Fluid property detection device

Abstract

To provide a fluid property detection device enabling monitoring for sensitively detecting a change in properties of fluid.SOLUTION: A fluid property detection device comprises: a resonance circuit 8 in which a capacitor C1 formed by a ground electrode and a detection electrode 21 immersed in fluid and an inductor portion 3101 are electrically coupled with each other; an excitation signal oscillation unit 3102 that excites the resonance circuit 8 with an excitation signal of a predetermined oscillatory frequency; and a control unit 3112 that controls the oscillatory frequency such that a phase difference between the excitation signal and an output signal of the resonance circuit 8 is maintained to be a predetermined phase difference. The fluid property detection device detects the properties of the fluid according to a change in the oscillatory frequency.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a fluid property detection device.

Background Art

[0002] There is known a technique of outputting an excitation signal having a frequency close to the resonance frequency of a resonance circuit composed of a capacitor formed by a ground electrode and a detection electrode immersed in a fluid and an inductor, and monitoring the property of the fluid based on the phase difference between the excitation signal and the output signal of the resonance circuit (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above technique, as the phase difference changes, the sensitivity for detecting the phase difference decreases, and it has been difficult to sensitively monitor the property of the fluid in subsequent measurements.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a fluid property detection device capable of sensitively detecting and monitoring changes in the property of a fluid.

Means for Solving the Problems

[0006] The fluid property detection device according to the present invention includes a ground electrode immersed in a fluid, a detection electrode immersed in the fluid and arranged to face the ground electrode, and an inductor unit connected to the detection electrode. A resonance circuit in which a capacitor formed by the ground electrode and the detection electrode and the inductor unit are electrically coupled to each other, an excitation signal oscillation unit that excites the resonance circuit with an excitation signal having a predetermined oscillation frequency, an excitation signal, and a resonance circuit. A phase difference detection unit that detects the phase difference between the output signals, and a control unit that controls the oscillation frequency so that the phase difference maintains a predetermined phase difference. Due to the Aging change of the oscillation frequency, the Deterioration of the fluid is detected.

[0007] In this invention, since the oscillation frequency can always be controlled to be the frequency at which the phase change is the steepest in the resonance circuit, even if the capacitance of the capacitor, that is, the relative permittivity of the fluid changes, the oscillation frequency can follow the frequency, and the maximum sensitivity state can always be maintained with respect to the phase change. Therefore, by improving the detection sensitivity of the phase difference between the excitation signal and the output signal of the resonance circuit, it is possible to sensitively detect changes (deterioration over time) in the properties of the fluid.

[0008] In the fluid property detection device according to the present invention, an excitation electrode is further provided which is connected to the excitation signal oscillation unit and arranged close to the detection electrode in a state of being separated from the detection electrode. The excitation signal oscillation unit resonates by outputting the excitation signal to the resonance circuit through a parasitic capacitance formed between the excitation electrode and the detection electrode. It is characterized by exciting the circuit.

[0009] In this invention, since the excitation electrode to which the excitation signal is applied and the detection electrode are spatially separated, there is no DC resistance component between the excitation electrode and the detection electrode, and the two are electrically coupled through the parasitic capacitance. Therefore, the Q value of the resonance circuit can be improved. As a result, by improving the detection sensitivity of the phase difference between the excitation signal and the output signal of the resonance circuit, it is possible to sensitively detect changes (deterioration over time) in the properties of the fluid.

[0010] In the fluid property detection device according to the present invention, the inductor unit is an equivalent inductor including a plurality of impedance elements that do not include an inductor, which is characterized in that.

[0011] In this invention, since the inductance can be set to be sufficiently larger than that of a normal inductor element, the resonance frequency of the resonance circuit can be set to a low value, and thereby the oscillation frequency can be set to a low value. Therefore, in addition to the inductor unit, the excitation signal oscillation unit and the phase difference detection unit can be constructed by combining general-purpose electronic components (semiconductor devices), and can be configured at low cost and in a small size.

[0012] In the fluid property detection device according to the present invention, the impedance element includes a first resistor connected to the detection electrode, a second resistor, a third resistor, a second capacitor, and a fourth resistor connected to the ground electrode, and forms a series circuit in which the first resistor, the second resistor, the third resistor, the second capacitor, and the fourth resistor are connected in series in this order, which is characterized in that.

[0013] In this invention, since the equivalent inductor is constructed by a so-called GIC (General Impedance Converter) circuit, a large inductance value can be obtained.

[0014] In the fluid property detection device according to the present invention, the fourth resistor includes a fifth resistor connected to the second capacitor, and a sixth resistor connected to the ground electrode and connected to the fifth resistor, and the sixth resistor is set to have a lower resistance value than the fifth resistor, and the output terminal of the resonance circuit extends from between the fifth resistor and the sixth resistor, which is characterized in that.

[0015] In this invention, since the output voltage of the resonance circuit (inductor unit) can be reduced, the oscillation of the resonance circuit (inductor unit) due to the output voltage can be suppressed.

[0016] In the fluid property detection device of the present invention, the control unit is characterized in that it sets the oscillation frequency to the resonance frequency of the resonance circuit or a frequency near the resonance frequency.

[0017] In the present invention, by setting the oscillation frequency to be at least close to the resonance frequency, the phase difference between the excitation signal (voltage) and the output signal (voltage) of the resonance circuit changes sensitively in response to changes in the state of the fluid, so that the detection sensitivity of the phase difference can be improved.

[0018] The fluid property detection device of the present invention further includes an amplitude detection unit that detects the amplitude of the output signal. The control unit searches for and detects a frequency region in which the amplitude becomes equal to or greater than a predetermined threshold by changing the oscillation frequency, and calculates the correlation between the oscillation frequency and the phase difference by detecting the phase difference between the excitation signal and the output signal while changing the oscillation frequency in the frequency region, and calculates a monitor frequency at which the phase difference becomes a predetermined phase difference based on the correlation.

[0019] In the present invention, since the monitor frequency (oscillation frequency) can be calculated with high precision within the range of the phase difference corresponding to the frequency at which the phase change is the steepest in the resonance circuit with respect to the phase difference between the excitation signal and the output signal, even if the capacitance of the capacitor, that is, the relative permittivity of the fluid changes, the monitor frequency (oscillation frequency) can accurately follow the frequency, and the state of maximum sensitivity to the phase change can always be maintained.

[0020] In the fluid property detection device of the present invention, the control unit searches for the frequency region by decreasing the oscillation frequency from a frequency higher than the frequency region when searching for the frequency region.

[0021] When the excitation signal includes a harmonic component and the harmonic component is close to the resonance frequency of the resonance circuit, there is a possibility that the resonance circuit may malfunction in searching for the frequency region in response to the harmonic component. However, in the present invention, since the frequency region is searched by decreasing the oscillation frequency from a frequency higher than the frequency region, the resonance circuit does not respond to the harmonic component, and the search for the frequency region can be reliably performed.

[0022] In the fluid property detection device of the present invention, a temperature sensor for measuring the temperature of the inductor part or the temperature of the fluid is further provided, and the control unit calculates a correction amount of the resonance frequency of the resonance circuit based on the temperature detected by the temperature sensor.

[0023] In this invention, by correcting the oscillation frequency information or the monitor frequency information based on the calculated correction amount, the fluid property can be detected with high accuracy and in a short time through the corrected oscillation frequency information or the corrected monitor frequency information regardless of the temperature change of the fluid.

[0024] In the fluid property detection device of the present invention, an amplitude detection unit for detecting the amplitude of the output signal is further provided, and the control unit changes the oscillation frequency when the amplitude becomes lower than a predetermined threshold value, searches for and detects a frequency region where the amplitude becomes equal to or higher than the threshold value, and controls the oscillation frequency in the frequency region.

[0025] In this invention, for example, when the fluid property or the electrode property changes in a short time and the resonance frequency changes rapidly, the output signal changes, and the phase difference between the excitation signal and the output signal of the resonance circuit may not be able to maintain a predetermined phase difference. Therefore, by detecting the frequency region where the output signal becomes equal to or higher than a predetermined amplitude and controlling the oscillation frequency in the frequency region, the oscillation frequency can be made to follow the resonance frequency again so that the phase difference between the excitation signal and the output signal of the resonance circuit becomes a predetermined phase difference.

Advantages of the Invention

[0026] According to the present invention, since the detection sensitivity of the phase difference can always be maintained in the state of maximum sensitivity, monitoring that can sensitively detect changes in the fluid property becomes possible.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0028] Hereinafter, this embodiment will be described with reference to the drawings.

