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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 omitted. 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.
