Liquid sensor and detection method

Abstract

The present invention provides a liquid sensor and a detection method capable of detecting a parameter related to the degree of deterioration of a liquid. The liquid sensor includes a pair of electrodes and a control unit. The pair of electrodes is used in a state of being immersed in a liquid. The control unit scans the frequency of the AC voltage applied between the pair of electrodes. The control unit detects the impedance of the liquid at each frequency, and calculates a second parameter associated with a first parameter that is a value having a correlation with the impedance or the impedance. The second parameter is a difference value between the first change degree and the second change degree. The first degree of change and the second degree of change each represent an amount of change in the first parameter with respect to an amount of change in the frequency. The liquid sensor further includes a storage unit. The storage unit stores relationship information indicating a correspondence relationship between a third parameter and a second parameter having a correlation with the degree of deterioration of the liquid. The control unit detects a third parameter based on the second parameter and the relationship information.

Description

Technical Field

[0001] The invention relates to a liquid sensor and a detection method. Background Art

[0002] Japanese Patent Publication No. 6910037 (Patent Document 1) discloses an oil state determination system. In the oil state determination system, the resistance value of the oil is measured, and when the change trend of the resistance value of the oil reverses from a decreasing trend to an increasing trend, it is determined that the oxidation state of the oil has changed (see Patent Document 1).

[0003] Patent Document 1: Japanese Patent No. 6910037

[0004] The oil state determination system disclosed in Patent Document 1 determines the change in the oxidation state of oil (an example of “liquid”), but does not detect a parameter correlated with the degree of oil degradation. Summary of the invention

[0005] The present invention has been made to solve such a problem, and an object of the present invention is to provide a liquid sensor and a detection method capable of detecting a parameter having a correlation with the degree of degradation of the liquid.

[0006] A liquid sensor according to one aspect of the present invention comprises a pair of electrodes and a control unit. The pair of electrodes are used in a state of being immersed in liquid. The control unit scans the frequency of the AC voltage applied between the pair of electrodes. The control unit detects the impedance of the liquid at each frequency and calculates a second parameter associated with a first parameter, the first parameter being a value or impedance having a correlation with the impedance. The second parameter is the difference between a first degree of change and a second degree of change. The first degree of change and the second degree of change respectively represent the amount of change of the first parameter relative to the amount of change of the frequency. The liquid sensor also comprises a storage unit. The storage unit stores relationship information representing the correspondence between a third parameter having a correlation with the degree of degradation of the liquid and the second parameter. The control unit detects the third parameter based on the second parameter and the relationship information.

[0007] The inventors (et al.) have found that the third parameter has a high correlation with the second parameter, and the third parameter has a correlation with the degree of degradation of the liquid. In the liquid sensor, the third parameter is detected based on the relationship information indicating the corresponding relationship between the third parameter and the second parameter and the calculated second parameter. Therefore, according to the liquid sensor, the third parameter can be detected with high accuracy.

[0008] In the above-mentioned liquid sensor, the first parameter may be the resistance value of the liquid or the electrostatic capacitance of the liquid.

[0009] In the above liquid sensor, the third parameter may be the alkalinity value of the liquid or the acidity value of the liquid.

[0010] The liquid sensor may also include a temperature sensor for detecting the temperature of the liquid, and the relationship information may be set according to each temperature of the liquid. The control unit may detect the third parameter based on the temperature of the liquid, the relationship information corresponding to the temperature of the liquid, and the second parameter.

[0011] The inventors (et al.) discovered that the relationship between the third parameter and the second parameter may be affected by the temperature of the liquid. In the liquid sensor, the third parameter is detected based on the temperature of the liquid, the relationship information corresponding to the temperature of the liquid, and the second parameter. Therefore, according to the liquid sensor, since the third parameter is detected based on the temperature of the liquid, the third parameter can be detected with higher accuracy.

[0012] In the above-mentioned liquid sensor, the control unit can switch which one of the resistance value and the electrostatic capacitance is used as the first parameter in response to the detected value of the third parameter.

[0013] The inventors (et al.) have found that which of the second parameter calculated based on the resistance value and the second parameter calculated based on the electrostatic capacitance has a higher correlation with the third parameter varies depending on the value of the third parameter. In the liquid sensor, which of the resistance value and the electrostatic capacitance is used as the first parameter is switched in response to the value of the detected third parameter. Therefore, according to the liquid sensor, since the second parameter having a higher correlation with the third parameter is used for the detection of the third parameter, the third parameter can be detected with higher accuracy.

