JP2007085869A - Calibration method of gas sensor and gas analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for calibrating a gas sensor using a calibration gas containing measuring gas components of one or two kinds of concentrations, without having to use a calibration gas containing measuring gas components of four kinds of concentrations, and to provide a gas analyzer capable of selecting a plurality of calibration methods. <P>SOLUTION: A first calibration point, where the concentration of a measuring gas component is 0 ppm (zero gas) and a second calibration point where the concentration of the measuring gas component is 1/10 or larger than the desired measuring range a provided and the pumping current value preliminarily recorded at the first calibration point is calibrated to an actually measured value, while the ratio of the actually measured value at the second calibration point and the pumping current value preliminarily recorded as a standard calibration curve is calculated as a ratio correction value, and the reference calibration curve of a part excepting the first calibration point is multiplied by the ratio correction value to calibrate the gas sensor. By using this constitution, simple calibration work that uses only two calibration points is performed to enable high-precision calibration, in a region of low concentration and a desired measuring region. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas sensor calibration method and a gas analyzer having a plurality of calibration methods.

  In recent years, environmental technology has been actively researched and developed in order to suppress air pollution in Japan, which advocates advanced economies. In addition, neighboring countries including Japan are also required to introduce technologies to control air pollutants due to the strong demand for environmental standards that are increasing worldwide. In particular, there is an increasing need to apply highly accurate concentration measurement technology to nitrogen oxides in exhaust gas from industrial combustion engines such as power plants and boilers, which are one of the causes of air pollution. Yes. For this reason, in the measurement of nitrogen oxide concentration, development of a NOx meter that can be operated easily and economically while maintaining a high level of accuracy has been awaited.

Conventionally, various measurement methods and apparatuses have been proposed in order to know the concentration of a desired gas component in the gas to be measured. For example, as a method for measuring NOx in the gas to be measured such as combustion gas. Uses the NOx reducibility of Rh and measures the electromotive force between these electrodes using a sensor in which a Pt electrode and an Rh electrode are formed on an oxygen ion conductive solid electrolyte such as zirconia. Techniques are known.
In addition, a pair of electrochemical pump cells and sensor cells comprising a Pt electrode and an oxygen ion conductive solid electrolyte, and another set of electrochemical pump cells and sensor cells comprising a Rh electrode and an oxygen ion conductive solid electrolyte are combined. A method of measuring NOx based on the difference between pump current values is known.

  Patent Document 1 discloses a method capable of advantageously measuring NOx by the above-described NOx sensor using an oxygen ion conductive solid electrolyte, and the principle of the NOx sensor as shown in FIG. 1 is disclosed there. The element cross-sectional explanatory drawing shown is described. In FIG. 1, a gas to be measured is introduced into a first internal space 106 via a first diffusion-controlled passage 112, and the oxygen partial pressure in the first internal space 106 serves as oxygen concentration control means. The first electrochemical pump cell 156 is controlled to a predetermined, desirably low value at which NOx is not reduced. The atmosphere in the first internal space 106 in which the oxygen partial pressure is controlled is communicated from the first internal space 106 via the second diffusion-controlled passage 114. NOx is reduced in the second internal cavity 108, and the oxygen produced in the second internal cavity 108 is gas-limited using the second electrochemical pump cell 158 in the second internal cavity 108. The amount of NOx in the gas to be measured is measured by the pumping current value Ip that is pumped out and flows to the second electrochemical pump cell 58.

  In this method, the NOx concentration: Cn is obtained by Cn = K · Ip−A. However, K is a sensitivity coefficient, Ip is a current value flowing through the second electrochemical pump cell 158, and A is a constant due to a small amount of oxygen remaining in the first internal space 106. Here, most of Ip is due to oxygen generated by decomposition of the NOx component in the gas to be measured, and accurately measures even a very small amount of NOx without the influence of oxygen in the gas to be measured. It is possible.

  Further, in Patent Document 2, a third electrochemical pump that is a control means for a constant low oxygen partial pressure value and a measurement gas component introduced from the second space are reduced or decomposed, A third cavity, which is a space where a fourth electrochemical pump, which is a means for pumping out oxygen generated in the chamber, and the outer pump electrodes of the first and second electrochemical pumps are measured. A gas sensor comprising a duct for pumping air that is isolated so as not to be directly exposed to the gas and serves as a supply source of oxygen when oxygen is pumped into the first space; A drive unit for an electrochemical pump disposed in a third space, a calculation unit for calculating a pumping current flowing through the electrochemical pump into a measured gas component value, a display unit thereof, and a heater drive unit for the gas sensor; With NOx concentration Accurate monitoring can gas analyzer, and a calibration method using the same are disclosed.

  Here, in the NOx meter provided in Patent Document 2, the pumping current Ip for a plurality of known measurement gas component concentrations is measured, a calibration curve is created, and the gas analyzer is calibrated. That is, the pumping current Ip data for a plurality of known measurement gas component concentrations is accumulated in the calculation unit of the gas analyzer, and based on this data, the pumping current Ip of the target measurement gas component is changed to the measured gas component concentration. Convert and calibrate. For example, as shown in FIG. 2, measurement is performed using calibration gases (standard gases) having respective concentrations of a, b, and c, and pumping currents (Ia, Ib, Ic) at that time are respectively obtained, and calibration curves are obtained. This can be done by creating

Japanese Patent No. 2885336 JP 2001-159620 A

  In general, in the above-mentioned NOx meter using a solid electrolyte, the following calibration method has been adopted as means for ensuring effective accuracy when performing calibration in a maintenance operation at a customer site. That is, four types of calibration gas consisting of zero gas, middle gas, span gas, and high gas are prepared, gas sensor sensitivity is measured in each calibration gas, four calibration points are provided, and then the pumping current Ip is stored in advance. Calibration was performed by creating and recording a reference calibration curve based on the measured measured values of the pumping current at each of the four calibration points.

