DATASONICS PSA-916, User Manual, Page: 20 / 26

4-1 DATASONICS
User’s Manual March 1997
Section 4. Theory of Operation
This section describes the operation of the PSA-916. DO NOT ATTEMPT
REPAIR of the PSA-916 unless you are a trained electronics technician.
For help with any questions about using or maintaining the instrument,
contact your local Datasonics representative, or call our headquarters at
508/563-5511.
4.1 Operating Principle
The PSA-916 Sonar altimeter determines the round trip time for a sound
pulse to travel from the transducer through the water, reflecting off a
surface and returning to the transducer. Since the speed of sound is
known, the altimeter can determine the range utilizing this equation:
R = 1/2 (Cs)(t +/-
∆
t
)
Where:
Cs - the speed of sound in meters per second
t - the total round-trip travel time in seconds
R - range in meters
The nominal speed of sound is 1,500 meters per second in water, and is
used by the PSA-916. Note that the speed of sound is affected by
temperature, salinity, and pressure.
The
∆
t factor is the jitter or the ability of the detectors to accurately
determine the presence or absence of a pulse. Jitter is a function of
operating frequency, system bandwidth and signal to noise ratio. In the
PSA-916
∆
t is approximately 5 microseconds or approxi/-0.4 cm
total distance. Since the total travel time is divided by two in the above
formula, the jitter error is +/-0.2cm.
4.2 Board level description
Please refer to drawings D916-07008 and C916-06812