Ammonia gas concentration measuring method, semiconductor ammonia gas concentration measuring device, and livestock barn environment management method

Abstract

A method of measuring ammonia gas concentration according to one embodiment of the present invention enables accurate measurement of ammonia gas concentration, and uses a semiconductor-type device for measuring ammonia gas concentration, the device comprising a sensor element for sensing, as a gas concentration, a change in resistance value that arises when a metal oxide semiconductor comes into contact with an analyte ammonia gas. The method comprises: a calibration formula creation step S10 for measuring, at the sensor element, with regard to a plurality of types of different concentrations of the ammonia gas, concentrations of the ammonia gas of a known concentration for each of a plurality of analytes of different humidities, and creating a calibration formula indicating a relationship between the concentration of the ammonia gas and an output value of the sensor element for each of the humidities of the analytes; and a calculation step S20 for calculating the concentration of the ammonia gas on the basis of the output value when the sensor element senses the ammonia gas, a sensed humidity, and at least one calibration formula selected from a plurality of the calibration formulas.

Description

Ammonia gas concentration measuring method and semiconductor ammonia gas concentration measuring device

[0001] The present invention relates to a method for measuring the concentration of ammonia gas and a semiconductor-type ammonia gas concentration measurement device. The concentration measurement method and device of the present invention detect, as the gas concentration, a change in resistance that occurs when ammonia gas to be detected comes into contact with a metal oxide semiconductor.

[0002] A semiconductor sensor element has a gas sensitive part whose main component is a metal oxide semiconductor, and when the gas to be detected comes into contact with the gas sensitive part, the metal oxide semiconductor reacts with the gas, transferring electrons. This transfer of electrons changes the resistance value of the metal oxide semiconductor, and a gas sensor equipped with a semiconductor gas detection element can detect the target gas by detecting the change in the resistance value of the metal oxide semiconductor as a sensor output.

[0003] Patent Document 1 describes a semiconductor gas detection element that has a gas sensitive portion and a catalyst layer that covers the gas sensitive portion, with the aim of providing a semiconductor gas detection element that has gas selectivity over a long period of time. The catalyst layer in the semiconductor gas detection element in this document contains a metal composite oxide in which a specific metal element is solid-dissolved in a metal oxide semiconductor containing a specific metal oxide.

[0004] JP 2008-241430 A

[0005] However, the semiconductor gas detection element described in Patent Document 1 calculates the ammonia gas concentration without considering the effect of humidity, making it difficult to measure the ammonia gas concentration with high accuracy. An object of the present invention is to provide an ammonia gas concentration measurement method and a semiconductor ammonia gas concentration measurement device that can measure the ammonia gas concentration with high accuracy.

[0006] As a means for solving the above-mentioned problems, the present invention has the following configuration: A method for measuring the concentration of ammonia gas using a semiconductor-type ammonia gas concentration measuring device having a sensor element that detects, as the gas concentration, a change in resistance that occurs when a metal oxide semiconductor comes into contact with ammonia gas to be detected, the method comprising: a calibration formula creating step of measuring the concentration of the ammonia gas, whose concentration is known, for each of a plurality of detection targets with different humidities using the sensor element, for each of the ammonia gas concentrations, and creating a calibration formula that shows the relationship between the ammonia gas concentration and an output value of the sensor element for each of the humidity of the detection targets; and a calculation step of calculating the ammonia gas concentration based on the output value of the sensor element when detecting the ammonia gas, the detected humidity, and at least one calibration formula selected from the plurality of calibration formulas.

[0007] The method for measuring the concentration of ammonia gas involves creating multiple calibration equations for different humidities, and calculating the concentration of ammonia gas using the calibration equation corresponding to the detected humidity when detecting ammonia gas. This reduces the influence of humidity and enables the concentration of ammonia gas to be detected with high accuracy.

[0008] The calculation step may include calculating the concentration of the ammonia gas based on the calibration equation created at the humidity closest to the detected humidity among the plurality of calibration equations created at different humidities. By calculating the concentration of the ammonia gas using the calibration equation created under humidity conditions closest to the detected humidity when the concentration of the ammonia gas is detected, the effect of humidity on the sensor element can be reduced.

[0009] The calculation step may calculate the concentration of ammonia gas based on the output value at the time of detection, the detected humidity, and a first calibration formula and a second calibration formula created for two of the plurality of calibration formulas. Even when there is a difference between the humidity for which the calibration formulas are created and the detected humidity, the use of the plurality of calibration formulas reduces the influence of humidity and enables the concentration of ammonia gas to be detected with high accuracy.

[0010] The humidity for which the first calibration formula is created may be the humidity closest to the detected humidity among the plurality of humidities for which the calibration formulas are created. The humidity for which the second calibration formula is created may be the humidity second closest to the detected humidity among the plurality of humidities for which the calibration formulas are created. The detected humidity may be a value between the humidity for which the first calibration formula is created and the humidity for which the second calibration formula is created.

[0011] When calculating the concentration of ammonia gas based on two calibration equations, the use of the first and second calibration equations that satisfy the above-mentioned relationship with the detected humidity can more effectively reduce the influence of humidity, thereby improving the accuracy of measuring the concentration of ammonia gas.

