Measurement device

Abstract

Provided is a measurement device that measures, in a fluid flow path, the fluid pressure difference between a first position and a second position, said measurement device comprising a first pressure sensor that is provided at the first position and outputs a first potential corresponding to the pressure of the fluid, a second pressure sensor that is provided at the second position and outputs a second potential corresponding to the pressure of the fluid, and a potential difference detection unit that detects the potential difference between the first potential and the second potential and converts the detected potential difference to a pressure difference.

Description

Measuring equipment

[0001] The present invention relates to a measurement device.

[0002] Conventionally, a fuel cell cooling system is known in which a temperature sensor or a pressure sensor is disposed near a water pump (see, for example, Patent Document 1). Also, a configuration is known in which pressure sensors are provided on the coolant discharge side and coolant inlet side of an electric water pump equipped with a sensorless type brushless motor (see, for example, Patent Document 2). Furthermore, Patent Document 3 describes a diffuser for a low-pressure steam turbine stage. [Prior art documents] [Patent Documents] [Patent Document 1] JP 2018-181654 A [Patent Document 2] JP 2009-264288 A [Patent Document 3] JP 2014-1735 A General disclosure

[0003] (Problem to be solved) To accurately measure the flow rate of a fluid flowing in a cooling system. (Means for solving the problem)

[0004] In order to solve the above problems, a first aspect of the present invention provides a measurement device that measures a pressure difference of a fluid between a first position and a second position in a fluid flow path. The measurement device may include a first pressure sensor that is provided at the first position and outputs a first potential corresponding to the pressure of the fluid. Any of the measurement devices may include a second pressure sensor that is provided at the second position and outputs a second potential corresponding to the pressure of the fluid. Any of the measurement devices may include a potential difference detection unit that detects a potential difference between the first potential and the second potential and converts the potential difference into the pressure difference.

[0005] In any of the above measuring devices, the potential difference detection unit may detect the potential difference, which is the difference between a first potential analog signal indicating the first potential and a second potential analog signal indicating the second potential, and convert the potential difference into the pressure difference as a digital signal.

[0006] Any of the above measurement devices may further include a differential amplifier that amplifies the difference between a first potential analog signal indicating the first potential and a second potential analog signal indicating the second potential, and outputs a potential difference analog signal indicating the potential difference.

[0007] In any of the above measurement devices, the potential difference detection unit may acquire in advance an offset value, which is the potential difference when the fluid is not flowing through the flow path, and may correct the pressure difference using the offset value.

[0008] Any of the above measurement devices may further include a temperature sensor that detects a temperature of the fluid. In any of the above measurement devices, the potential difference detection unit may obtain the offset value for each temperature of the fluid.

[0009] In any of the above measurement devices, the flow path may have a connection point where three or more branch paths connect, and a plurality of pressure sensors including the first pressure sensor and the second pressure sensor may be attached to at least three of the branch paths at the connection point, and a potential difference between the plurality of pressure sensors may be detected.

[0010] In any of the above-described measuring devices, the branch path may include a main flow path of the flow path and a bypass path having a diameter smaller than that of the main flow path.

[0011] In any of the above measuring devices, an electronic valve or a solenoid valve that controls the flow rate of the fluid flowing through the branch path may be provided at the connection point.

[0012] Any of the above measurement devices may further include a temperature sensor that detects the temperature of the fluid.

[0013] Any of the above measurement devices may further include a flow rate calculation unit that calculates the flow rate of the fluid from the pressure difference.

[0014] The measuring device may be used in a cooling system that cools an object to be cooled by causing the fluid to flow through the flow path using a liquid pump. In the measuring device, the first pressure sensor and the second pressure sensor may be attached to the flow path between an intake port of the liquid pump and the object to be cooled.

[0015] In any of the above measurement devices, the distance from the suction port of the liquid pump to the first pressure sensor and the second pressure sensor may be ten times or more the diameter of the flow path.

[0016] To solve the above problem, a second aspect of the present invention provides a measurement device for measuring a pressure difference between a first position and a second position in a fluid flow path. The measurement device may include a first pressure sensor provided at the first position and outputting a first potential corresponding to the pressure of the fluid. Any of the measurement devices may include a second pressure sensor provided at the second position and outputting a second potential corresponding to the pressure of the fluid. Any of the measurement devices may include a potential difference detection unit that calculates the pressure of the fluid at the first position from the first potential and calculates the pressure of the fluid at the second position from the second potential. Any of the measurement devices may include a first low-pass filter provided between the first pressure sensor and the potential difference detection unit and filtering the first potential. Any of the measurement devices may include a second low-pass filter provided between the second pressure sensor and the potential difference detection unit and filtering the second potential.

[0017] The measurement device may be used in a cooling system that cools an object to be cooled by causing the fluid to flow through the flow path using a liquid pump. In the measurement device, the cutoff frequencies of the first low-pass filter and the second low-pass filter may be smaller than the reciprocal of a rotation period of the liquid pump.

[0018] The above summary of the invention does not list all of the necessary features of the present invention, and subcombinations of these features may also be inventions.

