Ion concentration measurement method, odor measurement method, and odor measurement device

Abstract

To provide an ion concentration measurement method, etc., capable of performing highly accurate measurement by suppressing fluctuation in dispersion among measurements of respective times.SOLUTION: An ion concentration measurement method uses an ion concentration measurement device which comprises an ion sensor and a reference electrode and outputs a sensing value corresponding to a state of a measurement target medium and a reference voltage. The ion concentration measurement method includes: a first step of changing the reference voltage under a first environment that a measurement medium not containing a measurement target component is supplied to the sensor, to acquire a sensing value and creating a correlation table between the reference voltage and the sensing value; and a second step of converting a sensing value, which is acquired when a predetermined reference voltage is applied under a second environment that a measurement target medium containing the measurement target component is supplied to the sensing section, into a voltage corresponding to the reference voltage on the basis of the correlation table.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for measuring ion concentration and odor, and an odor measuring device. [Background technology]

[0002] Patent Document 1 discloses an ion sensor for measuring the ion concentration in a solution, which includes a detection unit formed on a semiconductor substrate in which a plurality of unit detection units outputting an amount of charge corresponding to the ion concentration, and a signal processing unit including an integration circuit that outputs a signal value corresponding to the amount of charge output from the unit detection units.

[0003] Patent Document 2 discloses an odor measurement method using a gas measurement device that performs qualitative or quantitative analysis of a sample gas from a detection signal obtained when a gas sensor detects a sample gas and a detection signal obtained when a reference gas is detected, which serves as a measurement reference. When the reference gas is supplied, that is, when measuring a baseline or base signal level, a reference gas containing background odor components is supplied as the reference gas, and the signal level of the reference gas is used as the base. Next, when measuring the sample gas, the sensitivity is increased near the baseline or base signal level obtained by detecting the reference gas, thereby removing the influence of the background odor and detecting the odor of the measurement target with high sensitivity.

[0004] Patent Document 3 discloses an odor sensor that includes an ion sensor having an ion-sensitive portion, a substance adsorption membrane arranged on the ion-sensitive portion and adsorbing an odor substance to be detected, and an electrode that applies a reference voltage to the substance adsorption membrane. In the odor sensor, the substance adsorption membrane is in a state in which it releases protons when it adsorbs an odor substance, and when the substance adsorption membrane adsorbs an odor substance, the ion-sensitive portion can sense a change in electrical characteristics caused by the release of protons. In addition, by applying a reference voltage to the substance adsorption membrane, the odor substance is not adsorbed by the substance adsorption membrane, and a slight change in electrical characteristics from the state in which the reference voltage is applied to the substance adsorption membrane can be stably detected. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-132448 A [Patent Document 2] JP 2000-162170 A [Patent Document 3] JP 2020-197414 A Summary of the Invention [Problem to be solved by the invention]

[0006] An ion sensor with the above structure is called an ISFET (Ion Sensitive Field Effect Transistor). The potential Φ of the area facing the ion-sensitive membrane is determined by the reference voltage applied to the reference electrode and the ion concentration D in the vicinity of the ion-sensitive membrane, and the output value Vout of the sensor is determined by the potential Φ.

[0007] However, the Vgs-Id characteristics of the FET and the bias resistance value that applies a bias voltage to the ion-sensitive membrane depend on environmental conditions such as temperature and humidity, which causes the sensor output value to fluctuate, resulting in measurement variability and reducing measurement accuracy.

[0008] In view of the above, an object of the present invention is to provide an ion concentration measuring method, an odor measuring method, and an odor measuring device that can suppress the variation in the output value Vout of an ion sensor due to environmental changes and can measure the output value Vout with suppressed variation at high speed and in real time. [Means for solving the problem]

[0009] An ion concentration measurement method according to one aspect of the present invention is a method for measuring ion concentration using an ion concentration measurement device that includes an ion sensor having at least one sensing unit formed on a substrate, the sensing unit changing an electric potential depending on a state of a medium to be measured, and a reference electrode that applies a reference voltage to the sensing unit, and outputs a sensing value depending on the state of the medium to be measured and the reference voltage, a first step of varying the reference voltage to obtain the sensing value under a first environment in which the measurement target medium not containing a measurement target component is supplied to the sensing unit, and creating a correlation table between the reference voltage and the sensing value; and a second step of converting the sensing value obtained when a predetermined reference voltage is applied under a second environment in which the measurement target medium containing the measurement target component is supplied to the sensing unit, into a voltage equivalent to the reference voltage based on the correlation table.

[0010] According to the above invention, by creating a correlation table between the sensing value and the reference voltage in a first environment not containing the component to be measured, a correlation including the variability due to the measurement environment at the time of measurement is obtained in advance, and by converting the sensing value acquired in a second environment containing the component to be measured into a value equivalent to the reference voltage based on the correlation table, the variability due to the measurement environment can be cancelled, thereby suppressing the variability fluctuation for each measurement and enabling highly accurate measurement. Furthermore, since there is no need to sweep the reference voltage in the second environment, high-speed and real-time measurement is possible.

[0011] When the measurement target is a liquid, the reference electrode may be disposed at a position separated from the substrate and immersed in the measurement target liquid.

[0012] When the measurement target is a gas, the substrate may have at least one substance adsorption film that changes potential depending on the concentration of a specific component contained in the measurement target gas, and the reference electrode may be disposed at a position separated from the substrate and in contact with the substance adsorption film.