Even if the sensor has been calibrated at the time of shipment from the factory, the sensor characteristics may be altered depending on various conditions such as sensor installation conditions and aging. For this reason, there has been a demand for a calibration method using a calibration gas that can be easily obtained with a precision within a required range at a time desired by a customer.
However, in the conventional calibration method with a NOx meter using a solid electrolyte, a calibration method according to the measurement conditions and accuracy of the customer cannot be selected, and as many as four types of calibration gases with known concentrations are used. This was necessary each time and was a burden for calibration work. The present invention has been made in view of such conventional problems. The object of the present invention is to use one or two types of calibration gas without using four types of calibration gases. An object of the present invention is to provide a gas analyzer capable of appropriately selecting any one of a calibration method of a gas sensor to be calibrated and a plurality of calibration methods (calibration modes).

  In the present invention, as a result of intensive studies in view of the above-described conventional problems, without preparing four types of calibration gas, only one or two calibration modes using one or two types of calibration gas are used. In order to calibrate efficiently and simply in a short time, the error between the measured value at the calibration point and the reference calibration curve based on previously stored data is effectively reproduced within the desired measurement range and corrected. The present invention has been found out and the present invention has been completed.

  According to the present invention, in a gas sensor calibration method using an oxygen ion conductive solid electrolyte, calibration points are provided using a calibration gas containing one or two concentrations of measurement gas components, and each calibration point is provided. And measuring the pumping current of the sensor to obtain an actual measurement value, calculating a correction value from the pumping current value recorded in advance as a reference calibration curve and the actual measurement value, and calibrating the reference calibration curve using the correction value. A gas sensor calibration method is provided.

  In the above calibration method, a calibration point where the concentration of the measurement gas component is 0 ppm (zero gas) is provided, and the difference between the measured value at the calibration point and the pumping current value recorded in advance as a reference calibration curve is calculated as a difference correction value. It is preferable to calibrate by adding the difference correction value to the calibration curve.

  In the calibration method of the present invention, one calibration point having a measurement gas component concentration of 1/10 or more of the desired measurement range (middle gas, span gas, or high gas) is provided, and the actual measurement value at the calibration point and the reference calibration are set in advance. It is preferable to calculate the ratio of the pumping current value recorded as a line as a ratio correction value and calibrate the ratio correction value by multiplying the reference calibration curve. More specifically, the concentration of the measurement gas component is It is desirable to provide one calibration point within the range of 50 ppm or more and 500 ppm or less (middle gas, span gas or high gas).

  Furthermore, in the present invention, the first calibration point where the concentration of the measurement gas component is 0 ppm (zero gas), and the concentration of the measurement gas component is 1/10 or more of the desired measurement range (middle gas, span gas, or high gas). A second calibration point is provided, the pumping current value recorded in advance at the first calibration point is calibrated to an actual measurement value, and the actual measurement value at the second calibration point and the pumping current value previously recorded as a reference calibration curve It is preferable to calibrate by calculating the ratio as a ratio correction value and multiplying the ratio correction value by the reference calibration curve in the portion excluding the first calibration point. As for the concentration measurement range of the measurement gas component, it is desirable to provide one calibration point within the range of 50 ppm or more and 500 ppm or less (middle gas, span gas, or high gas) as described above.

  In the present invention, there is provided a gas analyzer characterized by comprising at least one calibration method from among the calibration methods of the respective gas sensors described above.

  The present invention also includes at least one calibration method from among the calibration methods for the respective gas sensors described above, and a gas sensor calibration method for performing calibration using a calibration gas containing a plurality of concentrations of measurement gas components. There is provided a gas analyzer characterized in that any one of the plurality of calibration methods can be selected.

According to the calibration method of the gas sensor of the present invention, it is easy to use a calibration gas containing one or two kinds of measurement gas components without using four kinds of calibration gases in the field maintenance work. And calibration work can be performed efficiently.
Moreover, according to the gas analyzer of the present invention, since various calibration methods (calibration modes) are provided, in the field where four kinds of calibration gases having known concentrations are provided, the calibration mode is more suitable. Highly accurate calibration is possible, and no calibration gas with 4 known concentrations is provided, calibration gas with 1 or 2 concentrations is provided or available early In the field, calibration can be performed by appropriately selecting a calibration mode corresponding to the mode.

  Next, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments, and the knowledge of those skilled in the art can be used without departing from the scope of the present invention. It goes without saying that various changes, modifications, and improvements can be added based on the above.

The basic technical idea of the present invention is that, in a gas sensor calibration method using an oxygen ion conductive solid electrolyte, calibration points are provided using calibration gases having one or two concentrations, and the sensor at each calibration point is provided. This is a calibration method in which a pumping current is measured to obtain an actual measurement value, a correction value is calculated from the pumping current value recorded in advance as a reference calibration curve and the actual measurement value, and the calibration curve is calibrated using the correction value.
When performing this calibration, a calibration point corresponding to the concentration measurement range of the desired measurement gas component is included, and the calibration method can be selected or changed as appropriate according to the desired accuracy.