[0012] When the detected humidity is HQ, the humidity for which the first calibration formula is created is H1, and the humidity for which the second calibration formula is created is H2, the calculation step determines O1 and O2 such that H1, H2, HQ, O1, O2, and OQ satisfy the following formula (1), where OQ is the output value at the time of detection, O1 is the output value at the ammonia gas concentration CQ in the first calibration formula, and O2 is the output value at the ammonia gas concentration CQ in the second calibration formula. The ammonia gas concentration CQ is determined to be the ammonia gas concentration when the output value in the first calibration formula is O1 and the output value in the second calibration formula is O2. HQ - H1:HQ - H2 = OQ - O1:OQ - O2 ... (1) With the above configuration, the true concentration CQ of the detected ammonia gas can be calculated based on the detected humidity HQ and the output value OQ at the time of detection.

[0013] The semiconductor ammonia gas concentration measuring device may be equipped with a heater capable of heating the sensor element, and may use the sensor element having the characteristic that when a plurality of types of ammonia gas with different concentrations are measured by setting the heating temperature of the heater to a predetermined temperature, the output decreases as the concentration of the ammonia gas increases under a plurality of conditions where the humidity of the detection object is different.

[0014] The semiconductor ammonia gas concentration measuring device may be equipped with a heater capable of heating the sensor element, and may use a sensor element having a characteristic that, when ammonia gas at concentrations of 20 ppm, 33 ppm, 66 ppm, and 100 ppm is measured at a heating temperature of the sensor element of 300°C, the output decreases as the concentration of the ammonia gas increases, regardless of whether the humidity of the detection object is 30%, 57%, or 66%.

[0015] By using a sensor element whose output decreases as the concentration of ammonia gas increases, calibration can be easily and accurately performed in measuring the concentration of ammonia gas.

[0016] The metal oxide semiconductor may be doped with a tungsten oxide-based metal oxide. The metal oxide semiconductor may be doped with tungsten trioxide as the metal oxide. By using the metal oxide semiconductor, the linearity of the calibration formula is improved, thereby improving the measurement accuracy of the ammonia gas concentration.

[0017] The calibration formula creating step may create the calibration formula, which formulates the relationship between the concentration C of the ammonia gas, whose concentration is known, and the output value of the sensor element when the ammonia gas is detected, under constant humidity, for at least three humidities within a humidity range in which the semiconductor-type ammonia gas concentration measuring device is used. The calculation step may, when the measured detected humidity Hm is a value between humidity Hi and humidity Hj included in the humidities for which the calibration formula is created in the calibration formula creating step, calculate a relational expression Rm(C) that shows the relationship between the concentration of the ammonia gas at the measured detected humidity Hm and the output value of the sensor element associated with changes in the resistance value, based on the calibration formula Ri(C) at humidity Hi and the calibration formula Rj(C) at humidity Hj, and calculate the concentration of the ammonia gas that becomes the output value when the ammonia gas is detected in the relational expression Rm(C) as the detected concentration of the ammonia gas.

[0018] The calibration equations Ri(C) and Rj(C) are expressed by the following equations (2) and (3): R(Hi)=Ri(C)=ai×C+bi ... (2) R(Hj)=Rj(C)=aj×C+bj ... (3) (In equations (2) and (3), ai, bi, aj, and bj are constants.) The relational equation Rm(C) at the detected humidity Hm is expressed by the following equation (4): Rm(C)=A×C+B ... (4) A=ai+[(aj-ai) / (Hj-Hi)]×(Hm-Hi) B=bi+[(bj-bi) / (Hj-Hi)]×(Hm-Hi) The ammonia gas concentration Cm at the detected humidity Hm may be calculated by the following equation (5): Cm=(Rm(C)-B) / A...(5)

[0019] The semiconductor-type ammonia gas concentration measuring device is provided with an ammonia gas detection sensor including a sensor element that detects, as gas concentration, a change in resistance that occurs when a metal oxide semiconductor material comes into contact with ammonia gas to be detected, and a heater that heats the metal oxide semiconductor material of the sensor element, and a humidity sensor. The semiconductor-type ammonia gas concentration measuring device can accurately measure the ammonia gas concentration because the humidity measured by the humidity sensor during concentration measurement can be used to calculate the ammonia gas concentration.

[0020] The semiconductor ammonia gas concentration measuring device may further include a memory unit that measures the ammonia gas concentration, the concentration of which is known, for each of a plurality of detection targets having different humidities using the sensor element, for each of the ammonia gas concentrations, and stores a calibration equation that indicates the relationship between the ammonia gas concentration and the output value of the sensor element for each of the humidity levels of the detection targets, and a calculation unit that calculates the ammonia gas concentration based on the output value of the sensor element when detecting ammonia gas, the detected humidity, and at least one calibration equation selected from the plurality of calibration equations.The semiconductor ammonia gas concentration measuring device can accurately measure the ammonia gas concentration by using the humidity measured by the humidity sensor during measurement by the ammonia gas detection sensor to calculate the ammonia gas concentration.

[0021] According to the present invention, when calculating the concentration of ammonia gas based on the output of the sensor element, the detected humidity at the time of detecting ammonia gas is used, thereby making it possible to measure the concentration of ammonia gas with high accuracy.