[0014] According to another aspect of the present invention, the detection method includes: a step of scanning the frequency of an AC voltage applied between a pair of electrodes immersed in a liquid; a step of detecting the impedance of the liquid at each frequency; and a step of calculating a second parameter associated with a first parameter, wherein the first parameter is a value or impedance having a correlation with the impedance. The second parameter is the difference between the first degree of change and the second degree of change. The first degree of change and the second degree of change respectively represent the amount of change of the first parameter relative to the amount of change of the frequency. The detection method also includes: a step of storing relationship information representing the corresponding relationship between a third parameter having a correlation with the degree of degradation of the liquid and the second parameter; and a step of detecting the third parameter based on the second parameter and the relationship information.

[0015] In this detection method, the third parameter is detected based on the relationship information indicating the correspondence relationship between the third parameter and the second parameter and the calculated second parameter. Therefore, according to this detection method, the third parameter can be detected with high accuracy.

[0016] Effects of the Invention

[0017] According to the present invention, it is possible to provide a liquid sensor and a detection method capable of detecting a parameter having a correlation with the degree of degradation of liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a diagram schematically showing the structure of a liquid sensor.

[0019] Figure 2 It is a diagram schematically showing a parallel equivalent circuit of a liquid.

[0020] Figure 3 This is a diagram schematically showing an example of the relationship between an AC voltage (input signal) applied between a pair of electrodes and a current (measurement signal) generated in a circuit including the pair of electrodes.

[0021] Figure 4 This is a diagram schematically showing the relationship between impedance, resistance value, electrostatic capacitance, and phase difference.

[0022] Figure 5 This is a flowchart showing an example of the generation flow of relationship information.

[0023] Figure 6 This is a diagram schematically showing an example of a graph generated by detecting a resistance value.

[0024] Figure 7 It is a diagram for explaining the calculation method of the first change degree and the second change degree.

[0025] Figure 8 This is a diagram showing an example of the relationship between the alkalinity value (estimated value) of the liquid detected using the relationship information and the analyzed value of the alkalinity value of the liquid.

[0026] Fig. 9 This is a diagram showing an example of the relationship between the alkalinity value (estimated value) of the liquid detected using the relationship information and the analyzed value of the alkalinity value of the liquid when one degree of change is used as the second parameter.

[0027] Fig.10 1 is a flowchart showing a flow of detecting the alkalinity value of liquid in the liquid sensor.

[0028] Fig.11 This is a diagram showing an example of the relationship between the acid value (estimated value) of the liquid detected using the relationship information and the analyzed value of the acid value of the liquid when the acid value of the liquid is used as the third parameter.

[0029] Fig.12 : is a flowchart showing the process of determining the relationship information used in the detection of the third parameter.

[0030] Fig.13 This is a diagram for explaining an image related to a change in the first parameter.

[0031] Fig.14This is a flowchart showing another example of the detection process of the alkalinity value of the liquid in the liquid sensor.

[0032] Description of Reference Numerals

[0033] 10. Liquid sensor; 20. Storage tank; 100. Detection system; 102. Measuring unit; 104. Control unit; 106. Storage unit; 108. Notification unit; 110. Substrate; 111. Substrate body; 112. Electrode; 113. Temperature sensor; DC1, DC2, degree of change; L1, liquid; P1-P5, points; RL1-RL4, baseline. DETAILED DESCRIPTION

[0034] Hereinafter, an embodiment according to one aspect of the present invention (hereinafter also referred to as "the present embodiment") will be described in detail with reference to the accompanying drawings. In addition, the same or corresponding parts in the figures are marked with the same reference numerals and their descriptions are not repeated. In addition, for ease of understanding, each of the drawings appropriately omits or exaggerates the schematic depiction of an object.

[0035] [1. Structure of liquid sensor]

[0036] Figure 1 2 is a diagram schematically showing the structure of the liquid sensor 10 according to the present embodiment. The liquid sensor 10 is installed in the storage tank 20 and is configured to detect a parameter (e.g., alkalinity) that is correlated with the degree of degradation of the liquid L1 (e.g., oil). For example, the liquid sensor 10 is installed in a fuel tank or a pipe of a vehicle or the like and detects the alkalinity of the oil. The alkalinity of the oil is correlated with the degree of degradation of the oil. The liquid sensor 10 is used in a state where at least a portion is immersed in the liquid L1.

