Method and apparatus for producing an analogue output proportional to rotational speed employing digital to analogue conversion
First Claim
1. A system for measuring the rotational speed of a variable speed shaft comprising:
- means for sensing at least a predetermined fractional rotation of said shaft;
means for supplying an oscillating signal of a predetermined frequency;
counter means having a capacity of a predetermined quantity of bits and responsive to said sensing means for counting the total number of cycles of said oscillating signal within the time interval of said predetermined fractional rotation of said shaft;
means for selecting a portion of said bits from the number in said counter means, the selected bits being a predetermined number of bits constituting the most significant bits of said number in said counter means;
means for determining the position in said counter means of the most significant bit of said selected bits; and
digital to analog converter means responsive to said selected bits and the position of said most significant bit for producing an analog output inversely proportional to said number in said counter means to provide an analog measure of shaft rotational speed.
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Accused Products
Abstract
A system and method for measuring the rotational speed of a variable speed drive shaft for a ship or the like with high accuracy over a wide range of speeds. Means associated with the shaft sense the time interval for each turn of the shaft, or fraction thereof. Such time interval is accurately measured and then converted to an r.p.m. value. Steps in the method include counting the number of cycles of an oscillating signal in binary form to measure the time interval for each turn, selecting a most significant portion of bits within the number counted, determining the positional weight of the most significant bit to obtain a scaling factor, and producing a voltage inversely proportional to the value of the selected portion of bits, which voltage is then scaled by the scaling factor.
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Citations
17 Claims
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1. A system for measuring the rotational speed of a variable speed shaft comprising:
- means for sensing at least a predetermined fractional rotation of said shaft;
means for supplying an oscillating signal of a predetermined frequency;
counter means having a capacity of a predetermined quantity of bits and responsive to said sensing means for counting the total number of cycles of said oscillating signal within the time interval of said predetermined fractional rotation of said shaft;
means for selecting a portion of said bits from the number in said counter means, the selected bits being a predetermined number of bits constituting the most significant bits of said number in said counter means;
means for determining the position in said counter means of the most significant bit of said selected bits; and
digital to analog converter means responsive to said selected bits and the position of said most significant bit for producing an analog output inversely proportional to said number in said counter means to provide an analog measure of shaft rotational speed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
- means for sensing at least a predetermined fractional rotation of said shaft;
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11. A system for measuring the rotational speed of a variable speed shaft comprising:
- means for sensing at least a predetermined fractional rotation of said shaft;
means supplying an oscillating signal with a predetermined frequency;
counter means having locations for twenty bits responsive to said sensing means for counting the total number of cycles of said oscillating signal within the time interval of said predetermined fractional rotation of said shaft;
shift register means for selecting the ten most significant bits in said counter means, said shift register means having a capacity of twenty bits into which said bits in said counter means are transferred, and means for shifting the positional locations of said bits in increments of one positional location until the most significant bit reaches the most significant location in said shift register means thereby positioning the ten most significant bits in the ten most significant locations in said shift register means;
shift counting means for counting the number of said incremental shifts accomplished; and
digital to analog converter means for producing an output voltage proportional to shaft rotational speed including first converter means producing a first voltage inversely proportional to the number value of the bits in the ten most significant locations in said shift register means, and scaling means for adjusting said first voltage by an amount proportional to the number of said incremental shifts counted by said shift counting means. - View Dependent Claims (12)
- means for sensing at least a predetermined fractional rotation of said shaft;
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13. A method for measuring shaft rotational speed using an oscillator which supplies a signal of a predetermined frequency and binary counter means, comprising the steps of:
- causing said binary counter means to count the total number of cycles of said oscillating signal within at least a predetermined fractional rotation of the shaft;
selecting a portion of the bits from the number in said binary counter means, the selected bits being a predetermined number of bits constituting the most significant bits of said number in said binary counter means;
determining the position in said binary counter means of the most significant bit of said selected bits; and
converting said selected bits and the position of said most significant bit into an analog output inversely proportional to the number in said binary counter means to provide an analog measure of shaft rotational speed. - View Dependent Claims (14)
- causing said binary counter means to count the total number of cycles of said oscillating signal within at least a predetermined fractional rotation of the shaft;
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15. A method for measuring the rotational speed of a variable speed shaft using an oscillator which supplies a signal of a predetermined frequency, binary counter means, and shift register means, comprising the steps of:
- causing said binary counter means to count the total number of cycles of said oscillating signal within at least a predetermined fractional rotation of the shaft;
transferring the bits in said binary counter means to said shift register means;
causing said shift register means to shift the positional locations of said bits in increments of one positional location until the most significant bit reaches a predetermined positional location whereby a most significant portion of bits are moved to predetermined locations in said shift register means;
counting the number of said incremental shifts accomplished;
producing an analog value inversely proportional to the number value of said most significant portion of bits; and
scaling said analog value by an amount proportional to the number of said incremental shifts counted. - View Dependent Claims (16)
- causing said binary counter means to count the total number of cycles of said oscillating signal within at least a predetermined fractional rotation of the shaft;
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17. A method for measuring the rotational speed of a variable-speed shaft using means for sensing at least a predetermined fractional rotation of said shaft, an oscillator which supplies a signal of a predetermined frequency, binary counter means and shift register means each having locations for twenty bits, and digital to analog converter means, comprising the steps of:
- causing said binary counter means to count the total number of cycles of said oscillating signal within at least a predetermined fractional rotation of the shaft;
transferring the bits in said counter to said shift register means;
causing said shift register means to shift the positional locations of said bits to positions of more significant bits in increments of one positional location until the most significant bit reaches the most significant location whereby the ten most significant bits are moved into the ten most significant locations in said shift register means;
counting the number of said incremental shifts accomplished;
causing said digital to analog converter means to produce a first analog voltage inversely proportional to the number value stored in the ten most significant locations in said shift register means, and scaling said first analog voltage by a factor proportional to the number of said incremental shifts counted to produce an analog output voltage proportional to shaft rotational speed.
- causing said binary counter means to count the total number of cycles of said oscillating signal within at least a predetermined fractional rotation of the shaft;
Specification