[0029] [Basic Configuration of Fluid Property Detection Device of First Embodiment] FIG. 1 is a perspective view of the fluid property detection device 1 according to this embodiment. FIG. 2 is a cross-sectional view of the fluid property detection device 1 of this embodiment. FIG. 3 is a cross-sectional view taken along line A-A of FIG. 2.

[0030] As shown in FIGS. 1 and 2, the fluid property detection device 1 includes a detection unit 2, a substrate unit 3 attached to the detection unit 2, a cylindrical cylinder cover 4 attached to the detection unit 2 and covering the substrate unit 3, and an end cover 5 closing the opening of the cylinder cover 4.

[0031] As shown in FIG. 2, the fluid property detection device 1 (detection unit 2, substrate unit 3, cylinder cover 4, end cover 5) has a cylindrical shape (concentric shape) centered on the central axis CL.

[0032] The fluid property detection device 1 is configured to detect the properties of hydraulic oil as the working fluid contained in a hydraulic device (not shown) such as a hydraulic cylinder. The fluid property detection device 1 is attached to a predetermined location such as a container provided in the hydraulic device for containing the hydraulic oil, i.e., a pipe 7, a tank, etc. Note that the inspection target of the fluid property detection device 1 is not limited to hydraulic oil, and may be various liquids and gases such as lubricating oil, cutting oil, mineral oil, fuel, solvent, chemical, etc., and is applicable without being limited to the viscosity of the fluid. Hereinafter, the case where the fluid property detection device 1 detects the properties of the hydraulic oil in the pipe 7 (FIG. 2) as the detection target fluid will be described.

[0033] Hereinafter, the direction parallel to the central axis CL is referred to as the axial direction of the fluid property detection device 1, and the direction orthogonal to this axial direction is referred to as the radial direction of the fluid property detection device 1. Also, the side where the end cover 5 is disposed is referred to as the proximal end side of the fluid property detection device 1, and the detection unit 2 side is referred to as the distal end side of the fluid property detection device 1.

[0034] The detection unit 2 includes a cylindrical detection electrode 21, a rod-shaped inner electrode 22 (ground electrode) disposed inside the detection electrode 21 and on the central axis CL, a housing 23 attached to the pipe 7 of the hydraulic device (not shown), and a mounting plate 24 made of metal as a fixing member that holds the inner electrode 22 and is fixed to the housing 23 by screws or the like.

[0035] The detection unit 2 includes an outer spacer 25 provided between the housing 23 and the detection electrode 21 to insulate the housing 23 and the detection electrode 21 and define the position of the detection electrode 21 with respect to the housing 23, and an inner spacer 26 provided between the detection electrode 21 and the inner electrode 22 to insulate the detection electrode 21 and the inner electrode 22 and define the positions of the detection electrode 21 and the inner electrode 22 with respect to the housing 23.

[0036] As shown in FIG. 3 (a cross-sectional view taken along line A-A in FIG. 2), the inner electrode 22, the inner spacer 26, the detection electrode 21, the outer spacer 25, and the housing 23 are arranged in order of decreasing diameter around the central axis CL. The inner spacer 26, the detection electrode 21, the outer spacer 25, and the housing 23 have a ring shape. Note that the inner spacer 26 and the outer spacer 25 may be constructed by integral molding.

[0037] The detection unit 2 has an excitation electrode 28 at a position on the tip side of the housing 23 that is radially opposed to the detection electrode 21. As shown in FIGS. 2 and 3, the excitation electrode 28 is rod-shaped and is arranged at a position radially separated from the detection electrode 21 by a predetermined distance, and is insulated from the detection electrode 21 with respect to direct current. Further, the side surface of the excitation electrode 28 and the axial surface on the tip side of the housing 23 are supported by the outer spacer 25. Also, the surface on the base end side of the excitation electrode 28 is supported by the inner spacer 26.

[0038] The detection unit 2 has a metal cover electrode 27 (ground electrode) attached to the opening of the housing 23 and covering the tip portions of the detection electrode 21 and the inner electrode 22.

[0039] The housing 23 is formed of a conductive metal material and has, in order from the tip side, a mounting portion 231, a flange portion 232, a nut portion 233, a cover receiving portion 234, and a cover insertion portion 235.

[0040] The mounting portion 231 has a male screw structure and is screwed into a mounting hole 71 (female screw) formed in the pipe 7. An annular recess 72 is arranged at a portion of the mounting hole 71 of the pipe 7 that contacts the housing 23 (flange portion 232), and an O-ring 6 is arranged in the recess 72. A flange portion 232 is formed at the base portion of the mounting portion 231, and the flange portion 232 is a surface facing the recess 72 (O-ring 6).

[0041] Therefore, when the mounting portion 231 is screwed into the mounting hole 71, the O-ring 6 is compressed between the flange portion 232 and the bottom surface of the recess 72, thereby sealing the space between the pipe 7 and the housing 23.

[0042] The nut portion 233 is formed in a hexagonal prism shape as shown in FIGS. 1 and 3. Therefore, by rotating the nut portion 233 with a tool such as a wrench, the attachment portion 231 can be easily attached to the attachment hole 71.

[0043] The cover insertion portion 235 is cylindrical and is the portion inserted inside the cylindrical cover 4. The cover receiving portion 234 is a flange portion protruding radially outward from the base end of the nut portion 233, and the tip surface of the cylindrical cover 4 abuts thereon.

[0044] With the cover insertion portion 235 inserted into the cylindrical cover 4 and the tip surface of the cylindrical cover 4 abutting on the cover receiving portion 234, the cylindrical cover 4 is fixed to the cover insertion portion 235 with a screw or the like.

[0045] The end cover 5 is fixed to the cylindrical cover 4 with a screw or the like in a state where the opening on the base end side of the cylindrical cover 4 is closed. The substrate unit 3 is housed in a housing space defined by the end cover 5, the cylindrical cover 4, and the detection unit 2 (housing 23).

[0046] The portion on the base end side of the housing 23 and inside the cover insertion portion 235 serves as a mounting plate housing portion 236, and the mounting plate 24 is attached to the mounting plate housing portion 236.

[0047] The substrate unit 3 includes a circuit board 31 and a substrate holding member 32 that holds the circuit board 31. The substrate holding member 32 is fixed to the mounting plate 24 of the detection unit 2 with a screw or the like.

[0048] The circuit board 31 has wiring (not shown) that is individually connected to the housing 23, the detection electrode 21, and the excitation electrode 28.

[0049] Here, the housing 23 is in direct contact with the pipe 7. Further, the metal cover electrode 27 is connected to the housing 23. The inner electrode 22 is electrically connected to the housing 23 via the mounting plate 24. Therefore, when the pipe 7 is grounded, the housing 23, the cover electrode 27, and the inner electrode 22 are grounded.

[0050] Also, if the cylindrical cover 4 and the end cover 5 are made of metal, the cylindrical cover 4 and the end cover 5 are also grounded. Thereby, the accommodation space is electrostatically shielded, and the circuit board 31 is protected from electrical disturbances.

[0051] As shown in FIG. 2, at least a part of the cover electrode 27 is immersed in the hydraulic oil. And a flow hole 271 is formed in the part (bottom surface, side surface) of the cover electrode 27 immersed in the hydraulic oil, whereby at least a part of the detection electrode 21 is immersed in the hydraulic oil. Also, a flow hole 211 is formed in the part (bottom surface, side surface) of the detection electrode 21 immersed in the hydraulic oil, whereby at least a part of the inner electrode 22 is immersed in the hydraulic oil.

[0052] The cover electrode 27, the detection electrode 21, and the inner electrode 22 are spaced apart from each other at a predetermined interval, and the hydraulic oil flows through the gap therebetween. Thereby, a capacitor C1 (FIG. 4, capacitance is, for example, several pF to 10 pF) in which the cover electrode 27, the detection electrode 21, and the inner electrode 22 sandwich the hydraulic oil as a dielectric material is formed. And the cover electrode 27, the detection electrode 21, and the inner electrode 22 are electrically coupled to an inductor part 3101 described later to construct a resonant tank that forms a resonant circuit 8 described later.

[0053] Also, the detection electrode 21 and the excitation electrode 28 are spaced apart from each other with the outer spacer 25 interposed therebetween. Thereby, a capacitor C2 (parasitic capacitance) (FIG. 3) in which the detection electrode 21 and the excitation electrode 28 sandwich the outer spacer 25 as a dielectric material is formed.

