COMPASS CALIBRATOR

• US 3,683,668 A
• Filed: 01/26/1971
• Issued: 08/15/1972
• Est. Priority Date: 01/26/1971
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: David R. Brickner, Donald H. Baker
• Inventors: Baker, Donald H., Brickner, David R.
• Primary Examiner(s): Swisher, S. Clement
• Application Number:
  US05/109,872
• Time in Patent Office: 567 Days
• Field of Search: 73/1E
• US Class Current: 73/1.76
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

A magnetic compass calibrator module, suitable for plug-in or integral operation with a vehicle compass system having a magnetic azimuth detector, measures and calibrates any magnetic error induced in the detector by the vehicle and/or its cargo. A feature of the compass calibrator is that of utilizing a portion of the electronic magnetic compass control system of the vehicle to perform the calibration computation functions and thereby reduce the size and complexity of the calibrator itself.

Claims

1. A calibration system for calibrating a magnetic detector housed within a vehicle comprising means responsive to said detector for providing an output signal, means for combining the output of said detector at each of two predetermined headings approximately 180* apart to obtain an equivalent value of the earth'"'"''"'"'s magnetic field, means for exciting said detector to produce a selected artificial magnetic heading output from said detector, means for calculating the expected output of said detector at said selected heading, means for algebraically adding the outputs of said combining means, said excited detector and said calculating means to obtain a resultant signal, means for displaying the difference between said resultant signal and said expected detector output, and means for compensating the output of said detector in accordance with said displayed difference to minimize said difference.

2. The apparatus of claim 1 wherein said magnetic detector comprises a precalibrated and preindexed flux valve.

3. The apparatus of claim 1 wherein said combining means comprises data processor means operably associated with said detector for producing a digital signal corresponding to said detector output signal at a first heading, and for producing a further digital signal corresponding to said detector output signal at a second heading rotating approximately 180* from said first heading, memory means for storing said digital signal obtained at said first heading and said data processor providing a signal corresponding to the difference between said stored signal and said further signal.

4. The apparatus of claim 3 wherein said combining means further comprises first means for algebraically adding to said digital signal at said first heading a signal corresponding to the misalignment of the vehicle and said first predetermined heading, and second means for algebraically adding to said digital signal at said second heading a signal corresponding to the misalignment of the vehicle and said second predetermined heading.

5. The apparatus as claimed in claim 1 wherein said displaying means comprises means for converting said difference signal to a binary coded decimal signal, means for displaying said coded signal as a numeric display, and means for additionally displaying the sense of said signal.

6. A method for calibrating a magnetic detector housed in a vehicle comprising deriving an output signal from said detector at each of two magnetic headings of said vehicle where said headings are approximately 180* to each other, combining each output of said headings to obtain a first resultant signal, imposing upon said detector an excitation equivalent to a preselected heading to produce an output signal from said detector equivalent to said preselected heading, calculating the expected output signal of said detector at said preselected heading, combining said detector output signal at said preselected heading with said calculated detector output signal and said first resultant signal to produce a second resultant signal, displaying sAid second resultant signal, and adjusting the output from said detector to minimize the value of said second resultant signal and thereby compensate for deviation errors in said detector.

7. The method as claimed in claim 6 wherein said step of deriving comprises orienting said vehicle to a first heading, storing the output signal of said detector at said first heading, reorienting said vehicle to a second heading approximately 180* greater than said first heading, and obtaining an output signal of said detector at said second heading.

8. The method as claimed in claim 7 comprising modifying the output signal at said first heading for misalignment of the vehicle with said first heading, and modifying the output signal of said second heading for misalignment of the vehicle with said second heading.

9. The method as claimed in claim 7 wherein said step of deriving comprises converting said detector output from an analog signal into a corresponding first digital signal, and storing said first digital signal in a memory.

10. The method as claimed in claim 9 wherein said step of combining comprises converting said detector output at said second heading from an analog signal to a corresponding second digital signal, combining said stored first digital signal with said second digital signal to obtain said first resultant signal, and converting said first resultant signal from a digital signal to an analog signal.

11. The method as claimed in claim 10 wherein said step of imposing comprises digitally computing the value of said excitation, and converting said digital value to an analog excitation value wherein said analog value is imposed on said detector, and said step of calculating comprises digitally computing the value of the expected output signal of said detector at said preselected heading, and converting said digital value to an analog value.

12. The method as claimed in claim 11 wherein said combining step comprises algebraically adding said analog values of said detector output, said calculated detector output, and said first resultant signal.

13. The method as claimed in claim 12 wherein said step of displaying comprises converting said second resultant signal from an analog value to a digital value, converting said digital value to a binary coded decimal value, and displaying said binary coded decimal value on an indicator.

14. In a magnetic compass system for navigable craft of the type wherein a magnetic detector mounted in said craft detects the direction of the earth'"'"''"'"'s magnetic field relative to the heading of said aircraft and supplies an alternating current signal corresponding thereto, wherein said system includes a closed loop servo for generating direct current signals proportional to said compass signal which are fed back to said detector for nulling said alternating current signal whereby said direct current signals are proportional to said craft magnetic heading and further including signal processor circuits responsive to said direct current signals for supplying output control signals proportional to the magnetic heading of said craft, said magnetic compass system including apparatus for calibrating said magnetic detector for the effects of local magnetic fields within said aircraft, said apparatus comprising calibration mode selector means for connecting said processor circuits into said detector servo loop, means for providing an output corresponding to the difference between the outputs of said detector at each of two vehicle headings 180* apart, whereby to provide an earth'"'"''"'"'s field cancelling signal, means for generating detector, plurality of signals corresponding to selected headings of said detector, means for algebraically combining said earth'"'"''"'"'s field cancelling signal and each of said plurality of generated signals to produce a summed signal, means for inserting said earth'"'"''"'"'s fIeld cancelling signal and said summed signal into said servo loop, whereby the total signal in said servo loop includes a signal corresponding to the actual heading of said magnetic detector, on earth'"'"''"'"'s field cancelling signal, a selected heading signal and a deviation error signal, means for segregating said deviation error signal, means for displaying said deviation signal, and means for inserting a signal into said servo loop to minimize said displayed signal.