Resistance detection sensor

Abstract

To provide a resistance detection sensor capable of suppressing a decrease in detection accuracy of an electric resistance value of a liquid.SOLUTION: A resistance detection sensor detects an electric resistance value of a liquid. The resistance detection sensor includes a pair of electrodes, a DC voltage application portion, an AC voltage application portion, and a control portion. The pair of electrodes are immersed in a liquid. The DC voltage application portion applies DC voltage having a first polarity between the pair of electrodes. The AC voltage application portion applies AC voltage between the pair of electrodes. The control portion calculates the electric resistance value of the liquid in a state where the DC voltage application portion applies the DC voltage between the pair of electrodes. The control portion controls the AC voltage application portion so as to apply the AC voltage starting from a second polarity opposite to the first polarity at a predetermined time interval between the pair of electrodes. The time period for which the AC voltage application portion applies the AC voltage between the pair of electrodes is not an integer multiple of the cycle of the AC voltage applied between the pair of electrodes.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a resistance detection sensor.

Background Art

[0002] Japanese Patent No. 3769119 (Patent Document 1) discloses a liquid purity monitoring device. This purity monitoring device includes a sensor unit. In the sensor unit, an amplifier is configured, and the sensor unit includes an internal electrode and an external electrode. In this purity monitoring device, with the internal electrode and the external electrode immersed in the liquid, a voltage is applied between the electrodes, and the electrical resistance value of the liquid is calculated based on the output voltage of the amplifier (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=3,4]] In the technology disclosed in the above Patent Document 1, for example, when calculating the electrical resistance value of a liquid containing moisture, an alternating voltage is applied between the electrodes. However, it is generally known that the detection accuracy of the electrical resistance value in the method of calculating the electrical resistance value of a liquid by applying an alternating voltage between the electrodes is lower than that in the method of calculating the electrical resistance value of a liquid by applying a direct voltage between the electrodes. Also, the measurement range of the electrical resistance value (for example, 10 ,

[0004] , , 16 , , 8 , , ، , , ,

[0003] , , , , -8 , , -3 , ,

[0005] -10 8 ) in the method of calculating the electrical resistance value of a liquid by applying an alternating voltage between the electrodes is narrower than the measurement range of the electrical resistance value (for example, 10 -8 -10 16 ) in the method of calculating the electrical resistance value of a liquid by applying a direct voltage between the electrodes.

[0005] On the other hand, if a DC voltage is applied between electrodes to calculate the electrical resistance of a liquid containing water, for example, the electrolysis of water in the liquid and the polarization of the components constituting the liquid are promoted. As a result, oxidation products or gases are generated at the surface of each electrode, causing errors in the calculation of the electrical resistance. In other words, the accuracy of detecting the electrical resistance decreases.

[0006] The present invention has been made to solve these problems, and its objective is to provide a resistance detection sensor that can suppress a decrease in the detection accuracy of the electrical resistance value of a liquid. [Means for solving the problem]

[0007] A resistance detection sensor according to the present invention detects the electrical resistance of a liquid. This resistance detection sensor comprises a pair of electrodes, a DC voltage application unit, an AC voltage application unit, and a control unit. The pair of electrodes are immersed in the liquid. The DC voltage application unit applies a DC voltage of a first polarity between the pair of electrodes. The AC voltage application unit applies an AC voltage between the pair of electrodes. The control unit calculates the electrical resistance of the liquid while a DC voltage is applied between the pair of electrodes by the DC voltage application unit. The control unit controls the AC voltage application unit to apply an AC voltage starting from a second polarity opposite to the first polarity between the pair of electrodes at predetermined time intervals. The time during which the AC voltage is applied between the pair of electrodes by the AC voltage application unit is not an integer multiple of the period of the AC voltage applied between the pair of electrodes.

[0008] In this resistance detection sensor, an AC voltage starting from a second polarity opposite to the first polarity is applied between a pair of electrodes at predetermined time intervals, and the time during which the AC voltage is applied between the pair of electrodes is not an integer multiple of the period of the AC voltage applied between the pair of electrodes. Therefore, with this resistance detection sensor, a voltage with the opposite polarity to the voltage applied for calculating the electrical resistance of the liquid is applied between the pair of electrodes at predetermined time intervals, thus suppressing the generation of polarization. As a result, this resistance detection sensor can suppress a decrease in the detection accuracy of the electrical resistance of the liquid.

[0009] In the above-described resistance detection sensor, the time during which an AC voltage is applied between the pair of electrodes by the AC voltage application unit may be the sum of half the period of the AC voltage applied between the pair of electrodes and an integer multiple of the period of the AC voltage applied between the pair of electrodes.

[0010] This resistance detection sensor ensures that a voltage with the opposite polarity to the voltage applied for calculating the electrical resistance of the liquid is applied to the pair of electrodes to the maximum extent possible, thereby further suppressing the generation of polarization. As a result, this resistance detection sensor can further suppress the decrease in the accuracy of detecting the electrical resistance of the liquid.