More specifically, as a preferred embodiment of the present invention (calibration method 1), a calibration point having a measurement gas component concentration of 0 ppm is provided, and an actual measurement value at the calibration point and a standard calibration curve are recorded in advance. There is a method of calculating a difference from the pumping current value as a difference correction value and adding the difference correction value to a reference calibration curve for calibration. In this case, it is only necessary to prepare one type of N ₂ gas as the calibration gas, and it is easy to obtain. In addition, since the concentration at the calibration point is 0 ppm, sufficient accuracy can be obtained when the measurement gas component has a low concentration.

  In another preferred embodiment of the present invention (calibration method 2), the concentration of the measurement gas component is 1/10 or more of the measurement range (middle gas, span gas, or high gas), specifically, for example, the measurement gas component Providing only one calibration point within a range of 50 ppm or more and 500 ppm or less, and calculating a ratio between an actual measurement value at the calibration point and a pumping current value recorded in advance as a reference calibration curve as a ratio correction value; There is a method of calibrating by multiplying the calibration curve by the ratio correction value. In the case of this method, since the error from the reference calibration curve of the NOx sensor tends to increase near the center of the measurement range, calibration with higher accuracy can be expected by providing a calibration point in this range. In this way, a simple calibration method can be obtained by reflecting the ratio correction value on the reference calibration curve.

  As another preferred embodiment of the present invention (calibration method 3), the first calibration point where the concentration of the measurement gas component is 0 ppm (zero gas) and the concentration of the measurement gas component is 10 minutes of the desired measurement range. 1 or more (middle gas, span gas or high gas), specifically, for example, a second calibration point in the range where the concentration of the measurement gas component is 50 ppm or more and 500 ppm or less is provided, and the first calibration point is recorded in advance. The pumping current value is calibrated to the actual measurement value, and the ratio between the actual measurement value at the second calibration point and the pumping current value previously recorded as the reference calibration curve is calculated as a ratio correction value. There is a method of calibrating by multiplying the reference calibration curve of the portion excluding the points. In the case of this method, the first calibration point is changed to the actual measurement value, and the ratio correction value is used for the correction of the second calibration point, so that the 0 ppm (zero gas) concentration (low concentration) region and the desired value can be obtained. Even in the measurement region, it is possible to perform calibration with higher accuracy, and it is possible to perform calibration with high accuracy even in a simple calibration operation using only two calibration points.

  Furthermore, a first calibration point where the concentration of the measurement gas component is 0 ppm (zero gas) and a second calibration point where the concentration of the measurement gas component is 1/10 or more of the desired measurement range (middle gas, span gas, or high gas). The difference between the measured value at the first calibration point and the pumping current value recorded in advance as a reference calibration curve is calculated as a difference correction value, and the difference correction value is recorded as the reference calibration curve in advance at the first calibration point. The ratio of the measured value at the second calibration point and the pumping current value recorded in advance as a reference calibration curve is calculated as a ratio correction value, and the ratio correction value is calculated as the first calibration point. It is also possible to calibrate by multiplying the reference calibration curve of the part excluding.

Next, a NOx-O ₂ meter as a gas analyzer according to the present invention will be described.
Gas analyzer of the present invention (NOx-O ₂ meters) is the calibration method (calibration mode) of various described above, and the calibration method for calibrating with calibration gas containing a measurement gas component four concentrations (Calibration mode), and one of the plurality of calibration methods (calibration mode) can be selected.

Since the gas analyzer (NOx-O ₂ meter) of the present invention includes a plurality of calibration methods (calibration modes), for example, a calibration gas including measurement gas components having known concentrations of four types is provided. Even in the work environment where only calibration gas containing one or two concentrations of measurement gas components can be prepared, the calibration operator can appropriately select a calibration mode corresponding to the calibration gas and perform calibration. . Of course, in the case where calibration gas containing four kinds of measurement gas components having known concentrations is provided, calibration can be performed with high accuracy by performing calibration in the calibration mode.

As the NOx-O ₂ meter as the gas analyzer of the present invention, for example, one having the configuration shown in FIG. 3 is preferably used. FIG. 3 is an explanatory view showing a specific example of the NOx—O ₂ meter according to the present invention. As shown in FIG. 3, the NOx-O ₂ meter 10 is attached to a flue K in an exhaust pipe of an engine, boiler, industrial furnace or the like, for example, and is included in a gas to be measured (exhaust gas) G flowing through the flue K. The detection means 1 which detects the density | concentration of the measurement gas component to be measured, and the analysis means 2 electrically connected to the detection means 1 are provided. The detection means 1 is inserted and fixed in the flue K, and the analysis means 2 is installed outside. That is, a cylindrical detection means insertion port 13 through which the detection means 1 can be inserted projects from the flue wall 12, and an annular flange portion 14 is formed on the outer peripheral edge of the detection means insertion port 13. ing. The detection means 1 is inserted into the flue K through the detection means insertion port 13, and the detection means 1 is fixed to the flange portion 14.

