Method and apparatus for monitoring oxygen concentration

• US 6,279,377 B1
• Filed: 11/16/1998
• Issued: 08/28/2001
• Est. Priority Date: 11/16/1998
• Status: Expired due to Term

• Current Assignee: Cobham Mission Systems Davenport Lss Inc.
• Original Assignee: Litton Systems Incorporated
• Inventors: Cao, Tuan Q.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Politzer, Jay L.
• Application Number:
  US09/192,211
• Time in Patent Office: 1,016 Days
• Field of Search: 73/233.1, 738/638.1, 73/10.6, 422/3, 422/4, 204/401
• US Class Current: 73/23.31
• CPC Class Codes: G01N 27/4175 Calibrating or checking the analyser

Abstract

Apparatus for measuring concentration of oxygen includes a plurality of status displays, identifying concentration status relative to a plurality of thresholds, an alarm for immediate and prominent identification of status relative to a threshold of particular significance, and a quantitative display indicative of an actual concentration. Although measurements are performed and results are indicated relative to a number of thresholds, only a single calibration procedure is required, using only a single calibration gas. The apparatus is calibrated by adjusting a circuit parameter of one of the circuit components to vary a sensed output value to correspond to a narrow range surrounding the known concentration of the calibration gas. Both the circuit parameter and the actually sensed output value are stored. In a monitoring operation, the circuit parameter is retrieved to reset the circuit component to its calibrated setting. The monitored unknown value of concentration is scaled based on a value in a look-up table and on the actually sensed output value of the calibration process. An interpolation between values of the look-up table is then used to identify a concentration corresponding to the scaled value.

Claims

1. An oxygen monitor comprising:

a sensor for sensing oxygen concentration by providing output values indicative thereof;

a status display representing a value of sensed oxygen concentration relative to a plurality of threshold values,

said monitor further comprising a control processor for generating status displays for a plurality of threshold values in accordance with calibration by a single calibration gas, wherein said monitor comprises a component varying an output of said sensor, and said control processor comprises;

calibrating means for calibrating said sensor by varying an operating parameter of said component of said monitor to a calibration value providing an output value of said sensor corresponding to a concentration of said calibration gas;

storage means for storing said calibration value of said component; and

retrieving means operable during a monitoring operation for retrieving said calibration value from said storage means and for setting said operating parameter of said component to said calibration value to perform the monitoring operation.

2. The oxygen monitor recited in claim 1, further comprising a concentration display for displaying concentration of oxygen being monitored thereby, said control processor controlling said concentration display to display said concentration for a plurality of ranges in accordance with said calibration by a single calibration gas.

3. The oxygen monitor recited in claim 2, wherein said monitor comprises a component varying an output of said sensor, and said control processor comprises:

calibrating means for calibrating said sensor by varying an operating parameter of said component of said monitor to a calibration value providing an output value of said sensor within a range of values corresponding to a concentration of said calibration gas;

storage means for storing said calibration value of said component and for storing said output value of said sensor within the range of values corresponding to the concentration of said calibration gas;

retrieving means operable during a monitoring operation for retrieving said calibration value and said output value of said sensor from said storage means and for setting said operating parameter of said component to said calibration value to perform the monitoring operation, and

scaling means for scaling a measured value of an unknown oxygen concentration obtained during the monitoring operation in accordance with said output value of said sensor within the range of values corresponding to the concentration of said calibration gas and for providing a scaled value of the unknown oxygen concentration.

4. The oxygen monitor recited in claim 3, wherein said storage means further stores a look-up table of nominal output values from said sensor for predetermined oxygen concentration values, and

wherein said control processor operates for determining an oxygen concentration for the unknown oxygen concentration from an output of said sensor by interpolating between predetermined oxygen concentration values corresponding to two nominal output values in said look-up table which are respectively greater than and less than said scaled value of the unknown oxygen concentration.

