Amplitude Demodulation for Condition Monitoring of Bearings

June 2, 2019

Far from straightforward, it’s not easy to track bearing damage. As one effective defect localizing solution, engineers use condition-based monitoring technology to monitor particular performance-biased subsets. Then, by applying some form of amplitude demodulation assessment, the condition monitoring techniques reveal behavioural information about a chosen bearing’s functions. Of some problem here, this is a mathematically inclined service, so bear with us as we crunch the numbers.

Extracting Usable Bearing Performance Data

Unlike an average maintenance technician, expert bearing maintenance techs can access a whole range of technically advanced instruments. There are even handheld models, which measure vibrational amplitudes and resonant frequencies. Hovering over a bearing mounting, a technician can carefully take note of the noise created by a bearing mounting. Those trained eyes can even interpret the data and reach a conclusion regarding the current condition of the equipment’s shaft supports. Frictional energies are monitored, vibrational forces identified, and potential defect-producing behaviours are recorded. This is condition monitoring, a maintenance-oriented job that exists solely to maximize bearing lifespan. Check out a few of these instruments:

• Digital tachometers
• Thermometers
• Spectrum analysers
• Stroboscopes
• Sound pressure meters

There’s even a series of stethoscopes. Unlike the instruments used to measure a patient’s heartbeat, these amplitude detecting devices pinpoint bearing noise.

Introducing Amplitude Demodulation Techniques

Back with a potentially defective bearing, all of the test instruments have been pulled out of their cases. Only, the spectrum analysers and tachometers can’t pick up a detailed image of the noise signature. Coming to the rescue, various engineering algorithms are used to extract the signal phase from the noise of that waveform’s amplitude. Like some kind of an amplitude demodulation circuit, as used in an old transistor radio, the algorithms separate the phased vibrational signal from a bearing’s amplitude or “loudness” profile. Essentially, by using computer power, this condition monitoring technology demodulates and highlights the damage frequency. Again, there’s a lot of number crunching going on behind this noise envelope analysis work, but the signal processing techniques do yield accurate results when weak defect signals are nigh-on impossible to clear.

A maintenance technician can record frictional heat as it rises off a bearing housing in waves. He can hear the noise and intuit a defect. Equipped with a spectrum analyser and a digital tachometer, a trained engineer goes beyond simple intuition. He uses algorithms and condition monitoring technology to record real-time bearing information. Yet, that data is hard to interpret. The noise and thermal energy clouds the data. To really clear up the defect frequency, to lift it out of the background noise, we use amplitude demodulation algorithms.

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