Importance

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Abstract

A knotmeter impeller eliminator system is provided which includes a circuit that simulates the pulsed output of an impeller-type transducer system by generating pulses having a pulse repetition rate corresponding to speed, with the speed being derived from a navigation unit such as a LORAN, GPS, SAT/NAV or OMEGA unit which provides as an output thereof a standardized NMEA 0183 coded signal corresponding to calculated speed. In one embodiment, a switching system is provided which switches the knotmeter input between either the impeller output or the simulated output to provide a speed indication regardless of whether or not the impeller is jammed by seaweed, eel grass, or other debris. In one embodiment, the pulse generating system involves the utilization of a transistor, the base of which is controlled to turn the transistor on at a rate related to the calculated speed, with pulses to the base of the transistor being generated by a pulse generator which detects a digital signal representing calculated speed and produces a corresponding analog voltage that is in turn coupled to a voltage-controlled oscillator circuit. Alternatively, calculated speed may be transformed into the requisite number of pulses per second via an internal clock and count-down circuits within the CPU used to detect the NMEA 0183 speed sentence.

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First Claim