5. A method for monitoring oxygen concentration comprising the steps of:

calibrating a sensor using a single calibration gas;

sensing an unknown oxygen concentration and providing output values indicative thereof;

generating status displays relative to a plurality of threshold values in accordance with said calibration by said single calibration gas;

displaying concentration of the oxygen being monitored for a plurality of ranges in accordance with said calibration by said single calibration gas;

wherein said calibrating step comprises varying an operating parameter of a component varying an output of said sensor to obtain a calibration value corresponding to a concentration of said calibration gas;

storing said calibration value of said component; and

during a monitoring operation, retrieving said calibration value for setting said operating parameter of said component to said calibration value to perform the monitoring operation.

6. The oxygen monitoring method recited in claim 5, wherein said calibrating step comprises varying an operating parameter of a component varying an output of said sensor to obtain a calibration value within a range of values corresponding to a concentration of said calibration gas;

storing said calibration value of said component and storing said calibration value of said sensor within the range of values corresponding to the concentration of said calibration gas;

during a monitoring operation, retrieving said calibration value and said output value of said sensor for setting said operating parameter of said component to said calibration value to perform the monitoring operation, and

scaling a measured value of an unknown oxygen concentration during the monitoring operation in accordance with said calibration value within the range of values corresponding to the concentration of said calibration gas and providing a scaled value of the unknown oxygen concentration.

7. The oxygen monitoring method recited in claim 6, wherein said step of storing further comprises storing a look-up table of nominal output values from said sensor for predetermined oxygen concentration values, and

determining an oxygen concentration for the unknown oxygen concentration from an output of said sensor by interpolating between predetermined oxygen concentration values corresponding to two nominal output values in said look-up table which are respectively greater than and less than said scaled value of the unknown oxygen concentration.

8. A gas concentration monitor comprising:

a sensor for sensing concentration of a gas and providing output values indicative of the concentration;

a status display which provides an indication of a relationship between a value of the sensed gas concentration and a plurality of threshold values;

a control processor for generating signals to drive said status display for indicating said relationship to said plurality of threshold values in response to a calibration by a single calibration gas; and

a concentration display for displaying the concentration of the gas being monitored, said control processor controlling said concentration display to display said concentration in accordance with said calibration by a single calibration gas.

9. The gas concentration monitor recited in claim 8, further comprising:

a variable gain amplifier receiving an output from said sensor and having a variable gain for scaling said output to provide a calibrated output value corresponding to a concentration of a calibration gas;

an electrically erasable potentiometer responsive to said control processor for controlling the gain of said variable gain amplifier;

a non-volatile memory connected to said control processor, to said variable gain amplifier and to said electrically erasable potentiometer;

said non-volatile memory storing a setting of said electrically erasable potentiometer used to obtain said calibrated output value from said sensor when sensing said calibration gas;

said non-volatile memory further storing an output value from said sensor when sensing said calibration gas and said electrically erasable potentiometer is adjusted to obtain said calibrated output value;

said control processor programmed for implementing a calibration procedure when said sensor senses said calibration gas by;

controlling said electrically erasable potentiometer to a setting which varies the gain of said variable-gain amplifier to obtain from said sensor an output value within a predetermined narrow range about a known concentration of said calibration gas;

controlling said non-volatile memory to store said output value within said predetermined narrow range as said calibrated output value; and

controlling said non-volatile memory to store said setting of said electrically erasable potentiometer which obtains said calibrated output value.

10. The gas concentration monitor recited in claim 9, wherein said control processor is further programmed for implementing monitoring of an unknown concentration of a gas by:

retrieving said setting of said electrically erasable potentiometer and setting said electrically erasable potentiometer thereto in order to vary the gain of said variable-gain amplifier;

scaling an output value from said sensor when sensing said unknown concentration by a factor including a ratio of a known output value for said calibration gas to said calibrated output value; and

performing an interpolation between two predetermined gas concentration values corresponding to two nominal output values of said sensor which are respectively greater than and less than said scaled value of the unknown gas concentration, thereby obtaining a concentration value of the gas to which said sensor is exposed.

