www.sdtnorthamerica.com introduction. what is ultrasound? frequency band of sound: infrasound...
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Introduction
What is Ultrasound?
Frequency band of sound:
Infrasound Audible Sound Ultrasound
20Hz 2000Hz / 20Khz
Range of most human hearingLow inaudible Soundwaves High inaudible Soundwaves
ul-tra-sound • is a cyclic sound pressure wave with a frequency greater than the upper limit of human hearing.
Normal Sound Ultrasound
Characteristics of Ultrasound Waves:
Ultrasound waves act physically different than audible sound waves:
• Stays where it starts• Low Penetrating Power• Short wavelengths don’t stray from source
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Sound Perception
AnimalRange of frequencies
perceived
Elephant 5 Hz – 10.000 Hz
Humans 20 Hz – 20.000 Hz
Dog 50 Hz – 45.000 Hz
Cat 45 Hz – 85.000 Hz
Bat 52.000 Hz – 120.000 Hz
Dolphin 80.000 Hz – 200.000 Hz
Ultrasonic Range = above of human hear perception
Infrasonic Range = below of human hear perception
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Example
Distance Intensity
1 m 200 units
2 m 50 units
3 m 22.2 units
4m 12.5 units
5 m 8 units
Intensity and Distance
Inverse Square Rule
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Definition of the dB Alexander Graham Bell
• dB is logarithmic unit used to describe a ratio. The ratio may be power, sound pressure, voltage or intensity.
• SDT’s reference value is 0dB = 1 µv
The Decibel Definition
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The Decibel Scale
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Ultrasound Applications
Generalities
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Naturally occurring ultrasound(Passive)
• Friction• Turbulence• Electrical
Ultrasound Sources
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• Friction– Bearings– Gear meshing– Coupling– Sheaves and Belts
• Turbulence– Leaks
• Internal - External
• Electrical
Passive Ultrasound
Ultrasound Detector
Uses different sensors to detect ultrasound waves
Converts ultrasound waves into audible sound waves
• Airborne Sensors• Contact Sensors
Only detects Ultrasound waves.
Audible range sound waves are ignored.
+20Khz
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•Airborne– Pressure– Vacuum– Steam traps– Electrical
•Structure borne– Vacuum– Valves & Steam traps– Bearings– Hydraulic
Introduction
Medium of Transport
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• Convert inaudible to audible - heterodyne
• Maintain ultrasound representation
• Measure ultrasound intensity for trending
How it Works
Standard Uses
• Compressed Air Leaks
• Steam Traps
• Condition Monitoring – Bearings, Motors, Fans
• Acoustic Lubrication
• Electrical Inspections
• Tightness Testing
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Turbulence• Leaks in Pressurized Systems• Leaks in Vacuum Systems• Leaks in Hydraulic Systems• Leaks in Steam Systems
Friction and Impacts• Wear from Mechanical Parts• Couplings, Gears, Bearings
Electrical Arcing• Faults in Electrical Systems• Arcing, Tracking, Corona Discharge, RTV Interference
Sources of Natural Ultrasonic Noises