Pathfinder DVL Guide
April
2018
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
Page 77
Zinc Anode Inspection and Replacement
The Pathfinder has three zinc anodes on the instrument housing, one anode on the top of the transducer
housing, and two on the bottom of the housing. If the Pathfinder does not have exposed bare metal, a
properly installed anode helps protect the Pathfinder from corrosion while deployed. Read all instructions
before doing the required actions.
Zinc Anode Inspection
The life of a zinc anode is not predictable. An anode may last as long as one year, but dynamic sea condi-
tions may reduce its life. Use a six-month period as a guide. If the total deployment time for the anodes
has been six months or more, replace the anodes. Replace all anodes every year.
To inspect the anodes:
1. Inspect the anodes on the transducer assembly and housing for corrosion and pitting. If most of
an anode still exists, it may not need to be replaced.
2. Inspect the RTV-covered screws that fasten each anode. If the RTV has decayed enough to let wa-
ter enter between the screws and the anode, replace the RTV.
3. If there are doubts about the condition of the anodes, remove and replace the anode.
Zinc Anode Electrical Continuity Check
Check the electrical continuity using a digital multi-meter (DMM). Measure the resistance between the
two anodes attached to the same part of the instrument (transducer or housing). The resistance should be
less than two ohms. If not, reinstall the affected anode.
Zinc Anode Replacement
To remove and replace the zinc anode/s:
1. Remove the RTV from the anode screw heads. Remove the screws.
2. The anode may stick to the Pathfinder because of the RTV used during assembly. To break this
bond, first place a block of wood on the edge of the anode to protect the housing anodizing and
paint. Carefully strike the block to loosen the anode.
3. Clean the bonding area under the anode. Remove all foreign matter and corrosion. Look for signs
of corrosion such as white deposits. If corrosion caused part of the housing to be visibly damaged,
do not redeploy the system. Send it back to TRDI for inspection (see
). Clean the mounting hole with a thin brush and lime based product. Flush the hole with
the lime based product if there is no brush available. Be sure to clean and remove any signs of cor-
rosion.
TRDI knows from our experience that it is difficult to anodize sharp edges on threaded holes
such as these. In marine and fresh water environments, poor anodizing on aluminum will lead
to corrosion problems. Although TRDI has rarely seen corrosion around the anode mounting
holes,
we would like to remind our customers that it is good practice to always inspect for
corrosion in this (and all) areas between deployments.
4. Apply a thin bead of RTV sealant around the edge of the threaded anode mounting hole.
5. Set the new anode in place and tighten the screw to 1.7 ± 0.2 N-M (15 ± 1.5 IN-LB).
6. Fill the counter bore above the screw head with RTV. Pop any air bubbles in the RTV and wipe off
any excess RTV at the base or on top of the anode. The RTV protects the screw heads from water
and prevents breaking the electrical continuity between the anode, screw, and housing. Allow the
RTV to cure for two hours at room temperature.