A gas sensor 11 (NOx-O ₂ gas sensor) is fixed in the detection means 1, and a calibration gas supply pipe 71 for supplying calibration gas to the tip of the gas sensor 11 is disposed. A gas cylinder (not shown) having a calibration gas P containing a measurement gas component having a predetermined concentration is connected to the outside of the calibration gas supply pipe 71 and flows from one end of the calibration gas supply pipe 71. The calibration gas P flows out from the other end of the calibration gas supply pipe 71 and is supplied to the tip of the gas sensor 11.

  The detection means 1 includes a cylindrical support cylinder 21 having one end opened, and a flange portion 22 is formed at the opening edge of the support cylinder 21. The support cylinder 21 is inserted into the detection means insertion port 13, and the bolt 23, with the seal member S interposed between the outer surface of the flange portion 14 of the flue wall 12 and the inner surface of the flange portion 22 of the support cylinder 21, The support cylinder 21 is fastened and fixed to the flue wall 12 by a nut 24.

  A housing portion 32 that allows the distal end portion of the gas sensor 11 to be housed and fixed is formed through the distal end wall 31 of the support tube 21. An L-shaped communication path 34 that communicates with the inside of the housing portion 32 is formed. Further, an annular filter support portion 35 protrudes from the periphery of the opening portion of the tip wall 31, and a dustproof filter 36 is fixed to the tip portion of the filter support portion 35.

The gas sensor 11 is fixed to the housing portion 32. The gas sensor 11 includes a cylindrical sensor case 42, and a sensor nut 43 is formed near the tip of the outer peripheral surface of the sensor case 42. Further, on the outer peripheral surface of the sensor case 42, a screw portion 44 is formed on the tip side of the sensor nut 43, and a plurality of gas introduction holes 45 are formed on the tip side of the screw portion 44. They are arranged and formed at predetermined intervals in the direction. The sensor case 42 is fixed to the distal end wall 31 by inserting the distal end portion of the sensor case 42 into the accommodating portion 32 of the distal end wall 31 and tightening the screw portion 44 of the sensor case 42.
Inside the sensor case 42 is a high temperature operation type sensor element (not shown) formed in a plate shape or a rod shape by an oxygen ion conductive solid electrolyte such as zirconia and a heater (not shown) for heating the sensor element. Is housed. The sensor element is provided with a pair of electrodes, and by measuring a current (pumping current) generated due to a difference in chemical potential (corresponding to a potential) between the two electrodes (corresponding to a potential difference), It is possible to detect the concentration of the measurement gas component (for example, NOx gas, O ₂ gas) in the measurement gas G. In the heater, the solid electrolyte body is heated and held at a predetermined temperature. One end of a plurality of lead wires 46 for extracting the output voltage from the gas sensor 11 is connected to both electrodes, and the other end of each lead wire 46 is a lead wire pressing member 47 attached to the proximal end portion of the sensor case 42. It is derived to the outside through. Further, the gas sensor 11 is provided with a heater, and one end of a plurality of lead wires 46 for supplying power is connected to the heater, and the other end of each lead wire 46 is also connected to the outside via a lead wire holding member 47. Has been derived. The lead wire holding member 47 is formed in a disk shape from a rubber material having elasticity, heat resistance and insulation (for example, fluorine rubber, silicon rubber, etc.), and has the same number of lead wire insertion holes as the number of lead wires 46. Are arranged in a ring shape. One lead wire 46 is inserted through each lead wire insertion hole of the lead wire pressing member 47 one by one. Each lead wire 46 is bundled by being inserted into a lead wire insertion tube 48. A single male connector 49 is connected to the other end of each lead wire 46 whose one end is connected to the gas sensor 11.

  A rectangular parallelepiped terminal box 51 is fixed to the flange portion 14 of the flue wall 12 via bolts 23. That is, on the outer surface of the one side wall 51a on the flue wall 12 side of the terminal box 51, the pair of support members 52, 52 are fixed by welding. The support member 52 is formed in an L-shaped cross section from a support portion 52a fixed to the outer surface of one side wall 51a of the terminal box 51 and a fixed portion 52b protruding outward so as to be orthogonal to the support portion 52a. . The terminal box 51 is fixed to the flange portion 14 by tightening the fixing portion 52 b with the bolt 23 and the nut 53. An insertion hole 54 is formed at the center of one side wall 51 a of the terminal box 51, and a pair of arc-shaped bolt insertion holes 55 are formed around the insertion hole 54. Further, in the terminal box 51, one end of the air supply pipe 56 is fixed to the other side wall 51b facing the one side wall 51a through a tube joint 57, and the other end is also connected through the insertion hole 54 of the one side wall 51a. It is introduced into the support tube 21. The tube joint 57 is connected to a compressed air source (not shown) that generates cooling air, and the cooling air that flows in from one end of the air supply pipe 56 flows out from the other end of the air supply pipe 56. Is supplied to the base end. That is, the other end of the air supply pipe 56 is a nozzle portion 56 a that supplies cooling air to the base end portion of the gas sensor 11. Further, the other end of the output extraction cable 58 having one end connected to the analyzer 11b is introduced into the terminal box 51 via a cable joint 59 fixed below the tube joint 57 on the other side wall 51b. Yes. A female connector 60 is connected to the other end of the output cable 58, and the female connector 60 is connected to the male connector 49 in the terminal box 51.

