Calibration sequence and method for an electronic compass

• US 4,720,992 A
• Filed: 11/17/1986
• Issued: 01/26/1988
• Est. Priority Date: 12/27/1985
• Status: Expired due to Term

• Current Assignee: Siemens VDO Automotive Electronics Corp (Continental AG)
• Original Assignee: Chrysler Motors Corp (Stellantis NV)
• Inventors: Hormel, Ronald F.
• Primary Examiner(s): Noland, Tom
• Application Number:
  US06/931,766
• Time in Patent Office: 435 Days
• Field of Search: 73/1 E, 364/569, 364/571, 33/363 Q, 33/363 R, 33/355 R, 33/356, 33/361, 33/362
• US Class Current: 73/1.76
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

A calibration sequence and method for use with an electronic compass which allows for the separation of the vehicle'"'"'s magnetic field from the earth'"'"'s magnetic field so that the earth'"'"'s field can be measured and used to give vehicle direction; such calibration sequence being done with a mirrored 180 degree re-orientation of the vehicle.

Claims

1. A calibration method for use in an electronic compass control circuit that includes a microcomputer, a flux-gate, a flux-gate driver, a bandpass filter, a synchronous detector, an integrator and a summing amplifier;

the control circuit equipped with a ranging circuit that includes an operational amplifier with resistive negative feedback connected to the output of the integrator;

an RC charging network connected to the non-inverting input to the operational amplifier;

a gate switch connected between the RC charging network and the microcomputer such that the microcomputer charges the RC charging network when the gate switch is closed; and

comparator means to respond to the output of the integrator to control the operation of the gate switch;

the calibration technique for use with a vehicle equipped with a display for indicating information to the operator of the vehicle and a calibration button for communication between the operator of the vehicle and the electronic compass control circuit;

the calibration technique comprising;

positioning the vehicle in an open area;

engaging the calibration button;

waiting for an indication from the display that a first reading has been taken by the electronic compass control circuit;

turning the vehicle 180 degrees;

engaging the calibration button; and

waiting for an indication from the display that a second reading has been taken by the electronic compass control circuit.

2. A calibration method for use in an electronic compass control circuit that includes a microcomputer, a flux-gate, a flux-gate driver, a bandpass filter, a synchronous detector, an integrator and a summing amplifier;

the control circuit equipped with a ranging circuit that includes an operational amplifier with resistive negative feedback connected to the output of the integrator;

an RC charging network connected to the non-inverting input to the operational amplifier;

a gate switch connected between the RC charging network and the microcomputer such that the microcomputer charges the RC charging network when the gate switch is closed; and

comparator means to respond to the output of the integrator to control the operation of the gate switch;

the calibration technique for use with a vehicle equipped with a display for indicating information to the operator of the vehicle and a calibration button for communication between the operator of the vehicle and the electronic compass control circuit;

the calibration method for each magnetic component comprising;

holding the gate switch closed;

presenting a high voltage level to the noninverting input to the operational amplifier that charges the RC charging network;

monitoring the output voltage of the integrator;

opening the gate switch when the output of the integrator is within a calibration range;

monitoring the charge time of the RC charging network;

storing the charge time;

controlling the gate switch for the charge time associated with each magnetic component whenever that component is measured;

waiting for a signal from the engagement of the calibration button by the operator of the vehicle indicating that the vehicle is in an open area and that calibration can begin;

measuring and storing the voltage value of each magnetic component as a first reading;

driving the display to indicate to the operator of the vehicle that the vehicle must be turned 180 degrees from its position at the beginning of the calibration;

waiting for the operator of the vehicle to engage the calibration button indicating that the vehicle has been turned 180 degrees;

measuring and storing the voltage value of each magnetic component as a second reading;

computing calibration offset values for each magnetic component by adding the first reading to the second reading and dividing the result by two; and

storing and using the offset values for each magnetic component in the computation of the compass heading thereby eliminating the effects of the vehicle'"'"'s magnetic field on the reading of the direction that the vehicle is pointed in the earth'"'"'s magnetic field.