[0037] like Figure 1 As shown, the liquid sensor 10 includes a detection system 100 and a substrate 110. When the liquid sensor 10 is used, the substrate 110 is immersed in the liquid L1. The shape of the substrate 110 is, for example, roughly rectangular when viewed from above. The substrate 110 includes a substrate body 111, a pair of electrodes 112, and a temperature sensor 113. The substrate body 111 is a so-called fluorine-containing resin substrate. Since the fluorine-containing resin substrate has excellent weather resistance and drug resistance, the substrate 110 including the substrate body 111 can withstand use in harsh environments. In addition, the substrate body 111 does not necessarily need to be composed of a fluorine-containing resin substrate, for example, it is preferably composed of a substrate with excellent drug resistance.

[0038] A pair of electrodes 112 is formed on the substrate body 111. The pair of electrodes 112 is used to detect the impedance of the liquid L1. Each electrode 112 has a comb-tooth shape. In the substrate 110, the pair of electrodes 112 is configured so that the tooth portions of each electrode 112 exist alternately. The pair of electrodes 112 is formed, for example, by patterning a conductive layer formed on one side of the substrate body 111.

[0039] The temperature sensor 113 is mounted on the substrate body 111. The temperature sensor 113 is used to detect the temperature of the liquid L1. The temperature sensor 113 is composed of a temperature detection element such as a resistance temperature detector (RTD), a thermistor, or a thermocouple. In addition, the temperature sensor 113 is not necessarily required.

[0040] The detection system 100 includes a storage unit 106, a measuring unit 102, a control unit 104, and a notification unit 108. The storage unit 106 is composed of an auxiliary storage device such as a flash memory. The storage unit 106 stores, for example, "relationship information" for detecting the alkalinity of the liquid L1. The relationship information will be described in detail later.

[0041] The measuring unit 102 includes, for example, a power supply and an ammeter. The measuring unit 102 applies a measuring voltage (AC voltage) between the pair of electrodes 112 and measures the current generated in the circuit including the pair of electrodes 112. In addition, the measuring unit 102 applies a measuring voltage to the temperature sensor 113 and measures the current generated in the circuit including the temperature sensor 113.

[0042] The control unit 104 includes, for example, a calculation circuit, a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory). The control unit 104 detects the impedance between the pair of electrodes 112 based on, for example, the voltage value applied between the pair of electrodes 112 and the current value generated in the circuit including the pair of electrodes 112. When the pair of electrodes 112 are entirely immersed in the liquid L1, the impedance between the pair of electrodes 112 is regarded as the impedance of the liquid L1.

[0043] The details will be described later, but the control unit 104 uses the resistance value of the liquid L1 (hereinafter, also referred to as "resistance value") in the detection of the alkalinity value of the liquid L1. The control unit 104 calculates the resistance value of the liquid L1 based on the impedance of the liquid L1. An example of the process of calculating the resistance value of the liquid L1 based on the impedance of the liquid L1 is described below.

[0044] Figure 2 Schematically shows the parallel equivalent circuit of liquid L1. Figure 2 As shown in FIG. 1 , the liquid L1 can be regarded as electrically equivalent to a circuit in which a resistor and a capacitor are connected in parallel. That is, the impedance Z1 of the liquid L1 can be divided into the resistance value R1 and the electrostatic capacitance C1.

[0045] Figure 31 is a diagram schematically showing an example of the relationship between an AC voltage (input signal) applied between a pair of electrodes 112 and a current (measurement signal) generated in a circuit including the pair of electrodes 112. Figure 3 , the horizontal axis represents time, and the vertical axis represents voltage value or current value. In this example, the difference between the phase of the input signal and the phase of the measurement signal is θ. The control unit 104 detects the phase difference θ based on the input signal and the measurement signal.

[0046] Figure 4 Schematically shows the relationship between the impedance Z1, the resistance value R1, the electrostatic capacitance C1, and the phase difference θ. Figure 4 , the control unit 104 calculates the resistance value R1 by integrating cosθ on the detected impedance Z1. Through such a process, the control unit 104 calculates the resistance value R1 of the liquid L1 based on the impedance Z1 of the liquid L1. The details will be described later, but the control unit 104 detects the alkalinity of the liquid L1 by using the resistance value R1 of the liquid L1 and the relationship information.

