ORIGINS OF REAL-WORLD SIGNALS AND THEIR UNITSOF MEASUREMENT
In this book, we will primarily be dealing with the processing of real-world signalsusing both analog and digital techniques. Before starting, however, let's look at afew key concepts and definitions required to lay the groundwork for things to come.
Webster's New Collegiate Dictionary defines a signal as "A detectable (ormeasurable) physical quantity or impulse (as voltage, current, or magnetic fieldstrength) by which messages or information can be transmitted." Key to thisdefinition are the words: detectable, physical quantity, and information.Figure 1.1By their very nature, signals are analog , whether DC, AC, digital levels, or pulses.It is customary, however, to differentiate between analog and digital signals in thefollowing manner: Analog (or real-world) variables in nature include all measurablephysical quantities. In this book, analog signals are generally limited to electricalvariables, their rates of change, and their associated energy or power levels.
Sensorsare used to convert other physical quantities (temperature, pressure, etc.) toelectrical signals. The entire subject of signal conditioning deals with preparingreal-world signals for processing and includes such topics as sensors (temperature
SIGNAL CHARACTERISTICSSignal CharacteristicsSignals are Physical QuantitiesSignals are MeasurableSignals Contain InformationAll Signals are AnalogUnits of MeasurementTemperature: °CPressure: Newtons/m2