[0011] The above-mentioned resistance detection sensor further comprises an operational amplifier, and in the resistance detection sensor, an amplification circuit including the operational amplifier is configured, one electrode of the pair of electrodes is connected to the input side of the operational amplifier, and the other electrode of the pair of electrodes is connected to the output side of the operational amplifier, and the control unit may calculate the electrical resistance value of the liquid based on the output voltage of the operational amplifier.

[0012] In the above-described resistance detection sensor, the period during which the electrical resistance value of the liquid is calculated and the period during which an AC voltage is applied between the pair of electrodes may be the same.

[0013] With this resistance detection sensor, the period during which the electrical resistance value of the liquid is calculated is the same as the period during which an AC voltage is applied between the pair of electrodes, thus suppressing the occurrence of polarization each time. As a result, this resistance detection sensor can suppress a decrease in the accuracy of detecting the electrical resistance value of the liquid.

[0014] In the above-described resistance detection sensor, the liquid may be a liquid lubricant.

[0015] According to this resistance detection sensor, a voltage with the opposite polarity to the voltage applied for calculating the electrical resistance of the liquid lubricant is applied between the pair of electrodes at predetermined time intervals, thereby suppressing the generation of polarization. As a result, this resistance detection sensor can suppress a decrease in the accuracy of detecting the electrical resistance of the liquid lubricant.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a resistance detection sensor capable of suppressing a decrease in detection accuracy of the electrical resistance value of a liquid.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram schematically showing a partial electrical configuration of a resistance detection sensor. [Figure 2] It is a diagram for explaining what problems occur when an AC voltage is not applied at a predetermined time interval. [Figure 3] It is a diagram for explaining the effect of applying an AC voltage between electrodes at a predetermined time interval. [Figure 4] It is a diagram for explaining the operations in each of the sensor unit and the control unit. [Figure 5] It is a flowchart showing an example of an operation procedure in a resistance detection sensor. [Figure 6] It is a diagram for explaining an example in which the time when an AC voltage is applied between electrodes is half of the period of the AC voltage. [Figure 7] It is a diagram schematically showing other examples of each electrode used in a resistance detection unit. [Figure 8] It is a diagram schematically showing a partial electrical configuration of a resistance detection sensor which is another embodiment. [Figure 9] It is a diagram showing the transition of current when the DC voltage applied between electrodes becomes substantially 0V at the timing when an AC voltage is applied between electrodes.

Mode for Carrying Out the Invention

[0018] Hereinafter, embodiments 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 drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated. Also, each drawing is schematically drawn with appropriate omissions or exaggerations of the subject for easy understanding.

[0019] [1. Configuration of the resistance detection sensor] Figure 1 is a schematic diagram showing a part of the electrical configuration of a resistance detection sensor 10 according to this embodiment. Referring to Figure 1, the resistance detection sensor 10 is configured to detect the electrical resistance value of a liquid.

[0020] Examples of liquids include liquid lubricants such as mineral oil, synthetic oil, animal and vegetable oils, and water-based lubricants; semi-solid lubricants such as lithium soap grease, calcium soap grease, urea grease, and silicone grease; and aqueous solutions such as hydrochloric acid. Liquid lubricants include, for example, hydraulic fluid, gear oil, turbine oil, bearing lubricant, guide surface oil, compressor oil, refrigeration oil, plastic processing oil, heat treatment oil, cutting oil, engine oil, ATF (Automatic Transmission Fluid), CVTF (Continuously Variable Transmission Fluid), and brake fluid.

[0021] The resistance detection sensor 10 includes a sensor unit 100 and a control unit 200. The sensor unit 100 includes a positive power supply V1, a negative power supply V2, an operational amplifier 130, a resistance detection unit 140, resistors 150, 151, 152, and a capacitor 160.

[0022] The positive power supply V1 is electrically connected to terminal Te2 via terminal Te1 and resistor 152. Terminal Te2 is electrically connected to the positive terminal of the operational amplifier 130, and is also electrically connected to the negative power supply V2 via resistor 151 and terminal Te5. Furthermore, terminal Te2 is electrically connected to terminal Te8 of the control unit 200 via capacitor 160. Terminal Te8 is the output terminal of the control unit 200.

[0023] As will be described in detail later, the control unit 200 is configured to apply an AC voltage to the sensor unit 100 at predetermined time intervals. The control unit 200 receives power from, for example, an external AC power source for the resistance detection sensor 10 and applies an AC voltage to the sensor unit 100. When an AC voltage is applied to the sensor unit 100, an AC signal is output from terminal Te8.