[0054] In addition, for the circuit parts other than the inductor part 3101 (FIG. 4) described later, the substrate unit 3 does not need to be attached to the housing 23, and may be arranged apart from the pipe 7 and electrically connected to the detection electrode 21, the inner electrode 22, the cover electrode 27, and the excitation electrode 28 via wiring. Thereby, the waterproof property of the substrate unit 3 can be ensured and a short circuit can be prevented.

[0055] [Circuit diagram] FIG. 4 is a circuit diagram of the fluid property detection device 1 according to the present embodiment. On the circuit board 31 (FIG. 2) of the fluid property detection device 1, an inductor section 3101, an excitation signal oscillation section 3102, a first comparator 3103, a second comparator 3104, a phase comparator 3105, a first voltage sensor 3107, a second voltage sensor 3108, a temperature sensor 3110, and a control section 3112 are arranged.

[0056] In addition, in the circuit constituting the fluid property detection device 1, a first circuit A in which an excitation signal reaches the first comparator 3103 starting from the excitation signal oscillation section 3102, and a second circuit B in which the excitation signal reaches the second comparator 3104 starting from the excitation signal oscillation section 3102 via a capacitor C2 (excitation electrode 28, detection electrode 21) are provided, and a resonance circuit 8 described later is connected to the second circuit B.

[0057] As described above, the capacitor C1 has a structure formed by the detection electrode 21, the inner electrode 22, and the cover electrode 27 (ground electrode) and sandwiches the hydraulic oil. The capacitor C1 has the detection electrode 21 side connected to the non-inverting input terminal (+) of the second comparator 3104 and the input / output terminal I / O of the inductor section 3101 described later, and the inner electrode 22 and the cover electrode 27 (ground electrode) side are grounded. Here, the ground electrode refers to the entire circuit region that becomes substantially zero potential (ground potential) with respect to the AC signal component.

[0058] The capacitor C2 is formed by the excitation electrode 28 and the detection electrode 21. In the first embodiment, the excitation signal oscillation section 3102 outputs a sine wave excitation signal. When the excitation signal includes a harmonic component, a low-pass filter (the first low-pass filter 3115 shown in FIG. 8) is arranged between the excitation signal oscillation section 3102 and the excitation electrode 28.

[0059] One end of the inductor section 3101 serves as the input / output terminal I / O (Fig. 5) described later and is connected to the capacitor C1 and the non-inverting input terminal (+) of the second comparator 3104. On the other hand, the other end of the inductor section 3101 is grounded. Therefore, the inductor section 3101 forms a parallel resonance circuit 8 together with the capacitor C1. At this time, the resonance frequency f0 of the resonance circuit 8 is as shown in the following equation (1).

Equation

[0060] Also, another resonance frequency f1 that characterizes the frequency characteristics of the intensity of the signal excited in this resonance circuit 8 appears as the resonance frequency f1 of the resonance circuit 8 electrically coupled to the capacitor C2 and is as shown in the following equation (2).

Equation

[0061] The intensity of the output signal excited in the resonance circuit 8 takes the maximum value between these two resonance frequencies. Since the capacitor C2 is the parasitic capacitance formed between the excitation electrode 28 and the detection electrode 21, its size is sufficiently smaller than that of the capacitor C1. For this reason, the two resonance frequencies f0 and f1 become very close values.

[0062] As shown in Fig. 5, for example, the inductor section 3101 is a GIC circuit in which an operational amplifier U1 and an operational amplifier U2 are connected to a series circuit connected in series with a resistor R1, a resistor R2, a resistor R3, a capacitor C4, and a resistor R5 in this order. That is, the inductor section 3101 is an equivalent inductor (virtual inductor) composed of impedance elements that do not include an inductor. One end of the series circuit (resistor R1 side) serves as the input / output terminal I / O of the inductor section 3101, and the other end (resistor R5 side) is grounded. Here, grounding means connecting to a substantially zero potential (ground potential) with respect to the AC signal component.

[0063] In operational amplifier U1, the non-inverting input terminal (+) is connected to the connection midpoint of capacitor C4 and resistor R5, the inverting input terminal (-) is connected to the connection midpoint of resistors R2 and R3, and the output terminal is connected to the connection midpoint of resistors R1 and R2.

[0064] In operational amplifier U2, the non-inverting input terminal (+) is connected to the input / output terminal I / O, the inverting input terminal (-) is connected to the connection midpoint of resistors R2 and R3, and the output terminal is connected to the connection midpoint of resistor R3 and capacitor C4.

[0065] In the above configuration, the impedance Z of the inductor section 3101 as seen from the input / output terminal I / O is Z = jω(R1R3C4R5) / (R2), and the inductance L is (R1R3C4R5) / (R2). Here, if R2 and R3 are set to the same resistance value, the inductance L can be set to a large value by setting C4, R1, and R5 to large values, and thereby the resonance frequencies f0 and f1 can be set to low values (for example, several kHz).

[0066] In addition, it is preferable that the inductance L of the inductor section 3101 is about 100 [H]. At this time, it is preferable to set, for example, C4 to 0.01 [μF], R1 to 1 [MΩ], R5 to 10 [kΩ], and R2 to 1 [kΩ].

[0067] As shown in FIG. 4, the excitation signal oscillation section 3102 outputs an excitation signal of a predetermined oscillation frequency f to the excitation electrode 28 (capacitor C2) and the first comparator 3103. Further, the excitation signal oscillation section 3102 can change the oscillation frequency f based on a control signal input from the control section 3112. As the excitation signal oscillation section 3102, an oscillation circuit capable of oscillating a relatively low-frequency (about several kHz) sine wave, such as a CR oscillation circuit, is applied. In addition, a square wave is applied as the excitation signal in the second embodiment described later.

[0068] The first comparator 3103 (first square wave generation unit) has an excitation signal input to its non-inverting input terminal (+) and its inverting input terminal (-) grounded. The first comparator 3103 compares the magnitude relationship between the voltage of the excitation signal and the reference voltage, and outputs a first square wave that becomes 1 (High) when the voltage of the excitation signal is equal to or higher than the reference voltage, and becomes 0 (Low) when the voltage of the excitation signal is less than the reference voltage.

[0069] The second comparator 3104 (second square wave generation unit) has the output signal (voltage) of the resonance circuit 8 input to its non-inverting input terminal (+) and its inverting input terminal (-) grounded. The second comparator 3104 compares the magnitude relationship between the output signal (voltage) of the resonance circuit 8 and the reference voltage, and outputs a second square wave that becomes 1 (High) when the output signal (voltage) is equal to or higher than the reference voltage, and becomes 0 (Low) when the voltage of the excitation signal is less than the reference voltage.

[0070] The phase comparator 3105 outputs a third square wave, which is the logical product of the first square wave and the second square wave, to the control unit 3112. That is, the third square wave becomes 1 (High) when the first square wave is 1 (High) and the second square wave is 1 (High), and becomes 0 (Low) otherwise. Therefore, the pulse width of the third square wave matches the widths of the first square wave and the second square wave when there is no time difference (phase difference) between the first square wave and the second square wave, but decreases as the time difference increases when such a time difference (phase difference) exists.

[0071] Note that even if the third square wave generated by the phase comparator 3105 is the logical sum or exclusive logical sum of the first square wave and the second square wave, the relationship between the increase and decrease of the phase difference and the increase and decrease of the generated pulse width is different, but functionally has the same effect. Alternatively, an equivalent effect can also be achieved by using an edge-triggered flip-flop to generate a third square wave according to the rising or falling time difference between the first square wave and the second square wave.

[0072] The first voltage sensor 3107 detects the excitation signal (voltage) (V1) and outputs it to the control unit 3112.

[0073] The second voltage sensor 3108 detects the output signal (voltage) (V2) of the resonance circuit 8 and outputs it to the control unit 3112.

[0074] The temperature sensor 3110 detects the temperature of the hydraulic oil (detection electrode 21, inner electrode 22, cover electrode 27) and outputs it to the control unit 3112. When the detection electrode 21 and the inductor unit 3101 are arranged adjacent to each other and the temperature difference between them is low, the temperature sensor 3110 detects the temperature of the inductor unit 3101 as the temperature of the hydraulic oil and outputs it to the control unit 3112.

[0075] The control unit 3112 is constituted by, for example, a microcomputer, and drives the fluid property detection device 1 (fluid property detection method) according to a predetermined program.

[0076] The voltage (V1) of the excitation signal is input to the control unit 3112 from the first voltage sensor 3107, and the voltage (V2) of the output signal of the resonance circuit 8 is input from the second voltage sensor 3108.

