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richard.soderberg@mi*.ki*.se* reports:
>This message describes an on-land incident where an Aladin air-x computer
>malfunctioned.
>Prior to the incident the computer logged some 40 dives.
>The dive computer and a cellular phone (Ericsson GH337) were stored in
>the same bag and possibly in physical contact.
>The telephone rang and at the same time the computer started logging a
>dive at 2m. No combination of "contact touching" could reverse this.
>I contacted the Swedish vendor, CBM who promptly replaced the whole
>system without making any trouble. They pressure tested the air-x and it
>appeared to log a depth exactly 2m too deep.
>During this "computer dive" I noticed that an active cellular phone would
>influence the depth displayed at a distance of 50 cm (about 20 inches).
>The effect was a decereasing depth as the phone got closer.

Dive computer functionality is dependent on its pressure/depth transducer.
Any electronic device/system using transducers is susceptible, in varying
degrees, to Radio Frequency Interference (RFI).  Most transducers generate
very weak signals that require amplification.  Solid-state amplification
circuitry invariably contains non-linear components capable of demodulating
RF signals.  End result, any source of RF signal (e.g., radio transmitter of
any kind) is capable of introducing a DC offset signal into transducer
amplifiers.  THE most common symptom when this happens is a measurement that
varies as a function of the distance between transducer (depth sensor in a
dive computer) and the source of a radio transmission. 




Rocky Daniels

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