[0047] Refer again Figure 1 The control unit 104 detects the resistance value of the temperature sensor 113, for example, based on the voltage applied to the temperature sensor 113 and the current generated in the circuit including the temperature sensor 113. The control unit 104 detects the temperature of the liquid L1 based on the resistance value of the temperature sensor 113. In the storage unit 106, for example, the relationship between the temperature and the resistance value is pre-stored.

[0048] The notification unit 108 includes, for example, a display. The notification unit 108 displays, for example, an image showing the alkalinity value detected by the control unit 104. Thus, the user is notified of the alkalinity value of the liquid L1.

[0049] [2. Use relationship information to detect base value]

[0050] For example, there is a technology that detects changes in the oxidation state of oil (an example of liquid L1) and determines the timing of oil replacement. However, this technology does not directly detect a parameter (such as alkalinity) that is correlated with the degree of deterioration of the liquid L1. On the other hand, if a parameter that is correlated with the degree of deterioration of the liquid L1 is directly detected, for example, the timing of liquid L1 replacement can be determined with higher accuracy.

[0051] The first parameter, the second parameter, and the third parameter are defined as follows. The first parameter is a value correlated with the impedance Z1 of the liquid L1 or a parameter corresponding to the impedance Z1 itself (e.g., the resistance value R1 of the liquid L1). The second parameter is the difference between the first degree of change and the second degree of change. The control unit 104 is configured to scan the frequency of the measurement voltage applied between the pair of electrodes 112. The control unit 104 is configured to detect the resistance value R1 of the liquid L1 when measurement voltages of a plurality of specified frequencies (e.g., frequencies f1, f2, f3, f4 (f1 < f2 < f3 < f4)) are applied. The first degree of change and the second degree of change respectively represent the change amount of the first parameter with respect to the frequency change amount (e.g., the first degree of change is the change amount of the first parameter with respect to the frequency f4 - (subtracting) the frequency f1, and the second degree of change is the change amount of the first parameter with respect to the frequency f3 - (subtracting) the frequency f2). The third parameter is a parameter correlated with the degree of deterioration of the liquid L1 (e.g., the base number of the liquid L1).

[0052] The inventor(s) found that the third parameter correlated with the degree of deterioration of the liquid L1 has a high correlation with the second parameter. In the liquid sensor 10 according to the present embodiment, the above relationship information represents the correspondence relationship between the third parameter and the second parameter, and the third parameter is detected based on the calculated second parameter and the relationship information. Therefore, according to the liquid sensor 10, the third parameter can be detected with high accuracy. As described above, the relationship information is generated in advance and stored in the storage unit 106. The generation process of the relationship information will be described below.

[0053] Figure 5 is a flowchart showing an example of the generation process of the relationship information. Each process shown in this flowchart is performed by the control unit 104 or the operator. In addition, a plurality of specimens (liquid L1) each having a different base number from each other are prepared in advance, and the processes shown in this flowchart are started when any one of the plurality of specimens enters the storage tank 20 ( Figure 1 ). In addition, the actual base number of each of the plurality of specimens is measured in advance.

[0054] Refer to Figure 5 , with the measurement voltage of each frequency applied between the pair of electrodes 112, the control unit 104 detects the resistance value R1 of the liquid L1 (step S100), and completes the detection of the resistance value for all specimens at all the preset frequencies (step S110).

[0055] Figure 6 is a diagram schematically showing an example of a graph generated by detecting the resistance value R1 of the liquid L1. This diagram shows the relationship between the frequency of the measurement voltage and the resistance value R1 for a specific specimen. Refer to Figure 6The horizontal axis represents the frequency of the measurement voltage, and the vertical axis represents the detected resistance value R1. Each point P1 represents the resistance value R1 of a specific sample (liquid L1) when a measurement voltage of a specific frequency is applied between a pair of electrodes 112. By repeating the scanning of the measurement voltage and the detection of the resistance value R1 for each sample, a measurement voltage is generated for each of all samples. Figure 6 A graph like the one shown in .