  A bottomed cylindrical connecting pipe 61 having an open end is fixed to the outer surface of one side wall 51a of the terminal box 51. That is, a pair of fixing members 62 located on the opposite sides of the proximal end portion of the connecting pipe 61 are fixed by welding or the like. The fixing member 62 is formed in an L shape from a connecting pipe side fixing wall 62 a fixed to the outer peripheral surface of the connecting pipe 61 and a terminal box side fixing wall 62 b fixed to one side wall 51 a of the terminal box 51. Further, a bolt insertion hole 63 is formed in the terminal box side fixed wall 62b. Then, by inserting the bolt 64 from the inside of the terminal box 51 into the bolt insertion hole 55 of the one side wall 51a of the terminal box 51 and the bolt insertion hole 63 of the terminal box side fixed wall 62b, and tightening the nut 65, the connecting pipe 61 is It is fixed to the outer surface of one side wall 51a of the terminal box 51. A fitting hole 66 is formed in the distal end wall of the connecting pipe 61 so that the sensor nut 43 of the gas sensor 11 can be fitted. In a state where the connecting pipe 61 is fixed to the one side wall 51 a of the terminal box 51 and the flange portion 22 of the support cylinder 21 and the fixing portion 52 b of the terminal box 51 are fixed to the flange portion 14 of the detection means insertion port 13. Is held in a state in which the sensor nut 43 is fitted in the fitting hole 66. A plurality of air introduction holes 67 are formed at a predetermined interval in the circumferential direction of the connection pipe 61 on the proximal end side of the connection pipe 61. A plurality of air outlet holes 68 are formed at predetermined intervals in the circumferential direction of the connecting pipe 61 slightly closer to the tip than the center in the longitudinal direction of the connecting pipe 61. Between the inner peripheral surface of the support cylinder 21 and the outer peripheral surface of the connection pipe 61, a calibration gas supply pipe 71 for supplying a calibration gas P for calibrating the analyzing means 2 is inserted. The distal end portion of the calibration gas supply pipe 71 is screwed into an opening portion on the inner surface side of the distal end wall 31 in the communication path 34 formed in the distal end wall 31 of the support cylinder 21. Further, the base end portion of the calibration gas supply pipe 71 is led out to the side through the space between the one side wall 51a of the terminal box 51 and the flange portion 22 of the support cylinder 21 to supply the external calibration gas. It is connected to a source, for example a gas cylinder. Therefore, the calibration gas P from the gas cylinder is supplied to the accommodating portion 32 through the calibration gas supply pipe 71 and the communication path 34.

The analysis unit 2 includes a drive unit, an amplification unit, a calculation unit, and a heater control unit (not shown). Oxygen pumping control by the drive unit, amplification of the pumping current value by the amplification unit, NOx and Ox from the pumping current value ₂ control of the heater in operation and in the gas sensor of the concentration is performed. When the above-described calibration method is performed, calibration is realized on software in the calculation unit. Further, the analysis means 2 is provided with a concentration display output unit and a NOx-O ₂ display switching unit (not shown). By switching the NOx-O ₂ display switching unit to the NOx gas side or the O ₂ gas side, the concentration is output. The display output unit displays and outputs the concentration of each gas. Further, the analysis means 2 is provided with a calibration mode selection unit (not shown), and this calibration mode display selection unit is added to a calibration mode (calibration method) using four calibration points that has been conventionally performed. The calibration mode (calibration method) of the present invention described above is provided, the calibration gas that can be prepared by the calibration operator, and the various modes of the calibration mode display selection unit according to the measurement conditions and accuracy of the customer. It comes to choose.

Next, an example in which each calibration method of the present invention is specifically performed with NO gas and O ₂ gas using the gas analyzer (NOx-O ₂ meter) will be described in detail.

(Example 1: NOx gas)
Table 1 shows the concentrations of the four types of NOx using the gas analyzer (NOx-O ₂ meter) and the calibration method using the initial Ip value (μA) before calibration and the four calibration points of the prior art. The pumping current at (0 ppm, 50 ppm, 250 ppm, 500 ppm), that is, the measured value of the four-point calibration Ip (μA) is shown. FIG. 4 is a graph of Table 1.

  The initial Ip value referred to here is a numerical value on a reference calibration curve that is measured at the time of shipment from the factory and is created based on the accumulated pumping current. The reference calibration curve is composed of a linear straight line, a multi-curve or the like, and the reference calibration curve can be automatically created in the calculation unit. However, in the present invention, since the focus is on a calibration method based on a reference calibration curve prepared in advance, the conventional calibration method using four calibration points is a simple four-point method for explanation. Use a straight line.

This initial Ip value varies depending on the characteristics of each sensor, and an error occurs from the actual NOx concentration due to a change with time after shipment. As shown in FIG. 6, this error was calibrated based on the measurement results of calibration points at four points of zero gas (0 ppm), middle gas (50 ppm), span gas (250 ppm), and high gas (500 ppm). However, it is added that the density values at each of the four points referred to here are numerical values that can be appropriately changed according to the applied conditions. In each calibration method of Example 1, N ₂ was used as the zero gas, and NO was used as the middle gas, the span gas, and the high gas. In Example 1, NO was used for the middle gas, the span gas, and the high gas, but calibration can be performed using other nitrogen oxides such as NO ₂ .