[0013] Further, an odor measurement method according to one aspect of the present invention is an odor measurement method using an odor sensor that includes an ion sensor having at least one sensing unit formed on a substrate, the sensing unit having at least one substance adsorption film that changes its potential depending on the state of a gas to be measured, and a reference electrode that applies a reference voltage to the substance adsorption film, and outputs a sensing value depending on the state of the gas to be measured and the reference voltage, a first gas introduction section that introduces a reference gas that does not contain a measurement target odor component into the odor sensor; a second gas introduction section that introduces an odor gas that contains the measurement target odor component into the odor sensor; and a flow path switching section that is connected by piping to three sides of the odor sensor, the first gas introduction section, and the second gas introduction section, and that switches the gas introduced into the odor sensor to either the reference gas or the odor gas; a step of acquiring the sensing value by changing the reference voltage when the gas introduced into the odor sensor by the flow path switching unit is the reference gas, and creating a correlation table between the reference voltage and the sensing value for each of the sensing units; The method includes a step of converting the sensing value acquired when the gas introduced into the odor sensor is switched to the odor gas by the flow path switching unit into a voltage equivalent to the reference voltage based on the correlation table.

[0014] According to the above invention, by creating a correlation table between the sensing value and the reference voltage when a reference gas that does not contain the odor component to be measured is introduced, a correlation including the variation factors due to the measurement environment at the time of measurement is obtained in advance, and the sensing value obtained when an odor gas containing the odor component to be measured is introduced is converted to a value equivalent to the reference voltage based on the correlation table, so that the variation factors due to the measurement environment, etc. can be canceled, thereby suppressing the variation fluctuation for each measurement and enabling highly accurate measurement. Furthermore, since there is no need to sweep the reference voltage when the odor gas is introduced, high-speed and real-time measurement is possible.

[0015] It is preferable that the odor gas is generated by extracting a portion of the reference gas and adding the odor to be measured. By using the same gas as the source of the reference gas and the odor gas, the composition, temperature, and humidity conditions of the reference gas and the odor gas can be made the same, so that the phenomenon of false detection, in which the sensor reacts due to differences in these conditions, can be eliminated.

[0016] In addition, an odor measuring device according to one embodiment of the present invention includes an ion sensor having at least one sensing unit formed on a substrate, the sensing unit having at least one substance adsorption film that changes its potential depending on the state of a gas to be measured, and an odor sensor unit that includes a reference electrode that applies a reference voltage to the substance adsorption film and outputs a sensing value depending on the state of the gas to be measured and the reference voltage; A first gas container for storing a reference gas that does not contain an odor component to be measured; A second gas container for storing an odor gas containing an odor component to be measured; a flow path switching unit that is connected to three sides of the first gas container, the second gas container, and the odor sensor unit by piping and switches between flowing between the first gas container and the odor sensor or flowing between the second gas container and the odor sensor; an air suction unit connected to the odor sensor unit by a pipe and configured to extract the gas flowing into the odor sensor unit at a constant flow rate; a correlation table generating unit that changes the reference voltage to obtain the sensing value and generates a correlation table between the reference voltage and the sensing value for each of the sensing units, by controlling the flow path switching unit so that the reference gas flows from the first gas container to the odor sensor, and and a calculation unit that converts the sensing value acquired when the flow path switching unit is switched so that the odor gas flows from the second gas container to the odor sensor into a value equivalent to the reference voltage based on the correlation table.

[0017] According to the above invention, by creating a correlation table between the sensing value and the reference voltage when a reference gas that does not contain the odor component to be measured is introduced, a correlation including the variation factors due to the measurement environment at the time of measurement is obtained in advance, and the sensing value obtained when an odor gas containing the odor component to be measured is introduced is converted to a value equivalent to the reference voltage based on the correlation table, so that the variation factors due to the measurement environment, etc. can be canceled, thereby suppressing the variation fluctuation for each measurement and enabling highly accurate measurement. Furthermore, since there is no need to sweep the reference voltage when the odor gas is introduced, high-speed and real-time measurement is possible.

[0018] In addition, an odor measuring device according to one embodiment of the present invention includes an ion sensor having at least one sensing unit formed on a substrate, the sensing unit having at least one substance adsorption film that changes its potential depending on the state of a gas to be measured, and an odor sensor unit that includes a reference electrode that applies a reference voltage to the substance adsorption film and outputs a sensing value depending on the state of the gas to be measured and the reference voltage; A gas container for storing a reference gas that does not contain the odor component to be measured; a first flow path and a second flow path connected to the gas container and through which the reference gas flows; a flow path switching unit that is connected to three sides of the first flow path, the second flow path, and the odor sensor by piping and switches between flowing the gas of the first flow path to the odor sensor or flowing the gas of the second flow path to the odor sensor; an odor gas generator located in the second flow path and configured to generate an odor gas by adding an odor component to be measured to the reference gas; an air suction unit connected to the odor sensor unit by a pipe and configured to extract the gas flowing into the odor sensor unit at a constant flow rate; a correlation table generating unit that causes the flow path switching unit to circulate the gas in the first flow path to the odor sensor, changes the reference voltage to acquire the sensing value, and creates a correlation table between the reference voltage and the sensing value for each of the sensing units; and a calculation unit that converts the sensing value, which is acquired when the flow path switching unit is switched so that the gas in the second flow path is circulated to the odor sensor, into a value equivalent to the reference voltage based on the correlation table.