[0024] Furthermore, the negative power supply V2 is electrically connected to the negative terminal of the operational amplifier 130 via terminals Te5, Te6, resistor 150, and terminal Te4. The operational amplifier 130 is electrically connected to terminal Te7 of the control unit 200 via terminal Te3. Terminal Te7 is an input terminal of the control unit 200. Terminal Te3 is connected to terminal Te4 via the resistance detection unit 140.

[0025] The resistance detection unit 140 includes electrodes 110 and 120. Electrodes 110 and 120 form a pair of electrodes. Each of electrodes 110 and 120 is composed of, for example, a conductive plate containing metal. Each of electrodes 110 and 120 is immersed in liquid F1. In other words, in the resistance detection sensor 10, a non-inverting amplifier circuit is formed by a positive power supply V1, a negative power supply V2, an operational amplifier 130, the resistance detection unit 140, and resistors 150, 151, and 152.

[0026] In the resistance detection sensor 10, the voltage values ​​of the positive power supply V1 and the negative power supply V2 are known, and the resistance values ​​of resistors 151 and 152 are known. Therefore, at least when no AC voltage is applied to the sensor unit 100, the input voltage Vin of the operational amplifier 130 is known. Also, the resistance value of resistor 150 is known. When the resistance value of resistor 150 is R1 and the resistance value in the resistance detection unit 140 is R2, the following relationship (1) holds in the non-inverting amplifier circuit.

[0027] The output voltage of op-amp 130 is Vout = (R1 + R2)Vin / R1 ... (1)

[0028] Since R1 and Vin are known, the control unit 200 can calculate R2 by detecting the output voltage Vout of the operational amplifier 130. That is, in the resistance detection sensor 10, the electrical resistance value of the liquid F1 is detected based on the output voltage Vout of the operational amplifier 130 when a DC voltage due to the positive power supply V1 is applied between electrodes 110 and 120.

[0029] The control unit 200 includes, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory). The control unit 200 controls each component within the resistance detection sensor 10 according to information processing. Also, as described above, the control unit 200 calculates the electrical resistance value of the liquid F1 based on, for example, the output voltage Vout (analog signal) of the operational amplifier 130. The control unit 200, for example, converts the analog signal to a digital signal during the calculation process and controls the output of the digital signal to the outside of the resistance detection sensor 10.

[0030] Furthermore, as described above, the control unit 200 receives power from an external AC power source for the resistance detection sensor 10, for example, and performs control to apply an AC voltage to the sensor unit 100 at predetermined time intervals. The reason why an AC voltage is applied to the sensor unit 100 at predetermined time intervals will be explained next.

[0031] In the resistance detection sensor 10, power is supplied to the operational amplifier 130 by a positive power supply V1 and a negative power supply V2. That is, the positive power supply V1 is connected to the positive power supply voltage application terminal of the operational amplifier 130, and the negative power supply V2 is connected to the negative power supply voltage application terminal of the operational amplifier 130. Power is supplied to the control unit 200 by, for example, the positive power supply V1, or by another power supply.

[0032] [2. Suppression of the decrease in detection accuracy of electrical resistance values] Figure 2 illustrates the problems that might arise if an AC voltage is not applied at predetermined time intervals.

[0033] Referring to the left portion of Figure 2, electrodes 121 and 111 are immersed in a liquid containing water. Each of electrodes 121 and 111 contains, for example, a metal. Electrode 121 is connected to the positive electrode of battery B1 via switch SW1, and electrode 111 is connected to the negative electrode of battery B1. Switch SW1 is open. In this state, most of the water in the liquid remains as water (H2O).

[0034] Referring to the central part of Figure 2, when switch SW1 is closed, a DC voltage is applied between electrodes 121 and 111, generating a current. When a DC voltage is applied between electrodes 121 and 111, the electrolysis of water contained in the liquid and the polarization of electrodes 121 and 111 are promoted. Oxygen ions produced by the electrolysis of water are attracted to electrode 121, and hydrogen ions produced by the electrolysis of water are attracted to electrode 111.

[0035] Referring to the right portion of Figure 2, if the switch SW1 remains closed, oxidation products (rust) are generated on the outer circumference of electrode 121, and a hydrogen gas layer GL1 is formed around electrode 111.

[0036] Referring again to Figure 1, if an AC voltage is not applied between electrodes 110 and 120 at predetermined time intervals, and only a DC voltage is continuously applied between electrodes 110 and 120, the problems described in Figure 2 may occur. Specifically, oxidation products are generated on the outer circumference of electrode 120, and a hydrogen gas layer is formed around electrode 110. This causes errors in the calculation of the electrical resistance value of liquid F1, and reduces the detection accuracy of the electrical resistance value of liquid F1.

[0037] Figure 3 is a diagram illustrating the effect of applying an AC voltage between electrodes 110 and 120 at predetermined time intervals. Referring to Figure 3, the horizontal axis represents time and the vertical axis represents current. The upper part of Figure 3 shows the change in DC current between electrodes 110 and 120 between times t0 and t4. The lower part of Figure 3 shows the change in AC current between electrodes 110 and 120 between times t0 and t4.

