Calibration Method of Concentration Sensor

Abstract

To enhance detection accuracy regarding a method for calibrating a concentration sensor.SOLUTION: A concentration sensor comprises a resonator and a signal processing unit. A method for calibrating the concentration sensor comprises: a first step of setting a calibration jig to a first impedance depending on a first alcohol concentration and connecting it to a cathode of a varactor diode; a second step of obtaining a first resonance characteristic with the first impedance connected in the signal processing unit; a third step of setting the calibration jig to a second impedance depending on a second alcohol concentration and connecting it to the cathode of the varactor diode; a fourth step of obtaining a second resonance characteristic with a second impedance connected in the signal processing unit; a fifth step of calculating a coefficient between the first alcohol concentration and the second alcohol concentration from the first resonance characteristic and the second resonance frequency characteristic; and a sixth step of storing the coefficient in a storage unit.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for calibrating a concentration sensor.

Background Art

[0002] Patent Document 1 discloses a gas concentration sensor equipped with a calibration curve for converting a detection signal of a sensor into a concentration signal.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the conventional calibration curve is a conditional expression obtained by previously confirming the correlation between the actual measurement value by the concentration sensor and the gas concentration. For this reason, characteristic variations based on assembly errors of components such as capacitors and inductors that make up individual concentration sensors are not taken into consideration, and it has been difficult to improve the detection accuracy of the concentration sensor.

[0005] Therefore, the present disclosure aims to solve such problems and improve the detection accuracy of the concentration sensor.

Means for Solving the Problems

[0006] The calibration method of the concentration sensor in one aspect of the present disclosure is in a concentration sensor including a resonator and a signal processing unit. The resonator has an inductor, a first capacitor, and a varactor diode. The signal processing unit has an arithmetic unit and a storage unit. The method includes: a first step of setting a calibration jig to a first impedance corresponding to a first alcohol concentration and connecting it to the cathode of the varactor diode; a second step of obtaining a first resonance characteristic in the signal processing unit with the first impedance connected; a third step of setting the calibration jig to a second impedance corresponding to a second alcohol concentration and connecting it to the cathode of the varactor diode; a fourth step of obtaining a second resonance characteristic in the signal processing unit with the second impedance connected; a fifth step of calculating a coefficient between the first alcohol concentration and the second alcohol concentration from the first resonance characteristic and the second resonance characteristic; and a sixth step of storing the coefficient in the storage unit.

Effect of the Invention

[0007] By this calibration method, the detection accuracy of the concentration sensor can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0009] Hereinafter, a calibration method for a concentration sensor according to an embodiment of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below shows a preferred specific example of the present disclosure. Therefore, the shapes, components, arrangements, and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Thus, among the components in the following embodiments, the components not described in the independent claims indicating the highest-level concept of the present invention are described as optional components.

[0010] Each figure is a schematic diagram and is not necessarily drawn precisely. In each figure, the same reference numerals are given to substantially the same structures, and overlapping descriptions are omitted or simplified.

[0011] FIG. 1 is a schematic diagram showing a calibration method for a concentration sensor 100 that detects the concentration of alcohol contained in a mixed fuel. The concentration sensor 100 includes an oscillator 10, a resonator 20, and a signal processing unit 30. A calibration jig 40 is attached to the concentration sensor 100. Note that the hatching shown in the resonator 20 indicates the mixed fuel 1.

[0012] The oscillator 10 outputs an inspection signal Vd0. The inspection signal Vd0 is a signal of a predetermined voltage having a predetermined frequency. The inspection signal Vd0 is, for example, a signal having a frequency of 100 MHz and an amplitude of ±5 V.

[0013] The resonator 20 is composed of an inductor 21, a capacitor 22, and a varactor diode 23. The capacitor 22 and the varactor diode 23 are connected in parallel to form a composite capacitor 24. A capacitor 25 disposed between the cathode side of the varactor diode 23 and the capacitor 22 is a capacitor for DC cut with respect to the control signal Vt. The resonator 20 is, for example, a series resonance type resonance circuit composed of an inductor 21 and a composite capacitor 24 connected in series with each other. Note that one end of the composite capacitor 24 is grounded, but one end may be an open end. Further, the resonator 20 may be a parallel resonance type resonance circuit composed of an inductor 21 and a composite capacitor 24 connected in parallel with each other.