[0022] It is a block diagram of a semiconductor type ammonia gas concentration measuring device. It is a graph showing the relationship between the concentration of ammonia gas and the output of the sensor element. It is a graph showing the relationship between the concentration of ammonia gas and the output of the sensor element. It is a graph showing the relationship between the concentration of ammonia gas and the output of the sensor element. It is a graph showing the relationship between the concentration of ammonia gas and the output of the sensor element. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2A for each ambient temperature at a humidity of 30%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2A for each ambient temperature at a humidity of 60%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2A for each ambient temperature at a humidity of 75%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2B for each ambient temperature at a humidity of 30%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2B for each ambient temperature at a humidity of 60%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2B for each ambient temperature at a humidity of 75%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2C for each ambient temperature at a humidity of 30%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2C for each ambient temperature at a humidity of 60%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2C for each ambient temperature at a humidity of 75%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2D for each ambient temperature at a humidity of 30%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2D for each ambient temperature at a humidity of 60%. It is a graph showing the relationship between the heater temperature and the output of the sensor element in FIG. 2D for each ambient temperature at a humidity of 75%. It is a flowchart of a method for measuring the concentration of ammonia gas. It is a graph explaining the calibration formula creation step and the calculation step. It is a graph showing the relationship between calibration curve 1, calibration curve 2, the detected humidity when measuring the ammonia gas to be detected, and the output value of the sensor element. It is a graph showing the relationship between calibration curve 1, calibration curve 2, the detected humidity when measuring the ammonia gas to be detected, and the output value of the sensor element in 3D.1 is a graph illustrating a calibration formula creation step (calibration) in a method for measuring the concentration of ammonia gas. 2 is a graph showing the output of a sensor element in a measurement example in a chicken coop. 3 is a graph showing the detected humidity in a measurement example in a chicken coop. 4 is a graph showing the calculation result of the concentration of ammonia gas based on the output of a sensor element and the detected humidity in a measurement example in a chicken coop.

[0023] [Semiconductor-type ammonia gas concentration measuring device] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a block diagram showing a semiconductor-type ammonia gas concentration measuring device 1 of this embodiment. As shown in the figure, the semiconductor-type ammonia gas concentration measuring device 1 includes an ammonia gas detection sensor 2 and a humidity sensor 3.

[0024] The ammonia gas detection sensor 2 includes a sensor element 21 and a heater 23. The sensor element 21 has a metal oxide semiconductor material 22, and detects a change in resistance value that occurs when the metal oxide semiconductor material 22 comes into contact with ammonia gas, which is the detection target, as the gas concentration.

[0025] From the viewpoint of providing a sensor element 21 with output characteristics that are highly linear with respect to the concentration of ammonia gas, the metal oxide semiconductor material 22 is preferably a tungsten oxide-based metal oxide, and more preferably tungsten trioxide.

[0026] The sensor element 21 included in the ammonia gas detection sensor 2 is preferably a metal oxide sensor (MEMS-MOx sensor) fabricated using MEMS (Micro Electro Mechanical Systems) technology, which integrates electronic circuits and the like on a substrate using microfabrication technology.

[0027] The MEMS-MOx sensor has a small heat capacity because it is fabricated in a minute area on a thin membrane. Therefore, when a MEMS-MOx sensor is used as the sensor element 21, there is an advantage in that the current value flowing through the heater 23 that heats the sensor element 21 is small. In addition, since it can be easily packaged together with other sensors and a digital signal processing IC, it is advantageous in terms of miniaturizing the semiconductor-type ammonia gas concentration measuring device 1.

[0028] The heater 23 is used to heat the metal oxide semiconductor material 22 of the sensor element 21 .

[0029] The humidity sensor 3 measures the humidity of a detection sample containing ammonia gas when detecting ammonia gas, which is the detection target of the ammonia gas detection sensor 2. The humidity sensor 3 is provided based on the knowledge that the output of a sensor element when detecting ammonia gas changes depending on the humidity of the detection target. By measuring the detected humidity with the humidity sensor 3 during measurement by the ammonia gas detection sensor 2, it becomes possible to calculate the concentration of ammonia gas using the detected humidity. Therefore, the effect of the detected humidity on the output of the sensor element 21 can be reduced, and the concentration of ammonia gas can be measured with high accuracy.

[0030] The semiconductor-type ammonia gas concentration measuring device 1 of this embodiment includes a storage unit 4 and a calculation unit 5 in addition to an ammonia gas detection sensor 2 and a humidity sensor 3 .

[0031] The memory unit 4 stores a calibration formula showing the relationship between the concentration of ammonia gas at a predetermined humidity and the output value of the sensor element 21, and a general memory means is used. The calibration formula stored in the memory unit 4 is created based on the results of measuring ammonia gas with a known concentration using the sensor element 21 under multiple conditions with different ammonia gas concentrations for multiple detection targets with different humidities. The measurement of ammonia gas used to create the calibration formula is performed by setting the heater 23 of the ammonia gas detection sensor 2 shown in Figure 1 at a constant temperature.

[0032] The calculation unit 5 calculates the concentration of ammonia gas based on the output value of the sensor element 21 when ammonia gas is detected, the detected humidity, and at least one calibration formula selected from a plurality of calibration formulas stored in the memory unit 4. The calculation unit 5 is configured as part of a central processing unit (CPU) or a program. The creation of the calibration formula to be stored in the memory unit 4 and the calculation of the ammonia gas concentration by the calculation unit 5 will be described later as a method for measuring the concentration of ammonia gas.

[0033] [Type of Metal Oxide Added and Properties of Metal Oxide Semiconductor Material] Figures 2A to 2D are graphs showing the relationship between the concentration of ammonia gas and the output of a sensor element 21 equipped with a metal oxide semiconductor material 22 to which various metal oxides have been added, for each humidity level. In Figure 2A, SnO2 and VO5 are added as metal oxides to the metal oxide semiconductor material 22; in Figure 2B, In2O3; in Figure 2C, SnO2 and Pd; and in Figure 2D, WO3 and OsO4. When detecting ammonia gas using the sensor element 21, the heater 23 was set to a temperature of 400°C in the measurement example shown in Figure 2A, and 300°C in the measurement examples shown in Figures 2B, 2C, and 2D. The graphs shown in Figures 2A to 2D are examples of measurement results necessary for creating a calibration formula in the calibration formula creation step described below.