[0019] According to the above invention, by creating a correlation table between the sensing value and the reference voltage when a reference gas that does not contain the odor component to be measured is introduced, a correlation including the variation factors due to the measurement environment at the time of measurement is obtained in advance, and the sensing value obtained when an odor gas containing the odor component to be measured is introduced is converted to a value equivalent to the reference voltage based on the correlation table, so that the variation factors due to the measurement environment, etc. can be canceled, thereby suppressing the variation fluctuation for each measurement and enabling highly accurate measurement. Furthermore, since there is no need to sweep the reference voltage when the odor gas is introduced, high-speed and real-time measurement is possible.

[0020] Furthermore, by using a single gas container as the source of the reference gas and the odor gas, the composition, temperature, and humidity conditions of the reference gas and the odor gas are the same, eliminating the phenomenon of false detection in which the sensor reacts due to differences in these conditions. Effect of the Invention

[0021] According to one aspect of the present invention, it is possible to provide an ion concentration measurement method, an odor measurement method, and an odor measurement device that can suppress variation fluctuations from measurement to measurement, thereby enabling highly accurate measurement, and also enabling high-speed, real-time measurement. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an ion measuring device according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing a configuration example of an ion sensor using an ISFET. [Diagram 3] FIG. 3 is a diagram showing a configuration example of an odor sensor using an ISFET. [Figure 4]FIG. 4 is a graph showing an example of calculating an ion concentration from a sensor characteristic curve in a comparative example. [Diagram 5] FIG. 5 is a graph showing the characteristic curve of the sensor. [Figure 6] FIG. 6 is a diagram showing an output waveform during measurement. [Figure 7] FIG. 7 is a diagram showing an output waveform converted into a Vref value. [Figure 8] FIG. 8 is a diagram illustrating an example of the configuration of an odor measuring device according to the second embodiment. [Figure 9] FIG. 9 is a diagram showing an example of the configuration of an odor measuring device in a modified example of the second embodiment. [Figure 10] FIG. 10 is a diagram illustrating an example of the configuration of an odor measuring device according to the third embodiment. [Figure 11] FIG. 11 is a diagram illustrating an example of the configuration of an odor measuring device according to the third embodiment. [Figure 12] FIG. 12 is a diagram showing an example of the configuration of the periphery of the odor sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, the embodiment described below is merely an example of the present invention, and is not intended to limit the technical scope of the present invention. In each drawing, the same components are given the same reference numerals, and their description may be omitted.

[0024] [First embodiment] FIG. 1 is a diagram showing a configuration example of an ion concentration measuring device according to a first embodiment of the present invention. The ion concentration measuring device according to the present embodiment includes an ion sensor 3, a reference electrode 5, a reference voltage control unit 6, a correlation table generating unit 7, and a calculation unit 8. The ion sensor 3 is formed by forming a sensing unit 2 including an ion-sensitive membrane 1 that changes its potential depending on the state of the gas or liquid to be measured that it comes into contact with on a substrate. The reference electrode 5 applies a reference voltage Vr to the ion-sensitive membrane 1 via a bias resistor 4. The reference voltage control unit 6 generates a reference voltage Vr and applies it to the reference electrode 5. The reference voltage control unit 6 can control the reference voltage Vr to be applied to the reference electrode 5, and can perform sweep control to gradually change the reference voltage Vr. The correlation table generating unit 7 generates a correlation table from the output value Vout of the ion sensor 3 when the reference voltage Vr is swept. The correlation table generating unit 7 further stores the generated correlation table. The calculation unit 8 converts the output value Vout of the ion sensor 3 into a voltage equivalent to the reference voltage based on the correlation table.

[0025] The ion sensor 3 has a structure based on an ISFET 9 (Ion Sensitive Field Effect Transistor), as shown in Fig. 2 or Fig. 3. Here, Fig. 2 shows the ion sensor 3 when the measurement target is a liquid, and Fig. 3 shows the ion sensor 3 when the measurement target is a gas, i.e., an odor sensor.

[0026] The basic portion of the ion sensor 3 is an n-type semiconductor substrate on which, from the left, an n+ type injection diode portion (ID portion), a floating diffusion portion (FD portion), and a reset drain portion (RD portion) are formed. A p-type diffusion layer 11 is formed between the ID portion and the FD portion of the semiconductor substrate, and an n-type region (dotted line portion) doped to n-type is formed on the surface of the diffusion layer 11.

[0027] Moreover, an input control gate electrode (ICG electrode), a transfer gate electrode (TG electrode), and a reset gate electrode (RG electrode) are formed on the main surface of the semiconductor substrate via an insulating protective film, and an ion-sensitive film 1 is formed on the semiconductor surface of the diffusion layer 11. The structure is provided with a circuit that outputs a Vout signal amplified by an amplifier that converts the amount of charge accumulated in the FD section into a voltage.

[0028] The ISFET 9 has a structure in which the gate electrode of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is replaced with an ion-sensitive membrane 1. The ion-sensitive membrane 1 is a material that changes the electric potential according to the change in the ion concentration in the vicinity of the membrane, and may be made of, for example, Si3N4. The ion-sensitive membrane 1 uses an appropriate material depending on the substance to be measured.

