ABSTRACT
As mentioned previously, an electrical signal is a time function that represents variations in certain physical phenomena; for example, temperature, position, speed, speech, and so on. Signals are usually obtained through special devices called transducers. Examples of transducers include:
Thermocouples. These convert temperature differences to electrical variations. Microphones. These transform pressure waves caused by speech into proportional electrical variations. Loudspeakers. These change electrical signals representing sound into acoustical waves. Strain gauges. These resistors are used to measure the deformation in a member of a structure or a machine under loading conditions by measuring corresponding changes in its resistance. Tachometers. These measure the speed of a rotating device; for example, a motor. Quartz crystals. These special-cut crystals are piezoelectric; that is, they produce a voltage difference if subjected to mechanical stresses, or vice versa. Solar cells. These produce voltage differences if subjected to illuminationespecially sunlight.