[0038] At time t0-t1, only a DC current is generated between electrodes 110 and 120. That is, at time t0-t1, only a DC voltage is applied between electrodes 110 and 120, and no AC voltage is applied between electrodes 110 and 120. The control unit 200 calculates the electrical resistance value in the resistance detection unit 140 based on the output voltage Vout of the operational amplifier 130 at time t0-t1.

[0039] Between times t1 and t4, a current is generated between electrodes 110 and 120, which is the DC current shown in the upper part of Figure 3 plus the AC current shown in the lower part of Figure 3. In other words, between times t1 and t4, both a DC voltage and an AC voltage are applied between electrodes 110 and 120. The purpose of applying an AC voltage between electrodes 110 and 120 between times t1 and t4 is to suppress the polarization of each electrode caused by the DC voltage applied between electrodes 110 and 120 between times t0 and t4.

[0040] Between times t0 and t4, a DC voltage of the first polarity (positive polarity) is applied between electrodes 110 and 120. Between times t1 and t4, an AC voltage starting with the second polarity (negative polarity), which is the opposite of the first polarity, is applied between electrodes 110 and 120. At time t2, the polarity of the AC voltage reverses from negative to positive, and at time t3, the polarity of the AC voltage reverses from positive to negative. In other words, in this example, the time during which the AC voltage is applied between electrodes 110 and 120 is the sum of half the period of the AC voltage applied between electrodes 110 and 120 and an integer multiple (1x) of the period of the AC voltage applied between electrodes 110 and 120.

[0041] The effect of the AC voltage on the polarization of electrodes 110 and 120 at time t2-t3 is canceled out by the effect of the AC voltage on the polarization of electrodes 110 and 120 at time t3-t4. Similarly, the effect of the DC voltage on the polarization of electrodes 110 and 120 at time t0-t4 is canceled out by the effect of the AC voltage on the polarization of electrodes 110 and 120 at time t1-t2.

[0042] In other words, the frequency and amplitude of the AC voltage applied between electrodes 110 and 120 are set, for example, so that the effect of the DC voltage applied between electrodes 110 and 120 on the polarization of each electrode is canceled out. However, it is not necessary for the AC voltage applied between electrodes 110 and 120 to completely cancel out the effect of the DC voltage on the polarization of each electrode; it is sufficient if the effect of the DC voltage on the polarization of each electrode is suppressed to some extent.

[0043] The control unit 200 may also determine whether the AC voltage applied between electrodes 110 and 120 starts with a second polarity (negative polarity) opposite to the first polarity. For example, a voltage sensor (not shown) that detects the input voltage Vin or output voltage Vout of the operational amplifier 130 may be provided, and the control unit 200 may determine whether the AC voltage applied between electrodes 110 and 120 starts with a second polarity based on the detection result of the voltage sensor. Alternatively, a current sensor (not shown) that detects the current generated in the resistance detection unit 140 may be provided, and the control unit 200 may determine whether the AC voltage applied between electrodes 110 and 120 starts with a second polarity based on the detection result of the current sensor. For example, if the control unit 200 determines that the AC voltage applied between electrodes 110 and 120 does not start with a second polarity, it may perform control to transmit a warning to the user.

[0044] Figure 4 is a diagram illustrating the operation of the sensor unit 100 and the control unit 200, respectively. Referring to Figure 4, the upper part shows the operation of the sensor unit 100, and the lower part shows the operation of the control unit 200.

[0045] In the sensor unit 100, a state in which only a direct current (DC) voltage is applied between electrodes 110 and 120, and a state in which both a direct current (DC) voltage and an alternating current (AC) voltage are applied between electrodes 110 and 120 are repeated at a predetermined period. When both a direct current (DC) voltage and an alternating current (AC) voltage are applied between electrodes 110 and 120, polarization at each of electrodes 110 and 120 is suppressed.

[0046] In the control unit 200, the electrical resistance value of the liquid F1 (Figure 1) is calculated at a predetermined period based on the output voltage Vout of the operational amplifier 130 when only a DC voltage is applied between electrodes 110 and 120. The calculation of the electrical resistance value may involve converting the analog signal to a digital signal.

[0047] As shown in Figure 4, the period during which the electrical resistance of liquid F1 is calculated is the same as the period during which an AC voltage is applied between electrodes 110 and 120. With the resistance detection sensor 10, since the period during which the electrical resistance of liquid F1 is calculated is the same as the period during which an AC voltage is applied between electrodes 110 and 120, the occurrence of polarization at each of electrodes 110 and 120 can be suppressed each time. As a result, the resistance detection sensor 10 can suppress a decrease in the detection accuracy of the electrical resistance of liquid F1.