[0056] Figure 7 2 is a diagram for explaining the first degree of change and the second degree of change. Figure 7 As described above, each point P1 represents the resistance value R1 of a specific sample (liquid L1) when a measurement voltage of a specific frequency is applied between a pair of electrodes 112. The degree of change DC1 is an example of a first degree of change, and the degree of change DC2 is an example of a second degree of change. The degrees of change DC1 and DC2 respectively represent the change in the resistance value R1 (first parameter) relative to the change in the frequency of the measurement voltage. In this example, the degree of change DC1 represents the change in the resistance value R1 relative to the frequency f3-(minus) frequency f2, and the degree of change DC2 represents the change in the resistance value R1 relative to the frequency f4-(minus) frequency f1. Each degree of change DC1, DC2 can also be said to be the slope of a straight line connecting any two points representing the correspondence between the frequency of the measurement voltage and the resistance value R1.

[0057] Refer again Figure 5 , the operator plots the difference between the first degree of change and the second degree of change in a specific combination of the first degree of change and the second degree of change for all samples (step S120). Thus, a curve graph representing the corresponding relationship between the difference between the first degree of change and the second degree of change and the alkalinity of the liquid L1 is generated. The operator completes the plotting of the difference between the first degree of change and the second degree of change in a specific combination of the first degree of change and the second degree of change for all samples for all combinations of the first degree of change and the second degree of change (step S130). Thus, for each combination of the first degree of change and the second degree of change, a curve graph representing the corresponding relationship between the difference between the first degree of change and the second degree of change and the alkalinity of the liquid L1 is generated.

[0058] The operator calculates the correlation coefficient based on each generated curve graph (each drawing result) (step S140). In the calculation of the correlation coefficient, for example, various well-known methods are used. For example, the correlation coefficient is calculated by using a computer. The operator generates "relationship information" (step S150) based on the curve graph with the largest correlation coefficient. The relationship information is generated through such a process. The relationship information can be, for example, a linear function, a quadratic function, or a function of three or more degrees. In addition, in the relationship information, the correspondence between the difference between the first degree of variation and the second degree of variation in the combination of the first degree of variation and the second degree of variation used in the generation of the curve graph with the largest correlation coefficient and the alkalinity value of the liquid L1 (an example of the third parameter) is represented. That is, in the relationship information, two frequencies for calculating the first degree of variation are predetermined, and two frequencies for calculating the second degree of variation are predetermined.

[0059] Figure 8 1 is a diagram showing an example of the relationship between the alkalinity value (estimated value) of the liquid L1 detected by the liquid sensor 10 according to the present embodiment using the relationship information and the analyzed value of the alkalinity value of the liquid L1. Figure 8 , the horizontal axis represents the analysis value, and the vertical axis represents the estimated value or error. The white points P2 represent the estimated value related to the liquid L1 having a specific analysis value, and the black points P3 represent the error between the estimated value and the analysis value. The reference line RL1 represents the upper limit of the error specified in the JIS standard (JIS K 2501:2003 Potentiometric titration (base value·hydrochloric acid method), and the reference line RL2 represents the lower limit of the error specified in the JIS standard.

[0060] like Figure 8 As shown, the error of each estimated value is within the error range specified in the JIS standard. It can be seen that the second parameter (the difference between the first degree of change and the second degree of change) has a high correlation with the third parameter (for example, the base number). In the liquid sensor 10 according to this embodiment, the relationship information represents the corresponding relationship between the third parameter and the second parameter, and the third parameter is detected based on the calculated second parameter and the relationship information. Therefore, according to the liquid sensor 10, the third parameter can be detected with high accuracy.

[0061] Assume that the second parameter is not the difference between the first and second change degrees, but a change degree (the change amount of the first parameter relative to the change amount of the frequency). In this case, it is assumed that relationship information indicating the correspondence between the third parameter and the second parameter is generated in advance. In addition, it is assumed that the alkalinity of the liquid L1 is estimated using this relationship information.

[0062] Fig. 9 1 is a diagram showing an example of the relationship between the alkalinity value (estimated value) of the liquid L1 detected using the relationship information and the analyzed value of the alkalinity value of the liquid L1 when a change degree is set as the second parameter. Fig. 9As shown, the errors of some estimated values ​​are not within the error range specified in the JIS standard. It can be seen that when a change degree is set as the second parameter, the second parameter and the third parameter do not have a high correlation.

[0063] In the liquid sensor 10 according to this embodiment, the difference between the first change degree and the second change degree is used as the second parameter, and the third parameter is detected based on the calculated second parameter and the relationship information. Therefore, according to the liquid sensor 10, the third parameter can be detected with high accuracy.

[0064] [3. Alkalinity value detection process]

[0065] Fig.10 1 is a flowchart showing a flow of detecting the alkalinity value of the liquid L1 in the liquid sensor 10 . The processing shown in the flowchart is executed by the control unit 104 .

