ABSTRACT
Signal modification is an important function in many applications of vibration. The tasks of signal
modification may include: signal conditioning (e.g., amplification, and analog and digital filtering); signal
conversion (e.g., analog-to-digital conversion, digital-to-analog conversion, voltage-to-frequency
conversion, and frequency-to-voltage conversion); modulation (e.g., amplitude modulation, frequency
modulation, phase modulation, pulse-width modulation, pulse-frequency modulation, and pulse-code
modulation); and demodulation (the reverse process of modulation). In addition, many other types of
useful signal modification operations can be identified. For example, sample and hold circuits are used in
digital data acquisition systems. Devices such as analog and digital multiplexers and comparators are
needed in many applications of data acquisition and processing. Phase shifting, curve shaping, offsetting,
and linearization can also be classified as signal modification. This chapter describes signal conditioning
and modification operations that are useful in vibration applications. Signal modification plays a crucial
role in component interfacing. When two devices are interfaced, it is essential to ensure that a signal
leaving one device and entering the other will do so at proper signal levels (voltage, current, power), in
the proper form (analog, digital), and without distortion (loading and impedance considerations). A
signal should be properly modified for transmission by amplification, modulation, digitizing, and so on,
so that the signal/noise ratio of the transmitted signal is sufficiently large at the receiver. The significance
of signal modification is clear from these observations.