[0048] [3. Operation of the resistance detection sensor] Figure 5 is a flowchart showing an example of the operation procedure in the resistance detection sensor 10. The process shown in this flowchart starts with only a DC voltage applied between electrodes 110 and 120 and is repeatedly executed by the control unit 200 at a predetermined period.

[0049] Referring to Figure 5, the control unit 200 starts calculating the electrical resistance value of liquid F1 based on the output voltage Vout of the operational amplifier 130 (step S100). That is, the control unit 200 generates the electrical resistance value (digital signal) of liquid F1 based on the detected output voltage Vout (analog signal) and sequentially outputs the generated digital signal (electrical resistance value) to the outside of the resistance detection sensor 10. Note that the control unit 200 does not necessarily have to sequentially output the generated digital signal to the outside of the resistance detection sensor 10. For example, the control unit 200 may use the generated digital signal inside the resistance detection sensor 10, or it may output the digital signal to the outside of the resistance detection sensor 10 when a digital signal of a certain capacitance has been generated.

[0050] The control unit 200 determines whether a first predetermined time has elapsed since it started detecting the output voltage Vout of the operational amplifier 130 (step S110). The first predetermined time is a predetermined time, which is the time during which the electrical resistance value of the liquid F1 is continuously calculated in one cycle of this flowchart.

[0051] If it is determined that the first predetermined time has not elapsed since the start of detecting the output voltage Vout of the operational amplifier 130 (NO in step S110), the control unit 200 continues to calculate the electrical resistance value of the liquid F1. On the other hand, if it is determined in step S110 that the first predetermined time has elapsed since the start of detecting the output voltage Vout of the operational amplifier 130 (YES in step S110), the control unit 200 performs control to apply an AC voltage between electrodes 110 and 120 (step S120).

[0052] The control unit 200 stops calculating the electrical resistance of liquid F1 based on the output voltage Vout for a first predetermined time period once it has finished calculating the electrical resistance of liquid F1 (step S130). The control unit 200 determines whether a second predetermined time has elapsed since the application of the AC voltage between electrodes 110 and 120 began (step S140). The second predetermined time is a predetermined time, which is the time obtained by adding an integer multiple (1) of the period of the AC voltage applied between electrodes 110 and 120 to half the period of the AC voltage applied between electrodes 110 and 120.

[0053] If it is determined that the second predetermined time has not elapsed since the application of the AC voltage between electrodes 110 and 120 began (NO in step S140), the control unit 200 waits until the second predetermined time has elapsed. On the other hand, if it is determined that the second predetermined time has elapsed since the application of the AC voltage between electrodes 110 and 120 began (YES in step S140), the control unit 200 performs control to stop the application of the AC voltage between electrodes 110 and 120 (step S150). After that, the control unit 200 executes the process in step S100 again.

[0054] [4. Features] As described above, in the resistance detection sensor 10 according to this embodiment, an AC voltage starting with the opposite polarity (negative polarity) to the polarity (positive polarity) of the DC voltage is applied between electrodes 110 and 120 at predetermined time intervals, and the time during which the AC voltage is applied between electrodes 110 and 120 is not an integer multiple of the period of the AC voltage applied between electrodes 110 and 120. Therefore, with the resistance detection sensor 10, a voltage with the opposite polarity to the polarity of the DC voltage applied for the calculation of the electrical resistance value of liquid F1 is applied between electrodes 110 and 120 at predetermined time intervals, thus suppressing the generation of polarization. As a result, with the resistance detection sensor 10, a decrease in the detection accuracy of the electrical resistance value of liquid F1 can be suppressed.

[0055] Furthermore, in the resistance detection sensor 10, the time during which an AC voltage is applied between electrodes 110 and 120 at predetermined time intervals is the sum of half the period of the AC voltage applied between electrodes 110 and 120 and an integer multiple of the period of the AC voltage applied between electrodes 110 and 120 (for example, 1). Therefore, with the resistance detection sensor 10, a voltage with the opposite polarity to the DC voltage applied for calculating the electrical resistance value of liquid F1 is applied to the electrodes 110 and 120 to the maximum extent possible, thereby further suppressing the occurrence of polarization. As a result, the resistance detection sensor 10 can further suppress the decrease in detection accuracy of the electrical resistance value of liquid F1.

[0056] Furthermore, with the resistance detection sensor 10, the period during which the electrical resistance value of liquid F1 is calculated is the same as the period during which an AC voltage is applied between electrodes 110 and 120, so the occurrence of polarization can be suppressed each time. As a result, the resistance detection sensor 10 can suppress a decrease in the detection accuracy of the electrical resistance value of liquid F1.

[0057] The resistance detection sensor 10 is an example of a "resistance detection sensor" in the present invention. The electrodes 110 and 120 are an example of a "pair of electrodes" in the present invention. The configuration including the positive power supply V1 and the negative power supply V2 is an example of a "DC voltage application unit" in the present invention. At least a part of the control unit 200 is an example of an "AC voltage application unit" in the present invention. At least a part of the control unit 200 is an example of a "control unit" in the present invention. The operational amplifier 130 is an example of an "operational amplifier" in the present invention. The liquid F1 is an example of a "liquid" in the present invention.

