Electronic analogue compass

• US 6,141,881 A
• Filed: 11/03/1998
• Issued: 11/07/2000
• Est. Priority Date: 11/03/1997
• Status: Expired due to Fees

• Current Assignee: Invotronics Manufacturing (Flex, Ltd.)
• Original Assignee: Invotronics Manufacturing (Flex, Ltd.)
• Inventors: Hall, Douglas, Ayres, Craig A., Ayres, John A.
• Primary Examiner(s): HIRSHFELD, ANDREW HOWARD
• Application Number:
  US09/185,078
• Time in Patent Office: 735 Days
• Field of Search: 33/361, 33/356, 33/355 R, 33/366.11, 33/366.25, 33/366.26, 33/366.27, 33/363 Q, 33/352, 33/363 R, 33/362, 324/247, 324/252
• US Class Current: 33/361
• CPC Class Codes: G01C 17/28 Electromagnetic compasses with north seeking magnetic elements and having electric pick-offs G01C17/26

Abstract

An compass having an electronic magnetic field sensor and an analog directional display is disclosed wherein a signal from the field sensor proportional to one component of the earth'"'"'s magnetic field is alternated in polarity and integrated to produce a triangular waveform the frequency of which is proportional to the strength of that field component and wherein a triangular waveform having a frequency proportional to the second component of the earth'"'"'s magnetic field is produced in the same manner. These values are used by a microcontroller to control an air-core gauge such that a disk with reference markings attached to the gauge remains positioned with one of the reference markings facing either magnetic or true north. A resistor ladder network is also connected in parallel to the inputs of the integrators and controlled by the microprocessor through a shift register in order keep the integrators out of saturation.

Claims

1. An analogue compass comprising:

sensing means for sensing first and second components of a magnetic field and for producing first and second outputs proportional to said first and second components;

an integrating means in communication with said sensing means for performing an integrate on said first output, and for performing an integrate on said second output, each of said integration operations continuing until a first pre-determined voltage is reached and then reversing in direction of integration until a second pre-determined voltage is reached and then reversing in direction, the time of changing from said first to said second pre-determined voltage being inversely proportional to said first and second outputs, respectively, so as to generate a first and a second triangle form integration signal, having a first and a second frequency, respectively, dependent on said first and second outputs, respectively;

microprocessor means in communication with said integrating means for determining true north based on said first and second triangle form integration signals;

a gauge motor having a rotary output shaft;

a disk coaxial mounted on said output shaft for rotation therewith, said disk including at least one reference marking;

a gauge controller for controlling said gauge motor to vary the orientation of said reference marking on said disk with respect to said magnetic field;

said microprocessor means communicating with said gauge controller to cause said reference marking on said disk to point toward true north.

2. The compass of claim 1 including anti-drift circuit means in communication with said integrating means and said microprocessor means for maintaining said first and second triangle form integration signals within a given range.