[0066] Reference Fig.10 , the control unit 104 detects the resistance value R1 (first parameter) of the liquid L1 when a measurement voltage of a specified frequency (for example, any one of the four frequencies pre-set in the relationship information) is applied between a pair of electrodes 112 (step S200). The control unit 104 determines whether the resistance value R1 is detected when the measurement voltages of a plurality of (for example, four) predetermined frequencies are respectively applied between a pair of electrodes 112 (step S210). When it is determined that the detection of the resistance value R1 is not completed for at least part of the frequencies (no in step S210), the control unit 104 controls the measurement unit 102 to scan the frequency of the measurement voltage (step S220). Thereafter, the process of step S200 is performed again.

[0067] When it is determined that the detection of the resistance value R1 is completed for all the specified frequencies (Yes in step S210), the control unit 104 calculates the first change degree and the second change degree based on the detection results of the resistance value R1 (step S230). The control unit 104 calculates the difference (second parameter) between the first change degree and the second change degree (step S240). The control unit 104 detects the alkalinity (third parameter) of the liquid L1 by substituting the second parameter into the relationship information (e.g., function) stored in the storage unit 106 (step S250).

[0068] [4. Features]

[0069] As described above, the liquid sensor 10 according to the present embodiment includes a pair of electrodes 112 and a control unit 104. The pair of electrodes 112 is used in a state of being immersed in the liquid L1. The control unit 104 scans the frequency of the AC voltage applied between the pair of electrodes 112. The control unit 104 detects the impedance of the liquid L1 at each frequency, and calculates a second parameter associated with a first parameter (e.g., resistance value R1), the first parameter being a value or impedance having a correlation with the impedance. The second parameter is the difference between the first degree of change and the second degree of change. The first degree of change and the second degree of change respectively represent the amount of change of the first parameter relative to the amount of change in frequency. The liquid sensor 10 also includes a storage unit 106. The storage unit 106 stores relationship information representing the correspondence between a third parameter (e.g., alkalinity) having a correlation with the deterioration degree of the liquid L1 and the second parameter. The control unit 104 detects the third parameter based on the second parameter and the relationship information. According to the liquid sensor 10, the third parameter and the second parameter have a high correlation, and the third parameter is detected based on the relationship information and the second parameter representing the correspondence between the third parameter and the second parameter, so that the third parameter can be detected with high accuracy.

[0070] [5. Other implementations]

[0071] The concept of the above-described embodiment is not limited to the above-described embodiment. Hereinafter, an example of another embodiment to which the concept of the above-described embodiment can be applied will be described.

[0072] <5-1>

[0073] In the above embodiment, the first parameter is set to the resistance value R1 of the liquid L1. However, the first parameter may not necessarily be the resistance value R1 of the liquid L1. The first parameter may be, for example, the electrostatic capacitance C1 of the liquid L1 or the impedance Z1 of the liquid L1. The relationship information may be generated in advance based on the electrostatic capacitance C1 or the impedance Z1 of the liquid L1 as the first parameter. Fig.10 The flowchart shown detects a third parameter of the liquid L1.

[0074] <5-2>

[0075] In the above embodiment, the third parameter is set to the alkalinity of the liquid L1. However, the third parameter may not necessarily be the alkalinity of the liquid L1. The third parameter may be, for example, the acidity of the liquid L1. It is also possible to pre-generate the relationship information based on the acidity of the liquid L1 being set as the third parameter, and then Fig.10 The flowchart shown detects a third parameter of the liquid L1.

[0076] Fig.11This is a diagram showing an example of the relationship between the acid value (estimated value) of the liquid L1 detected using the relationship information and the analyzed value of the acid value of the liquid L1 when the acid value of the liquid L1 is used as the third parameter. Fig.11 , the horizontal axis represents the analysis value, and the vertical axis represents the estimated value or error. The white points P4 represent the estimated value (acid value) related to the liquid L1 with a specific analysis value (acid value), and the black points P5 represent the error between the estimated value and the analysis value. The reference line RL3 represents the upper limit of the error specified in the JIS standard (JIS K2501: 2003 Potentiometric titration (acid value)), and the reference line RL4 represents the lower limit of the error specified in the JIS standard. Fig.11 As shown, the errors of the estimated values ​​are within the error range specified in the JIS standard.

