491 Echo Sounder Operations Manual
Page 5
To prevent delays, it is critical that you first obtain a Return
Materials Authorization (RMA) number before returning your
unit to the factory. If you purchased your 491 through a
dealer, to get an RMA number, call the dealer with the serial
number. The 491’s serial number is located at the top of the
unit.
The 491 should be shipped in a properly designed carton with
packing material. Please reference the RMA number on the
outside of the carton.
Shipments to Northstar should be made to the following
address:
Northstar Technologies
30 Sudbury Road
Acton, MA 01720
If you have overnight or second-day shipping requirements,
please call the Northstar factory for turnaround time and
freight costs before shipping your 491.
How echo sounding works
An echo sounder produces high-voltage electrical pulses that
the transducer converts into sound waves (called “pings”). The
sound waves are sent downward through the water. When a
sound wave hits and reflects off an object, such as fish, debris,
seaweed, or the seabed, the reflected sound wave (an “echo”)
returns back to the transducer along an imaginary vertical line
called a “water column.” The transducer converts this echo
into a tiny electrical pulse. The 491 digitizes these pulses and
sends them to the navigator, so that echo sounding pictures of
the water and seabed can be displayed and analyzed on the
echo sounder screen. In essence, this system lets you see a
real-time cross section of what’s happening underneath your
vessel.
Figure 1, ”957/958 echo sounder system components,” below,
and Figure 2, ”961/962 echo sounder system components,”
below, show how the 491 connects to these navigators to
enable echo sounding functions.
