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Today’s more evolved ultrasound data collectors present results that take reliability practitioners beyond the single decibel. Using only an overall dB value may indicate something inside the machine has changed since last readings were taken. But it provides no additional insight to determine what type of defect may be present.
Moreover, a single dB only provides a useful trend if the inspector has control of the acquisition time during data collection. Acquisition time needs to be adjusted in concert with the speed of the machine. More time for low speed applications and less for high. The aim should be to capture a minimum of 2-3 full shaft rotations.
The SDT270 takes inspectors beyond the single decibel by presenting ultrasound data in terms of machine condition. We call them Condition Indicators and there are four (RMS, Max RMS, Peak, and Crest Factor (CF)) and are abbreviated as 4CI. Ultrasound identifies defects in machines when those defects produce one or more of the following phenomena: FRICTION, IMPACTING, or TURBULENCE (FIT).
Some examples:

  • A bearing that requires lubrication will present higher levels of friction. Therefore, an RMS danger alarm will be triggered at 8 dB and an RMS/CF alarm when severity increases.
  • A bent shaft produces higher levels of friction and therefore present danger and alert warnings with the RMS condition indicator.
  • Electrical defects such as arcing, tracking, and corona are first alarmed with the RMS condition indicator and severely alarmed with Max RMS and CF.
  • A faulty steam trap is detected with an elevation in Temperature and Max RMS.

Traditional ultrasound is useful for trending decibel levels that alert us when machine condition changes. Evolved ultrasound goes beyond the single decibel to recruit Condition Indicators that help inspectors determine the type of defect that is creating the alarm. SDT’s Four Condition Indicators demonstrate how ultrasound must be used for both defect alarm and identification.
SDT Troubleshooting Chart

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, , , by Allan Rienstra - SDT Ultrasound Solutions