(Calibration method 1)
Next, an example of the gas sensor calibration method of the present invention was carried out. First, an actual measurement value is measured using zero gas, and a difference from a pumping current value recorded as a reference calibration curve including an initial Ip value is calculated as a difference correction value. As shown in Table 2, the difference correction value here is
0.164 (μA) −0.085 (μA) = 0.079 (μA)
It becomes. By adding this value to the reference calibration curve and calibrating, the values shown in the remaining three points (middle gas, span gas, and high gas) in Table 2 are obtained, so that calibration can be performed. At this time, one type of N ₂ may be prepared as a calibration gas, and it is easy to obtain at the customer site. Further, since the calibration point concentration is 0 ppm, sufficient accuracy can be obtained when the gas to be measured has a low concentration. FIG. 5 is a graph of Table 2.

(Calibration method 2)
Next, another gas sensor calibration method of the present invention was carried out.
That is, as a calibration point where the concentration of the measurement gas component is 1/10 or more of the desired measurement range (the concentration of the measurement gas component is in the range of 50 ppm or more and 500 ppm or less) (one of middle gas, span gas, and high gas) The ratio between the measured value at the calibration point and the pumping current value recorded in advance as a reference calibration curve is calculated as a ratio correction value. Here, span gas (250 ppm) was used as a calibration point. That is, the ratio correction value of the initial Ip value of 0.940 (μA) with respect to the actual measurement value of 1.287 (μA) in the span gas is
1.287 (μA) ÷ 0.940 (μA) = 1.369
It is. By multiplying this value by the standard calibration curve, the remaining three points (zero gas, middle gas, and high gas) can be calibrated as shown in Table 3. The obtained result is shown in FIG.

(Calibration method 3)
Another gas sensor calibration method of the present invention was carried out.
That is, the first calibration point that is zero gas and the second calibration in which the concentration of the measurement gas component is one-tenth or more of the desired measurement range (middle gas, span gas, or high gas concentration is in the range of 50 ppm or more and 500 ppm or less) Set a point. Here, span gas is used. A ratio between the actually measured value 1.287 (μA) at the second calibration point and the pumping current value 0.940 (μA) recorded in advance as a reference calibration curve is calculated as a ratio correction value. The ratio correction value is
1.287 (μA) ÷ 0.940 (μA) = 1.369
It is. This value is multiplied by the reference calibration curve of the portion excluding the first calibration point (0 point) to obtain a ratio correction calibration curve.

  Further, the zero point pumping current value (initial Ip value) 0.085 (μA) previously recorded as the reference calibration curve at the first calibration point (zero gas) is changed to an actual measurement value 0.164 (μA) ( Proofread). Therefore, by changing the first calibration point to the actual measurement value and multiplying the ratio correction value by the reference calibration curve of the portion excluding the first calibration point, the zero point and the remaining two points (as shown in Table 4) Middle gas and high gas) can be calibrated. The obtained results are shown in FIG.

(Example 2: O ₂ gas)
Table 5 shows four types of O _{2 obtained} by a calibration method using an initial Ip value (μA) before calibration and four calibration points according to the prior art, using a gas analyzer (NOx-O ₂ meter). The pumping current at the concentration (0 ppm, 50 ppm, 250 ppm, 500 ppm), that is, the measured value of the four-point calibration Ip (μA) is shown. FIG. 8 is a graph of Table 5.

As shown in FIG. 8, the error was calibrated based on the measurement results of four calibration points of zero gas (0 ppm), middle gas (50 ppm), span gas (250 ppm), and high gas (500 ppm). However, it is added that the density values at each of the four points referred to here are numerical values that can be appropriately changed according to the applied conditions. In each calibration method of Example 2, N ₂ was used as the zero gas, and O ₂ was used as the middle gas, the span gas, and the high gas.

(Calibration method 1)
Next, an example of the gas sensor calibration method of the present invention was carried out. First, an actual measurement value is measured using zero gas, and a difference from a pumping current value recorded as a reference calibration curve including an initial Ip value is calculated as a difference correction value. As shown in Table 6, the difference correction value here is
0.174 (μA) −0.102 (μA) = 0.072 (μA)
It becomes. By adding this value to the reference calibration curve and calibrating, the values shown in the remaining three points (middle gas, span gas, and high gas) can be obtained as shown in Table 6, and can be calibrated. At this time, one type of N ₂ may be prepared as a calibration gas, and it is easy to obtain at the customer site. In addition, since the concentration at the calibration point is 0 ppm, sufficient accuracy can be obtained when the measurement gas component has a low concentration. FIG. 9 is a graph of Table 6.

(Calibration method 2)
Next, another gas sensor calibration method of the present invention was carried out.
That is, as a calibration point where the concentration of the measurement gas component is 1/10 or more of the desired measurement range (the concentration of the measurement gas component is in the range of 50 ppm or more and 500 ppm or less) (one of middle gas, span gas, and high gas) The ratio between the measured value at the calibration point and the pumping current value recorded in advance as a reference calibration curve is calculated as a ratio correction value. Here, span gas (250 ppm) was used as a calibration point. That is, the ratio correction value of the initial Ip value 7.360 (μA) with respect to the actual measurement value 8.464 (μA) in the span gas is
8.464 (μA) ÷ 7.360 (μA) = 1.150
It is. By calibrating by multiplying this value by the reference calibration curve, the values shown in the remaining three points (zero gas, middle gas, and high gas) are obtained as shown in Table 7, and can be calibrated. The obtained result is shown in FIG.