[0029] In a MOSFET, a voltage is applied to the gate electrode with low impedance, so the potential Φ of the opposing region is stable. However, in an ISFET 9, the electrical impedance of the ion-sensitive membrane 1 is very high, so if no bias voltage is applied, the potential Φ of the opposing region becomes unstable, making it susceptible to the effects of external disturbance noise, and operation is also likely to become unstable. For this reason, a mechanism is required to apply a bias voltage to the ion-sensitive membrane 1 with a relatively high resistance value.

[0030] When the object to be measured is a liquid, an ion sensor as shown in Fig. 2 is used. In the ion sensor, the space above the ion-sensitive membrane 1 is filled with the liquid 10 to be measured as shown in Fig. 2, and since liquid has a resistance value, the liquid 10 to be measured itself can be made to function as a bias resistor. In this case, the reference electrode 5 is preferably disposed at a position separated from the substrate side and immersed in the liquid 10 to be measured.

[0031] When the ion concentration near the ion-sensitive membrane 1 increases or decreases due to a change in the state of the measurement target liquid 10, a change in potential occurs according to the increase or decrease in the ion concentration, and the potential Φ of the potential well of the diffusion layer 11 facing the ion-sensitive membrane 1 changes. This changes the output value Vout of the sensor.

[0032] Furthermore, when the measurement target is a gas (vapor), an odor sensor is used in which a substance adsorption film 13 that adsorbs an odorant 12 to be detected is disposed on top of the ion-sensitive film 1, as shown in Fig. 3. That is, the odor sensor in Fig. 3 is configured by adding a substance adsorption film 13 to the ion sensor in Fig. 2. The substance adsorption film 13 can not only adsorb the odorant 12 but also function as a bias resistor. In this case, it is preferable that the reference electrode 5 is disposed at a position away from the substrate and in contact with the substance adsorption film 13.

[0033] The substance adsorption film 13 is a polyaniline film or the like, which has the property of releasing protons when it adsorbs the odorant to be detected. When the substance adsorption film 13 on the ion-sensitive membrane 1 adsorbs the odorant 12 to be detected, protons are released from the substance adsorption film 13, and cations resulting from the proton release are generated and retained near the ion-sensitive membrane 1, increasing the ion concentration. Then, in the ion-sensitive membrane 1, a change in potential occurs in response to the increase in the ion concentration, and the potential Φ of the potential well of the diffusion layer 11 facing the ion-sensitive membrane 1 changes. This causes a change in the output value Vout of the sensor, similar to an ion sensor.

[0034] Whether the measurement target is a liquid or a gas, the potential Φ of the region facing the ion-sensitive membrane 1 is determined according to the reference voltage Vr applied to the reference electrode 5 and the ion concentration D in the vicinity of the ion-sensitive membrane 1. Furthermore, the output value Vout of the sensor is obtained as a function of the potential Φ, for example, in the form of Vout ≒ a·Φ + b. The coefficients a and b in the function showing the relationship between the output value Vout and the potential Φ are determined by the Vgs-Id characteristics (Vgs: gate-source voltage, Id: drain current) of the ISFET 9 constituting the ion sensor, and the resistance of the measurement target liquid and the substance adsorption film. However, since these Vgs-Id characteristics and the resistance of the measurement target liquid and the substance adsorption film change depending on the use environment such as temperature and humidity, a and b are not constant, and fluctuations occur in the output value Vout of the sensor. Therefore, in order to properly measure the ion concentration even when the use environment such as temperature and humidity changes, the following ion concentration measurement method is used.

[0035] Here, an ion concentration measurement method in a comparative example will be described with reference to Fig. 4. The ion concentration measurement in the comparative example is performed in the following procedure.

[0036] <Step 1> The reference voltage Vr is swept in an environment of a reference liquid or gas that does not contain the component to be measured in the measurement liquid or gas, to obtain the value of the sensor output Vout, and a first sensor characteristic curve f1: Vout = f1 (Vr) is obtained, which indicates the relationship between the reference voltage Vr and the sensor output Vout at this time. The reference liquid or reference gas is a liquid or gas that does not contain the component to be measured and serves as a reference for measuring the ion concentration of the liquid or gas to be measured. In this specification, the reference liquid or reference gas may be referred to as a "reference medium."

[0037] <Step 2> The reference voltage Vr is swept in the environment of the liquid or gas to be measured to obtain the sensor output value Vout, and a second sensor characteristic curve f2: Vout = f2 (Vr) is obtained, which indicates the relationship between the reference voltage Vr and the sensor output Vout at this time. The liquid or gas to be measured is a liquid or gas containing a component to be measured. In this specification, the liquid or gas to be measured is sometimes referred to as a "medium to be measured."

[0038] <Step 3> Based on the first sensor characteristic curve f1 and the second sensor characteristic curve f2, a shift amount ΔVr in the Vr-axis direction at a predetermined Vout value (=Va) is obtained, and an ion concentration D is calculated based on ΔVr.

[0039] It is preferable to select a value for Va where the change in slope is small near the middle of the linear region of the sensor characteristic curve. In the above method, the ion concentration D is calculated from ΔVr related to the change in potential ΔΦ in the region facing the ion-sensitive membrane 1.

[0040] However, in the above-mentioned method of determining ΔVr by sweeping the reference voltage Vr for both the reference liquid or gas and the liquid or gas to be measured, in order to accurately and stably plot the sensor characteristic curve, it is necessary to set the voltage intervals when sweeping the reference voltage Vr finely and wait for the sensor response to stabilize at each voltage, which requires a long sweep time of tens of seconds to several minutes.

