SDT International SDT170, Руководство пользователя

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7. Presentation
7.1 O
PERATING PRINCIPLE OF THE
SDT 170
General
Ultrasonic waves are sound waves beyond the range of human hearing (>20 kHz).
To be detected, we need to use equipment like the
SDT 170 , with the capability to
receive ultrasonic frequencies and convert them to corresponding audible sounds.
Ultrasonic frequencies travel through gases (air) and solids (bearing housings) in
a very directional nature; unlike audible sounds which disperse in all directions.
Ultrasounds are low energy sound waves, therefore they are quickly absorbed by
the medium through which they travel. Ultrasonic waves are generated by:

Naturally occurring mechanical phenomena (friction of rotating equipment),
pressure or vacuum leaks (pneumatic, gas, steam) or arcing and corona
(electrical problems).

Artificially by means of a transmitter (like the SDT 200 mW or the SDT 8
(8 x 125 mW ) for tightness testing.
Applying ultrasonic waves on the SDT 170
The SDT 170 detects ultrasonic signals, converts them to audible frequencies,
and amplifies them. The challenge is to transpose the received signal, using the
heterodyne technology, into an interpretable audible signal. This solution extends
the ability of the human ear beyond the simple audible range and into the
ultrasonic one.
The main function of the SDT 170 is converting high frequency signals into audible.
001
It is to be noticed that the central band frequency of the detector can be set to a
specific frequency between 15.1 to 190.7 kHz (see
Chapter 12.3 ) ; the standard
frequency band being 38.4 kHz.