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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