[0077] The third square wave is input to the control unit 3112 from the phase comparator 3105. The control unit 3112 detects the phase difference between the excitation signal and the output signal of the resonance circuit 8 by detecting the rising time and falling time of the third square wave input from the phase comparator 3105, and controls the excitation signal oscillation unit 3102 (oscillation frequency f) so that the phase difference becomes a predetermined phase difference (θ0 (for example, π / 2)). Here, the shorter the time difference between the rising time and the falling time of the third square wave, the larger the phase difference between the excitation signal and the output signal of the resonance circuit 8, and conversely, the longer the time difference, the smaller the phase difference.

[0078] Note that a configuration may be applied in which the third square wave output from the phase comparator 3105 is smoothed by a low-pass filter (not shown), and the control unit 3112 calculates the phase difference between the excitation signal and the output signal of the resonance circuit 8 based on the magnitude of the DC voltage obtained by the smoothing. In this case, the larger the magnitude of the DC voltage, the smaller the phase difference, and conversely, the smaller the magnitude of the DC voltage, the larger the phase difference.

[0079] The control unit 3112 controls the excitation signal oscillation unit 3102 (oscillation frequency f) as described later. Also, temperature information is input to the control unit 3112 from the temperature sensor 3110.

[0080] [Board diagram] FIG. 6 is a diagram for explaining the gain and the phase difference θ detected by the fluid property detection device 1 according to the present embodiment. FIG. 6 is a board diagram of a circuit including the resonance circuit 8 and the capacitor C2, where the upper figure represents the gain and the lower figure represents the phase difference θ. In the present embodiment, the gain is obtained by calculating (V2 / V1) using the voltage V1 detected by the first voltage sensor 3107 and the voltage V2 detected by the second voltage sensor 3108 shown in FIG. 4. The phase difference is arg(V2 / V1).

[0081] By the way, since the voltage V1 (amplitude, phase) of the excitation signal is known, the gain and the phase difference θ may be calculated from only V2. Therefore, in FIG. 6, the voltage (V2) is applied as the gain, and arg(V2) is applied as the phase difference θ.

[0082] As shown in FIG. 6, in the circuit including the resonance circuit 8 and the capacitor C2, the phase difference θ changes greatly before and after the resonance frequency f0 formed by the inductance L equivalent to the capacitor C1 and the resonance frequency f1 formed by the combined capacitance of the capacitors C1 and C2 and the inductance L. Since the capacitor C2 is sufficiently smaller than the capacitor C1, the difference between the resonance frequency f0 and the resonance frequency f1 is small as described above (in FIG. 6, the resonance frequency f0 and the resonance frequency f1 are shown slightly separated from each other to ensure visibility).

[0083] If limited to a narrow frequency range near the resonance frequency f0 and the resonance frequency f1, the amplitude and phase of the voltage applied to the excitation electrode 28 can be regarded as constant. Therefore, as shown in FIG. 6, when viewed from the high-frequency side, the phase difference θ is 0 up to the resonance frequency f0, but rises rapidly as it moves to the lower-frequency side, becomes θ0 (for example, π / 2) at the resonance frequency f1, and becomes π at a lower frequency than that.

[0084] The frequency f at which the gain (voltage V2) peaks p is between the resonance frequency f1 and the resonance frequency f0 and is adjacent to the resonance frequency f1.

[0085] In the present invention, as will be described later, the phase difference θ between the excitation signal and the output signal of the resonance circuit 8 is detected at the frequency at which the slope of the curve showing the phase difference θ shown in FIG. 6 is the largest under the condition that the properties of the hydraulic fluid (fluid) are normal.

[0086] When the properties of the hydraulic fluid filled between the detection electrode 21, the inner electrode 22, and the cover electrode 27 change and the electrical parameter (relative permittivity) of the hydraulic fluid changes, the capacitance C1 changes, and the resonance frequencies f0 and f1 change. Generally, when oil or the like deteriorates, its relative permittivity increases, so the resonance frequencies f0 and f1 shift to the lower frequency side. Even if this shift amount is small, since the slope of the curve showing the phase difference θ in FIG. 6 is very steep, even if the relative permittivity changes slightly while the oscillation frequency f of the excitation signal is constant, this can be sensitively detected as the phase difference θ.

[0087] Also, in the present invention, as will be described later, the oscillation frequency f is searched in the frequency region near the resonance frequency f1 where the phase difference θ can be sensitively detected, and the monitor frequency f at which the phase difference θ becomes a predetermined phase difference (θ0) m is calculated. Then, the monitor frequency f m is set by feedback control (FIG. 7) so that the phase difference θ maintains a predetermined phase difference (θ0). Therefore, in the present invention, the properties of the hydraulic fluid can be sensitively detected by the change in the monitor frequency f. m At this time, the oscillation frequency f is constantly changing in a mode of reciprocating around the resonance frequency f1.

[0088] Furthermore, in the present invention, for example, it is also possible to estimate the absolute value of the electrical parameter (relative permittivity) of the hydraulic oil by searching for the oscillation frequency f and finding the oscillation frequency f (resonance frequency f1) when the phase difference θ becomes π / 2, and using the capacitors C1 and C2 (assumed to be known). Similarly, it is also possible to estimate the absolute value of the electrical parameter (relative permittivity) of the hydraulic oil by searching for the oscillation frequency f and finding the oscillation frequency f (resonance frequency f0) when the phase difference θ becomes zero, and using the capacitor C1 (assumed to be known).

[0089] In the prior art (see Patent Document 1), taking the present embodiment as an example, the excitation electrode 28 to which the excitation signal is applied is directly connected to the detection electrode 21, there is no capacitor C2 shown in FIG. 4, and the internal resistance component (output impedance) of the element that outputs the excitation signal is directly connected to the resonance circuit 8. In this case, the internal resistance component is included in the Q value determined by the ratio of the magnitude of the inductance component to the magnitude of the resistance component of the circuit including the resonance circuit 8, and thus it is difficult to increase the Q value. Therefore, the peak of the gain shown in FIG. 6 cannot be sharpened, and the change in the phase difference θ also becomes gentle. Consequently, the detection sensitivity of the phase difference θ decreases, and it is difficult to perform monitoring that sensitively detects changes in the properties of the hydraulic oil.

[0090] On the other hand, in the present embodiment, a capacitor C2 (parasitic capacitance) is interposed between the internal resistance component (output impedance) of the excitation signal oscillation unit 3102 and the resonance circuit 8, and the internal resistance component of the excitation signal oscillation unit 3102 is separated from the resonance circuit 8. Also, as described above, the inductor unit 3101 can set the inductance L to a large value by setting C4, R1, and R5 to large resistance values. Since the Q value in the resonance circuit 8 is determined by the ratio of the impedance of the inductance L to the resistance component equivalently present in the inductor unit 3101, the Q value can be set to a very large value. Therefore, the peak of the gain shown in FIG. 6 can be sharpened, and the change in the phase difference θ also becomes sharp. Consequently, the detection sensitivity of the phase difference θ is improved, and it becomes possible to perform monitoring that sensitively detects changes in the properties of the hydraulic oil.

[0091] [Control in the First Embodiment] FIG. 7 is a control flow of the fluid property detection device 1 according to the first embodiment.

[0092] In step S701, when the power of the device is turned on, the control unit 3112 initially sets the oscillation frequency f of the excitation signal to a frequency f higher than the resonance frequency f0 (first control). max to set (first control).

[0093] In step S702, the control unit 3112 searches for an oscillation frequency f at which the amplitude (voltage V2) of the output signal of the resonance circuit 8 becomes equal to or higher than a predetermined threshold voltage (Vr) (is located in the vicinity of the resonance frequencies f0 and f1) (first control).

[0094] In the first control, as shown in FIG. 6, the control unit 3112 initially sets the oscillation frequency f of the excitation signal to a frequency f higher than the resonance frequency f0. max and decreases the oscillation frequency f. When the voltage V2 reaches Vr (the oscillation frequency f is f in FIG. 6). s ) and stops searching (scanning) for the oscillation frequency f as the first control. In this way, since the frequency region where the voltage V2 is near the peak is searched from the high-frequency side, even if there are high-frequency components in the excitation signal, the resonance circuit 8 will react to the high-frequency components and the voltage V2 will exceed Vr, avoiding incomplete search. If there is no influence of high-frequency components, control may be performed to increase the frequency from a frequency f lower than the resonance frequency f0 and the resonance frequency f1 until the voltage V2 reaches Vr. min from and increasing the frequency until the voltage V2 reaches Vr.

