JP2017166845A - Method for adjusting sensor to improve signal output stability for mixed gas measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method or technique for adjusting a gas sensor by applying pulse discharge in order to adjust a mixed electric potential gas sensor to detect gases generally found in combustion exhaust.SOLUTION: The present invention provides measurement of sensor impedance by applying an AC sine wave to between sensor electrodes. It uses the measured impedance value to monitor the operation temperature of a sensor by controlling the operation temperature of the sensor within a stipulated temperature range or monitoring the impedance.SELECTED DRAWING: Figure 2

Description

  The present invention relates generally to improvements in the inventor's method or technique claimed in the related art, which method or technique uses a pulsed discharge to adjust a mixed potential gas sensor that detects gases commonly found in combustion exhaust. A method or technique for adjusting a gas sensor by application of

  The detection element used in the zirconia oxygen sensor is generally formed of zirconia thimble, and this zirconia thimble is coated with metal (usually platinum) on the inside and outside to form an electrode. This electrode is used to measure the oxygen concentration difference between the measurement gas outside the thimble and the reference gas (usually the atmosphere) inside the thimble. The oxygen concentration difference can be calculated by measuring the voltage between the two electrodes.

  Solid electrolyte oxygen sensors with gas-impermeable zirconia ceramic separating two conductive (Pt) electrodes are widely used for combustion control in power systems and combustion control in exhaust systems of automotive internal combustion engines . To use an oxygen sensor for industrial combustion control, the sensor has a certain performance criterion, typically 3-5% relative accuracy (or 0.1-0.2% absolute accuracy), It must exhibit a response time of less than 10 seconds and a service life typically longer than one year.

  An improved method of activating these sensors is described in U.S. Patent No. 7,585,402 and a later continuation application, U.S. Patent Application No. 11 / 152,971, which is described in the inventor's own related prior art. A typical schematic of the pulsed discharge technique is shown in FIG. 1 below. FIG. 1 is a depiction of the sensor adjustment of the previous invention.

Sensors made using our own activation method provide a great number of improvements in performance. Such a thimble sensor can not only be used competitively with a planar design as an oxygen sensor, but also as a mixed potential sensor that directly and directly measures NO _x and O ₂ using the same sensor electrode. can do. This dual function of the mixed potential sensor can have the advantages described in the related art compared to the current automotive (ie exhaust gas oxygen (EGO)) planar O ₂ sensor, but the sensor from the thimble sensor The stability of the reading has several operational challenges caused by its own thimble design shape and orientation. Assuming that the stability of these sensors and the output of the sensors are adversely affected by moisture, they are only effective in environments with high dew points. Planar sensors generally incorporate heating elements on the sensor surface to know the sensor surface temperature or to control the sensor surface temperature, but such a solution is not possible due to changes in the three-dimensional shape of the thimble sensor. Be practical.

  Therefore, in order to obtain the advantage of stable sensor resolution at a very low concentration and for a gas mixture, it is measured when the sensor impedance is within an appropriate range, preferably within such an appropriate range. It would be beneficial to be able to control the sensor impedance.

  An improvement to the above pulsed discharge technique is proposed by continuously measuring the gas sensor impedance (resistance) at high temperatures. The measured impedance value is used to control the sensor operating temperature within a specified temperature range, or monitor the sensor operating temperature by monitoring impedance. The proposed improvement provides the use of a lambda sensor as a broadband sensor in the combustion exhaust gas without the need to install a thermocouple in the immediate vicinity of the sensor location by controlling the impedance within the operating parameter range, and It becomes possible.

Further improvements are proposed for using lambda sensors to measure NO _x , CO and oxygen mixing.

A further improvement provides measurement of sensor impedance by applying an alternating current (AC) sine wave between the sensor electrodes. This uses a practical and highly accurate lambda sensor for O ₂ measurement. In an alternative application, alternating current (AC) sine waves can be replaced with positive and negative direct current (DC) pulse waves to achieve similar results.

  The advantages and features of the present invention will become better understood with reference to the following more detailed description and appended claims when taken in conjunction with the accompanying drawings. In the drawings, identical elements are identified by identical reference numerals.

FIG. 1 is a schematic diagram of sensor adjustment in the prior art.

FIG. 2 is a proposed refinement according to a preferred embodiment of the present invention, whereby a further known resistor 2 (Rb) in series with the gas sensor is installed.

FIG. 3 shows the voltage between the sensor electrodes and the charging current.

FIG. 4 is a calibration curve of sensor resistance with respect to temperature. FIG. 5 is a lambda sensor response to NO concentration change.