[0034] As shown in these figures, the output of the sensor element 21 changes with the change in the concentration of ammonia gas, and is also significantly affected by the humidity of the measurement target containing ammonia gas. In other words, when the concentration of ammonia gas is the detection target, it was found that the output of the sensor element 21 changes depending on the humidity. Therefore, if the concentration of ammonia gas is calculated based on the output of the sensor element 21 without considering the influence of humidity, it will be affected by the detected humidity at the time of detection, making it difficult to measure the concentration of ammonia gas with high accuracy.

[0035] 1, the semiconductor-type ammonia gas concentration measuring device 1 is equipped with a humidity sensor 3 in addition to an ammonia gas detection sensor 2. Therefore, when calculating the concentration of ammonia gas, the detected humidity measured by the humidity sensor 3 can be used in addition to the output of the ammonia gas detection sensor 2. Therefore, it is possible to accurately calculate the concentration of ammonia gas based on the detected humidity when ammonia gas is detected.

[0036] 2A to 2D, the output characteristics of the sensor element 21 vary depending on the type of metal oxide added to the metal oxide semiconductor material 22. The sensor element 21 shown in FIG. 2D , which includes the metal oxide semiconductor material 22 doped with WO and OsO, exhibits a characteristic in which, when measuring a variety of ammonia gases with different concentrations at a predetermined heating temperature of the heater 23, the output decreases with increasing ammonia gas concentration under a variety of conditions with different humidity levels in the detection target, i.e., the humidity levels of the moisture contained in the ammonia gas atmosphere in the detection target. Specifically, when measuring ammonia gases with concentrations of 20 ppm, 33 ppm, 66 ppm, and 100 ppm at a heater 23 temperature of 300°C, the output of the sensor element 21 continuously decreases with increasing ammonia gas concentration, regardless of whether the humidity level in the detection target is 30%, 57%, or 66%.

[0037] That is, the sensor element 21 including the metal oxide semiconductor material 22 to which WO3 and OsO4 are added has a higher linearity of output with respect to the concentration of ammonia gas than the sensor element 21 including the metal oxide semiconductor material 22 to which other metal oxides are added. Therefore, from the viewpoint of measuring the concentration of ammonia gas with high accuracy, the sensor element 21 including the metal oxide semiconductor material 22 to which WO3 and OsO4 are added is preferable.

[0038] 2A to 2D while changing the temperature of the heater 23 at 30%, 60%, and 75% humidity in a constant temperature and humidity chamber containing no ammonia gas. The results are shown in Figures 3A to 3L. The output of the sensor element 21 was least affected by humidity and ambient temperature when the sensor element 21 included the metal oxide semiconductor material 22 to which WO3 and OsO4 had been added and the heater 23 was set to a temperature of 300°C.

[0039] 3J to 3L, the sensor element 21 shown in Fig. 2D obtained an output of about 57,000 regardless of humidity and ambient temperature by setting the temperature of the heater 23 to 300°C. Therefore, from the viewpoint of suppressing the effects of humidity and ambient temperature on the output and improving measurement accuracy, it is preferable to use a sensor element 21 including a metal oxide semiconductor material 22 to which WO3 and OsO4 have been added, and to set the temperature of the heater 23 during measurement to 250 to 350°C, and more preferably 280 to 320°C.

[0040] In addition to the metal oxides used in the measurements shown in FIGS. 2A to 2D, other metal oxides that can be added to the metal oxide semiconductor material 22 include MnO, CuO, FeO, CrO, MoO, ZnO, CoO, TiO, and NiO.

[0041] [Method for measuring ammonia gas concentration] The method for measuring ammonia gas concentration using a semiconductor ammonia gas concentration measuring device will be described below. Fig. 4 is a flowchart of the method for measuring ammonia gas concentration according to this embodiment. The method for measuring ammonia gas concentration includes a calibration formula creation step S10 and a calculation step S20.

[0042] In the calibration equation creation step S10, ammonia gas is measured at a plurality of concentrations, each of which is clear for each humidity, using an ammonia gas detection sensor equipped with a sensor element under a plurality of conditions with different humidity levels. Based on the measurement results, a calibration equation is created that shows the relationship between the ammonia gas concentration and the output value of the sensor element for each humidity level.

[0043] The calibration formula creation step S10 may be performed on the sensor element (ammonia gas detection sensor) that detects ammonia gas alone, rather than on the semiconductor ammonia gas concentration measuring device. The calibration formula creation step S10 may be performed on the ammonia gas detection sensor alone, and the created calibration formula may be stored in a memory unit. The semiconductor ammonia gas concentration measuring device may be configured using the memory unit in which the calibration formula is recorded, the ammonia gas detection sensor, the humidity sensor, and the calculation unit.

[0044] By measuring ammonia gas with a known concentration using a sensor element, the relationship between the ammonia gas concentration and the output of the sensor element can be obtained. By performing this measurement for multiple types of ammonia gas with known concentrations under constant humidity conditions, the relationship between the ammonia gas concentration and the output of the sensor element can be obtained.

[0045] The temperature at which the calibration formula is prepared is the temperature at which the metal oxide semiconductor material 22 is heated by the heater 23 of the sensor element 21, and is set, for example, in the range of about 100 to 400° C. The number of ammonia gases with different known concentrations measured to prepare the calibration formula may be two or more, but from the viewpoint of the efficiency and accuracy of preparing the calibration curve, three to five is preferable.