[0095] In step S703, the control unit 3112 reduces the search speed compared to the first control and reduces the oscillation frequency f until the voltage V2 reaches the peak voltage and begins to decrease (second control). That is, the oscillation frequency f is in the vicinity of the frequency f at which the voltage V2 peaks. p of and at a frequency f. pReduce it until it becomes a lower frequency (Fig. 6). In this case, for example, calculate the difference between the current data and the previous data of the voltage V2, and end the process of step S703 when the sign of the difference is reversed.

[0096] In step S704, the control unit 3112 determines that the phase difference θ is θ0 - θ s to θ0 + θ s While slowly searching for the oscillation frequency f in the frequency range where the oscillation frequency f is calculated by calculating the index value θ1 of the phase difference θ, a large number of dot data 3117 indicating the coordinate positions of the oscillation frequency f and the index value θ1 in the coordinate space with the oscillation frequency f and the phase difference θ as the coordinate axes are acquired (second control). Note that θ s Is an arbitrary value at which the first control can function. The control unit 3112 also has a memory (not shown) for storing the dot data 3117.

[0097] In step S705, the control unit 3112 calculates a regression equation representing the correlation between the oscillation frequency f and the phase difference θ as a linear function 3118 from a large number of dot data 3117 using the coordinate space (second control). Here, the regression equation is θ = A·f + B, and A and B in the regression equation are calculated. After calculating the regression equation, the control unit 3112 erases the dot data 3117 stored in the memory (not shown).

[0098] In step S706, the control unit 3112 calculates the monitor frequency f m at which the phase difference θ becomes θ0 (for example, π / 2) using the regression equation (second control).

[0099] In step S707, the control unit 3112 determines whether the calculated monitor frequency f m is equal to or lower than the upper limit frequency f H If YES, it proceeds to step S708, and if NO, it proceeds to step S709.

[0100] In step S708, the control unit 3112 determines whether the monitor frequency f m is equal to or higher than the lower limit frequency f LDetermine whether it is as above. If YES, transfer to step S710; if NO, transfer to step S709.

[0101] In step S709, the control unit 3112 outputs a warning signal to the outside. Here, when the control unit 3112 transfers from step 707 to step S709, it outputs an upper limit warning signal to the outside. When other oil types or air bubbles are mixed into the hydraulic oil, the capacitor C1 decreases, and as a result, the resonance frequencies f0 and f1 increase, making it difficult to accurately measure the change in the electrical parameter (relative permittivity) of the hydraulic oil. Therefore, in the present invention, when the monitor frequency f m (oscillation frequency f) exceeds the upper limit frequency f H , it is determined that other oil types or air bubbles are mixed into the hydraulic oil and reported to the outside.

[0102] The upper limit warning signal (and the lower limit warning signal described later) is converted into, for example, voice output from a speaker, lighting display of a warning lamp, warning display on an image display device, etc. and transmitted to the operator. Thereby, the operator can be notified of the replacement of the hydraulic oil.

[0103] When the control unit 3112 transfers from step S708 to step S709, it outputs a lower limit warning signal to the outside. The relative permittivity of the hydraulic oil increases due to the oxidation of the hydraulic oil and the mixing of contaminants (metal pieces) generated by the wear of a hydraulic device (not shown) where the pipe 7 is provided into the hydraulic oil. The increase in the relative permittivity of the hydraulic oil increases the capacitance of the capacitor C1, and as a result, the monitor frequency f calculated by the second control under the state where the first control is functioning m decreases. The change in the monitor frequency f m appears as a change in the electrical parameter (relative permittivity) of the hydraulic oil.

[0104] Therefore, in the present invention, when the calculated monitor frequency f m (oscillation frequency f) is lower than the lower limit frequency f L , it is determined that it is time to replace the hydraulic oil and reported to the outside. The lower limit warning signal is the same as the above-mentioned upper limit warning signal, but it is preferably in a form that allows the operator to distinguish between the two.

[0105] In step S710, the control unit 3112 determines whether the power of the device is ON. If YES, it proceeds to step S711; if NO, the control ends.

[0106] In step S711, the control unit 3112 determines whether the voltage V2 is equal to or greater than Vr. If YES, it proceeds to step S703; if NO, it proceeds to step S701. By setting NO in step S711, it is possible to recover from a state where the second control cannot be executed.

[0107] As shown in FIG. 5, the inductor unit 3101 has resistors R1, R2, R3, and R5, but their resistance values change with temperature changes. Also, since the operational amplifiers U1 and U2 are semiconductor devices, their operating characteristics are affected by temperature. Therefore, the inductance L changes due to the temperature change of the inductor unit 3101. In addition, the relative permittivity of the hydraulic oil changes with temperature, and as a result, the capacitor C1 (capacitance) changes.

[0108] Therefore, the control unit 3112 associates the temperature of the inner electrode 22 (the temperature of the hydraulic oil) (or the temperature of the inductor unit 3101) with the change amount (correction amount) of the monitoring frequency f m (oscillation frequency f) of the excitation signal in a state where the first control is functioning. Then, based on the temperature information of the inductor unit 3101 input from the temperature sensor 3110, the control unit 3112 extracts the change amount (correction amount) of the resonance frequency f0 (or resonance frequency f1) from the map, and corrects (temperature correction) the information of the oscillation frequency f of the excitation signal in a state where the first control is functioning with the change amount (correction amount). As a result, the temperature error of the calculated monitoring frequency f m (oscillation frequency f) information can be corrected.

[0109] The control unit 3112 uses the information of the monitoring frequency f m (oscillation frequency f), or the monitoring frequency f m(Oscillation frequency f) and the lower limit frequency f L It is also possible to execute control to output information on the difference from the outside. As a result, since an operator can set a threshold according to the type of hydraulic oil or the usage status of the equipment, etc., it is possible to optimize the timing for replacing the hydraulic oil used in the equipment.

[0110] [Second Embodiment] FIG. 8 is a circuit diagram of the fluid property detection device 1 according to the second embodiment. In the fluid property detection device 1 of the second embodiment, the excitation signal is a square wave. Further, although the control unit 3112 is composed of a microcomputer, it can output an excitation signal. The excitation signal is a digital square wave (rectangular wave) with a duty ratio of 50%, and its oscillation frequency f is controlled by the microcomputer.

[0111] The control unit 3112 outputs an excitation signal to the phase comparator 3105 and the excitation electrode 28 using a counter or an internal oscillation module of the microcomputer. A first low-pass filter 3115 is arranged between the control unit 3112 and the excitation electrode 28, and the excitation signal that has passed through the first low-pass filter 3115 is output to the excitation electrode 28.

[0112] The first low-pass filter 3115 is a low-pass filter whose cut-off frequency is set to about the resonance frequency f0.

[0113] The inductor unit 3101 has the same configuration as that of the first embodiment, but the output terminal extends from between the capacitor C4 and the resistor R5.

[0114] The output of the inductor unit 3101 is output to the third comparator 3113 and the rectifier circuit 3114 via the buffer U3.

[0115] The third comparator 3113 shapes the output from the inductor unit 3101 (the output signal of the resonance circuit 8) into a digital square wave and outputs it to the phase comparator 3105. The output signal of the third comparator 3113 is a signal that reflects the phase of the output signal of the resonance circuit 8.

[0116] The rectifier circuit 3114 rectifies the output from the inductor section 3101 (the output signal of the resonance circuit 8) into a direct current and outputs it to the second low-pass filter 3116.

[0117] The second low-pass filter 3116 smoothes the output of the rectifier circuit 3114 and outputs it to the control section 3112. The output of the second low-pass filter 3116 serves as an index of the amplitude of the output signal of the resonance circuit 8 (corresponding to the voltage V2 in the first embodiment).

[0118] The phase comparator 3105 measures the rising (or falling) timing of the excitation signal output from the control section 3112 and the rising (or falling) timing of the output signal of the third comparator 3113 (the output signal of the resonance circuit 8), and outputs a square wave (the third square wave in the first embodiment) representing the phase difference θ between the excitation signal and the output signal of the resonance circuit 8 to the control section 3112 based on the time difference.

[0119] The phase comparator 3105 may be configured by an exclusive OR circuit (XOR gate). In this case, one input is the excitation signal, the other input is the output signal of the third comparator 3113, and the output becomes a square wave corresponding to the time difference between the rising edges of one input and the other input and the time difference between the falling edges of one input and the other input.

[0120] Also, the phase comparator 3105 may be configured by a D flip-flop. In this case, for example, if a D flip-flop equivalent to 74LS74 is used, the excitation signal is input to the CK terminal, the output signal of the third comparator 3113 (the signal with the voltage inverted) is input to the D terminal, and the - output signal of the third comparator 3113 is input to the CLR terminal, a square wave corresponding to the delay phase of the output signal of the third comparator 3113 with respect to the excitation signal can be output from the Q terminal. However, the maximum detectable phase difference θ is 180° (π).

