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9 AUTOMOTIVE INSTRUMENTATION

Figure 9.7
Data
Demultiplexer

FPO

SAMPLING
Only one variable can be The measurement of any quantity takes place only when the input and
sampled by the com- output switches (MUX and DEMUX) functionally connect the corresponding
puter at a time. The sensor and display to the computer, respectively. There are several variables to
other variables must wait be measured and displayed, but only one variable can be accommodated at any
a set period of time given instant. Once a quantity has been measured, the system must wait until
before being sampled the other variables have been measured before that particular variable is
again by the computer. measured again. This process of measuring a quantity intermittently is called
sampling, and the time between successive samples of the same quantity is called
the sample period, as explained in Chapter 2.
One possible scheme for measuring several variables by this process is to
sample each quantity sequentially, giving each measurement a fixed time slot, t,

304 UNDERSTANDING AUTOMOTIVE ELECTRONICS