[0046] The concentration of ammonia gas to be measured is not particularly limited. When measuring the output of the sensor element at four different concentrations, for example, ammonia gas concentrations of 15 to 25 ppm, 28 to 38 ppm, 61 to 71 ppm, and 90 to 100 ppm are measured.

[0047] 5 is a graph illustrating the calibration formula creation step S10 and the calculation step S20, showing an example of a calibration curve created based on the ammonia gas concentration and the sensor element output in FIG. 2D. In the example shown in the figure, the relationship between the ammonia gas concentration and the sensor element output is measured at humidities of 30%, 57%, and 66%, and the calibration formula is created based on the measurement results at each of these humidities. The calibration formula showing the calibration curve can be obtained as a regression line using the least squares method for the measurement results at each humidity.

[0048] In calculation step S20, the concentration of ammonia gas is calculated based on at least one calibration formula selected from the plurality of calibration formulas, the output value of the sensor element 21 when detecting ammonia gas, and the detected humidity. The plurality of calibration formulas are created in calibration formula creation step S10. The output of the sensor element and the detected humidity, which is the humidity detected by the humidity sensor, are obtained when ammonia gas of unknown concentration is measured.

[0049] In the calculation step S20, the ammonia gas concentration can be calculated, for example, by using a calibration formula created at a humidity closest to the detected humidity among multiple calibration formulas created at different humidities. The smaller the difference between the humidity conditions when the calibration formula was created and the detected humidity, the smaller the error between the calculated ammonia gas concentration and the true ammonia gas concentration. Therefore, the effect of humidity on the ammonia gas concentration can be reduced, and the ammonia gas concentration can be calculated with high accuracy.

[0050] 5, the calibration formula used to calculate the concentration of ammonia gas is a 30% humidity calibration formula when the detected humidity is 38.5% or less, a 57% humidity calibration formula when the detected humidity is greater than 38.5% and less than 61.5%, and a 66% humidity calibration formula when the detected humidity is greater than 61.5%. In this way, by using a calibration formula created for a humidity closest to the detected humidity, the concentration of ammonia gas can be detected with high accuracy, taking into account the influence of humidity.

[0051] Alternatively, the ammonia gas concentration may be calculated based on a first calibration equation and a second calibration equation, each of which is created under two different humidity conditions, rather than using a single calibration equation. By using multiple calibration equations, the effect of the detected humidity on the output value of the sensor element 21 can be more appropriately reflected. Therefore, by calculating the ammonia gas concentration using two calibration equations, the accuracy of measuring the ammonia gas concentration is improved compared to when a single calibration equation is used.

[0052] In the example of FIG. 5, for example, a combination of calibration formulas for 30% and 57% humidity, 57% and 66% humidity, or 66% and 30% humidity may be used.

[0053] As described above, the smaller the difference between the humidity conditions when the calibration formula was created and the detected humidity, the more the influence of humidity can be reduced, and therefore the smaller the error between the calculated ammonia gas concentration and the true ammonia gas concentration. Even in this case, from the viewpoint of more effectively reducing the influence of humidity, it is desirable to use a calibration formula created under humidity conditions as close as possible to the detected humidity. In light of the above, it is preferable to use the calibration formula for the humidity closest to the detected humidity among the multiple humidity conditions for which the calibration formulas were created as the first calibration formula. Furthermore, it is preferable to use the calibration formula for the humidity second closest to the detected humidity among the multiple humidities for which the calibration formulas were created as the second calibration formula. The first and second calibration formulas may be selected so that the detected humidity is included between the humidity for which the first calibration formula was created and the humidity for which the second calibration formula was created.

[0054] When using the measurement results shown in Figure 5, for example, if the detected humidity is 50%, which is between 30% and 57%, the calibration formula for the 57% humidity, which is closest to the detected humidity of 50%, is designated as the first calibration formula, and the calibration formula for the 30% humidity, which is second closest to the detected humidity of 50%, is designated as the second calibration formula. Note that if the detected humidity is 48%, 48% humidity is the intermediate value between 30% humidity and 66% humidity. Therefore, even though the detected humidity is between 30% humidity and 57%, the calibration formula for 66% humidity may be used as the second calibration formula. By using a calibration formula created for a humidity close to the detected humidity, the influence of humidity can be more effectively reduced, thereby improving the accuracy of ammonia gas concentration measurement.

[0055] Figure 6A shows the relationship between calibration curve 1 obtained based on measurements at humidity H1 and calibration curve 2 obtained based on measurements at humidity H2, and the detected humidity HQ and the output value OQ of the sensor element when measuring the ammonia gas to be detected.

[0056] 6B is a graph showing the relationship between ammonia gas concentration, sensor element output, and humidity (detected humidity), where the X-coordinate of the mutually orthogonal XYZ coordinate system represents ammonia gas concentration, the Y-coordinate represents the sensor element output, and the Z-coordinate represents the humidity at the time of creating the calibration curve and the humidity at the time of measurement.

[0057] As shown in Figure 6B, when the concentration of ammonia gas is constant, the output value of the sensor element changes linearly with changes in humidity. Using this characteristic, the true concentration CQ of the detected ammonia gas can be calculated as follows:

[0058] Let HQ be the detected humidity, H1 be the humidity for which the first calibration equation is created, and H2 be the humidity for which the second calibration equation is created. In this case, in calculation step S20, the output value at the time of detection is OQ, the output value of the ammonia gas concentration CQ in the first calibration equation is O1, and the output value of the ammonia gas concentration CQ in the second calibration equation is O2. At this time, O1 and O2 may be found such that H1, H2, HQ, O1, O2, and OQ satisfy the following equation (1), and the ammonia gas concentration CQ at which the output value in the first calibration equation is O1 and the output value in the second calibration equation is O2 may be taken as the ammonia gas concentration. HQ - H1:HQ - H2 = OQ - O1:OQ - O2 (1) By using the above equation (1), the true concentration CQ of the detected ammonia gas can be calculated based on the detected humidity HQ and the output value OQ at the time of detection.