[0121] Furthermore, the phase comparator 3105 may be composed of two D flip - flops. In this case, for example, an excitation signal is input to the CK terminal of the first D flip - flop, the input of the D terminal of the first D flip - flop is set to H (high potential), the output signal of the third comparator 3113 is input to the CK terminal of the second D flip - flop, the D terminal of the second D flip - flop is connected to the Q terminal of the first D flip - flop, and the output of the NAND gate with the outputs of the Q terminal of the first flip - flop and the Q terminal of the second flip - flop as inputs is input to the CLR - terminal of the first flip - flop and the CLR - terminal of the second flip - flop. By doing so, a square wave corresponding to the delayed phase of the output signal of the third comparator 3113 with respect to the excitation signal can be output from the Q - terminal of the first D flip - flop over a phase difference θ of 360° (2π).

[0122] Note that some microcomputers have a built - in function to measure the time difference (phase difference θ) between two signals. Therefore, when the microcomputer used in the control unit 3112 has this function, the phase comparator 3105 may be omitted.

[0123] The control flow executed by the control unit 3112 is the same as that of the first embodiment.

[0124] In step S702 described above, the control unit 3112 searches for the oscillation frequency f at which the output voltage of the second low - pass filter 3116 becomes equal to or higher than a predetermined threshold voltage (a voltage corresponding to the threshold voltage (Vr) of the first embodiment), that is, in the vicinity of the resonance frequencies f0 and f1 (first control).

[0125] In step S703 described above, the control unit 3112 reduces the oscillation frequency f until the output voltage of the second low - pass filter 3116 reaches the peak voltage and starts to decrease, while reducing the search speed compared to the first control (second control).

[0126] Incidentally, since the inductor section 3101 (GIC circuit) is a circuit excited via the capacitor C2, the electrical signal is generally small and prone to noise. In particular, not only in the inductor section 3101 but also the signals flowing through each part of the circuit itself become signals of the same frequency as the excitation signal. Therefore, there is a risk that these signals resonate the resonance circuit 8 through the parasitic capacitances existing in each part of the circuit, causing the circuit operation to become unstable.

[0127] Therefore, as shown in the region surrounded by the dashed-dotted line in the rectangle of FIG. 8, it is preferable to divide the resistor R5 into R6 and R7 and configure the output terminal to extend from between R6 and R7. At this time, for example, R5 = R6 + R7, and it is preferable to set R7 to a resistance value about one-tenth of R6. Thereby, since the output voltage of the inductor section 3101 is divided into a voltage of one-tenth or less, unnecessary resonance, that is, resonance of the resonance circuit 8 by the output signal output from the inductor section 3101 can be suppressed.

[0128] Although not shown, in actuality, for the resistor R7, two resistor elements having a resistance value twice that of the resistor R7 are connected in parallel to the resistor R6, one resistor element is grounded, and the other resistor element is connected to a positive power supply line (for example, 5V) (not shown). Therefore, the other resistor element is grounded with respect to the AC signal (excitation signal) input from outside the inductor section 3101, and a DC bias of half the power supply voltage is applied. Thereby, for example, operation with a 5V DC power supply is made possible.

[0129] Note that the effects of the second embodiment are the same as those of the first embodiment.

[0130] [Third Embodiment] FIG. 9 is a cross-sectional view of the inner electrode 22, the detection electrode 21, and the cover electrode 27 that constitute the fluid property detection device 1 according to the third embodiment. As shown in FIG. 9, the inner electrode 22, the detection electrode 21, and the cover electrode 27 of the modified example have a star (hexagram) shape in the radial cross-sectional shape. For example, a flow hole 271 is formed in a saddle portion having a star shape in the cover electrode 27, and similarly, a flow hole 211 is also formed in the detection electrode 21. With the above configuration, the opposing areas between the detection electrode 21 and the inner electrode 22, and between the detection electrode 21 and the cover electrode 27 increase. Accordingly, the capacitance C1 can be increased accordingly, and the resonance frequency f0 shown in Equation (1) and the resonance frequency f1 shown in Equation (2) can be set lower.

[0131] [Configuration, Operation, and Effect of the Present Embodiment] Hereinafter, the configuration, operation, and effect of the present embodiment (the first to third embodiments) will be collectively described.

[0132] The fluid property detection device 1 according to the present embodiment includes a ground electrode (inner electrode 22, cover electrode 27) immersed in a fluid, a detection electrode 21 immersed in the fluid and arranged to face the ground electrode (inner electrode 22, cover electrode 27), and an inductor unit 3101 connected to the detection electrode 21. A resonance circuit 8 in which a capacitor C1 formed by the ground electrode (inner electrode 22, cover electrode 27) and the detection electrode 21 and the inductor unit 3101 are electrically coupled to each other, an excitation signal oscillation unit 3102 that excites the resonance circuit 8 with an excitation signal having a predetermined oscillation frequency f, a phase difference detection unit (first comparator 3103, second comparator 3104, phase comparator 3105) that detects a phase difference θ between the excitation signal and an output signal of the resonance circuit 8, and a control unit 3112 that controls the oscillation frequency f so that the phase difference θ maintains a predetermined phase difference (θ0). The fluid property is detected by a change in the oscillation frequency f.

[0133] With the above configuration, the oscillation frequency f can always be controlled so as to be the frequency at which the phase change is the steepest in the resonance circuit 8. Therefore, even if the capacitance of the capacitor C1, i.e., the relative permittivity of the fluid, changes, the oscillation frequency f can follow the frequency and always maintain the state of maximum sensitivity to the phase change. Thus, by improving the detection sensitivity of the phase difference θ between the excitation signal and the output signal of the resonance circuit 8, it becomes possible to monitor the change (deterioration over time) in the properties of the fluid sensitively.

[0134] In the fluid property detection device 1 of the present embodiment, an excitation electrode 28 is further provided which is connected to the excitation signal oscillation unit 3102 and is arranged close to the detection electrode 21 while being separated from the detection electrode 21. The excitation signal oscillation unit 3102 excites the resonance circuit 8 by outputting an excitation signal to the resonance circuit 8 through a parasitic capacitance (capacitor C2) formed between the excitation electrode 28 and the detection electrode 21.

[0135] With the above configuration, since the excitation electrode 28 to which the excitation signal is applied and the detection electrode 21 are spatially separated, there is no DC resistance component between the excitation electrode 28 and the detection electrode 21, and the two are electrically coupled through the parasitic capacitance (capacitor C2). Therefore, the Q value of the resonance circuit 8 can be improved. Thus, by improving the detection sensitivity of the phase difference θ between the excitation signal and the output signal of the resonance circuit 8, it becomes possible to monitor the change (deterioration over time) in the properties of the fluid sensitively.

[0136] In the fluid property detection device 1 of the present embodiment, the inductor unit 3101 is an equivalent inductor including a plurality of impedance elements not including an inductor.

[0137] With the above configuration, the inductance L can be set to be sufficiently larger than that of a normal inductor element, so that the resonance frequency f0 and the resonance frequency f1 can be set to low values, and thereby the oscillation frequency f can be set to a low value. Therefore, in addition to the inductor section 3101, the excitation signal oscillation section 3102 and the phase difference detection section (the first comparator 3103, the second comparator 3104, the phase comparator 3105) can be constructed by combining general-purpose electronic components (semiconductor devices), and can be configured at low cost and in a small size.

[0138] In the fluid property detection device 1 of the present embodiment, the impedance element includes a first resistor (R1) connected to the detection electrode 21, a second resistor (R2), a third resistor (R3), a second capacitor (C4), and a fourth resistor (R5) connected to the ground electrode (the inner electrode 22, the cover electrode 27), and forms a series circuit in which the first resistor (R1), the second resistor (R2), the third resistor (R3), the second capacitor (C4), and the fourth resistor (R5) are connected in series in this order.

[0139] With the above configuration, an equivalent inductor is constructed by a so-called GIC circuit, so that a large inductance value can be obtained.

[0140] In the fluid property detection device 1 of the present embodiment, the fourth resistor (R5) includes a fifth resistor (R6) connected to the second capacitor (C4), and a sixth resistor (R7) connected to the ground electrode (the inner electrode 22, the cover electrode 27) and connected to the fifth resistor (R6). The sixth resistor (R7) is set to have a lower resistance value than the fifth resistor (R6), and the output terminal of the resonance circuit 8 extends from between the fifth resistor (R6) and the sixth resistor (R7).

