Page 325 - Understanding Automotive Electronics

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9 AUTOMOTIVE INSTRUMENTATION

Figure 9.15
Vehicle Speed
Measurement

FPO

The computer reads the number P in the binary counter, then resets
the counter to zero to prepare it for the next count. After performing
computations and filtering, the computer generates a signal for the display
to indicate the vehicle speed. A digital display can be directly driven by the
computer. Either mph or kph may be selected. If an analog display is used, a
D/A converter must drive the display. Both mph and kph usually are
calibrated on an analog scale.

DISPLAY DEVICES
One of the most important components of any measuring instrument is
the display device. In automotive instrumentation, the display device must
present the results of the measurement to the driver in a form that is easy to
read and understand. The speedometer, ammeter, and fuel quantity gauge were
originally electromechanical devices. Then automotive manufacturers began
using warning lamps instead of gauges to cut cost. A warning lamp can be
considered as a type of electro-optical display.

312 UNDERSTANDING AUTOMOTIVE ELECTRONICS