Field Service Bulletin FSB-236
Title: Explorer DVL Loss of Bottom Track and Communication
Date: May 3, 2016
Abstract
1.
The Explorer DVL would lose bottom and fail to re-acquire bottom lock in certain situations at low
altitudes.
2.
The Explorer DVL would become unresponsive (loss of communication) in certain situations after being
powered down for an extended period of time.
Instrument/Program Affected
Explorer DVL (both piston and PHA) with firmware version 34.16 and earlier.
Description
The Explorer DVL is specified for a minimum bottom track altitude of 0.5 meters or lower if a low-altitude feature
key has been installed:
Minimum altitude without feature key
Minimum altitude WITH feature key
Piston
0.5 m
0.31 m
Phased Array
0.5 m
0.25 m
If the Explorer DVL is operated without the low-altitude feature key, it can then lose the bottom and fail to reacquire it. The root cause is when the system locates the bottom at an altitude below 0.5 meters (for example 0.35
meters) – when this happens the bottom lock is marked as “bad” because it is below the minimum altitude, but
the Explorer does not search for the bottom because a bottom was “found”. Therefore it will lose bottom lock and
fail to re-acquire until power is cycled or the deployment is restarted.
The primary symptom of this failure mode is a constant ping time – if the unit has genuinely “lost” the bottom,
then the ping times will vary as the system is in search mode. When the Explorer is stuck in this failure mode then
the ping time will remain constant despite changes in altitude.
There were also reports where the user removed power to the Explorer DVL for weeks to months at a time and
then repowers it, but DVL is unresponsive. The main communication was lost because the programming flash
memory device was corrupted and failed to configure the FPGA. Without the FPGA configuration, the system
cannot communicate via its main communication channels.
Solution/Action
We have isolated the possible causes for these failures and have made improvements to our firmware to prevent
these rare issues.
It is highly recommended to upgrade your ExplorerDVL with the latest Explorer DVL firmware 34.17 and greater
versions as it has been demonstrated to resolve these issues during our testing as well as with our customers.
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