Simplified calibration technique and auto ranging circuit for an electronic compass control circuit

• US 4,622,843 A
• Filed: 12/27/1985
• Issued: 11/18/1986
• Est. Priority Date: 12/27/1985
• Status: Expired due to Fees

• Current Assignee: Chrysler Corporation (Stellantis NV)
• Original Assignee: Chrysler Corporation (Stellantis NV)
• Inventors: Hormel, Ronald F.
• Primary Examiner(s): Levy, Stewart J.
• Assistant Examiner(s): NOLAND, THOMAS
• Application Number:
  US06/813,897
• Time in Patent Office: 326 Days
• Field of Search: 73/1 E, 33/363 Q, 33/363 R, 33/355 R, 33/356, 364/559, 364/571
• US Class Current: 73/1.76
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

A technique is provided to combine software and hardware; the hardware being used to place voltage levels into narrow ranges and the software being used to perform the precise calibration.

Claims

1. In a control circuit for an electronic compass, including a microcomputer, a flux-gate, a flux-gate driver, a bandpass filter, a synchronous detector, an integrator, a summing amplifier, a ranging circuit to put a designated current through the flux-gate comprising:

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.

2. The ranging circuit of claim 1 where the RC charging network comprises:

a resistor connected between the gate switch and the non-inverting input to the operational amplifier; and

a capacitor connected between the non-inverting input to the comparator and ground.

3. The ranging circuit of claim 1 where the comparator means controls the operation of the gate switch in response to the output from the integrator such that the output from the integrator is within a calibration range.

4. A calibration technique 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 each magnetic component comprising;

holding the gate switch closed;

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

5. 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.