ArticleSpike Energy Measurement & Case Studies In Machinery Condition Monitoring
by Ming Xu
A full description of the Spike Energy signal processing technique is the subject of this paper. Differences between this high frequency processing technique and others such as acceleration enveloping are described. The need for proper sensor mounting to obtain consistent measurements is stressed. Three case histories are presented at the end to illustrate Spike Energy’s effectiveness in detecting problems in machines.
Spike Energy was developed in the late 1970’s to detect the signals emitted from defective rolling-element bearings. The term “Spike Energy” was used to describe the very short pulses, i.e., spikes, of vibratory energy generated by the impact of rolling-elements against microscopic cracks and spalls. Spike Energy is a measure of the intensity of energy generated by such repetitive transient mechanical impacts. These impacts or pulses typically occur as a result of surface flaws in rolling-element bearings, gear teeth or other metal-to-metal contacts, such as rotor rub, insufficient bearing lubrication, etc. The measurement showed that Spike Energy is also sensitive to other ultrasonic signals, such as cavitation, high pressure steam or air flow, turbulence in liquids, control valve noise, etc.
Spike Energy measurement utilizes an accelerometer to detect the vibration energy over a pre-determined high frequency range. The mechanical impacts tend to excite the mounted natural frequencies of the accelerometers as well as the natural frequencies of machine components and structures in this high frequency range. These resonant frequencies act as carrier frequencies and the bearing defect frequency modulates with the carriers. The intensity of impact energy is a function of pulse amplitude and repetition rate. The signal induced by such impacts can be measured by accelerometers and processed by a unique filtering and detection circuitry. The measured magnitude of the signal is expressed in “gSE” units (acceleration units of Spike Energy).
Since its introduction, Spike Energy has been used successfully in many industrial applications and gained acceptance in various industries. Spike Energy measurement can provide early indications of machinery faults and is a very useful tool in vibration analysis. In addition to the traditional Spike Energy overall measurement, Spike Energy spectrum and Spike Energy time waveform were also developed and used in diagnostic analysis in recent years. Although Spike Energy has been used in the field for twenty years, there still exist misunderstanding and improper applications of Spike Energy measurement. For example, Spike Energy is a high frequency measurement and is inherently different as compared to the conventional vibration parameters, such as displacement, velocity or acceleration. In the conventional vibration measurements, the measured vibration signal is within the linear range of a transducer’s frequency response curve. In the Spike Energy measurements, the Spike Energy frequency detection range is beyond the mounted resonant frequencies of most industrial transducers. Consequently, Spike Energy is sensitive to the transducer mounted resonant frequencies as well as mounting methods.”
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