[0059] 6A and 6B show the case where the detected humidity HQ is between the humidity H1 used to create calibration curve 1 and the humidity H2 used to create calibration curve 2, i.e., the case where H1<HQ<H2. However, even in the cases of HQ

[0060] [Modification] The calibration equation creation step S10 may create a calibration equation that formulates the relationship between the concentration C of ammonia gas whose concentration is known and the output value of the sensor element when ammonia gas is detected, under constant humidity, for at least three humidities within the humidity range in which the semiconductor-type ammonia gas concentration measuring device is used.

[0061] ​In this case, when the measured detected humidity Hm is a value between the humidity Hi and humidity Hj included in the humidities for which the calibration formula was created in the calibration formula creation step S10, a calculation step S20 calculates a relational expression Rm(C) that shows the relationship between the ammonia gas concentration at the measured detected humidity and the output value of the sensor element associated with changes in resistance, based on the calibration formula Ri(C) at humidity Hi and the calibration formula Rj(C) at humidity Hj. Then, the ammonia gas concentration that becomes the output value when ammonia gas is detected in the relational expression Rm(C) is calculated as the detected ammonia gas concentration.

[0062] For example, in calibration formula creation step S10, calibration formula 1, calibration formula 2, and calibration formula 3 are created for three humidities H1, H2, and H3. Here, it is assumed that H1<H2<H3. In this case, when the detected humidity Hm is H1<Hm<H2, in calculation step S20, a relational formula Rm(C) showing the relationship between the measured ammonia gas concentration at the detected humidity Hm and the output value of the sensor element associated with changes in resistance is calculated based on calibration formula R1(C) at humidity H1(Hi) as calibration formula Ri(C) at humidity Hi and calibration formula R2(C) at humidity H2(Hj) as calibration formula Rj(C) at humidity Hj.

[0063] 7 is an explanatory diagram illustrating a method for measuring the concentration of ammonia gas, in which a calibration equation is created by a modified method and the true concentration of ammonia gas is calculated. As shown in the figure, the calibration equations Ri(C) and Rj(C) expressed by equations (2) and (3) are determined based on the measurement results. R(Hi) = Ri(C) = ai x C + bi ... (2) R(Hj) = Rj(C) = aj x C + bj ... (3) (In equations (2) and (3), ai, bi, aj, and bj are constants.)

[0064] In this case, the relational expression Rm(C) for the detected humidity Hm is expressed by the following expression (4) using the constants in the calibration expressions Ri(C) and Rj: Rm(C) = A × C + B (4) A = ai + [(aj - ai) / (Hj - Hi)] × (Hm - Hi) B = bi + [(bj - bi) / (Hj - Hi)] × (Hm - Hi)

[0065] Therefore, the concentration Cm of ammonia gas at the detected humidity Hm can be calculated by the following formula (5): Cm=(Rm(C)-B) / A (5)

[0066] [Example of calibration curve] Using the modified method shown in Fig. 7, the following calibration equation was obtained from the measurement results of a sensor element in which WO3 and OsO4 were added as metal oxides to a metal oxide semiconductor material. As a result of determining the slope using a linear approximation equation, the intercept values ​​for humidities of 30%, 57%, and 66% were almost the same, and therefore the intercepts of the calibration equation at each humidity were set to 57,000.

[0067] The sensor element used to measure the ammonia gas concentration was a different individual element, but had the same composition as the sensor element shown in Figures 2D and 5. Therefore, the sensor element used in this measurement example and the sensor element shown in Figures 2D and 5 both exhibit a simple decrease in ammonia gas concentration, tending to decrease more at low humidity and less at high humidity, but the intercept and slope of the linear approximation equation are different.

[0068] When the humidity is 30%, R = -46.611 x C + 57000 ... (6) When the humidity is 57%, R = -28.743 x C + 57000 ... (7) When the humidity is 66%, R = -10.022 x C + 57000 ... (8)

[0069] Since the intercepts bi and bj of each calibration equation are set to 57,000, the above equations (2) to (5) become the following equations (2a) to (5a). R(Hi) = Ri(C) = ai x C + 57,000 ... (2a) R(Hj) = Rj(C) = aj x C + 57,000 ... (3a) (In equations (2a) and (3a), ai and aj are constants.) Rm(C) = A x C + 57,000 ... (4a) A = ai + [(aj - ai) / (Hj - Hi)] x (Hm - Hi) Cm = (Rm(C) - 57,000) / A ... (5a)

[0070] When the detected humidity Hm is a value between 30% and 57%, that is, when 30% < Hm < 57%, the above formula (6) corresponds to formula (2a), and formula (7) corresponds to formula (3a). Substituting the constants in formulas (6) and (7) into formulas (4a) and (5a) gives the following: Rm(C) = A × C + 57000 ... (4b) A = -46.61 + [(-28.743 + 46.611) / (57 - 30)] × (Hm - 30) Cm = (Rm(C) - 57000) / A ... (5b)

