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                                   BULLETIN
                       FSB-005 - ALUMINUM PRESSURE CASES
                  DATE/REV:  12APR89 / 0 (previously FSB 1-5)
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ABSTRACT:  Describes possible pressure case corrosion and continuity problems.

INSTRUMENT/PROGRAM AFFECTED:  All DR and SC narrowband ADCPs (NBADCP).

DESCRIPTION:  In corrosive environments, pinhole corrosion may occur around
the screws that hold the protective zinc anodes in place.  These screws also
provide the electrical connection to the pressure case.  If this electrical
connection is open, the protection is lost and damage may occur to the pres-
sure case.

SOLUTION/ACTION:  Take the following steps to determine if corrosion and con-
tinuity problems exist.

a.  Inspect the zinc anode and screws for corrosion under the screw heads.

b.  Measure the continuity between the zinc anode and the screws.  The measur-
    ed resistance should be less than 1 Ohm.

c.  On newer transducers, we have installed zinc anodes between the beams and
    near the thermistor.  The measured resistance between the transducer zinc
    anodes and the pressure case zinc anodes should be less than 1 Ohm.

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