Slide 1Other PdM Techniques
Vibration Analysis and Oil / Particle Analysis are the main PdM techniques.
Other standard techniques include:
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Ultrasound
Defined as sound waves that have frequency levels above 20 kHz, higher than hearing range of a human ear.
Sound is a microscopic oscillation at the molecular level of a substance.
Vibration is a macroscopic oscillation of structures, caused by a force that is pushing or pulling them.
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Airborne Ultrasound
Operates in the lower ultrasonic spectrum of 20 kHz to 100 kHz.
Properties:
easily blocked by small objects.
does not penetrate solid surfaces (though they will go through cracks).
radiates in a straight line.
Does not travel a great distance.
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Most machines emit consistent sound patterns under normal operating conditions.
Abnormal conditions in machines change the nature of this sound pattern.
Fluid leakage in any system is another source of ultrasound.
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It is a lightweight, hand-held device.
can be easily carried within the plant and in confined spaces.
It is easy to use.
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Headphones.
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Contact type for valve, steam traps, pump casings, bearing housings.
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Ultrasound Translator
Ability to adjust the frequency response between 20 kHz to 100 kHz (isolating competing ultrasound signals).
An ultrasonic transmitter called a tone generator is often included.
This generates ultrasound of required frequency (by means of heterodyning).
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Bearing and mechanical inspection.
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Electrical inspection:
Corona, arcing.
Compressor inspection:
Every object whose temperature is above absolute zero emits energy.
As the temperature rises the energy emission increases.
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Thermography
Technique that produces a visible graph or thermographic image of thermal energy radiated from objects.
Utilizes a portion of the infrared band of the electromagnetic spectrum between approximately 1 and 14 microns.
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Electronic instruments utilize a lens system.
The lens focus the invisible energy radiated from the first 1/1000 of an inch of an object’s surface onto the infrared sensitive detector(s).
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The various energy levels are measured by the detectors.
They are then transformed into a visible image with each energy level represented by a different color or gray scale level.
Image is viewed on an LCD or CRT display.
can be stored digitally or on video, for review, analysis, and reporting at a later date.
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Does not involve any hazards.
Can be used in hazardous zones.
Not affected by electromagnetic waves.
Used when systems are live and operating.
Can provide instant information.
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Cost of the hardware is high.
Some systems experience limitations in software.
Emissivity of the objects must be calculated or should be known.
Ambience should be homogenous with respect to the thermal energy.
Distance, atmospheric conditions and temperature can affect the quality of details.
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Auxiliary equipment such as fuses, relay contacts, switchgear, distribution boards and transformers can suffer from loose connections, imbalanced loads and corrosion, resulting in resistive heating.
The above can be spotted by Thermography...
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Motor problems.
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Thermography: Electrical Systems
Cold cooling fins due to low oil level in a transformer
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Leaking valves, blocked pipes.
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Thermography: Mechanical
Applications in boiler and steam systems, flues, heat exchangers and regenerators:
Insulation, refractory, brickwork and poor joints of furnaces.
Operation of blast furnace stoves, burner’s flame pattern and water-cooled systems.
View of a furnace