The Electro-Reckoner
An Electromagnetic Flow-Meter for Underwater Navigation
The Electro-Reckoner is a prototype device to assist divers (specifically military divers with a requirement for silence) in sub-surface navigation by gauging water flow as a means of dead-reckoning with greater precision than counting flipper strokes. It functions by generating a magnetic field between the coils that is oriented perpendicularly to the flow of a conductive liquid (saltwater). This produces a measurable voltage across the flowing liquid that is proportional to the flow rate. The magnetic field orientation is rapidly switched in the design to remove interference sources by measuring a difference between the two directions rather than an absolute potential difference, which would be affected by the Earth's magnetic field.
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