Method and apparatus for compensating a sensor

• US 4,198,677 A
• Filed: 01/30/1978
• Issued: 04/15/1980
• Est. Priority Date: 01/30/1978
• Status: Expired due to Term

• Current Assignee: Exxon Enterprises, Inc. (Exxon Mobil Corporation)
• Original Assignee: Exxon Research and Engineering Company (Exxon Mobil Corporation)
• Inventors: Bartley, George S., Brunner, Stanley N.
• Primary Examiner(s): Morrison, Malcolm A.
• Assistant Examiner(s): Chin, Gary
• Application Number:
  US05/873,596
• Time in Patent Office: 806 Days
• Field of Search: 364/571, 364/556, 364/602, 340/347 CC, 324/130
• US Class Current: 702/104
• CPC Class Codes: G01D 18/004 Continuous recalibration
• CPC Class Codes: G01D 3/00 Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
• CPC Class Codes: G05B 2219/37009 Calibration of vision system, camera, adapt light level
• CPC Class Codes: G05B 2219/37151 Handling encoder signal, compensation for light variation, stray light

Abstract

A sensor is compensated through the use of a closed loop comprising a digital processor, a digital-to-analog converter and a comparator having inputs coupled to the converter and the sensor and an output fed back to the digital processor. During calibration of the sensor, a signal from the sensor is tracked by the digital processor and at least one of the values characteristic of the sensor signal is stored in the digital processor. The stored value is used as or in the computation of a reference by the digital processor which is compared with the sensor signal during operation of the sensor to appropriately compensate the sensor for gain, offset, drift or degradation in the quality of the sensor signal.

Claims

1. The method of using a sensor producing an analog signal with a processing means comprising the following calibration steps:

converting a digital output value from said processing means to an analog signal value;

comparing the sensed analog signal value with the converted digital output value;

changing the digital output value of said processing means in the absence of a predetermined relationship between the analog signal value and the converted digital output value;

reiterating the foregoing steps until a predetermined relationship exists between the analog signal value and the digital output value;

repeating the foregoing steps for different instantaneous analog signal values; and

storing at least one of said digital output values having said predetermined relationship in said processing means so as to represent a selected characteristic of said analog signal;

said method further comprising the following measuring steps;

generating a sensor calibrated digital output value at the output of said processing means from said at least one of said stored digital output values;

converting said sensor calibrated digital output value to a calibrated analog signal value

comparing the calibrated analog signal value to said analog signal.

2. The method of claim 1 including the further calibration step of computing at least one sensor calibrated digital output value from said at least one stored digital output value.

3. The method of claim 1 wherein the analog signal is substantially sinusoidal.

4. The method of claim 3 wherein the stored digital values comprise the maximum and minimum of the sinusoidal signal.

5. The method of claim 4 including the step of computing at least one value representing ##EQU3## where D=the angle of said sinusoidal signal corresponding to said stored digital value.

6. Apparatus for compensating a sensor comprising:

digital processing means;

digital-to-analog converter means;

comparator means having a first input coupled to the output of said converter means, a second input adapted to be coupled to said sensor, and an output coupled to said processing means to form a closed loop;

said digital processing means iteratively computing digital output values and coupling said iteratively computed digital values to said converter means, said computing continuing until at least one of said iteratively computed digital values as converted corresponds with an instantaneous sensor output as determined by the output of said comparator, said digital processing means iteratively producing other digital values corresponding to other instantaneous values of said sensor output and storing at least one of said digital values corresponding to a selected characteristic of said sensor, said digital processing means generating a sensor calibrated digital output value from said at least one of said digital values corresponding to a selected characteristic of said sensor;

said converter means converting said sensor calibrated digital output value to a calibrated analog signal value; and

said comparator comparing the calibrated analog signal value to said sensor output.

7. The apparatus of claim 6 wherein said digital processing means computes at least one digital value from said at least one stored digital value to generate said sensor calibrated digital output value.

8. The apparatus of claim 6 wherein said stored value is compared with the output of said sensor after conversion by said converter means.