ideal sensor
responds only to one physical quantity or stimulus. However, real sensors are
rarely, perfect and will generally respond in some way to outside stimuli. Signal
processing can potentially correct for such defects.
Displays and Actuators

Automotive display To be useful for measurement purposes, an electronic instrumentation
devices, typically analog system must somehow make the results of measurement available to the user. This
or digital meters, provide is done through the display, which yields numerical values to the user. As in other
a visual indication of the aspects of electronic systems, the display can be analog or digital. Both types of
measurements made by display are described in detail in Chapter 9.
the sensors. Displays, like sensors, are energy conversion devices. They have bandwidth,
dynamic range, and calibration characteristics, and, therefore, have the same types
of errors as do sensors. As with sensors, many of the shortcomings of display devices
can be reduced or eliminated through the imaginative use of signal processing.
Actuators convert elec- An actuator is an energy conversion device having an electrical input
trical inputs to an action signal and an output signal that is mechanical (e.g., force or displacement).
such as a mechanical Automotive actuators include electric motors and solenoid-controlled valves
movement. and switches. These are used, for example, in throttle positioners for cruise
control.

52 UNDERSTANDING AUTOMOTIVE ELECTRONICS