Self-calibration of an NDIR gas sensor
AssigneeGaztech Corporation
InventorJacob Y. Wong
Life of this patent
Estimating the term…
Abstract
Some cyclic variables include within each cycle a value that can be determined extrinsically. In such case, the sensed value may differ from the known value by an amount that is a combination of long-term drift of the sensor and random measuring error. The drift component can be evaluated and eliminated by the following method. Once each cycle, for a number of cycles, the sensor measures the variable at a time when its value should equal the extrinsically-known value. The differences are plotted versus time, and a best-fitting straight line is determined, which indicates the drift. Throughout the next cycle as the variable is continuously sensed, the drift determined from the best-fitting straight line is continuously applied to correct the sensed value.
Claims5
A method for drift compensation of a sensor used for measuring a cyclical variable X that is known to lie within a known range extending from a low value X.sub.L to a high value X.sub.H during a part of each cycle, said sensor producing an electrical signal x(t) representative of the instantaneous value of X at time t, said method comprising the steps of:
- a) determining when x(t) is between x.sub.L and x.sub.H where x.sub.L and x.sub.H denote the values of x(t) corresponding to x.sub.L and x.sub.H respectively;
- b) sampling x(t) during each cycle when x(t) is between x.sub.L and x.sub.H and storing a representative quiescent value of x(t) for each cycle;
- c) determining a linear function E(t) that best fits the representative quiescent values of x(t) that were stored in a number of successive cycles;
- d) extrapolating the linear function E(t) to the present time t.sub.0, thereby obtaining E(t.sub.0);
- e) determining a corrected value x.sub.c (t.sub.0) for the signal x(t) at the present time t.sub.0 which is compensated for sensor drift;
- and,
- f) producing an enabling signal when x.sub.c (t.sub.0) exceeds a preset threshold level.
A method for drift compensation of a sensor used for measuring a cyclical variable X that is known to attain a constant maximum value X.sub.MAX during each cycle, said sensor producing an electrical signal x(t) representative of the instantaneous value of X at time t, said method comprising the steps of:
- a) determining for each cycle the maximum value X.sub.MAX corresponding to X.sub.MAX ;
- b) storing the maximum values determined in successive cycles;
- c) determining a linear function E(t) that best fits the maximum values stored in a number of successive cycles;
- d) extrapolating the linear function E(t) to the present time t.sub.0, thereby obtaining E(t.sub.0);
- e) determining a corrected value x.sub.c (t.sub.0) for the signal x(t) at the present time t.sub.0 which is compensated for sensor drift;
- and,
- f) producing an enabling signal when x.sub.c (t.sub.0) exceeds a preset threshold level.
A method for drift compensation of a sensor used for measuring a cyclical variable X that is known to attain a constant minimum value X.sub.MIN during each cycle, said sensor producing an electrical signal x(t) representative of the instantaneous value of X at time t, said method comprising the steps of:
- a) determining for each cycle the minimum value x.sub.MIN corresponding to x.sub.MIN ;
- b) storing the minimum values determined in successive cycles;
- c) determining a linear function E(t) that best fits the minimum values stored in a number of successive cycles;
- d) extrapolating the linear function E(t) to the present time t.sub.0, thereby obtaining E(t.sub.0);
- e) determining a corrected value x.sub.c (t.sub.0) for the signal x(t) at the present time t.sub.0 which is compensated for sensor drift;
- and,
- f) producing an enabling signal when x.sub.c (t.sub.0) exceeds a preset threshold level.
A method for drift compensation of a sensor used for measuring a cyclical variable X that is known to attain a known particular value X.sub.K at some known phase of each cycle, said sensor producing an electrical signal x(t) representative of the instantaneous value of X at time t, said method comprising the steps of:
- a) sampling the value of x(t) once in each cycle at said known phase of each cycle;
- b) storing the values sampled in successive cycles;
- c) determining a linear function E(t) that best fits the values stored in a number of successive cycles;
- d) extrapolating the linear function E(t) to the present time t.sub.0, thereby obtaining E(t.sub.0);
- e) determining a corrected value x.sub.c (t.sub.0) for the signal x(t) at the present time t.sub.0 which is compensated for sensor drift;
- and
- f) producing an enabling signal when x.sub.c (t.sub.0) exceeds a preset threshold level.
A method for drift compensation of a sensor used for measuring a cyclical variable X that is known to have the same average value X for each cycle, said sensor producing an electrical signal x(t) representative of the instantaneous value of X at time t, said method comprising the steps of:
- a) determining the average value x of x for each cycle;
- b) storing the average values determined in step a) for each cycle;
- c) determining a linear function E(t) that best fits the average values stored in a number of successive cycles;
- d) extrapolating the linear function E(t) to the present time t.sub.0, thereby obtaining E(t.sub.0);
- e) determining a corrected value x.sub.c (t.sub.0) for the signal x(t) at the present time t.sub.0 which is compensated for sensor drift;
- and,
- f) producing an enabling signal when x.sub.c (t.sub.0) exceeds a preset threshold level.
Dependencies are inferred from the claim text.