[0141] With the above configuration, the output voltage of the resonance circuit 8 (inductor section 3101) can be reduced, so that the oscillation of the resonance circuit 8 (inductor section 3101) due to the output voltage can be suppressed.

[0142] In the fluid property detection device 1 of the present embodiment, the control unit 3112 is characterized in that it sets the oscillation frequency f to the resonance frequency (resonance frequencies f0, f1) of the resonance circuit 8 or a frequency in the vicinity of the resonance frequency (resonance frequencies f0, f1).

[0143] With the above configuration, by setting the oscillation frequency f to at least in the vicinity of the resonance frequency (resonance frequencies f0, f1), the phase difference θ between the excitation signal (voltage) and the output signal (voltage) of the resonance circuit 8 changes sensitively in response to changes in the state of the fluid. Therefore, the detection sensitivity of the phase difference θ can be improved.

[0144] In the fluid property detection device 1 of the present embodiment, it further includes an amplitude detection unit (second voltage sensor 3108, second low-pass filter 3116, control unit 3112) for detecting the amplitude of the output signal. The control unit 3112 changes the oscillation frequency f to search for and detect a frequency region where the amplitude (voltage V2) becomes equal to or greater than a predetermined threshold value (Vr), and while changing the oscillation frequency f in the frequency region, detects the phase difference θ between the excitation signal and the output signal, thereby calculating the correlation relationship (dot data 3117, linear function 3118) between the oscillation frequency f and the phase difference θ, and based on the correlation relationship (dot data 3117, linear function 3118), calculates the monitor frequency f at which the phase difference θ becomes a predetermined phase difference (θ0). m It is characterized by this.

[0145] With the above configuration, within the range of the phase difference θ corresponding to the frequency at which the phase change is the steepest in the resonance circuit 8 with respect to the phase difference θ between the excitation signal and the output signal, the monitor frequency f m (oscillation frequency f) can be calculated with high precision. Therefore, even if the capacitance of the capacitor C1, that is, the relative permittivity of the fluid changes, the monitor frequency f m (oscillation frequency f) can accurately follow the frequency, and the state of maximum sensitivity to the phase change can always be maintained.

[0146] In the fluid property detection device 1 of the present embodiment, when searching for the frequency range, the control unit 3112 is characterized by searching for the frequency range by decreasing the oscillation frequency f from a frequency higher than the frequency range.

[0147] When the excitation signal includes a harmonic component and the harmonic component is close to the resonance frequency (resonance frequency f0, resonance frequency f1) of the resonance circuit 8, there is a possibility that the resonance circuit 8 will malfunction in searching for the frequency range in response to the harmonic component. However, with the above configuration, since the frequency range is searched by decreasing the oscillation frequency from a frequency higher than the frequency range, the resonance circuit 8 does not respond to the harmonic component, and the search for the frequency range can be reliably performed.

[0148] The fluid property detection device 1 of the present embodiment further includes a temperature sensor 3110 that measures the temperature of the inductor unit 3101 or the temperature of the fluid, and the control unit 3112 is characterized by calculating a correction amount for the resonance frequency (resonance frequency f0, resonance frequency f1) of the resonance circuit 8 based on the temperature detected by the temperature sensor 3110.

[0149] With the above configuration, by correcting the information on the oscillation frequency f or the monitor frequency f based on the calculated correction amount, the information on the corrected oscillation frequency f or the corrected monitor frequency f can be used to detect the properties of the fluid (hydraulic oil) with high accuracy and in a short time regardless of the temperature change of the fluid. m regardless of the temperature change of the fluid (hydraulic oil), the information on the corrected oscillation frequency f or the corrected monitor frequency f m via the information, the properties of the fluid (hydraulic oil) can be detected with high accuracy and in a short time.

[0150] In the fluid property detection device 1 of the present embodiment, the control unit 3112 determines that the information on the oscillation frequency f or the monitor frequency f m is lower than a predetermined lower limit frequency f L or higher than a predetermined upper limit frequency f H and outputs a warning signal to the outside.

[0151] With the above configuration, when the information on the oscillation frequency f or the monitor frequency f mWhen the information exceeds a predetermined upper limit frequency f H a warning signal is output to inform the operator that an abnormality has occurred in the fluid. When the information of the oscillation frequency f or the monitoring frequency f m is lower than a predetermined lower limit frequency f L a warning signal can be output to inform the operator that the fluid should be replaced.

[0152] In the fluid property detection device 1 of the present embodiment, the control unit 3112 outputs at least one of the information of the oscillation frequency f, the difference information between the oscillation frequency f and the predetermined lower limit frequency f L , the information of the monitoring frequency f m , the information of the monitoring frequency f m and the difference information between the monitoring frequency f L and the lower limit frequency f to the outside.

[0153] With the above configuration, at least one of the information of the oscillation frequency f, the difference information between the oscillation frequency f and the predetermined lower limit frequency f L , the information of the monitoring frequency f m , the information of the monitoring frequency f m and the difference information between the monitoring frequency f L and the lower limit frequency f is output to the outside, so that the operator can set a threshold according to the type of fluid and the usage status of the device, etc., and thus the replacement timing of the fluid used in the device can be optimized.

[0154] In the fluid property detection device 1 of the present embodiment, an amplitude detection unit (the second voltage sensor 3108, the second low-pass filter 3116, the control unit 3112) for detecting the amplitude of the output signal is further provided. When the amplitude (voltage V2) is lower than a predetermined threshold (Vr), the control unit 3112 changes the oscillation frequency f to search for and detect a frequency region where the amplitude (voltage V2) is equal to or higher than the threshold (Vr), and controls the oscillation frequency f in the frequency region.

[0155] With the above configuration, for example, when the properties of the fluid or the properties of the electrode change in a short period of time and the resonance frequency (resonance frequency f0, resonance frequency f1) changes rapidly, the output signal changes, and there are cases where the phase difference θ between the excitation signal and the output signal of the resonance circuit 8 cannot maintain a predetermined phase difference (θ0). Therefore, by detecting while searching for the frequency region where the output signal becomes equal to or greater than a predetermined amplitude (Vr) and controlling the oscillation frequency f in that frequency region, the oscillation frequency f can be made to follow the resonance frequency (resonance frequency f0, resonance frequency f1) again so that the phase difference θ between the excitation signal and the output signal of the resonance circuit 8 becomes a predetermined phase difference (θ0).

[0156] The fluid property detection device 1 of the present embodiment (second embodiment) further includes a low-pass filter (first low-pass filter 3115) disposed between the excitation signal oscillation unit 3102 and the excitation electrode 28.

[0157] When the excitation signal includes a harmonic component and the harmonic component is close to the resonance frequency (resonance frequency f0, resonance frequency f1) of the resonance circuit 8, there is a possibility that the resonance circuit 8 responds to the harmonic component and causes problems in the search for that frequency region. However, with the above configuration, the input of the harmonic component of the excitation signal to the resonance circuit 8 is restricted, so the response of the resonance circuit 8 to the harmonic component is suppressed, and the search for that frequency region can be performed reliably.

[0158] In the fluid property detection device 1 of the present embodiment (first embodiment), when the excitation signal output from the excitation signal oscillation unit 3102 is a sine wave, the phase difference detection unit (first comparator 3103, second comparator 3104, phase comparator 3105) includes a first square wave generation unit (first comparator 3103) that outputs a first square wave based on one of the positive and negative signs of the excitation signal, a second square wave generation unit (second comparator 3104) that outputs a second square wave based on the sign that is the same as the one of the positive and negative signs of the output signal, and a phase comparator 3105 that detects the phase difference θ by acquiring information on the time difference between the rising or falling edges of the first square wave and the second square wave.

[0159] With the above configuration, it is possible to detect the phase difference θ between the excitation signal and the output signal of the resonance circuit 8 with a simple configuration.

[0160] In the fluid property detection device 1 of the present embodiment (second embodiment), when the excitation signal oscillated by the excitation signal oscillation unit 3102 is a square wave, the phase difference detection unit (phase comparator 3105) is characterized by detecting the phase difference θ by acquiring information on the time difference between the rise or fall of the excitation signal and the output signal.

[0161] With the above configuration, it is possible to detect the phase difference θ between the excitation signal and the output signal of the resonance circuit 8 with a simple configuration.

[0162] In the fluid property detection device 1 of the present embodiment (third embodiment), the surfaces of the ground electrodes (inner electrode 22, cover electrode 27) facing the detection electrode 21 and the surfaces of the detection electrode 21 facing the ground electrodes (inner electrode 22, cover electrode 27) each have a waveform shape.