[0041] In ion concentration measurement, odor measurement, and even odor discrimination, not only the final value of the change in the sensor output when transitioning from a reference gas to a measurement target gas, but also the response waveform (i.e., the change over time in the sensor output) during the transition process from the reference liquid or reference gas to the measurement target liquid or measurement target gas is important information. However, while switching of the liquid or gas introduced into the sensor is completed within a few seconds, if it takes tens of seconds to several minutes to sweep the reference voltage Vr, it is not possible to capture the response waveform during the transition process.

[0042] In order to capture the response of the transition process, measurements without delay elements in the measurement system are required. Therefore, in the above comparative example, there was no choice but to adopt a method of observing the waveform of Vout, accepting that the sensor output value Vout will be affected by the usage environment, such as temperature and humidity.

[0043] In order to solve the problems in the comparative example as described above, the ion concentration measurement method of this embodiment is performed as follows. The following ion concentration measurement method of this embodiment focuses on the fact that although the characteristic curve of the ion sensor 3 changes depending on the temperature, humidity, etc., it does not change suddenly but changes gradually over a period of several hours to days, and that the characteristic curve in the reference medium and the characteristic curve in the measurement target medium have characteristics that shift in parallel in the Vr axis direction by ΔVr, and realizes measurement converted into a Vr value in real time by converting the measured Vout value to a Vr value without sweeping the reference voltage Vr in the measurement target medium.

[0044] <Step 1: Correlation table generation step> First, in a first environment using a reference gas or reference liquid that does not contain the component to be measured in the measurement gas or liquid, the reference voltage control unit 6 sweeps the reference voltage Vr to obtain the output value Vout of the ion sensor 3, and the correlation table generation unit 7 creates a correlation table between the reference voltage Vr and the output value Vout of the ion sensor 3.

[0045] In order to improve the accuracy of the correlation table, it is preferable to set the step interval of the reference voltage Vr finely. Moreover, after changing the reference voltage Vr, it is preferable to wait a certain time for a response from the ion sensor 3 before acquiring the output value Vout.

[0046] <Step 2: Measurement step> Next, the reference voltage Vr is fixed at a predetermined voltage Vo, the first environment is changed to a second environment in which the target gas or liquid contains a target component, and then the environment is returned to the first environment, and the output value Vout of the ion sensor 3 is acquired. At this time, the time change of the output value Vout of the ion sensor 3 is measured to acquire a response waveform. The acquired output value Vout is converted by the calculation unit 8 into a voltage equivalent to the reference voltage based on a correlation table.

[0047] Here, the above-mentioned ion concentration measuring method will be described in detail with reference to FIGS.

[0048] In step 1, when the reference voltage Vr is swept by the reference voltage control unit 6 to obtain the output value Vout of the ion sensor 3 under the above-mentioned first environment, a curve as shown in Fig. 5 can be drawn as the characteristic curve of the sensor. However, since the detected output value Vout varies depending on the measurement environment such as temperature and humidity, the slope and offset of the relationship between the reference voltage Vr and the output value Vout changes as shown in characteristic curve A and characteristic curve B. Therefore, the correlation table generated here differs depending on the measurement environment, such as correlation table A based on characteristic curve A or correlation table B based on characteristic curve B, as shown in Tables 1 and 2 below.

[0049] [Table 1]

[0050] [Table 2]

[0051] Next, in step 2, the reference voltage Vr is fixed to a predetermined voltage Vo (see FIG. 5) and measurement is performed. Here, the measurement target gas or liquid is introduced into the ion sensor 3 and measurement is performed, but in order to measure the change over time in the output value Vout of the ion sensor 3, the environment is changed from the first to the second environment as described above, and then changed back to the first environment to perform measurement.

[0052] When the potential near the ion-sensitive membrane 1 changes by ΔΦ, as explained in FIG. 4 above, the characteristic curve in FIG. 5 shifts by ΔVr in the Vr-axis direction. Even if the shift amount ΔVr is the same, if the slope or offset is different in the specific curve of the sensor, such as characteristic curve A or characteristic curve B, the output value Vout fluctuates. Therefore, as shown in the output waveform (time change of the output value Vout) during measurement in FIG. 6, the waveform of the output value Vout becomes output waveform A in the case of characteristic curve A, and output waveform B in the case of characteristic curve B, and the output waveform fluctuates up and down. Note that ΔVr may be a positive value as in FIG. 4, but may also be a negative value. When ΔVr is positive, the characteristic curve shifts to the right of the graph, but when ΔVr is negative, the characteristic curve shifts to the left of the graph.

[0053] Therefore, based on the correlation table obtained earlier, the output value Vout is converted to a value equivalent to the reference voltage Vr. As a result, even if the output value Vout varies depending on the measurement environment, an output value that does not fluctuate up and down and has the influence of variation suppressed can be obtained as shown in Figure 7.

[0054] That is, according to the correlation table generated in the reference medium, the relationship between the reference voltage Vr and the output value Vout under the reference medium can be obtained. In contrast, when the reference voltage Vr is fixed to a predetermined voltage Vo and measurement is performed under the medium to be measured, the output value Vout at the predetermined voltage Vo is measured, but this output value Vout is different from the output value Vout under the reference medium. Here, when the output value Vout is converted to a reference voltage Vr corresponding to the output value Vout based on the correlation table, a reference voltage Vr having a value different from the predetermined voltage Vo is obtained. This reference voltage Vr indicates the reference voltage Vr at which the output value Vout is obtained under the reference medium. The difference between the reference voltage Vr at which the output value Vout is obtained under the reference medium and the predetermined voltage Vo at which the output value Vout is obtained under the medium to be measured indicates ΔVr. Therefore, it is possible to obtain ΔVr by the above method.