[0077] <5-3>

[0078] In the above-mentioned embodiment, the same relationship information is always used in the detection of the third parameter. However, the relationship information used to detect the third parameter can be changed according to the specified conditions. For example, a plurality of relationship information can be prepared in advance, and the plurality of relationship information can correspond to different temperature zones of the liquid L1. For example, a plurality of relationship information can be generated in advance by changing the temperature of a plurality of samples (liquid L1). A plurality of relationship information can also be stored in the storage unit 106.

[0079] Fig.12 1 is a flowchart showing a process of determining the relationship information used in detecting the third parameter. The processing shown in the flowchart is executed by the control unit 104, for example. Fig.12 The control unit 104 detects the temperature of the liquid L1 based on the output of the temperature sensor 113 (step S300). The control unit 104 determines the relationship information corresponding to the detected temperature of the liquid L1 (step S310). The determined relationship information can be used and Fig.10 The flowchart shown is used to detect the third parameter of the liquid L1.

[0080] The inventors (et al.) discovered that the relationship between the third parameter and the second parameter may be affected by the temperature of the liquid L1. In the liquid sensor 10, the third parameter is detected based on the temperature of the liquid L1, the relationship information corresponding to the temperature of the liquid L1, and the second parameter. Therefore, according to the liquid sensor 10, since the third parameter is detected based on the temperature of the liquid L1, the third parameter can be detected with higher accuracy.

[0081] <5-4>

[0082] In the above embodiment, the resistance value R1 is used as the first parameter regardless of the value of the third parameter. However, what is used as the first parameter may be changed in response to the value of the third parameter.

[0083] Fig.13 2 is a diagram for explaining an image related to a change in the first parameter. Fig.13 For example, when the base value (third parameter) is 4 or more, the electrostatic capacitance C1 can be used as the first parameter, and when the base value is less than 4, the resistance value R1 can be used as the first parameter. The inventors (et al.) have found that which of the second parameter calculated based on the resistance value R1 and the second parameter calculated based on the electrostatic capacitance C1 has a higher correlation with the third parameter varies depending on the value of the third parameter. More specifically, the inventors (et al.) have found that: the higher the base value, the higher the correlation between the second parameter calculated based on the electrostatic capacitance C1 and the third parameter, and the lower the base value, the higher the correlation between the second parameter calculated based on the resistance value R1 and the third parameter.

[0084] Fig.14 1 is a flowchart showing another example of the flow of detecting the alkalinity value of the liquid L1 in the liquid sensor 10 . The processing shown in this flowchart is executed by the control unit 104 .

[0085] Reference Fig.14 , the control unit 104 detects the resistance value R1 (first parameter) of the liquid L1 when a measurement voltage of a specified frequency (for example, any one of the four frequencies pre-set in the relationship information) is applied between a pair of electrodes 112 (step S400). The control unit 104 determines whether the resistance value R1 is detected when the measurement voltages of the respective predetermined multiple (for example, four) specified frequencies are applied between a pair of electrodes 112 (step S405). When it is determined that the detection of the resistance value R1 is not completed for at least part of the frequencies (no in step S405), the control unit 104 controls the measurement unit 102 to scan the frequency of the measurement voltage (step S410). Thereafter, the process of step S400 is performed again.

[0086] When it is determined that the detection of the resistance value R1 is completed for all the specified frequencies (Yes in step S405), the control unit 104 calculates the first change degree and the second change degree based on the detection results of the resistance value R1 (step S415). The control unit 104 calculates the difference (second parameter) between the first change degree and the second change degree (step S420). The control unit 104 detects the alkalinity (third parameter) of the liquid L1 by substituting the second parameter into the relationship information (e.g., function) stored in the storage unit 106 (step S425). The relationship information used here is pre-generated based on the frequency characteristics of the resistance value R1.

[0087] The control unit 104 determines whether the detected alkalinity is greater than a predetermined value (e.g., "4") (step S430). If it is determined that the detected alkalinity is less than the predetermined value (No in step S430), the process shown in the flowchart ends, and the alkalinity detected in step S425 is regarded as the alkalinity of the liquid L1.