  In the embodiment of the present application, span gas (250 ppm) is used as a calibration point in calibration method 2 and the remaining three points (zero gas, middle gas, high gas) are calibrated, but middle gas or high gas is used as the calibration point. The remaining three points (zero gas, span gas, high gas) or (zero gas, middle gas, span gas) may be calibrated. In the calibration method 3, the span gas (250 ppm) is used as the calibration point and the remaining two points (middle gas and high gas) are calibrated. However, the middle gas or high gas is used as the calibration point, and the remaining two points ( Span gas, high gas) or (middle gas, span gas) may be calibrated.

(Calibration method 3)
Another gas sensor calibration method of the present invention was carried out.
That is, the first calibration point that is zero gas and the second calibration in which the concentration of the measurement gas component is one-tenth or more of the desired measurement range (middle gas, span gas, or high gas concentration is in the range of 50 ppm or more and 500 ppm or less) Set a point. Here, span gas is used. A ratio between the actually measured value 8.464 (μA) at the second calibration point and the pumping current value 7.360 (μA) recorded in advance as a reference calibration curve is calculated as a ratio correction value. The ratio correction value is
8.464 (μA) ÷ 7.360 (μA) = 1.150
It is. This value is multiplied by the reference calibration curve of the portion excluding the first calibration point (0 point) to obtain a ratio correction calibration curve.

  Further, the zero point pumping current value (initial Ip value) 0.102 (μA) previously recorded as the reference calibration curve at the first calibration point (zero gas) is changed to an actual measurement value 0.174 (μA) ( Proofread). Therefore, by changing the first calibration point to the actual measurement value and multiplying the ratio correction value by the reference calibration curve of the portion excluding the first calibration point, the zero point and the remaining two points ( Middle gas and high gas) can be calibrated. The obtained results are shown in FIG.

(Discussion)
In the calibration method 1 calibrating at one point of zero gas, using easily available N ₂ gas as zero gas (0 ppm) enables efficient and simple calibration in a short time, and the measurement gas component Although the calibration error is small when the concentration is low, the calibration error at a point with a high concentration may not be properly corrected. Further, in the calibration method 2 in which the concentration of the measurement gas component is calibrated at one point of the gas within the desired measurement range range (eg, span gas), the calibration is performed at one point of the gas within the measurement range range. In addition, the calibration error can be reduced efficiently and easily when the measurement gas component has a high concentration, but the calibration error at the point of low concentration can be corrected appropriately as in calibration method 1. It may not be possible.
In such a case, in the calibration method 3 where the concentration of the zero gas and the measurement gas component is calibrated at two points of the gas within the desired measurement range range (eg, span gas), the actual value measured with the zero gas and the ratio correction with the span gas are corrected. By introducing correction by value, the problems of the calibration method 1 and the calibration method 2 are solved.

In the embodiment of the present application, in the calibration method 3, in the NOx gas of Example 1, the zero point pumping current value (initial Ip value) 0.085 (μA) previously recorded as the reference calibration curve for the first calibration point (zero gas). ) Is changed to an actually measured value of 0.164 (μA), and in the O ₂ gas of Example 2, the pumping current value (initial Ip value) of 0.102 (μA) at the first calibration point is measured to 0.174 (μA). Although changed to (μA), it may be as follows.
For NOx gas, the difference between the measured value 0.164 (μA) of the first calibration point and the pumping current value (initial Ip value) 0.085 (μA) recorded in advance as a standard calibration curve is calculated as a difference correction value. . The difference correction value is
0.164 (μA) −0.085 (μA) = 0.079 (μA)
It is.
The first correction point is calibrated by adding this difference correction value to the zero point pumping current value (initial Ip value) 0.085 (μA). Even in this case, calibration can be performed as shown in Table 4 and FIG.
In the case of O ₂ gas, the difference between the measured value 0.174 (μA) of the first calibration point and the pumping current value (initial Ip value) 0.102 (μA) recorded in advance as a standard calibration curve is used as a difference correction value. calculate. The difference correction value is
0.174 (μA) −0.102 (μA) = 0.072 (μA)
It is.
The first correction point is calibrated by adding this difference correction value to the zero point pumping current value (initial Ip value) 0.102 (μA). Even in this case, calibration can be performed as shown in Table 8 and FIG.
That is, the difference correction value is added to the zero-point pumping current value actually recorded as the reference calibration curve in advance of the first calibration point, and the ratio correction value is multiplied by the reference calibration curve of the portion excluding the first calibration point. Try to calibrate. In this way, more accurate calibration is possible in the low concentration region and the desired measurement region similar to the calibration method 3 of the first and second embodiments, and the simple method of using only two calibration points. Can be calibrated with high accuracy even in a simple calibration process.

The embodiment of the present application may be modified as follows.
In the embodiment of the present application, as shown in FIG. 3, the gas analyzer (NOx-O ₂ meter) provided with the gas sensor for measuring NOx and O ₂ gas is implemented, but CO, CO ₂ , SO ₂ , H ₂ , Each gas sensor for measuring gases such as NH ₃ , O ₂ , and HCL and a gas analyzer equipped with the sensor are used with the calibration gas containing one or two kinds of measurement gas components of the present invention described above. It is also possible to use a calibration method of the sensor to be calibrated. It is also possible to provide a gas analyzer that can appropriately select any one of a plurality of calibration methods (calibration modes).