[0055] Since the correlation table is obtained as discrete values, it is preferable to perform an interpolation process as necessary.

[0056] According to the above, by creating a correlation table, it is possible to obtain in advance a correlation including variation factors due to the measurement environment at the time of measurement, and by converting a sensing value (i.e., output value Vout) acquired in a second environment (or measurement environment) containing the measurement target component into a value equivalent to the reference voltage Vr based on the correlation table, it is possible to cancel the variation factors due to the measurement environment. This makes it possible to suppress the variation fluctuation for each measurement and perform highly accurate measurement. In addition, since it is not necessary to further sweep the reference voltage Vr in the second environment (or measurement environment) after performing a sweep to create the correlation table in the first environment, high-speed and real-time measurement is possible.

[0057] In addition, in measuring and distinguishing odors, the adsorption rate and desorption rate of the odor substance 12 to the substance adsorption film 13 also contain important information. That is, in addition to ΔVr (amount of change in Vr) when the first environment changes to the second environment, which corresponds to the adsorption process, the temporal change rate of Vr (ΔVr / Δt) is also important information. In addition to ΔVr when the second environment changes to the first environment, which corresponds to the desorption process, the temporal change rate of Vr is also important information. According to this embodiment, real-time measurement is possible, so that accurate information on the change rate (also called the change rate) of Vr can be obtained.

[0058] [Second embodiment] Next, an odor measurement device according to a second embodiment of the present invention will be described. The odor measurement device according to this embodiment has a similar configuration to the ion concentration measurement device according to the first embodiment, and the description of the configuration having the same function may be omitted.

[0059] FIG. 8 shows an odor measuring device according to a second embodiment of the present invention. This device includes an odor sensor 14, a first gas introduction section 15, a second gas introduction section 16, a flow path switching section 17, and an air suction section 18, which constitute a gas flow path. The odor sensor 14 outputs a sensing value (i.e., an output value Vout) according to the state of the measurement target gas and the reference voltage Vr. The first gas introduction section 15 introduces a reference gas that does not contain the odor component of the measurement target into the odor sensor 14. The second gas introduction section 16 introduces an odor gas that contains the odor component of the measurement target into the odor sensor 14. The flow path switching section 17 is connected to the odor sensor 14, the first gas introduction section 15, and the second gas introduction section 16 by piping, and switches the gas introduced into the odor sensor 14 to either the reference gas or the odor gas. The air suction section 18 is connected to the odor sensor 14 by piping, and draws out the gas that has flowed into the odor sensor 14 at a constant flow rate. In order to perform accurate measurements, it is preferable to use, as the reference gas, a gas that does not contain the odor components to be measured, such as clean air or nitrogen gas.

[0060] The odor measuring device of this embodiment further includes a reference voltage control unit 6, a correlation table generating unit 7, and a calculation unit 8. The reference voltage control unit 6 is capable of generating a reference voltage Vr and performing sweep control. The correlation table generating unit 7 switches the flow path switching unit 17 so that the reference gas from the first gas introduction unit 15 flows through the odor sensor 14, changes the reference voltage Vr, acquires the output value Vout of the odor sensor 14, and creates a correlation table between the reference voltage Vr and the output value Vout. The calculation unit 8 converts the output value Vout acquired by switching the flow path switching unit 17 so that the odor gas from the second gas introduction unit 16 flows through the odor sensor 14 into a value equivalent to the reference voltage Vr based on the correlation table.

[0061] The operation procedure of the device is as follows: first, when the gas introduced into the odor sensor 14 is switched to the reference gas by the flow path switching unit 17, the reference voltage Vr is changed to obtain the output value Vout, and a correlation table between the reference voltage Vr and the output value Vout is created. Next, the output value Vout obtained when the gas introduced into the odor sensor 14 is switched to the odor gas by the flow path switching unit 17 is converted into a voltage equivalent to the reference voltage Vr based on the correlation table. At this time, as in the first embodiment, the environment is changed from a first environment in which the reference gas is introduced to a second environment in which the odor gas is introduced, and then changed back to the first environment, measurements are performed, and the change over time of the output value Vout is measured.

[0062] According to the odor measuring device, a correlation table between the output value Vout and the reference voltage when a reference gas not containing the odor component to be measured is created, and a correlation including a variability factor due to the measurement environment at the time of measurement is obtained in advance, and the output value Vout obtained when an odor gas containing the odor component to be measured is introduced is converted to a value equivalent to the reference voltage Vr based on the correlation table, thereby canceling the variability factor due to the measurement environment, etc., and thus it is possible to suppress the variability fluctuation for each measurement and perform highly accurate measurement. Furthermore, after the reference gas is introduced and the sweep is performed to create the correlation table, there is no need to further sweep the reference voltage when the odor gas is introduced, and thus high-speed, real-time measurement is possible.

[0063] The first gas introduction section 15 may be composed of, for example, a first gas container 19 that stores a reference gas that does not contain the odor component to be measured, and a first flow path 20 that includes a pipe that connects the first gas container 19 and the flow path switching section 17. The second gas introduction section 16 may be composed of, for example, a second gas container 21 that stores an odor gas that contains the odor component to be measured, and a second flow path 22 that includes a pipe that connects the second gas container 21 and the flow path switching section 17.