[0014] The capacitor 22 constituting the resonator 20 is composed of a pair of electrodes 22A and 22B. In concentration detection, the pair of electrodes 22A and 22B are disposed in the mixed fuel 1. The capacitor 22 is composed of the electrodes 22A and 22B and a portion 1A between the electrodes 22A and 22B of the mixed fuel 1. Therefore, the capacitance of the capacitor 22 is proportional to the relative permittivity of the mixed fuel 1. That is, the resonance frequency of the resonator 20 is proportional to the relative permittivity of the mixed fuel 1. The mixed fuel 1 is a fuel obtained by mixing a petroleum-based fuel and alcohol. In the embodiment, the mixed fuel 1 is a fuel obtained by mixing gasoline, which is a petroleum-based fuel, and ethanol, which is alcohol. Note that the petroleum-based fuel of the mixed fuel 1 may be a fuel other than gasoline such as light oil, and the alcohol may be an alcohol other than ethanol such as methanol. The concentration sensor 100 in the embodiment can detect the concentration of alcohol in the mixed fuel 1 in the same manner as gasoline and ethanol. The inspection signal Vd0 is output as an inspection signal Vd1 via the resonator 20. Specifically, the inspection signal Vd0 is input to the input terminal 201 of the resonator 20 and output as the inspection signal Vd1 from the output terminal 202 of the resonator 20. The capacitance of the varactor diode 23 constituting the resonator 20 is controlled by a control signal Vt output from the signal processing unit 30. The control signal Vt is input to the input terminal 203 of the resonator 20.

[0015] The signal processing unit 30 outputs a control voltage Vt. The control signal Vt is controlled such that the impedance of the resonator 20 becomes maximum. That is, the control signal Vt is controlled such that the inspection signal Vd1 output from the resonator 20 becomes maximum. In other words, the control signal Vt is controlled according to the resonance characteristics of the resonator 20.

[0016] The inspection signal Vd1 is input to the signal processing unit 30. Note that the inspection signal Vd1 input to the signal processing unit 30 is preferably a DC signal. In this case, it can be converted into a DC signal by arranging a detection circuit 60 between the output terminal 202 of the resonator 20 and the signal processing unit 30. The detection circuit 60 can be configured by, for example, a Schottky diode. The signal processing unit 30 extracts the voltage of the control signal Vt at which the value of the inspection signal Vd1 becomes maximum. The signal processing unit 30 outputs the concentration of ethanol in the mixed fuel 1 as an output signal Vout to the output port 70 based on the voltage of the extracted control signal Vt.

[0017] Fig. 2 shows the relationship between the control signal Vt and the ethanol concentration. In Fig. 2, the vertical axis represents the voltage of the control signal Vt, and the horizontal axis represents the ethanol concentration in the mixed fuel 1. Curve A shows the relationship between the control signal Vt and the ethanol concentration in the concentration sensor 100. Note that curve A shows the relationship between the ethanol concentration and the control signal Vt based on the theoretical values of the components such as the inductor 21, capacitor 22, and varactor diode 23 that make up the resonator 20. That is, the ethanol concentration can be derived by extracting the control signal Vt in the concentration sensor 100.

[0018] The signal processing unit 30 includes an arithmetic unit 301 and a storage unit 302. In the arithmetic unit 301, an arithmetic expression 301A approximating the curve A shown in FIG. 2 is programmed. In the storage unit 302, a coefficient 302A in the arithmetic expression 301A is stored. The arithmetic unit 301 is configured to execute arithmetic processing according to the arithmetic expression 301A by referring to the coefficient 302A stored in the storage unit 302. By adopting such a configuration that the coefficient 302A of the arithmetic expression 301A is stored in the storage unit 302, the arithmetic expression 301A can be updated by replacing the storage unit 302 or rewriting the coefficient 302A stored in the storage unit 302.