[0058] [5. Other Embodiments] The concept of the above embodiments is not limited to those described above. Below, we will describe an example of another embodiment to which the concept of the above embodiments can be applied.

[0059] <5-1> In the resistance detection sensor 10 according to the above embodiment, the waveform of the AC voltage applied between electrodes 110 and 120 was a square wave. However, the waveform of the AC voltage applied between electrodes 110 and 120 does not necessarily have to be a square wave. The waveform of the AC voltage applied between electrodes 110 and 120 may be, for example, a sine wave.

[0060] <5-2> In the resistance detection sensor 10 according to the above embodiment, the time for which an AC voltage is applied between electrodes 110 and 120 was the sum of half the period of the AC voltage applied between electrodes 110 and 120 and one time equal to the period of the AC voltage applied between electrodes 110 and 120. However, the time for which an AC voltage is applied between electrodes 110 and 120 is not limited to this. For example, the time for which an AC voltage is applied between electrodes 110 and 120 may be the sum of half the period of the AC voltage applied between electrodes 110 and 120 and two or more integer multiples of the period of the AC voltage applied between electrodes 110 and 120. Alternatively, the time for which an AC voltage is applied between electrodes 110 and 120 may be half the period of the AC voltage applied between electrodes 110 and 120.

[0061] Figure 6 illustrates an example where the AC voltage is applied between electrodes 110 and 120 for half the period of the AC voltage. Referring to Figure 6, the horizontal axis represents time and the vertical axis represents current. The upper part of Figure 6 shows the change in DC current between electrodes 110 and 120 between times t10 and t12. The lower part of Figure 6 shows the change in AC current between electrodes 110 and 120 between times t10 and t12.

[0062] Between times t10 and t11, only a DC current is generated between electrodes 110 and 120. That is, between times t10 and t11, only a DC voltage is applied between electrodes 110 and 120, and no AC voltage is applied between electrodes 110 and 120. The control unit 200 calculates the electrical resistance value in the resistance detection unit 140 based on the output voltage Vout of the operational amplifier 130 between times t10 and t11.

[0063] Between times t11 and t12, a current is generated between electrodes 110 and 120, which is the DC current shown in the upper part of Figure 6 plus the AC current shown in the lower part of Figure 6. In other words, between times t11 and t12, both a DC voltage and an AC voltage are applied between electrodes 110 and 120.

[0064] At times t10-t12, a DC voltage of the first polarity (positive polarity) is applied between electrodes 110 and 120. At times t11-t12, an AC voltage starting with the second polarity (negative polarity), which is the opposite of the first polarity, is applied between electrodes 110 and 120. For example, in this example, the time for which the AC voltage is applied between electrodes 110 and 120 is half the period of the AC voltage applied between electrodes 110 and 120. The time for which the AC voltage is applied between electrodes 110 and 120 may be any other.

[0065] The effect of the DC voltage on the polarization of electrodes 110 and 120 at time t10-t12 is canceled out by the effect of the AC voltage on the polarization of electrodes 110 and 120 at time t11-t12. The frequency and amplitude of the AC voltage applied between electrodes 110 and 120 are set, for example, so that the effect of the DC voltage applied between electrodes 110 and 120 on the polarization of each electrode is canceled out. However, it is not necessary for the effect of the DC voltage on the polarization of each electrode to be completely canceled out by the AC voltage applied between electrodes 110 and 120; it is sufficient if the effect of the DC voltage on the polarization of each electrode is suppressed to some extent. In short, the time during which the AC voltage is applied between electrodes 110 and 120 does not need to be an integer multiple of the period of the AC voltage applied between electrodes 110 and 120.

[0066] <5-3> Figure 7 is a schematic diagram showing another example of each electrode used in the resistance detection unit 140. As shown in Figure 7, each of electrodes 110A and 120A is immersed in liquid F1. Each of electrodes 110A and 120A has a comb-like shape. Electrodes 110A and 120A are arranged so that their combs are staggered. In the resistance detection sensor 10 according to the above embodiment, electrodes with a shape like electrodes 110A and 120A may be used instead of electrodes 110 and 120. In short, the shape of each of electrodes 110 and 120 is not particularly limited. If electrodes with a shape like electrodes 110A and 120A are used instead of electrodes 110 and 120, the control unit 200 may, for example, detect the capacitance between electrodes 110A and 120A while an AC voltage is applied between electrodes 110A and 120A. Furthermore, the control unit 200 may calculate the electrical resistance value of the liquid F1 when, for example, an AC voltage is applied between electrodes 110A and 120A.