[0064] As a modified example, as shown in FIG. 9, for example, the second gas container 21 may store a reference gas that does not contain the odor component to be measured, and an odor gas generator 23 that adds the odor component to be measured to the reference gas may be inserted in the middle of the second flow path 22.

[0065] [Third embodiment] Next, an odor measurement device according to a third embodiment of the present invention will be described. The odor measurement device according to this embodiment has a similar configuration to the ion concentration measurement device according to the first embodiment and the odor measurement device according to the second embodiment, and the description of the configuration having the same function may be omitted.

[0066] FIG. 10 shows an odor measuring device according to a third embodiment of the present invention. This device includes an odor sensor 14, a gas container 24, a first flow path 20, a second flow path 22, a flow path switching unit 17, and an air suction unit 18, which constitute a gas flow path. The odor sensor 14 outputs a sensing value (i.e., an output value Vout) according to the state of the measurement target gas and the reference voltage Vr. The gas container 24 stores a reference gas that does not contain the odor component to be measured in the odor sensor 14. The first flow path 20 is connected to the gas container 24 and allows the reference gas to flow. The second flow path 22 is connected to the gas container 24 and allows the odor gas to flow. The flow path switching unit 17 is connected to three directions, the odor sensor 14, the first flow path 20, and the second flow path 22, by piping, and switches the gas to be introduced into the odor sensor 14 between the reference gas and the odor gas. The air suction section 18 is located midway through the second flow path 22 and is connected by piping to the odor gas generation section 23, which generates an odor gas by adding the odor component to be measured to a reference gas, and to the odor sensor 14, and draws out the gas that flows into the odor sensor 14 at a constant flow rate.

[0067] The odor measurement device of this embodiment further includes a reference voltage control unit 6, a correlation table generation unit 7, and a calculation unit 8. The correlation table generation unit 7 switches the flow path switching unit 17 so that the reference gas flows from the gas container 24 to the odor sensor 14 through the first flow path 20, changes the reference voltage Vr, acquires the output value Vout of the odor sensor 14, and creates a correlation table between the reference voltage Vr and the output value Vout. The calculation unit 8 converts the output value Vout, acquired by switching the flow path switching unit 17 so that the odor gas flows from the gas container 24 to the odor sensor 14 through the second flow path 22, into a value equivalent to the reference voltage Vr based on the correlation table.

[0068] According to the odor measuring device, a correlation table between the output value Vout and the reference voltage when a reference gas not containing the odor component to be measured is created, and a correlation including a variability factor due to the measurement environment at the time of measurement is obtained in advance, and the output value Vout obtained when an odor gas containing the odor component to be measured is introduced is converted to a value equivalent to the reference voltage based on the correlation table, thereby canceling the variability factor due to the measurement environment, etc., thereby suppressing the variability fluctuation for each measurement and enabling highly accurate measurement. Furthermore, after the reference gas is introduced and the sweep is performed to create the correlation table, there is no need to further sweep the reference voltage when the odor gas is introduced, enabling high-speed, real-time measurement.

[0069] Furthermore, by using a single gas container as the source of the reference gas and the odor gas, the composition, temperature, and humidity conditions of the reference gas and the odor gas are the same, eliminating the phenomenon of false detection in which the sensor reacts due to differences in these conditions.

[0070] 11, a reference gas introduced from the gas container 24 through a third flow path 27 may be selectively branched into the first flow path 20 and the second flow path 22 by a first flow path switching unit 25. In this configuration, it is possible to completely prevent the odor components to be measured added by the odor gas generating unit 23 from flowing back into the gas container 24.

[0071] As shown in FIG. 12, the configuration around the odor sensor 14 may be configured to include an odor sensor 14 having a sensor element 29 with multiple substance adsorption films 13 with different odorant adsorption properties arranged on a single sensor substrate 28, a sensor driving circuit 30 that generates a sensor driving signal and a reference voltage Vr, and a signal processing circuit 31 that converts the signal Vout output from the odor sensor 14 into a value equivalent to Vr based on a correlation table and outputs a corrected sensor signal, and the area of ​​the odor sensor 14 mounted on the sensor substrate 28 may be covered by a gas flow path 32.

[0072] According to the above configuration, the electronic circuit and other parts other than the odor sensor are not exposed to gas, so that problems such as corrosion of the electronic component terminals can be avoided. [Explanation of symbols]

[0073] 1...Ion-sensitive membrane 2. Sensing section 2. Step 3...Ion sensor 4. Bias resistor 5...Reference electrode 6…Reference voltage control section 7...Correlation table generator 8...Arithmetic section 9. ISFET 10...Liquid to be measured 11... Diffusion layer 12...Odor substances 13...Substance adsorption membrane 14...Odor sensor 15...First gas inlet 16...Second gas inlet 17...Flow path switching section 18…Air suction part 19…First gas bottle 20…First flow path 21...Second gas bottle 22...Second flow path 23...Gas generating section 24...Gas bottle 25...First flow path switching section 27...Third flow path 28…Sensor board 29...Sensor element 30...Sensor drive circuit 31...Signal processing circuit 32...Gas flow path

Claims

1. An ion concentration measuring method using an ion concentration measuring device that includes an ion sensor having at least one sensing portion formed on a substrate, the sensing portion changing a potential depending on a state of a medium to be measured, and a reference electrode that applies a reference voltage to the sensing portion, and outputs a sensing value depending on the state of the medium to be measured and the reference voltage, a first step of acquiring the sensing value by changing the reference voltage under a first environment in which the measurement target medium not containing a measurement target component is supplied to the sensing unit, and creating a correlation table between the reference voltage and the sensing value; a second step of converting the sensing value obtained when a predetermined reference voltage is applied under a second environment in which the measurement target medium containing the measurement target component is supplied to the sensing unit, into a voltage equivalent to the reference voltage based on the correlation table.

