SPECIALIZED UNITS OF MEASUREMENT (cont.)

HFD, expressed in gS units is similar to Spike Energy, Bearing Condition Units, and Shock Pulse in that all these measurements display a single numerical overall value proportional to the overall signal level within a high frequency bandpass. Due to their use of the vibration transducer's natural resonant frequency to provide mechanical amplification, the numerical values measured with HFD, BCU, Spike Energy and Shock pulse are not necessarily proportional to each other.

Bearing Condition Units (BCU): This is considered an equivalent to Spike Energy. The word equivalent is used loosely here, since I have found variations in data trended consecutively in both these units. This unit is acquire by processing the signal of an AS-011 accelerometer (35kHz Fn) with a Vibraport in the BEARCON mode.

High Frequency Detection (HFD): A measurement designed to pick up high frequency, low amplitude vibration generated by small flaws within a rotating element bearing in order to provide earliest warning of an eventual failure.

Shock Pulse: An accelerometer (32kHz Fn) is electronically processed to give a numeric value in dBn (decibels normalized). This unit is use with instruments manufactured by SPM Instruments.

Spike Energy: This unit is derived from a series of processing techniques. The signal from a model 970 accelerometer (27kHz Fn) is filtered with a high-pass filter (5 kHz) to remove most of the mechanically related vibration signal. This technique gives a high frequency weighting to the signal. As a result of the weighting, ultrasonic background noises, such as steam leaks and electrical arcing (common to generator pick-up brushes), may affect the measurements. It is considered a "figure of merit" related to the high frequency energy generated by repetitive transient mechanical impacts which typically occur as a result of surface flaws in rolling element bearings or gear teeth. This figure of merit is expressed in "g/SE" units and is called Spike Energy, trademarked by EntekIRD International.

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Last updated: November 24, 2002