It is not the intention of this Chapter to be a technical manual of vibration measuring equipment. Suffice it to say that just as the voltages generated are a function of the property being measured, so the analyserto which they are attached by cable, can reconvert the signals backs to velocity or acceleration. Furthermore, due to the mathematical relationships which exist, the addition of an integrator in the circuitry allows the other vibration properties to be obtained.
Low and high pass filters are included, and these can be adjusted to limit the frequency range to that of interest for examination, whilst linear to logarithmic converters enable the signal to be displayed correctly. Output sockets are also provided so that a complete vibration signature over the full frequency spectrum can be obtained and displayed on a chart recorder, oscilloscope or tape recorder.
ISO 14695 gives full information on the mounting of fans, measuring equipment and the positioning of transducers.
It will have been realized from Section 15.4, that vibrations measured at the fan bearings may only provide an indication of vibratory stresses or motions within the fan. They do not necessarily give evidence of the actual vibratory stresses or motions of critical parts, nor do they ensure that excessive local vibratory stresses may not occur within the fan itself due to some internal resonance.
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