In the embodiment of the present application, the NOx-O ₂ meter of the present invention includes three calibration methods for calibrating with a calibration gas containing one or two concentrations of measurement gas components, and four types of measurement gases. A calibration method using a calibration gas containing components, and one of the plurality of calibration methods can be selected, but one or two concentrations of measurement gas Only three calibration methods for performing calibration with a calibration gas containing components may be provided, and any one of these three calibration methods may be selected. Even if it does in this way, the same effect can be acquired.
Further, at least one calibration method may be provided from among three calibration methods in which calibration is performed with one or two types of calibration gases. Thus, if at least one calibration method is provided, the calibration operation can be performed easily and efficiently.

According to the present invention, in the concentration measurement of nitrogen oxide (NOx) and oxygen (O ₂ ) that are the cause of air pollution, calibration of a gas sensor that can be operated simply and economically while maintaining a high level of accuracy. A gas analyzer comprising the method and its calibration method is provided. In particular, very in the case of calibrating engine, boiler, a gas analyzer for measuring the concentration of industrial furnaces such as nitrogen oxides attached to the exhaust pipe through the flue of the exhaust pipe of (NOx) and oxygen (O ₂₎ It is effective for.

It is element cross-sectional explanatory drawing which shows the principle of the conventional NOx sensor. It is a schematic diagram which shows the calibration method of the conventional NOx meter. It is an explanatory diagram showing a specific example of a NOx-O ₂ meter according to the present invention. It is a graph obtained by embodiments of the calibration method of the NOx concentration of the four points of the NOx-O ₂ meter of the present invention. Is a graph obtained by embodiments of the calibration method of the NOx concentration of the NOx-O ₂ meter of the present invention (calibration method 1). Is a graph obtained by another embodiment of the calibration method of the NOx concentration of the NOx-O ₂ meter of the present invention (calibration method 2). It is a further graph obtained by another embodiment (calibration method 3) of the calibration method of the NOx concentration of the NOx-O ₂ meter of the present invention. Is a graph obtained by embodiments of the NOx-O ₂ meter oxygen four points (O ₂₎ concentration calibration method of the present invention. It is a graph obtained by embodiments of the calibration method of the oxygen (O ₂₎ concentration in the NOx-O ₂ meter of the present invention (calibration method 1). It is a graph obtained by another embodiment of the calibration method of the oxygen (O ₂₎ concentration in the NOx-O ₂ meter of the present invention (calibration method 2). It is a further graph obtained by another embodiment (calibration method 3) of the NOx-O ₂ meter oxygen (O ₂₎ concentration calibration method of the present invention.

Explanation of symbols

1 ... detecting means, 2 ... analyzing means, 10 ... gas analyzer (NOx-O ₂ meter), 11 ... gas sensor, 12 ... Kemuridokabe, 13 ... detection unit insertion opening, 14 ... flange portion, 21 ... support tube, DESCRIPTION OF SYMBOLS 22 ... Flange part, 46 ... Lead wire, 51 ... Terminal box, 52 ... Support member, 61 ... Connection pipe, 71 ... Piping for gas supply for calibration, 102 ... Sensor element, 106 ... First internal space, 108 ... Second internal space, 112... First diffusion-controlled passage, 114... Second diffusion-controlled passage, 156... First electrochemical pump cell, 158... Second electrochemical pump cell, G. , K ... flue, P ... calibration gas.

Claims (6)

In a calibration method of a gas sensor using an oxygen ion conductive solid electrolyte,
Calibration points were prepared using calibration gases containing one or two concentrations of measurement gas components, and the pumping current of the sensor at each calibration point was measured to obtain an actual measurement value, which was recorded in advance as a standard calibration curve A gas sensor calibration method, wherein a correction value is calculated from a pumping current value and an actual measurement value, and the reference calibration curve is calibrated using the correction value.   A calibration point where the concentration of the measurement gas component is 0 ppm (zero gas) is provided, and the difference between the measured value at the calibration point and the pumping current value recorded in advance as a reference calibration curve is calculated as a difference correction value. The gas sensor calibration method according to claim 1, wherein the calibration is performed by adding to the reference calibration curve.   One calibration point is provided in which the concentration of the measurement gas component is 1/10 or more of the desired measurement range (middle gas, span gas or high gas), and the actual measured value at the calibration point and the pumping current value recorded in advance as a reference calibration curve The gas sensor calibration method according to claim 1, wherein the ratio is calculated as a ratio correction value, and the ratio correction value is multiplied by the reference calibration curve for calibration.   A first calibration point where the concentration of the measurement gas component is 0 ppm (zero gas) and a second calibration point where the concentration of the measurement gas component is one-tenth or more of the desired measurement range (middle gas, span gas, or high gas) are provided. The pumping current value recorded in advance at the first calibration point is calibrated to the actual measurement value, and the ratio between the actual measurement value at the second calibration point and the pumping current value previously recorded as the reference calibration curve is calculated as a ratio correction value. And calibrating the ratio correction value by multiplying the reference calibration curve in a portion excluding the first calibration point.   A gas analyzer comprising the gas sensor calibration method according to claim 1.   A calibration method for a gas sensor according to at least one of claims 1 to 4, and a calibration method for a gas sensor that uses a calibration gas containing a plurality of concentrations of measurement gas components. A gas analyzer characterized in that any one calibration method can be selected from the above.

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