11. The gas concentration monitor recited in claim 10, wherein said control processor is further programmed for controlling said concentration display for displaying the concentration value of the gas to which said sensor is exposed obtained by said interpolation.

12. The gas concentration monitor recited in claim 11, wherein said non-volatile memory further stores a look-up table including nominal output values of said sensor which respectively correspond to predetermined values of concentration of the gas, and

said control processor is further programmed for accessing said look-up table to obtain said two predetermined gas concentration values corresponding to two nominal output values of said sensor which are respectively greater than and less than said scaled value of the unknown gas concentration.

13. The gas concentration monitor recited in claim 11, wherein said control processor is further programmed for controlling said status display to operate one of a plurality of indicators to indicate a relationship between said concentration value of the gas to which said sensor is exposed and a predetermined threshold.

14. The gas concentration monitor recited in claim 13, wherein said non-volatile memory further stores a look-up table including nominal output values of said sensor which respectively correspond to predetermined values of concentration of the gas, and

said control processor is further programmed for accessing said look-up table to obtain said two predetermined gas concentration values corresponding to two nominal output values of said sensor which are respectively greater than and less than said scaled value of the unknown gas concentration.

15. The gas concentration monitor recited in claim 10, wherein said non-volatile memory further stores a look-up table including nominal output values of said sensor which respectively correspond to predetermined values of concentration of the gas, and

said control processor is further programmed for accessing said look-up table to obtain said two predetermined gas concentration values corresponding to two nominal output values of said sensor which are respectively greater than and less than said scaled value of the unknown gas concentration.

16. The gas concentration monitor recited in claim 10, wherein said control processor is further programmed for controlling said status display to operate one of a plurality of indicators to indicate a relationship between said concentration value of the gas to which said sensor is exposed and a predetermined threshold.

17. An oxygen monitor comprising:

a sensor for sensing oxygen concentration by providing output values indicative thereof;

a status display representing a value of sensed oxygen concentration relative to a plurality of threshold values,

said monitor further comprising a control processor for generating status displays for a plurality of threshold values in accordance with calibration by a single calibration gas,

calibration display for displaying concentration of oxygen being monitored thereby, said control processor controlling said concentration display to display said concentration for a plurality of ranges in accordance with said calibration by a single calibration gas,

calibrating means for calibrating said sensor by varying an operating parameter of said component of said monitor to a calibration value providing an output value of said sensor within a range of values corresponding to a concentration of said calibration gas;

storage means for storing said calibration value of said component and for storing said output value of said sensor within the range of values corresponding to the concentration of said calibration gas;

retrieving means operable during a monitoring operation for retrieving said calibration value and said output value of said sensor from said storage means and for setting said operating parameter of said component to said calibration value to perform the monitoring operation, and

scaling means for scaling a measured value of an unknown oxygen concentration obtained during the monitoring operation in accordance with said output value of said sensor within the range of values corresponding to the concentration of said calibration gas and for providing a scaled value of the unknown oxygen concentration.

18. A method for monitoring oxygen concentration comprising the steps of:

calibrating a sensor using a single calibration gas;

sensing an unknown oxygen concentration and providing output values indicative thereof;

generating status displays relative to a plurality of threshold values in accordance with said calibration by said single calibration gas; and

displaying concentration of the oxygen being monitored for a plurality of ranges in accordance with said calibration by said single calibration gas,

wherein said calibration step comprises varying an operating parameter of a component varying an output of said sensor to obtain a calibration value within a range of values corresponding to a concentration of said calibration gas;

storing said calibration value of said component and storing said calibration value of said sensor within the range of values corresponding to the concentration of said calibration gas;

during a monitoring operation, retrieving said calibration value and said output value of said sensor for setting said operating parameter of said component to said calibration value to perform the monitoring operation, and

scaling a measured value of an unknown oxygen concentration during the monitoring operation in accordance with said calibration value within the range of values corresponding to the concentration of said calibration gas and providing a scaled value of the unknown oxygen concentration.