2. In the second step, the sensing value obtained when a predetermined reference voltage is applied while changing the environment in the order of the first environment and the second environment or the second environment and the first environment is converted into a voltage equivalent to the reference voltage based on the correlation table, and an amount of change or a rate of change over time of the voltage converted into the voltage equivalent to the reference voltage is measured. The ion concentration measuring method according to claim 1 .

3. The ion concentration measurement method is a method for measuring an ion concentration when the measurement target medium is a measurement target liquid, In the second environment, the liquid to be measured containing the component to be measured is filled above the sensing unit, 2. The ion concentration measuring method according to claim 1, wherein the reference electrode is disposed at a position separated from the substrate and immersed in the liquid to be measured.

4. The ion concentration measuring method is a method for measuring an ion concentration when the measurement target medium is a measurement target gas, comprising the steps of:

2. The ion concentration measuring method according to claim 1, wherein the ion sensor further comprises at least one substance adsorption film on the substrate, the substance adsorption film changing a potential depending on a concentration of a specific component contained in the measurement target gas.

5. 5. The ion concentration measuring method according to claim 4, wherein the reference electrode is disposed at a position separated from the substrate and in contact with the substance adsorption film.

6. An odor measurement method using an odor sensor comprising an ion sensor having at least one sensing unit formed on a substrate, the sensing unit having at least one substance adsorption film that changes potential depending on a state of a gas to be measured, and a reference electrode that applies a reference voltage to the substance adsorption film, the odor sensor outputting a sensing value depending on the state of the gas to be measured and the reference voltage, a first gas introduction section that introduces a reference gas that does not contain a measurement target odor component into the odor sensor; a second gas introduction section that introduces an odor gas that contains the measurement target odor component into the odor sensor; and a flow path switching section that is connected by piping to three sides of the odor sensor, the first gas introduction section, and the second gas introduction section, and that switches the gas introduced into the odor sensor to either the reference gas or the odor gas; a step of acquiring the sensing value by changing the reference voltage when the gas introduced into the odor sensor by the flow path switching unit is the reference gas, and creating a correlation table between the reference voltage and the sensing value for each of the sensing units; and converting the sensing value obtained when the gas introduced into the odor sensor is switched to the odor gas by the flow path switching unit into a voltage equivalent to the reference voltage based on the correlation table.

7. 7. The odor measuring method according to claim 6, wherein the odor gas is generated by extracting a portion of the reference gas and adding an odor to be measured.

8. an odor sensor unit including at least one sensing unit formed on a substrate and having at least one substance adsorption film that changes its potential depending on the state of the gas to be measured, and a reference electrode that applies a reference voltage to the substance adsorption film, and that outputs a sensing value depending on the state of the gas to be measured and the reference voltage; A first gas container for storing a reference gas that does not contain an odor component to be measured; A second gas container for storing an odor gas containing an odor component to be measured; a flow path switching unit that is connected to three sides of the first gas container, the second gas container, and the odor sensor unit by piping and switches between flowing between the first gas container and the odor sensor or flowing between the second gas container and the odor sensor; an air suction unit connected to the odor sensor unit by a pipe and configured to extract the gas flowing into the odor sensor unit at a constant flow rate; a correlation table generating unit that causes the flow path switching unit to flow the reference gas from the first gas container to the odor sensor, changes the reference voltage to acquire the sensing value, and creates a correlation table between the reference voltage and the sensing value for each of the sensing units; and a calculation unit that converts the sensing value acquired when the flow path switching unit is switched so that the odor gas flows from the second gas container to the odor sensor into a value equivalent to the reference voltage based on the correlation table.

9. an odor sensor unit including at least one sensing unit formed on a substrate and having at least one substance adsorption film that changes its potential depending on the state of the gas to be measured, and a reference electrode that applies a reference voltage to the substance adsorption film, and that outputs a sensing value depending on the state of the gas to be measured and the reference voltage; A gas container for storing a reference gas that does not contain the odor component to be measured; a first flow path and a second flow path connected to the gas container and through which the reference gas flows; a flow path switching unit that is connected to three sides of the first flow path, the second flow path, and the odor sensor by piping and switches between flowing the gas of the first flow path to the odor sensor and flowing the gas of the second flow path to the odor sensor; an odor gas generator located in the second flow path and configured to generate an odor gas by adding an odor component to be measured to the reference gas; an air suction unit connected to the odor sensor unit by a pipe and configured to extract the gas flowing into the odor sensor unit at a constant flow rate; a correlation table generating unit that causes the flow path switching unit to flow the gas in the first flow path to the odor sensor, changes the reference voltage to acquire the sensing value, and creates a correlation table between the reference voltage and the sensing value for each of the sensing units; and a calculation unit that converts the sensing value acquired when the flow path switching unit is switched so that the gas in the second flow path flows through the odor sensor into a value equivalent to the reference voltage based on the correlation table.

Images