FIG. 6 is the lambda sensor response to oxygen concentration change at NO = 0 ppm.

FIG. 7 is a sensor calibration for oximetry by using the sensor response to a positive voltage applied to the measurement electrode.

  The best mode of practicing the present invention is illustrated with respect to the preferred embodiments of the present invention represented herein in FIGS. In this preferred embodiment, an improvement to the pulsed discharge technique is proposed by continuously measuring the gas sensor impedance (resistance) at high temperatures. The measured impedance value is used to control the sensor operating temperature within a specified temperature range, or monitor the sensor operating temperature by monitoring impedance.

  The proposed improvement allows the use of a lambda sensor as a broadband sensor in the combustion exhaust gas without having to install a thermocouple in the immediate vicinity of the sensor location.

Further improvements provide the use of lambda sensors for NO _x , CO and O ₂ mixing measurements. During the charging phase of the process (stage I and stage III), a data acquisition system is used to continuously measure the voltage drop across a known resistor. The charge current can be calculated by dividing the voltage by the value of the known resistor. During the charging phase of the process, a data collection system is used to measure the voltage drop across the sensor electrodes.

A further improvement provides measurement of sensor impedance by applying an alternating current (AC) sine wave between the sensor electrodes. This uses a practical and highly accurate lambda sensor for O ₂ measurement.

  A charging current measurement curve and a voltage measurement curve between sensor electrodes are shown in FIG. A measured voltage between the two electrodes is obtained. This measured voltage is divided by the measured current. This divided result determines and provides the sensor impedance.

  Sensor impedance is directly related to sensor operating temperature. The ceramic measurement cell of the lambda sensor is placed in an external furnace, and the relationship between the sensor impedance and the sensor operating temperature is monitored by monitoring the furnace and its cell temperature using an external thermocouple placed in the immediate vicinity of the sensor element. A calibration curve is obtained (see FIG. 4).

  FIG. 5 shows the lambda sensor response to a pulsed discharge technique for different levels of NO at a constant oxygen concentration of 2%. FIG. 6 shows the sensor response to changes in oxygen concentration at NO = 0.

When a negative voltage is applied to the measurement electrode (stage III in the figure), the sensor response is sensitive to NO only and not sensitive to O ₂ . Alternatively, when a positive voltage is applied to the measurement electrode, the sensor response has no NO sensitivity, and the sensor response is sensitive only to O ₂ . As can be seen in FIG. 7, a mixed measurement of NO and O ₂ is possible.

By subtracting the negative voltage from the positive voltage (Vpos-Vneg), a pure NO response can be measured. When using the Vpos response, the O ₂ concentration can be measured.

  The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or intended to limit the invention to the precise forms disclosed, and many modifications and variations will become apparent in view of the above teachings. Is possible. The embodiments have been chosen and described in order to best explain the principles of the invention and the practical application of the invention. This allows other persons skilled in the art to best use the present invention and various embodiments with various modifications adapted to the particular intended use. It is intended that the scope of the invention be defined by the appended claims and their equivalents. Accordingly, the scope of the invention should be limited only by the following claims.

Claims (17)