[0071] When the detected humidity Hm is between 57% and 66%, i.e., when 57% < Hm < 66%, the above formula (7) corresponds to formula (2a), and the above formula (8) corresponds to formula (3a). Substituting the constants in formulas (6) and (7) into formulas (4a) and (5a) gives the following: Rm(C) = A × C + 57000 ... (4b) A = -28.743 + [(-10.022 + 28.743) / (66 - 57)] × (Hm - 57) Cm = (Rm(C) - 57000) / A ... (5b)

[0072] The ammonia gas concentration measurement method of this embodiment is based on the finding that the output value of a sensor element obtained as a result of measuring the ammonia gas concentration at a constant ambient temperature has humidity dependency. Furthermore, the concentration measurement method corresponds to a "calibration" step in the manufacturing process of a semiconductor-type ammonia gas concentration measurement device equipped with a sensor element, in which the output of the sensor element relative to the ammonia gas concentration is measured in an environment where the values ​​of temperature and humidity are controlled, and a correction formula for calculating the ammonia gas concentration is determined and recorded in the memory unit of the semiconductor-type ammonia gas concentration measurement device.

[0073] [Measurement Example] Figure 8A is a graph showing the output of the sensor element in measurements taken at a chicken farm poultry house, Figure 8B is a graph showing the detected humidity in the measurements, and Figure 8C is a graph showing the ammonia gas concentration calculated based on the sensor element output and detected humidity in the measurements. These graphs show the results of measuring the ammonia gas concentration using the semiconductor ammonia gas concentration measuring device of this embodiment while walking the route of six chicken houses over approximately 7,000 seconds. That is, the sensor element output data and detected humidity data were acquired, and calculations were performed based on the sensor element output and detected humidity to determine the ammonia gas concentration using the ammonia gas concentration measurement method of this embodiment. The ammonia gas concentration shown in Figure 8C was calculated using the above formulas (4b) and (5b).

[0074] The calculated values ​​in Figure 8C using the detected humidity shown in Figure 8B clearly show the differences in ammonia gas concentration along the chicken coop circulation route more clearly than the sensor element output shown in Figure 8A. For example, it can be seen that the measurement points indicated by circles in the graphs of Figures 8A to 8C at 2534 seconds, 4725 seconds, and 6454 seconds after the start of measurement have significantly higher ammonia gas concentrations than the other measurement points.

[0075] Note that the circled portions of the graphs in Figures 8A to 8C represent bottom values ​​in Figure 8A, whereas they represent peak values ​​in Figures 8B and 8C. This means that the smaller the output value of the sensor element, the higher the concentration of detected ammonia gas, and the higher the humidity, the higher the ammonia gas concentration.

[0076] It is known that the higher the humidity in a chicken coop, the higher the concentration of ammonia gas emitted from chicken manure, and the results shown in Figures 8A to 8C reflect this phenomenon. By identifying areas in the chicken coop with high ammonia gas concentrations, measures can be taken to reduce the ammonia gas concentration, thereby promoting chicken growth and improving the working environment within the chicken coop.

[0077] The accuracy of ammonia gas detection was improved by detecting humidity when measuring ammonia gas concentration and calculating the ammonia gas concentration using the detected humidity. Because ammonia gas concentration is important in environmental management of livestock houses such as chicken coops, accurately detecting ammonia gas concentration is useful for maintaining the livestock house environment and improving the health of livestock.

[0078] The embodiments disclosed in this specification are illustrative in all respects and are not limited to these embodiments. The scope of the present invention is defined by the claims rather than by the description of the above-described embodiments alone, and is intended to include all modifications within the meaning and scope of the claims.

[0079] The present invention is useful as an ammonia gas concentration measuring method and a semiconductor ammonia gas concentration measuring device used in the management of livestock barns, for example.

[0080] 1: Semiconductor type ammonia gas concentration measuring device 2: Ammonia gas detection sensor 21: Sensor element 22: Metal oxide semiconductor material 23: Heater 3: Humidity sensor 4: Memory unit 5: Calculation unit

Claims

1. A method for measuring the concentration of ammonia gas using a semiconductor-type ammonia gas concentration measuring device having a sensor element that detects a change in resistance value that occurs when a metal oxide semiconductor comes into contact with ammonia gas to be detected as a gas concentration, comprising: The ammonia gas to be detected is ammonia gas generated from feces excreted by livestock in a livestock barn, a calibration formula creation step of measuring the concentration of the ammonia gas, the concentration of which is known, for each of a plurality of detection targets having different humidities using the sensor element for a plurality of types of ammonia gas having different concentrations, and creating a calibration formula that indicates the relationship between the concentration of the ammonia gas and the output value of the sensor element for each of the humidity of the detection targets; a calculation step of calculating the concentration of the ammonia gas based on the output value of the sensor element when detecting the ammonia gas, the detected humidity, and at least one calibration formula selected from the plurality of calibration formulas.

2. 2. The method for measuring ammonia gas concentration according to claim 1, wherein the calculation step calculates the concentration of the ammonia gas based on the calibration formula created at the humidity closest to the detected humidity, among the plurality of calibration formulas created at different humidities.

3. 2. The method for measuring ammonia gas concentration according to claim 1, wherein the calculating step calculates the concentration of the ammonia gas based on the output value at the time of detection, the detected humidity, and a first calibration formula and a second calibration formula created for two of the humidities from among the plurality of calibration formulas.

4. 4. The method for measuring a concentration of ammonia gas according to claim 3, wherein the humidity for which the first calibration formula is created is closest to the detected humidity among the plurality of humidities for which the calibration formulas are created.