[0067] <5-4> In the resistance detection sensor 10 according to the above embodiment, the sensor unit 100 is configured with a non-inverting amplifier circuit including an operational amplifier 130. However, the amplifier circuit configured in the sensor unit 100 is not limited to this. For example, instead of the non-inverting amplifier circuit, an inverting amplifier circuit including an operational amplifier may be configured in the sensor unit 100. In this case as well, for example, electrode 110 is connected to the input side of the operational amplifier, and electrode 120 is connected to the output side of the operational amplifier. The control unit 200 calculates the electrical resistance value of the liquid F1 based on the output voltage of the operational amplifier, for example. Such a configuration is also possible.

[0068] <5-5> In the resistance detection sensor 10 according to the above embodiment, a DC voltage is constantly applied between electrodes 110 and 120. However, a DC voltage does not necessarily have to be constantly applied between electrodes 110 and 120. For example, a switch is provided that can switch the electrical connection state between each electrode (electrodes 110 and 120) and each DC power supply (positive power supply V1, negative power supply V2), and this switch may be in an open state when an AC voltage is applied between electrodes 110 and 120.

[0069] <5-6> Furthermore, in the resistance detection sensor 10 according to the above embodiment, a constant DC voltage is always applied between electrodes 110 and 120. However, the DC voltage applied between electrodes 110 and 120 does not necessarily have to be constant at all times. For example, at the timing when an AC voltage is applied between electrodes 110 and 120, the DC voltage applied between electrodes 110 and 120 may be approximately 0V.

[0070] Figure 8 schematically shows a part of the electrical configuration of a resistance detection sensor 10A, which is another embodiment. Here, we will mainly explain the parts that differ from the resistance detection sensor 10 according to the above embodiment, and will not repeat the explanation of overlapping parts.

[0071] Referring to Figure 8, the resistance detection sensor 10A is configured to detect the electrical resistance of a liquid. The resistance detection sensor 10A includes a sensor unit 100A and a control unit 200A. The sensor unit 100A includes a resistor 152A. The resistor 152A is provided between terminals Te1 and Te2. The resistor 152A is configured as a variable resistor. The electrical resistance of the resistor 152A is controlled, for example, by the control unit 200A. Note that the configuration of the sensor unit 100A is the same as that of the sensor unit 100 in the above embodiment, except that it includes a resistor 152A instead of a resistor 152.

[0072] The control unit 200A includes, for example, a CPU, RAM, and ROM. The control unit 200A controls each component in the resistance detection sensor 10A according to information processing. The control unit 200A calculates the electrical resistance value of the liquid F1 based on the output voltage Vout of the operational amplifier 130 when a DC voltage is applied between electrodes 110 and 120. The control unit 200A also controls the electrical resistance value of resistor 152A. This changes the input voltage Vin of the operational amplifier 130. Specifically, the control unit 200A controls the electrical resistance value of resistor 152A so that the DC voltage applied between electrodes 110 and 120 is approximately 0V at the time when an AC voltage is applied between electrodes 110 and 120. Note that the means for making the DC voltage applied between electrodes 110 and 120 approximately 0V at the time when an AC voltage is applied between electrodes 110 and 120 is not limited to the use of a variable resistor.

[0073] Furthermore, with respect to the control unit 200A, the control is the same as that of the control unit 200 in the above embodiment, except for the fact that it controls the electrical resistance value of resistor 152A at the timing when an AC voltage is applied between electrodes 110 and 120. For example, the flowchart shown in Figure 5 differs from the above embodiment only in that in step S120, the control unit 200A controls the application of an AC voltage between electrodes 110 and 120, and also controls resistor 152A so that the DC voltage applied between electrodes 110 and 120 is approximately 0V.

[0074] Figure 9 shows the current progression when the DC voltage applied between electrodes 110 and 120 is approximately 0V at the time an AC voltage is applied between electrodes 110 and 120. Referring to Figure 9, the horizontal axis represents time and the vertical axis represents current. The upper part of Figure 9 shows the progression of the DC current generated between electrodes 110 and 120 between times t20 and t24. The lower part of Figure 9 shows the progression of the AC current generated between electrodes 110 and 120 between times t20 and t24.

[0075] Between times t20 and t21, only a DC current is present between electrodes 110 and 120. That is, between times t20 and t21, only a DC voltage is applied between electrodes 110 and 120, and no AC voltage is applied between electrodes 110 and 120. The control unit 200A calculates the electrical resistance value in the resistance detection unit 140 based on the output voltage Vout of the operational amplifier 130 between times t20 and t21.

[0076] Between times t21 and t24, only alternating current is present between electrodes 110 and 120. That is, between times t21 and t24, only approximately alternating voltage is applied between electrodes 110 and 120. Between times t20 and t21, a DC voltage of the first polarity (positive polarity) is applied between electrodes 110 and 120. Between times t21 and t24, an alternating voltage starting with the second polarity (negative polarity), which is the opposite of the first polarity, is applied between electrodes 110 and 120.

