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AUTOMOTIVE INSTRUMENTATION 9

Automotive Instrumentation

Automotive instrumentation includes the equipment and devices that
measure engine and other vehicle variables and display their status to the
driver. From about the late 1920s until the late 1950s, the standard
automotive instrumentation included the speedometer, oil pressure gauge,
coolant temperature gauge, battery charging rate gauge, and fuel quantity
gauge. Strictly speaking, only the latter two are electrical instruments. In fact,
this electrical instrumentation was generally regarded as a minor part of the
automotive electrical system. By the late 1950s, however, the gauges for oil
pressure, coolant temperature, and battery charging rate were replaced by
warning lights that were turned on only if specified limits were exceeded.
This was done primarily to reduce vehicle cost and because of the
presumption that many people did not necessarily regularly monitor these
instruments.
Low-cost solid-state Automotive instrumentation was not really electronic until the 1970s.
electronics, including At that time, the availability of relatively low-cost solid-state electronics
microprocessors, display brought about a major change in automotive instrumentation; the use of
devices, and some sen- low-cost electronics has increased with each new model year. Some of the
sors, have brought about electronic instrumentation presently available is described in this chapter.
major changes in auto- In addition to providing measurements for display, modern automotive
motive instrumentation. instrumentation performs limited diagnosis of problems with various
subsystems. Whenever a problem is detected, a warning indicator alerts the
driver of a problem and indicates the appropriate subsystem. For example,
whenever self-diagnosis of the engine control system detects a problem, such as
a loss of signal from a sensor, a lamp illuminates the “Check Engine” message
on the instrument panel.

MODERN AUTOMOTIVE INSTRUMENTATION
The evolution of instrumentation in automobiles has been influenced by
electronic technological advances in much the same way as the engine control
system, which has already been discussed. Of particular importance has been
the advent of the microprocessor, solid-state display devices, and solid-state
sensors. In order to put these developments into perspective, recall the general
block diagram for instrumentation (first given in Chapter 2), which is repeated
here as Figure 9.1.
In electronic instrumentation, a sensor is required to convert any
nonelectrical signal to an equivalent voltage or current. Electronic signal
processing is then performed on the sensor output to produce an electrical
signal that is capable of driving the display device. The display device is read by

UNDERSTANDING AUTOMOTIVE ELECTRONICS 297