5. 5. The method for measuring a concentration of ammonia gas according to claim 4, wherein the humidity for which the second calibration formula is created is the second closest to the detected humidity among the plurality of humidities for which the calibration formulas are created.

6. 4. The method for measuring a concentration of ammonia gas according to claim 3, wherein the detected humidity is a value between the humidity for which the first calibration formula is created and the humidity for which the second calibration formula is created.

7. When the detected humidity is HQ, the humidity for which the first calibration equation is created is H1, and the humidity for which the second calibration equation is created is H2, The calculation step The output value at the time of detection is OQ, The output value when the concentration of the ammonia gas in the first calibration equation is CQ is O1, When the output value at the concentration C of the ammonia gas in the second calibration equation is O2, Determine O1 and O2 such that H1, H2, HQ, O1, O2, and OQ satisfy the following formula (1): The concentration CQ of the ammonia gas at which the output value becomes O1 in the first calibration formula and the output value becomes O2 in the second calibration formula is defined as the concentration of the ammonia gas. HQ-H1:HQ-H2=OQ-O1:OQ-O2...(1) The method for measuring the concentration of ammonia gas according to claim 3.

8. The semiconductor ammonia gas concentration measuring device includes a heater capable of heating the sensor element, When a plurality of types of ammonia gases having different concentrations are measured at a predetermined heating temperature of the heater, Under a plurality of conditions where the humidity of the detection target is different, 2. The method for measuring the concentration of ammonia gas according to claim 1, wherein the sensor element has a characteristic that its output decreases as the concentration of the ammonia gas increases.

9. The semiconductor ammonia gas concentration measuring device includes a heater capable of heating the sensor element, When the ammonia gas having concentrations of 20 ppm, 33 ppm, 66 ppm and 100 ppm was measured at a heating temperature of the sensor element of 300° C., In any of the cases where the humidity of the detection target is 30%, 57%, and 66%, 2. The method for measuring the concentration of ammonia gas according to claim 1, wherein the sensor element has a characteristic that its output decreases as the concentration of the ammonia gas increases.

10. 2. The method for measuring the concentration of ammonia gas according to claim 1, wherein the metal oxide semiconductor is doped with a tungsten oxide-based metal oxide.

11. 2. The method for measuring the concentration of ammonia gas according to claim 1, wherein the metal oxide semiconductor contains tungsten trioxide as a metal oxide.

12. The calibration formula creation step includes: At least three humidity levels within the humidity range in which the semiconductor-type ammonia gas concentration measuring device is used are used, and a calibration equation is created that formulates the relationship between the concentration C of the ammonia gas, the concentration of which is known, and the output value of the sensor element when detecting the ammonia gas, under a constant humidity condition; The calculation step When the measured detected humidity Hm is a value between the humidity Hi and humidity Hj included in the humidities for which the calibration formula was created in the calibration formula creating step, a relational formula Rm(C) indicating the relationship between the concentration of the ammonia gas at the measured detected humidity Hm and the output value of the sensor element associated with a change in the resistance value is calculated based on the calibration formula Ri(C) at the humidity Hi and the calibration formula Rj(C) at the humidity Hj; 2. The method for measuring the concentration of ammonia gas according to claim 1, wherein the concentration of the ammonia gas that becomes the output value when the ammonia gas is detected in the relational expression Rm(C) is calculated as the concentration of the detected ammonia gas.

13. The calibration equations Ri(C) and Rj(C) are expressed by the following equations (2) and (3): R(Hi)=Ri(C)=ai×C+bi…(2) R(Hj)=Rj(C)=aj×C+bj…(3) (In equations (2) and (3), ai, bi, aj, and bj are constants.) The relational expression Rm(C) for the detected humidity Hm is expressed by the following expression (4): Rm(C)=A×C+B…(4) A=ai+[(aj-ai) / (Hj-Hi)]×(Hm-Hi) B=bi+[(bj-bi) / (Hj-Hi)]×(Hm-Hi) The concentration Cm of the ammonia gas at the detected humidity Hm is calculated by the following formula (5): Cm=(Rm(C)-B) / A...(5) The method for measuring the concentration of ammonia gas according to claim 12.

14. an ammonia gas detection sensor including a sensor element that detects a change in resistance value that occurs when a metal oxide semiconductor material comes into contact with ammonia gas to be detected, as a gas concentration, and a heater that heats the metal oxide semiconductor material of the sensor element; A semiconductor-type ammonia gas concentration measuring device equipped with a humidity sensor.

15. a storage unit that measures the concentration of the ammonia gas, the concentration of which is known, for each of a plurality of detection targets having different humidities using the sensor element for a plurality of types of ammonia gas having different concentrations, and stores a calibration formula that indicates the relationship between the concentration of the ammonia gas and the output value of the sensor element for each humidity of the detection target; 15. The semiconductor-type ammonia gas concentration measuring device according to claim 14, further comprising: a calculation unit that calculates the concentration of the ammonia gas based on the output value of the sensor element when detecting the ammonia gas, the detected humidity, and at least one calibration formula selected from the plurality of calibration formulas.

16. While moving along a patrol route set in a livestock barn, the semiconductor ammonia gas concentration measuring device according to claim 14 or claim 15 is used to acquire output data from the sensor element and detected humidity data from the humidity sensor, Implementing the ammonia gas concentration measurement method according to any one of claims 1 to 13 to measure the ammonia gas concentration in the livestock house; From the measured ammonia gas concentration, a location in the livestock house where the ammonia gas concentration is high is identified, Take measures to reduce the concentration of ammonia gas in the identified location. Environmental management methods for livestock barns, including: