JPH11108877A - Temperature correction method for sensor electromotive force - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a correct electromotive force (gas concentration) at all times even when an operation temperature changes by several deg.C under a temperature control, and eliminate influences of a temperature change of an environment change, by simultaneously measuring an electromotive force and the operation temperature of a solid electrolyte sensor element, and obtaining a gas concentration by a preliminarily set calculation formula based on the measured values. SOLUTION: An electromotive force and an operation temperature of a solid electrolyte sensor element 1 are A/D converted almost simultaneously and read into a CPU 7. A gas concentration is calculated with the use of the read electromotive force and operation temperature according to a calculation formula programmed beforehand in the CPU 7, and is displayed at a display device. Since the electromotive force and operation temperature are read simultaneously to calculate the concentration, a change (error) of the gas concentration due to a temperature change of the sensor element is negated, so that highly accurate detection of the gas concentration is achieved. Since the electromotive force and operation temperature are read into the CPU 7 altogether, a change of the electromotive force due to the temperature change is corrected and the gas concentration is obtained correctly at all times. In other words, a correct concentration is obtained even if the operation temperature of the sensor element 1 changes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas concentration measuring method using a solid electrolyte sensor element capable of measuring a gas concentration or the like of a predetermined gas (for example, CO ₂ gas) present in a gas. The present invention relates to a sensor electromotive force temperature correction method capable of improving the detection accuracy of a sensor and simplifying the temperature control of the sensor by correcting the fluctuation of the electromotive force of the electrolyte sensor element due to the temperature.

[0002]

2. Description of the Related Art In recent years, in the field of various gas sensors (for example, CO ₂ gas sensors, etc.), solid electrolytes have been used in order to reduce the size of sensor elements, reduce costs, facilitate maintenance, and make them movable. The development of the gas concentration sensor used has been prosperous. The solid electrolyte sensor element generates an electromotive force by reacting with a substance to be detected as is known. Since this electromotive force has a certain relationship with the amount of the substance to be detected, the amount (gas concentration) of the substance to be detected can be measured by measuring the electromotive force.

[0003]

However, due to its characteristics, the solid electrolyte sensor element has an operating temperature of several hundred degrees Celsius, and it is necessary to maintain the sensor temperature at an operating temperature specific to the sensor. Also, since the electromotive force of the sensor fluctuates under the influence of the fluctuation of its operating temperature (that is, when the sensor temperature fluctuates due to a disturbance due to a change in room temperature or wind as shown in FIG. 3, the sensor electromotive force also fluctuates. In order to improve the detection accuracy of the sensor, accurate temperature control must be performed. Furthermore, even if temperature control is performed to keep the operating temperature constant, temperature changes caused by fluctuations in the environment in which the sensor is placed cannot be avoided due to the response delay of the control system, and changes in the operating temperature are measured by the sensor. There are problems such as an error.

[0004] For example, when a solid electrolyte sensor in which the concentration P of the substance to be detected, the electromotive force E and the operating temperature T are in the relationship of the following equation (1) is operated at 500 ° C, the operating temperature fluctuation 1 The effect on the measurement result of the concentration P of the substance to be detected per ° C is as follows. Concentration P = e ^{−2F (A + E) / RT} (1) where F: Faraday constant, G: gas constant, T: sensor operating temperature (absolute temperature K) E: sensor electromotive force, F: constant

From the above equation, the concentration P of the substance to be detected is about 0.5 (10,000 ppm) per 1 ° C. of the fluctuation of the operating temperature.
% To 1.6 (10 ppm)%. ± 1% for general temperature control (± 5 ° for 500 ° C)
Since there is a temperature fluctuation of about C), the measurement error of the gas concentration becomes even larger. In addition, this temperature fluctuation cannot be eliminated by general temperature control.

Accordingly, the present invention focuses on the fact that the electromotive force of a solid electrolyte sensor element has a certain relationship with the operating temperature of the sensor, and formulates this relationship into a mathematical expression and pre-programs it into a microprocessor (hereinafter referred to as CPU). By reading the electromotive force and the operating temperature together into the CPU and calculating the above formula, it is possible to always obtain an accurate gas concentration while correcting the fluctuation due to the temperature change of the sensor electromotive force. The aim is to propose a method. The interval from the reading of the electromotive force to the reading of the operating temperature is set to be as short as possible within one second in order to improve the accuracy. The operating temperature in this case is the temperature of the sensor element body, not the ambient temperature where the sensor element is placed.

By using this method, the correct electromotive force (ie, gas concentration) can always be measured even when the operating temperature changes by several degrees Celsius with simple temperature control, and the influence of the temperature change due to environmental changes and the like can be obtained. Can be eliminated. Further, since the present invention is a method of correcting a fluctuation due to a temperature change of the electromotive force, the control of the sensor operating temperature may be changed within a range where the sensor can operate, and the temperature control of the sensor can be greatly simplified. The above equation (1) is an example when a certain solid electrolyte sensor element is used.
In the case of another solid electrolyte sensor element, another known equation peculiar to the solid electrolyte sensor element or a relational expression obtained by experiments or the like is used.

[0008]

Accordingly, the technical solution adopted by the present invention is a gas concentration measuring method using a solid electrolyte sensor element, wherein the solid electrolyte sensor element electromotive force and the solid electrolyte sensor element operating temperature Are measured at substantially the same time, and the gas concentration can be obtained by a predetermined mathematical formula based on the measured value.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described with reference to the drawings. FIG. 1 is a system configuration diagram for measuring a gas concentration while correcting the temperature of a solid electrolyte sensor element, and FIG. 5 is a flowchart for performing temperature correction. In the figure, reference numeral 1 denotes a solid electrolyte sensor element. An operating temperature measuring unit 2 for detecting the temperature of the solid electrolyte sensor element body is provided in close contact with the element 1 by appropriate means, and the electromotive force of the solid electrolyte sensor element is detected. The electromotive force measuring unit 3 to be mounted is attached. Further, a heater 4 for raising the temperature of the element to the operating temperature is provided near the solid electrolyte sensor element, and the temperature of the heater 4 is controlled by a signal from a temperature control unit 5.

The amplifier 6 has a function of amplifying the measured value from the operating temperature measuring section 2 attached to the solid electrolyte sensor element and the measured value from the electromotive force measuring section 3.
The data is D-converted and input to the CPU 7. The CPU 7 always reads the temperature of the sensor element main body from the above-described operating temperature measurement unit, and also constantly reads the value of the sensor element electromotive force from the electromotive force measurement unit. Concentration P = e ^{−2F (A + E) / RT} (1) Calculate gas concentration P according to the following relational expression (1) with the operating temperature, and display the result calculated by the CPU as a gas concentration measurement result. .

As described above, even if the operating temperature of the solid electrolyte sensor element fluctuates, or even if there is a change in the temperature caused by the fluctuation of the environment where the sensor is placed due to the response delay of the temperature control system, the present system can be used. By using the sensor, it is possible to remove the fluctuation of the sensor electromotive force due to the fluctuation of the sensor operating temperature caused by various disturbances from the measurement atmosphere where the solid electrolyte sensor element is placed, and furthermore, the influence on the sensor operating temperature measurement result Can be eliminated. As a result, the influence of the fluctuation of the electromotive force due to the fluctuation of the operating temperature can be eliminated, and the gas concentration can be detected with high accuracy.

Next, a flowchart of the temperature correction in the CPU will be described. In step S1, the electromotive force of the solid electrolyte sensor element is A / D converted and read by the CPU. Step S2 is executed within one second thereafter, and the operating temperature of the solid electrolyte sensor element is A / D converted and read by the CPU. In step S3, the gas is calculated using the electromotive force and the operating temperature read in steps S1 and S2 according to the formula P = e ^{−2F (A + E) / RT} (1) previously programmed in the CPU. Calculate the concentration. Thereafter, the gas concentration is displayed on a display device (not shown) in step S4, and the program ends in step S5. As described above, by simultaneously reading and calculating the electromotive force and the operating temperature of the solid electrolyte sensor element, the fluctuation (error) of the gas concentration due to the temperature fluctuation of the solid electrolyte sensor element can be canceled, and the gas concentration with high accuracy can be eliminated. Detection is possible.

[0013]

As described in detail above, the present invention focuses on the fact that the electromotive force of a solid electrolyte sensor element has a certain relationship with the operating temperature of the sensor, and formulates this relationship into a mathematical expression beforehand to determine a microprocessor (hereinafter referred to as a microprocessor). By reading the electromotive force and the operating temperature together into the CPU and calculating the above equation, it is possible to correct the fluctuation due to the temperature change of the electromotive force and always obtain an accurate gas concentration. . In other words, even if the operating temperature of the solid electrolyte sensor element fluctuates, an accurate gas concentration can always be obtained. In addition, even if there is a change in temperature caused by a change in the environment where the sensor is placed due to a response delay of the temperature control system, it is possible to obtain an excellent effect that an accurate gas concentration can be obtained.

[Brief description of the drawings]

FIG. 1 is an example of an embodiment according to the present invention, and is a system configuration diagram for measuring a gas concentration while performing temperature correction of a solid electrolyte sensor element.

FIG. 2 is a flowchart for temperature correction in FIG. 1;

FIG. 3 is a graph showing how the sensor temperature and the sensor electromotive force fluctuate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid electrolyte sensor element 2 Operating temperature measurement part 3 Electromotive force measurement part 4 Heater 5 Temperature control part 6 Amplifier 7 CPU

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[Procedure amendment]

[Submission date] November 5, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction contents]

[0004] For example, when a solid electrolyte sensor in which the concentration P of the substance to be detected, the electromotive force E and the operating temperature T are in the relationship of the following equation (1) is operated at 500 ° C, the operating temperature fluctuation 1 The effect on the measurement result of the concentration P of the substance to be detected per ° C is as follows. Concentration P = e ^{−2F (A + E) / RT} (1) where F: Faraday constant, R: Gas constant, T: Sensor operating temperature (absolute temperature K) E: Sensor electromotive force, A: Constant

Claims (2)

[Claims] In a gas concentration measuring method using a solid electrolyte sensor element, the solid electrolyte sensor element electromotive force and the solid electrolyte sensor element operating temperature are measured, and a gas concentration is determined based on the measured values. A method for correcting a temperature of a sensor electromotive force. 2. The method according to claim 1, wherein the operating temperature of the solid electrolyte sensor element is a temperature of the sensor element body.