[0019] Updating this arithmetic expression 301A can improve the detection accuracy of the concentration sensor 100. That is, the concentration sensor 100 is based on the resonance frequency of the resonator 20 as described above. And individual components such as the inductor 21, capacitor 22, and varactor diode 23 that make up the resonator 20 include individual characteristic variations in mass production. For this reason, variations in resonance characteristics occur in individual resonators 20 during the mass production process of the concentration sensor 100. This variation in resonance characteristics is a factor causing deterioration of the detection accuracy of the concentration sensor 100. Therefore, by individually calibrating the arithmetic expression 301A according to the variations in resonance characteristics occurring in the mass production process, it is possible to suppress deterioration of the characteristics of the concentration sensor 100 in mass production.

[0020] Next, a calibration method for the concentration sensor 100 will be described. When calibrating the concentration sensor 100, a calibration jig 40 shown in FIG. 1 is used. The calibration jig 40 is composed of impedance elements that can be set to known impedances. The impedance element can be configured by connecting a resistor 401 and a capacitor 402 in parallel. One end of the calibration jig 40 is connected between the varactor diode 23 and the signal processing unit 30. The other end of the calibration jig 40 may be grounded. Note that the concentration sensor 100 is provided with a connector 50 to which the calibration jig 40 can be attached and detached. The calibration jig 40 can be detachably connected between the varactor diode 23 and the signal processing unit 30 via the connector 50.

[0021] The calibration jig 40 is an impedance element composed of a resistor 401 and a capacitor 402, and its impedance value can be appropriately set by changing the values of the capacitor 402 and the resistor 401. When the calibration jig 40 is connected to the resonator 20, the apparent impedance of the resonator 20 changes. The varactor diode 23 is controlled so that its capacitance changes to suppress the impedance change of the resonator 20. That is, the control signal Vt applied to the varactor diode 23 varies according to the impedance of the calibration jig 40. The impedance of the calibration jig 40 is set to a value that reproduces the impedance in the situation where the capacitor 22 constituting the resonator 20 is immersed in the blended fuel 1.

[0022] That is, if there are no characteristic variations in the inductor 21, capacitor 22, and varactor diode 23 that make up the resonator 20, the value of the control detection signal Vt corresponding to the ethanol concentration set by the calibration jig 40 will match the value derived from curve A shown in FIG. 2. On the other hand, when the inductor 21, capacitor 22, and varactor diode 23 that make up the resonator 20 include the above-mentioned characteristic variations, the value of the control detection signal Vt corresponding to the ethanol concentration calculated by the theoretical value will deviate from curve A shown in FIG. 2. That is, the arithmetic expression 301A of the concentration sensor 100 can improve the detection accuracy of the concentration sensor 100 by updating the expression in consideration of the characteristic variations of the components in the mass production process.

[0023] Next, the update of the arithmetic expression 301A incorporated in the concentration sensor 100 will be described. The arithmetic expression 301A divides the range of ethanol concentration from 0% to 100% into equal parts, and the arithmetic expressions in each divided section are obtained as first-order approximation expressions. The first-order arithmetic expression is represented as Vt = a·C + b, where Vt is the control signal, C is the concentration, and a and b are coefficients. The update of the coefficients a and b will be described by taking the linear interpolation in the section between the first ethanol concentration c1 (25.0% in the figure) and the second ethanol concentration c2 (37.5% in the figure) as an example.

[0024] First, as the first step, attach the calibration jig 40 to the connector 50 of the concentration sensor 100. The impedance of the calibration jig 40 at this time is set to the impedance that results in the first ethanol concentration c1 as the resonator 20 in the state where the calibration jig 40 is attached.

[0025] Next, as the second step, the oscillator 10 outputs an inspection signal Vd0. The signal processing unit 30 extracts the voltage Vt1 of the control signal Vt at which the inspection signal Vd1 becomes maximum.

[0026] Next, as the third step, set the impedance of the calibration jig 40 to the impedance that results in the second ethanol concentration c2 as the resonator 20 in the state where the calibration jig 40 is attached.