[0077] The effect of the AC voltage on the polarization of electrodes 110 and 120 at time t22-t23 is canceled out by the effect of the AC voltage on the polarization of electrodes 110 and 120 at time t23-t24. Also, the effect of the DC voltage on the polarization of electrodes 110 and 120 at time t20-t21 is canceled out by the effect of the AC voltage on the polarization of electrodes 110 and 120 at time t21-t22.

[0078] In other words, the frequency and amplitude of the AC voltage applied between electrodes 110 and 120 are set, for example, so that the effect of the DC voltage applied between electrodes 110 and 120 on the polarization of each electrode is canceled out. However, it is not necessary for the AC voltage applied between electrodes 110 and 120 to completely cancel out the effect of the DC voltage on the polarization of each electrode; it is sufficient if the effect of the DC voltage on the polarization of each electrode is suppressed to some extent. Such a configuration may be adopted.

[0079] <5-7> In the resistance detection sensor 10 according to the above embodiment, the control unit 200 generates an electrical resistance value (digital signal) of the liquid F1 based on the output voltage Vout (analog signal) of the operational amplifier 130, and sequentially outputs the generated digital signal (electrical resistance value) to the outside of the resistance detection sensor 10. In this case, the control unit 200 may, for example, perform convolution of the generated electrical resistance values ​​and sequentially output a digital signal showing the convolution result to the outside of the resistance detection sensor 10. This makes it possible to suppress a decrease in detection accuracy due to the presence of outliers.

[0080] <5-8> In the resistance detection sensor 10 according to the above embodiment, the control unit 200 may, for example, collect the output voltage Vout of the operational amplifier 130 when an AC voltage is applied between electrodes 110 and 120, and perform various analyses. For example, the frequency of the AC voltage applied between electrodes 110 and 120 may be adjusted as appropriate, and an analysis of the relationship between the frequency of the AC voltage and the electrical resistance value of the liquid F1 may be performed.

[0081] Embodiments of the present invention have been described illustratively above. That is, a detailed description and accompanying drawings have been disclosed for illustrative purposes. Therefore, some of the components described in the detailed description and accompanying drawings may not be essential for solving the problem. Consequently, the mere fact that these non-essential components are described in the detailed description and accompanying drawings does not mean that they should be immediately assumed to be essential.

[0082] Furthermore, the above embodiments are merely illustrative in every respect of the present invention. The above embodiments can be improved or modified in various ways within the scope of the present invention. That is, in carrying out the present invention, specific configurations can be appropriately adopted depending on the embodiment. [Explanation of symbols]

[0083] 10 Resistance detection sensor, 100 Sensor unit, 110, 111, 120, 121 Electrodes, 130 Operational amplifier, 140 Resistance detection unit, 150, 151, 152 Resistors, 160 Capacitor, 200 Control unit, B1 Battery, F1 Liquid, GL1 Gas layer, SW1 Switch, Te1, Te2, Te3, Te4, Te5, Te6, Te7, Te8 Terminals, V1 Positive power supply, V2 Negative power supply.

Claims

1. A resistance detection sensor for detecting the electrical resistance of a liquid, A pair of electrodes immersed in the aforementioned liquid, A DC voltage application unit that applies only a DC voltage of the first polarity between the pair of electrodes, An AC voltage application unit that applies an AC voltage between the pair of electrodes, The system includes a control unit that calculates the electrical resistance value of the liquid while a DC voltage is applied between the pair of electrodes by the DC voltage application unit, The control unit controls the AC voltage application unit to apply an AC voltage starting from a second polarity opposite to the first polarity between the pair of electrodes at predetermined time intervals. The time during which the AC voltage is applied between the pair of electrodes by the AC voltage application unit is not an integer multiple of the period of the AC voltage applied between the pair of electrodes, Equipped with an operational amplifier, In the aforementioned resistance detection sensor, an amplification circuit including the operational amplifier is configured, One electrode of the pair of electrodes is connected to the input side of the operational amplifier, and the other electrode of the pair of electrodes is connected to the output side of the operational amplifier. The control unit is a resistance detection sensor that calculates the electrical resistance value of the liquid based on the output voltage of the operational amplifier.

2. The resistance detection sensor according to claim 1, wherein the time for which the AC voltage is applied between the pair of electrodes by the AC voltage application unit is the sum of half the period of the AC voltage applied between the pair of electrodes and an integer multiple of the period of the AC voltage applied between the pair of electrodes.

3. The resistance detection sensor according to claim 1 or claim 2, wherein the period during which the calculation of the electrical resistance value of the liquid is performed is the same as the period during which an AC voltage is applied between the pair of electrodes.

4. The resistance detection sensor according to claim 1 or claim 2, wherein the liquid is a liquid lubricant.

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