Peak hold A mathematical operation resulting in the “largest-so-far” amplitude of each line of a spectrum to be always displayed. This is done by comparing each line of the most recent spectrum with the corresponding line in the preceding spectrum and displaying the larger of the two amplitudes. Although sometimes regarded as a form of averaging, “peak hold” does not involve averaging.
Peak-to-peak amplitude The difference between the highest positive value and the lowest negative value in a waveform. Displacement amplitudes are usually expressed in terms of the peak-to-peak amplitude.
Period The time taken to complete one oscillation or one cycle. Period is usually expressed in s (seconds) or ms (milliseconds). See also Frequency.
Periodic Having a pattern that is repeated over and over again, each cycle taking a fixed amount of time. See also Period and Repeating force.
Periodic force See Repeating force.
Periodic motion Motion of a pattern repeated over and over again, each cycle or oscillation taking a fixed amount of time. Examples of periodic motion are circular motion, simple harmonic motion, and most kinds of steadystate vibration. Periodic motion can be mathematically described by the arithmetic sum of a series of sinusoids. See also Period and Repeating force.
Copyright 2003 COMMTEST INSTRUMENTS
109
Beginner’s Guide To Machine Vibration