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BACKGROUND AND INTRODUCTION
One of the main reasons for the advances in condition monitoring programs has been the development and use of technologies such as ultrasound, oil analysis, vibration, and infrared. This article will examine one of these technologies, airborne/structure borne ultrasound. This technology can be considered an integrating technology since it can be used with infrared and vibration inspections as well as stand alone to perform a multiplicity of inspection activities. Instruments based on this technology can monitor a wide range of plant operations and yet are simple enough to be used with minimal training for basic, effective inspection routines.
Overview of the technology:
Light weight and portable, ultrasonic translators are often used to inspect a wide variety of equipment. Some typical applications include:
Bearing inspection, testing gears/gearboxes, pumps, motors, steam trap inspection, valve testing, detection/trending of cavitation, compressor valve analysis; leak detection in pressure and vacuum systems such as, boilers, heat exchangers, condensers, chillers, tanks, pipes, hatches, hydraulic systems, compressed air audits, specialty gas systems and underground leaks; testing for arcing, tracking, corona in electrical apparatus
What makes airborne ultrasound so effective? All operating equipment and most leakage problems produce a broad range of sound. The high frequency ultrasonic components of these sounds are extremely short wave in nature. A short wave signal tends to be fairly directional. Therefore it is relatively easy to detect their exact location by separating these signals from background plant and operating equipment noises. In addition, as changes begin to occur in mechanical equipment, the subtle, directional nature of ultrasound allows these potential warning signals to be detected early, before actual failure, often before they are detected by vibration or infrared.
Airborne ultrasound instruments, often referred to as "ultrasonic translators", provide information three ways: qualitative with the ability to "hear" ultrasounds through a noise- isolating headphone, quantitative via intensity (dB) readings on a meter or display panel and analytical with the use of spectral analysis software to review recorded sound samples.
Although the ability to gauge intensity and view sonic patterns is important, it is equally important to be able to "hear" the ultrasounds produced by various equipment. That is precisely what makes these instruments so popular. They allow inspectors to confirm a diagnosis on the spot by being able to clearly discriminate among various equipment sounds. This is accomplished in most ultrasonic instruments by an electronic process called "heterodyning" that accurately translates the ultrasounds sensed by the instrument into the audible range where users can hear and recognize them through headphones.
The high frequency, short wave characteristic of ultrasound enables users to accurately pinpoint the location of a leak or of a particular mechanical sound.
The basic advantages of ultrasound and ultrasonic instruments are:
- They are directional and can be easily located
- They provide early warning of impending mechanical failure
- They can be used to locate leaks and potential electric failure conditions
- Instruments can be used in loud, noisy environments
- They support and enhance other PDM technologies or can stand on their own in a maintenance program