[0027] Next, as the fourth step, the oscillator 10 outputs an inspection signal Vd0. The signal processing unit 30 extracts the voltage value Vt2 of the control signal Vt at which the inspection signal Vd1 becomes maximum.

[0028] Next, as the fifth step, the control circuit calculates the relationship between the ethanol concentration and the control voltage in the section from the first ethanol concentration to the second ethanol concentration.

[0029] Next, as the sixth step, obtain the relationship between the ethanol concentration C and the control voltage Vt in the section from ethanol concentration c1 to c2. The relationship between the ethanol concentration C and the control voltage Vt in this section is expressed as Vt = ((Vt2 - Vt1) / (c2 - c1))·C + Vt1. Therefore, with the coefficient a in the arithmetic expression in the section from the first ethanol concentration to the second ethanol concentration being (Vt2 - Vt1) / (c2 - c1) and the coefficient b being Vt1, rewrite the data in the storage unit.

[0030] By performing the same calculation for other concentration sections, the arithmetic expressions for each section where the ethanol concentration ranges from 0% to 100% can be updated.

[0031] In the above-described concentration sensor 100, although the arithmetic expression 301A showing the relationship between the ethanol concentration and the control signal Vt has been described as a first-order approximation expression, the present invention is not limited thereto. For example, Vt corresponding to concentrations at three or more points may be extracted in a predetermined concentration range, and a higher-order approximation expression based thereon may be used as the arithmetic expression 301A to update the coefficient 302A.

[0032] By updating the arithmetic expression 301A after manufacturing the concentration sensor 100 as described above, it is possible to suppress the influence of variations in the characteristics of the constituent members in each concentration sensor 100 during mass production. That is, it is possible to suppress the deterioration of characteristics during mass production of the concentration sensor 100. In addition, since the arithmetic expression 301A in the concentration sensor 100 can be freely updated, the arithmetic expression can be appropriately updated according to the object to be measured for the concentration. That is, it is possible to correspond to different measurement objects in one concentration sensor.

Industrial Applicability

[0033] The concentration detection method in the concentration sensor of the present disclosure is particularly effective in applications for measuring the concentration of a mixed fuel for an internal combustion engine such as an automobile.

Explanation of Signs

[0034] 1 Mixed fuel 10 Oscillator 20 Resonator 21 Inductor 22 Capacitor 23 Varactor diode 30 Signal processing unit 301 Arithmetic unit 301A Arithmetic expression 302 Storage unit 302A Coefficient 40 Calibration jig 100 Concentration sensor

Claims

【Claim 1】 The concentration sensor includes a resonator for detecting the concentration of the alcohol contained in the mixed fuel of the petroleum-based fuel and the alcohol, and a signal processing unit connected to the resonator. The resonator includes: an inductor having one end connected to an oscillator; a first capacitor having one end connected to the other end of the inductor and the other end configured to be grounded; a varactor diode having its cathode side connected between the inductor and the capacitor and its anode side configured to be grounded. The first capacitor is configured to be immersed in the mixed fuel when measuring the concentration of the alcohol. The signal processing unit has an arithmetic unit and a storage unit. The storage unit stores coefficients. The arithmetic unit has an arithmetic formula configured by referring to the coefficients stored in the storage unit. The calibration jig has an impedance element. The calibration method of the concentration sensor is as follows: A first step of setting the impedance of the calibration jig to a first impedance corresponding to a first alcohol concentration and connecting it to the cathode of the varactor diode; A second step of obtaining a first resonance characteristic from an inspection signal output from the resonator with the first impedance connected in the signal processing unit; A third step of setting the impedance of the calibration jig to a second impedance corresponding to a second alcohol concentration and connecting it to the cathode of the varactor diode; A fourth step of obtaining a second resonance characteristic from an inspection signal output from the resonator with the second impedance connected in the signal processing unit; A fifth step of calculating a coefficient in the arithmetic formula between the first alcohol concentration and the second alcohol concentration from the first resonance characteristic and the second resonance characteristic; A sixth step of storing the coefficient in the storage unit as the coefficient between the first alcohol concentration and the second alcohol concentration. A calibration method of a concentration sensor.

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