
P/N 95B-6156-00 (July 2023) Tasman DVL Integration Guide
Page 12 EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
Operational & Setup Integration
The following items must be taken into consideration when using the Tasman DVL.
Unfavorable Environments – There are certain environmental conditions where the DVL’s errors may be
large or where the instrument does not function at all.
•In the surf zone where waves are actively breaking, the acoustic beams may not be able to pene-
trate the bubble clouds, and even if they do, the sound speed may be significantly affected by the
high concentration of bubbles. This changes the Doppler scale factor.
•The dense growth of weeds or kelp on the bottom may prevent the DVL from detecting the true
bottom. If the DVL locks onto the top of the weeds by mistake, they may have motion relative to
the bottom due to wave action, which would give inaccurate velocity measurements.
•In areas of high salinity (>35ppt), the absorption of the sound by the water column will reduce
the altitude capability of the DVL. Absorption (maximum range) can also be affected by water
temperature.
•In areas where the salinity varies as a function of location and/or time, the Doppler scale factor
will be varying, and it may be necessary to integrate a speed-of-sound sensor into the navigation
system to keep the velocity measurement errors to an acceptable value. Temperature gradients
can cause similar issues. This is only for the Z-axis velocity, as Speed of Sound does not impact
2D velocities on a Phased Array Transducer.
Triggering – There are two methods for triggering the DVL:
•Sending ASCII Character through Serial Port.When the system is interfaced to a serial port (e.g. a
navigation computer), the system can be setup to wait for an input before each ping. To setup the
DVL in this fashion, clear the Auto Ping Cycle bit in the CF command by sending CFx0xxx, where
the x’s represent the settings of the other parameters. Start the DVL pinging with the CS com-
mand. The DVL will output a ‘<’ before each ping and wait for input. Send any valid ASCII charac-
ter to trigger the ping. The instrument will not enter sleep mode while it is waiting for the trigger.
•Using Low-Latency Triggering. The trigger methods shown above all have latencies ranging from a
few milliseconds to a few hundred milliseconds, which may be excessive for high-precision appli-
cations. Consequently, TRDI has developed a low-latency trigger method (see CX command). To
configure the DVL for low-latency triggering, set the CX command to enable trigger input.
Start the DVL pinging with the CS command. The DVL will then wait for a trigger before each
ping. Setting the trigger lines to a break state for no less than 10 microseconds sends the trigger.
The DVL will then ping within 1 millisecond of the leading edge of the break pulse. Note that it
is possible through the CX command settings to set a timeout for the DVL to wait for a Trigger
and then if no Trigger occurs during that time it will either Self Deploy and never look for Trig-
ger again or Ping once and then go back to waiting for Trigger. The input trigger voltage is
3.3VDC to 5VDC.
For more information, see the Tasman Guide, Chapter 2 – System Integration and Chapter 7 -
Commands.