Alpine VOLUME 1.3 - Manual (Page 16)

ULTRASOUND TECHNOLOGY
The technology of ultrasound is concerned with
sound waves that occur above human perception.
The average threshold of human perception is 16,500
Hertz. Although the highest sounds some humans
are capable of hearing is 21,000 Hertz, ultrasound
technology is usually concerned with frequencies
from 20,000 Hertz and up. Another way of stating
20,000 Hertz is 20 kHz, or KILOHERTZ. One
kiloHertz is 1,000 Hertz.
Since ultrasound is a high frequency , it is a short
wave signal. Its' properties are different from
audible or low frequency sounds. A low frequency
sound requires less acoustic energy to travel the
same distance as high frequency sound. (Fig. A)
The ultrasound technology utilized by the Ultraprobe is generally referred to as Airborne ultrasound. Airborne
ultrasound is concerned with the transmission and reception of ultrasound through the atmosphere without the
need of sound conductive (interface) gels. It can and does incorporate methods of receiving signals generated
through one or more media via wave guides.
There are ultrasonic components in practically all forms of friction. As an example, if you were to rub your
thumb and forefinger together, you will generate a signal in the ultrasonic range. Although you might be able
to very faintly hear the audible tones of this friction, with the Ultraprobe it will sound extremely loud.
The reason for the loudness is that the Ultraprobe converts the ultrasonic signal into an audible range and then
amplifies it. Due to the comparative low amplitude nature of ultrasound, amplification is a very important
feature.
Although there are obvious audible sounds emitted by most operating equipment, it is the ultrasonic elements
of the acoustic emissions that are generally the most important. For preventative maintenance, many times
an individual will listen to a bearing through some simple type of audio pick-up to determine bearing wear.
Since that individual is hearing ONLY the audio elements of the signal, the results of that type of diagnosis will
be quite gross. The subtleties of change within the ultrasonic range will not be perceived and therefore omit-
ted. When a bearing is perceived as being bad in the audio range it is in need of immediate replacement.
Ultrasound offers a predictable diagnostic capacity. When changes begin to occur in the ultrasonic range,
there is still time to plan appropriate maintenance. In the area of leak detection, ultrasound offers a fast,
accurate method of locating minute as well as gross leaks. Since ultrasound is a short wave signal, the
ultrasonic elements of a leak will be loudest and most clearly perceived at the leak site. In loud factory type
environments, this aspect of ultrasound makes it even more useful.
Most ambient sounds in a factory will block out the low frequency elements of a leak and thereby render audible
leak inspection useless. Since the Ultraprobe is not capable of responding to low frequency sounds, it will hear
only the ultrasonic elements of a leak. By scanning the test area, a user may quickly spot a leak.
Electrical discharges such as arcing, tracking and corona have strong ultrasonic components that may be readily
detected. As with generic leak detection, these potential problems can be detected in noisy plant environments
with the Ultraprobe.
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