Pendulous induction compass transmitter including means external to the transmitter to compensate for heading errors in turns due to the vertical component of the Earth's magnetic field and due to two cycle error
First Claim
1. In a pendulous induction compass transmitter compensated for errors due to the Earth'"'"'s vertical field during turns, the combination comprising:
- a. magnetic sensing means for producing modulated signals proportional to the strength of the Earth'"'"'s field along the fore/aft and athwartships axes of an aircraft;
b. means to demodulate the modulated signal representative of the sensed fore/aft field to produce a varying, DC, demodulated signal proportional to the sensed Earth'"'"'s field along the fore/aft axis of the aircraft and thus to the cosine of the magnetic heading angle ψ and
of the aircraft;
c. means to demodulate the modulated signal representative of the sensed athwartships field to produce a varying, DC, demodulated signal proportional to the sensed Earth'"'"'s field along the athwartships axis of the aircraft and thus to the sine of the magnetic heading angle ψ
of the aircraft;
d. means to compensate the demodulated signals for errors due to the Earth'"'"'s vertical field during turns, including;
1. means to generate a DC correction signal proportional to the product of the Earth'"'"'s magnetic field M, the sine of the magnetic dip angle D and the sine of the bank angle φ
,2. means to add said DC correcting signal algebraically to said demodulated DC signal proportional to the Earth'"'"'s field and thus to the sine of the magnetic heading angle ψ
to cancel the signal component due to the Earth'"'"'s vertical field sensed along the athwartships axis during turns.
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Accused Products
Abstract
The invention relates to an apparatus for compensating the output signals from a pendulous induction compass transmitter to eliminate heading errors during turns due to the vertical component of the Earth'"'"'s magnetic field as well as those due to the horizontal component of the Earth'"'"'s magnetic field perpendicular to the axis of tilt, i.e., two cycle error. By compensating for the effect of Earth'"'"'s vertical field component, instabilities and anomalies such as "Northerly Turning Error" are eliminated or minimized. Compensation for vertical field error is achieved by generating a signal proportional to the product of the Earth'"'"'s magnetic field M, the sine of the magnetic dip angle D at the given latitude and longitude and the sine of the aircraft bank or roll angle φ. This signal is combined (by summation) with the demodulated signal from the sin ψ channel (i.e., the signal from the windings of the compass transmitter which senses the field along the athwartships axis) to cancel vertical error. Similarly, a signal proportional to the cosine of the aircraft bank or roll angle φ is generated and combined with the corrected DC signal from the compass transmitter to cancel two cycle error. Since the magnitude of the bank angle φ or its trigonometric functions, i.e., sin φ and cos φ, can readily be obtained from the aircraft vertical gyroscope and the dip angle D is known for any latitude and longitude, these two compensating signals can easily be generated and applied to the output signal processing channels from the compass transmitter to cancel the effects of vertical field error and two cycle error during a turn.
13 Citations
5 Claims
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1. In a pendulous induction compass transmitter compensated for errors due to the Earth'"'"'s vertical field during turns, the combination comprising:
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a. magnetic sensing means for producing modulated signals proportional to the strength of the Earth'"'"'s field along the fore/aft and athwartships axes of an aircraft; b. means to demodulate the modulated signal representative of the sensed fore/aft field to produce a varying, DC, demodulated signal proportional to the sensed Earth'"'"'s field along the fore/aft axis of the aircraft and thus to the cosine of the magnetic heading angle ψ and
of the aircraft;c. means to demodulate the modulated signal representative of the sensed athwartships field to produce a varying, DC, demodulated signal proportional to the sensed Earth'"'"'s field along the athwartships axis of the aircraft and thus to the sine of the magnetic heading angle ψ
of the aircraft;d. means to compensate the demodulated signals for errors due to the Earth'"'"'s vertical field during turns, including; 1. means to generate a DC correction signal proportional to the product of the Earth'"'"'s magnetic field M, the sine of the magnetic dip angle D and the sine of the bank angle φ
,2. means to add said DC correcting signal algebraically to said demodulated DC signal proportional to the Earth'"'"'s field and thus to the sine of the magnetic heading angle ψ
to cancel the signal component due to the Earth'"'"'s vertical field sensed along the athwartships axis during turns. - View Dependent Claims (2, 3, 4, 5)
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Specification