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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)
Low Freq.
High Freq.
Figure 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.