[0088] On the other hand, if it is determined that the detected alkali value is greater than the specified value (Yes in step S430), the control unit 104 detects the electrostatic capacitance C1 (first parameter) of the liquid L1 while applying a measurement voltage of a specified frequency between a pair of electrodes 112 (step S435). The control unit 104 determines whether the detection of the electrostatic capacitance C1 is performed while the measurement voltages of each of the pre-set multiple specified frequencies are applied between a pair of electrodes 112 (step S440). When it is determined that the detection of the electrostatic capacitance C1 is not completed for at least part of the frequency (No in step S440), the control unit 104 controls the measurement unit 102 to scan the frequency of the measurement voltage (step S445). Thereafter, the process of step S435 is performed again.

[0089] When it is determined that the detection of the electrostatic capacitance C1 is completed for all specified frequencies (yes in step S440), the control unit 104 calculates the first degree of change and the second degree of change based on the detection results of the electrostatic capacitance C1 (step S450). The control unit 104 calculates the difference (second parameter) between the first degree of change and the second degree of change (step S455). The control unit 104 detects the alkalinity value (third parameter) of the liquid L1 by substituting the second parameter into the relationship information (such as a function) stored in the storage unit 106 (step S460). In addition, the relationship information used here is pre-generated based on the frequency characteristics of the electrostatic capacitance C1. If the alkalinity value is detected in step S460, the processing shown in the flowchart ends, and the alkalinity value detected in step S460 is regarded as the alkalinity value of the liquid L1.

[0090] Thus, in the liquid sensor 10, the use of the resistance value R1 and the electrostatic capacitance C1 as the first parameter is switched in response to the value of the third parameter. Therefore, according to the liquid sensor 10, since the second parameter having a higher correlation with the third parameter is used for the detection of the third parameter, the third parameter can be detected with higher accuracy.

[0091] The above is an exemplary description of the embodiments of the present invention. That is, the detailed description and the drawings are disclosed for the purpose of exemplary description. Therefore, the components described in the detailed description and the drawings may include components that are not necessary for solving the problem. Therefore, these non-essential components should not be directly regarded as necessary just because they are described in the detailed description and the drawings.

[0092] In addition, the above-mentioned embodiments are merely examples of the present invention in all aspects. The above-mentioned embodiments can be variously improved and changed within the scope of the present invention. For example, at least a part of the structure of any embodiment can be combined with at least a part of the structure of any other embodiment. That is, when implementing the present invention, a specific structure can be appropriately adopted in accordance with the embodiment.

Claims

1. A liquid sensor comprising: a pair of electrodes used in a state of being immersed in a liquid; and a control unit that scans the frequency of the AC voltage applied between the pair of electrodes, The control unit detects the impedance of the liquid at each frequency and calculates a second parameter associated with the first parameter, wherein: The first parameter is a value having a correlation with the impedance or the impedance, The second parameter is the difference between the first degree of change and the second degree of change, The first change degree and the second change degree respectively represent the change amount of the first parameter relative to the change amount of the frequency, The liquid sensor further includes a storage unit storing relationship information indicating a correspondence relationship between a third parameter and the second parameter, wherein the third parameter is correlated with a degree of degradation of the liquid. The control unit detects the third parameter based on the second parameter and the relationship information.

2. The liquid sensor according to claim 1, wherein: The first parameter is the resistance value of the liquid or the electrostatic capacitance of the liquid.

3. The liquid sensor according to claim 2, wherein: The third parameter is the alkalinity value of the liquid or the acidity value of the liquid.

4. The liquid sensor according to claim 1 or 2, wherein: The liquid sensor further includes a temperature sensor for detecting the temperature of the liquid. The relationship information is set according to each temperature of the liquid, The control unit detects the third parameter based on the temperature of the liquid, the relationship information corresponding to the temperature of the liquid, and the second parameter.

5. The liquid sensor according to claim 2, wherein: The control unit switches between the resistance value and the electrostatic capacitance to be used as the first parameter in response to the detected value of the third parameter.

6. A detection method comprising: a step of sweeping the frequency of an AC voltage applied between a pair of electrodes immersed in a liquid; The step of detecting the impedance of the liquid at each frequency; and a step of calculating a second parameter associated with a first parameter, wherein the first parameter is a value having a correlation with the impedance or the impedance, The second parameter is the difference between the first degree of change and the second degree of change, The first change degree and the second change degree respectively represent the change amount of the first parameter relative to the change amount of the frequency, The detection method further includes: a step of storing relationship information indicating a corresponding relationship between a third parameter and the second parameter, wherein the third parameter has a correlation with the degree of degradation of the liquid; and The step of detecting the third parameter based on the second parameter and the relationship information.

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