[0163] With the above configuration, by increasing the facing area of the ground electrodes (inner electrode 22, cover electrode 27) and the detection electrode 21, it is possible to increase the ratio of the effective capacitance in the capacitor C1 formed by the ground electrodes (inner electrode 22, cover electrode 27) and the detection electrode 21, and improve the sensitivity of detection.

[0164] The fluid property detection method according to this embodiment includes a grounding electrode (inner electrode 22, cover electrode 27) at least partially immersed in a fluid, a detection electrode 21 arranged so as to be at least partially immersed in the fluid and face the grounding electrode (inner electrode 22, cover electrode 27), and an inductor unit 3101 connected to the detection electrode 21. By this, a resonance circuit 8 in which a capacitor C1 formed by the grounding electrode (inner electrode 22, cover electrode 27) and the detection electrode 21 and the inductor unit 3101 are electrically coupled to each other is excited by an excitation signal having a predetermined oscillation frequency f, the phase difference θ between the excitation signal and the output signal of the resonance circuit 8 is detected, and the oscillation frequency f is controlled so that the phase difference θ maintains a predetermined phase difference (θ0). Thus, the property of the fluid is detected based on the change in the oscillation frequency f.

[0165] By the above method, the oscillation frequency f can always be controlled to be the frequency at which the phase change is the steepest in the resonance circuit 8. Therefore, even if the capacitance of the capacitor C1, that is, the relative permittivity of the fluid changes, the oscillation frequency f can follow this frequency and always maintain the state of maximum sensitivity to the phase change. Accordingly, by improving the detection sensitivity of the phase difference θ between the excitation signal and the output signal of the resonance circuit 8, it becomes possible to sensitively detect changes (deterioration over time) in the properties of the fluid for monitoring.

[0166] In the fluid property detection method of this embodiment, an excitation signal is applied to an excitation electrode 28 arranged at a position close to the detection electrode 21 while being separated from the detection electrode 21, and the resonance circuit 8 is excited by outputting the excitation signal to the resonance circuit 8 through a parasitic capacitance (capacitor C2) formed between the excitation electrode 28 and the detection electrode 21.

[0167] By the above method, since the excitation electrode 28 to which the excitation signal is applied and the detection electrode 21 are spatially separated, there is no resistance component between the excitation electrode 28 and the detection electrode 21, and since both are electrically coupled through the parasitic capacitance (capacitor C2), the Q value of the resonance circuit 8 can be improved. Thereby, by improving the detection sensitivity of the phase difference θ between the excitation signal and the output signal of the resonance circuit 8, it becomes possible to sensitively detect changes in the properties of the fluid for monitoring.

[0168] In the fluid property detection method of this embodiment, a frequency region where the amplitude (voltage V2) of the output signal exceeds a predetermined threshold value (Vr) is searched and detected, and while changing the oscillation frequency f in the frequency region, the phase difference θ between the excitation signal and the output signal is detected, thereby calculating the correlation relationship (dot data 3117, linear function 3118) between the oscillation frequency f and the phase difference θ, and based on the correlation relationship (dot data 3117, linear function 3118), the monitor frequency f at which the phase difference θ becomes a predetermined phase difference (θ0) m is calculated, which is characterized by this.

[0169] By the above method, the monitor frequency f m (oscillation frequency f) can always be accurately controlled to be the frequency with the steepest phase change in the resonant circuit 8, so even if the capacitance of the capacitor C1, that is, the relative permittivity of the fluid changes, the monitor frequency f m (oscillation frequency f) can accurately follow the frequency, and can always maintain the state of maximum sensitivity to the phase change.

[0170] In the fluid property detection method of this embodiment, when searching for the frequency region, it is characterized by searching for the frequency region by decreasing the oscillation frequency f from a frequency higher than the frequency region.

[0171] When the excitation signal contains a harmonic component and the harmonic component is close to the resonant frequency (resonant frequency f0, resonant frequency f1) of the resonant circuit 8, there is a possibility that the resonant circuit 8 will respond to the harmonic component and cause problems in the search for the frequency region. However, by the above method, since the frequency region is searched by decreasing the oscillation frequency f from a frequency higher than the frequency region, the resonant circuit 8 does not respond to the harmonic component, and the search for the frequency region can be surely performed.

[0172] As described above, this embodiment has been described, but the above embodiment only shows a part of the application examples of the present invention, and is not intended to limit the technical scope of the present invention to the specific configuration of the above embodiment.

Description of Symbols

[0173] 1 ··· Fluid property detection device, 21 ··· Detection electrode, 22 ··· Inner electrode, 27 ··· Cover electrode, 28 ··· Excitation electrode, 3101 ··· Inductor section, 3102 ··· Excitation signal oscillation section, 3103 ··· First comparator, 3104 ··· Second comparator, 3105 ··· Phase comparator, 3107 ··· First voltage sensor, 3108 ··· Second voltage sensor, 3110 ··· Temperature sensor, 3112 ··· Control section, 3113 ··· Third comparator, 3114 ··· Rectifier circuit, 3115 ··· First low-pass filter, 3116 ··· Second low-pass filter, 3117 ··· Dot data, 3118 ··· Linear function, 8 ··· Resonance circuit, C1 ··· Capacitor, C2 ··· Capacitor (parasitic capacitance)

Claims

1. A grounded electrode immersed in a fluid, a detection electrode immersed in the fluid and arranged to face the grounded electrode, and an inductor part connected to the detection electrode, wherein a capacitor formed by the grounded electrode and the detection electrode and the inductor part are electrically coupled to each other to form a resonant circuit; An excitation signal oscillation unit that excites the resonant circuit with an excitation signal having a predetermined oscillation frequency; A phase difference detection unit that detects a phase difference between the excitation signal and an output signal of the resonant circuit; A control unit that controls the oscillation frequency so that the phase difference maintains a predetermined phase difference, and the fluid property detection device is characterized by detecting deterioration of the fluid based on a change over time of the oscillation frequency.

2. Further comprising an excitation electrode that is connected to the excitation signal oscillation unit and is arranged close to the detection electrode while being separated from the detection electrode; The excitation signal oscillation unit excites the resonant circuit by outputting the excitation signal to the resonant circuit through a parasitic capacitance formed between the excitation electrode and the detection electrode. The fluid property detection device according to claim 1.

3. The inductor part is an equivalent inductor including a plurality of impedance elements not including an inductor. The fluid property detection device according to claim 1.

4. The impedance element includes a first resistor connected to the detection electrode, a second resistor, a third resistor, a second capacitor, and a fourth resistor connected to the grounded electrode, and forms a series circuit connected in series in the order of the first resistor, the second resistor, the third resistor, the second capacitor, and the fourth resistor. The fluid property detection device according to claim 3.

5. The fourth resistor includes a fifth resistor connected to the second capacitor and a sixth resistor connected to the grounded electrode and connected to the fifth resistor; The sixth resistor is set to have a lower resistance value than the fifth resistor. The output terminal of the resonance circuit extends from between the fifth resistor and the sixth resistor. The fluid property detection device according to claim 4.

6. The control unit sets the oscillation frequency to the resonance frequency of the resonance circuit or a frequency in the vicinity of the resonance frequency. The fluid property detection device according to claim 1.

7. The fluid property detection device further includes an amplitude detection unit that detects the amplitude of the output signal. The control unit changes the oscillation frequency to search for and detect a frequency range in which the amplitude becomes equal to or greater than a predetermined threshold value, and calculates the correlation between the oscillation frequency and the phase difference by detecting the phase difference between the excitation signal and the output signal while changing the oscillation frequency in the frequency range, and calculates a monitor frequency at which the phase difference becomes the predetermined phase difference based on the correlation. The fluid property detection device according to claim 1.

8. When searching for the frequency range, the control unit searches for the frequency range by decreasing the oscillation frequency from a frequency higher than the frequency range. The fluid property detection device according to claim 7.

9. The fluid property detection device further includes a temperature sensor that measures the temperature of the inductor part or the temperature of the fluid. The control unit calculates a correction amount of the resonance frequency of the resonance circuit based on the temperature detected by the temperature sensor. The fluid property detection device according to claim 1.

10. The fluid property detection device further includes an amplitude detection unit that detects the amplitude of the output signal. When the amplitude becomes lower than a predetermined threshold value, the control unit changes the oscillation frequency to search for and detect a frequency range in which the amplitude becomes equal to or greater than the threshold value, and controls the oscillation frequency in the frequency range. The fluid property detection device according to claim 1.

11. The fluid property detection device according to claim 1, wherein the control unit controls one of the oscillation frequencies so that the phase difference maintains a predetermined phase difference.

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