An improved pulsed discharge technique that uses a lambda sensor that does not require a thermocouple installed in the immediate vicinity of the lambda sensor position, Using a lambda sensor configured to be a potentiometric oxygen sensor in flow;
Using the lambda sensor for mixed measurements of NO _x , CO and O ₂ by measuring the sensor resistance by applying an external DC voltage during the charging phase;
In the continuous measurement of the voltage drop across a known resistor at a high temperature during the charging phase, the measured resistance value is used to control the operating temperature of the sensor within a specified temperature range, or the resistance A technique comprising: measuring the operating temperature of the sensor by monitoring; and measuring the sensor resistance by applying a current sine wave between the electrodes of the sensor.   Providing the ceramic measurement cell of the lambda sensor in an external furnace, and monitoring the furnace and the cell temperature of the furnace using an external thermocouple placed in the immediate vicinity of the sensor element; The improved pulsed discharge technique of claim 1, providing a calibration curve defining a relationship between sensor impedance and sensor operating temperature. A method for controlling the operating characteristics of a gas sensor having one or more thimble-type solid ion conductors that supports one or more pairs of metal electrodes and an internal heater, the method comprising: a. Heating the gas sensor to a high temperature by applying a current to the internal heater;
b. Continuously measuring the resistance of the gas sensor at the elevated temperature; and c. Monitoring the measured resistance and controlling an operating temperature of the sensor within a specified temperature range by controlling a current flowing through the internal heater.   The method of claim 3, wherein the sensor comprises a potentiometric oxygen sensor to control operating characteristics of a gas sensor.   The method of claim 4, wherein the sensor comprises an operating characteristic of a gas sensor, comprising a lambda sensor. The lambda sensor is further configured for mixed measurement of NO _x , CO and O ₂ d. Step a. And step b. 6. The method of claim 5, further comprising continuously measuring a voltage drop across a known resistor using a data acquisition system during the operation. A method for controlling the operating characteristics of a gas sensor having one or more thimble-type solid ion conductors that supports one or more pairs of metal electrodes and an internal heater, the method comprising: a. Heating the gas sensor to a high temperature by applying a current to the internal heater;
b. Continuously measuring the impedance of the gas sensor at the elevated temperature; and c. Monitoring the measured impedance and controlling an operating temperature of the sensor within a specified temperature range by controlling a current flowing through the internal heater;
Continuously measuring the impedance of the gas sensor includes applying a sinusoidal external voltage across the electrodes of the sensor, measuring a voltage drop across a known resistor connected in series with the sensor, and an AC signal. Determining the sensor response to the analysis gas by separating DC from the.   In an improved pulsed discharge technique, including continuously measuring the impedance of a gas sensor at high temperatures, using the measured impedance value to control the operating temperature of the sensor within a specified temperature range, or impedance A technique characterized by monitoring the operating temperature of the sensor by monitoring.   9. The method of claim 8, further characterized by using the lambda sensor configured to be a potentiometric oxygen sensor in the combustion exhaust gas flow without the need for a thermocouple installed in the immediate vicinity of the lambda sensor position. Improved pulse discharge technique. Further comprising using the lambda sensor for a mixed measurement of NO _x , CO and O ₂ ;
The improved pulsed discharge technique according to claim 9, wherein during the charging phase of the process, a data acquisition system is used to continuously measure the voltage drop across a known impedance device. An improved pulsed discharge technique that continuously measures the impedance of a gas sensor at an elevated temperature and uses the measured impedance value to control the operating temperature of the sensor within a specified temperature range Or measuring the operating temperature of the sensor by monitoring impedance;
Using said lambda sensor configured to be a potentiometric oxygen sensor in the combustion exhaust gas flow without the need for a thermocouple installed in the immediate vicinity of the lambda sensor position;
The lambda sensor is used for mixed measurements of NO _x , CO and O ₂ , using a data acquisition system and continuously measuring the voltage drop across a known impedance device during the charging phase of the process. And measuring the sensor impedance by applying a current sine wave between the electrodes of the sensor.   Providing the ceramic measurement cell of the lambda sensor in an external furnace, and monitoring the furnace and the cell temperature of the furnace using an external thermocouple placed in the immediate vicinity of the sensor element; The improved pulsed discharge technique of claim 11, providing a calibration curve defining a relationship between sensor impedance and sensor operating temperature.   In an improved pulsed discharge technique, including continuously measuring the impedance of a gas sensor at high temperatures, using the measured impedance value to control the operating temperature of the sensor within a specified temperature range, or impedance A technique characterized by monitoring the operating temperature of the sensor by monitoring.   14. The method of claim 13, further characterized by using the lambda sensor configured to be a potentiometric oxygen sensor in the combustion exhaust gas flow without the need for a thermocouple installed in the immediate vicinity of the lambda sensor position. Improved pulse discharge technique. Further comprising using the lambda sensor for a mixed measurement of NO _x , CO and O ₂ ;
The improved pulsed discharge technique of claim 14, wherein the voltage drop across a known impedance device is continuously measured using a data acquisition system during the charging phase of the process. An improved pulsed discharge technique wherein the lambda sensor is configured to be a potentiometric oxygen sensor in a combustion exhaust gas flow without the need for a thermocouple installed in the immediate vicinity of the lambda sensor position. To use;
Use the lambda sensor for mixed measurements of NO _x , CO and O ₂ , using the data acquisition system to continuously measure the voltage drop across a known impedance device during the charging phase of the process. ;
In continuously measuring the impedance of the lambda sensor at a high temperature, the measured impedance value is used to control the operating temperature of the sensor within a specified temperature range, or by monitoring the impedance. And measuring a sensor impedance by applying a current sine wave between the electrodes of the sensor.   17. The improved pulse discharge technique of claim 16, wherein the technique uses a ceramic measurement cell of the lambda sensor in an external furnace and an external thermocouple placed in the immediate vicinity of the sensor element. Providing a calibration curve that provides a relationship between sensor impedance and sensor operating temperature by providing monitoring of the furnace and cell temperature of the furnace.