Page 319 - Understanding Automotive Electronics

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9 AUTOMOTIVE INSTRUMENTATION

Computer-based instru- Another benefit of microcomputer-based electronic automotive
mentation is more accu- instrumentation is its improved performance compared with conventional
rate and, due to the instrumentation. For example, the conventional fuel gauge system has errors
computer’s program, that are associated with variations in the mechanical and geometrical
more easily changed characteristics of the tank, the sender unit, the instrument voltage regulator,
than conventional and the indicator (galvanometer). The electronic instrumentation system
instrumentation. eliminates the error that results from imperfect voltage regulation. Generally
speaking, the electronic fuel quantity measurement maintains calibration over
essentially the entire range of automotive electrical system conditions.
Moreover, it significantly improves the display accuracy by replacing the
electromechanical galvanometer display with an all-electronic digital display.
FUEL QUANTITY MEASUREMENT

Some fuel quantity sen- During a measurement of fuel quantity, the MUX switch functionally
sors use a float within connects the computer input to the fuel quantity sensor, as shown in Figure
the fuel tank; the float is 9.9. This sensor output is converted to digital format and then sent to the
mechanically linked to a computer for signal processing. (Note: In some automotive systems the analog
potentiometer that oper- sensor output is sent to the instrumentation subsystem, where the A/D
ates as a voltage divider. conversion takes place.)

Figure 9.9
Fuel Quantity
Measurement

FPO

306 UNDERSTANDING AUTOMOTIVE ELECTRONICS