[0019] 1 is a diagram illustrating an example of a cooling system 100 in which a measuring device 20 according to an embodiment of the present invention is used. FIG. 2 is a diagram illustrating a method for calculating a flow rate from a pressure. FIG. 3 is a diagram illustrating a circuit configuration of a measuring device 20 according to an example. FIG. 4 is a diagram illustrating the timing at which a potential difference detection unit 24 detects the output of a pressure sensor. FIG. 5 is a diagram illustrating a circuit configuration of a measuring device 200 according to a comparative example. FIG. 6 is a diagram illustrating the circuit configuration of a measuring device 200 according to another comparative example. FIG. 7 is a diagram illustrating the timing at which a potential difference detection unit 24 detects the output of a pressure sensor according to a comparative example. FIG. 8 is a diagram illustrating the results of flow rate calculations by the measuring device 20 according to the example. FIG. 9 is a diagram illustrating the results of flow rate calculations by the measuring device 200 according to the comparative example. FIG. 10 is a diagram illustrating a circuit configuration of a modified example of the measuring device 20. FIG. 11 is a diagram illustrating an example of a process for converting a potential difference into a pressure difference in the measuring device 20. FIG. 12 is a diagram illustrating the configuration and installation example of a pressure sensor according to an embodiment of the present invention. FIG. 13 is a diagram illustrating an example of the configuration of a portion of a measuring device 20 according to an embodiment of the present invention. FIG. 14 is a diagram illustrating the arrangement of a pressure sensor at a connection point 80 of a flow path 50. FIG. 15 is a diagram illustrating another example of the connection point 80. FIG. 16 is a diagram illustrating the circuit configuration of a measuring device 20 according to a second embodiment of the present invention. FIG. 17 is a diagram illustrating another example of the connection point 80. 16A and 16B. FIG. 17A is a diagram showing the output after the first low-pass filter 30-1 in FIG. 16. FIG. 17B is a diagram showing the output after the second low-pass filter 30-2 in FIG. 16. FIG. 17B is a diagram showing the output difference (potential difference) between FIG. 17A and FIG. 17B. FIG. 17B is a diagram showing the output of the first pressure sensor 21 in the comparative example. FIG. 17B is a diagram showing the output of the second pressure sensor 22 in the comparative example. FIG. 18A is a diagram showing the output difference (potential difference) between FIG. 18B.

[0020] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. In this specification and drawings, elements having substantially the same function and configuration are designated by the same reference numerals to avoid redundant description, and elements not directly related to the present invention are not shown. Furthermore, in one drawing, elements having the same function and configuration may be designated by the same reference numeral, and the reference numerals may be omitted for other elements.

[0021] In this specification, technical matters may be explained using orthogonal coordinate axes of the X-axis, Y-axis, and Z-axis. The orthogonal coordinate axes merely identify the relative positions of components and do not limit a specific direction. For example, the Z-axis does not limit the height direction relative to the ground. Note that the +Z-axis direction and the -Z-axis direction are opposite directions. When the Z-axis direction is described without specifying positive or negative, it means a direction parallel to the +Z-axis and -Z-axis.

[0022] In this specification, when we say "same" or "equal," it may also include cases where there is an error due to manufacturing variations, etc. The error is, for example, within 10%.

[0023] 1 is a diagram illustrating an example of a cooling system 100 in which a measuring device 20 according to an embodiment of the present invention is used. The cooling system 100 is a thermal management system for xEVs, such as electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and fuel cell vehicles (FCVs). The cooling system 100 cools an object to be cooled by circulating a fluid (coolant).

[0024] The cooling system 100 includes a liquid pump 10, a chiller 12, a valve 14, an object to be cooled 16, a measuring device 20, and a flow path 50. In Fig. 1, the arrows indicate the direction in which the fluid flows along the flow path 50. The components are connected by pipes or the like that form the flow path 50.

[0025] The liquid pump 10 is a water pump that causes a fluid to flow through a flow path 50 and circulates the fluid. The liquid pump 10 has an intake port 11 that draws in the fluid and an outlet port 13 that discharges the fluid. The chiller 12 controls the temperature of the fluid.

[0026] The valve 14 controls the flow rate of the fluid flowing through the flow path 50 leading to the object to be cooled 16. In this example, the valve 14 is a multi-way valve that controls the flow rate of the fluid flowing to the object to be cooled 16-1 and the object to be cooled 16-2. The valve 14 may be an electronic valve or a solenoid valve.

[0027] The object to be cooled 16 is, for example, a system for cooling various components such as a motor, a battery, or an inverter in an electric vehicle, or a cooling system for cooling the interior space. The cooling system 100 of this example cools the object to be cooled 16-1 and the object to be cooled 16-2.

[0028] Since the cooling performance of the cooling system 100 depends on the flow rate of the fluid flowing through the flow path 50, the temperature of the object to be cooled 16 is controlled within an appropriate range by controlling the flow rate. A common method for controlling the flow rate is to indirectly grasp and control the flow rate using control values ​​such as the rotation speed and power of the liquid pump 10. For example, the flow rate is increased by increasing the rotation speed of the liquid pump 10, and decreased by decreasing the rotation speed.

[0029] However, the above-described method suffers from the problem of being unable to control the flow rate when the correlation between the rotation speed of the liquid pump 10 and the flow rate is lost. For example, if a portion of the fluid flow path 50 becomes clogged, the flow rate may decrease or even stop. In such a case, if a system monitors and controls the flow rate based on the rotation speed of the liquid pump 10, increasing the rotation speed of the liquid pump 10 does not increase the actual flow rate, making it impossible to monitor the actual flow rate. As a result, the object to be cooled 16 may be damaged due to excessive heat, or the liquid pump 10 may be damaged due to excessive load. Furthermore, in the low flow rate region where the rotor of the liquid pump 10 rotates slowly, the induced voltage decreases, making it difficult to detect the rotation speed of the liquid pump 10 itself (see, for example, Patent Document 3). Therefore, it is desirable to measure the flow rate using other methods.

[0030] A measuring device 20 is attached to the cooling system 100 of this example. The measuring device 20 measures the flow rate of the fluid in the cooling system 100. The measuring device 20 of this example calculates the flow rate of the fluid by measuring the pressure of the fluid. The measuring device 20 includes a first pressure sensor 21 and a second pressure sensor 22.

[0031] Fig. 2 is a diagram illustrating a method for calculating a flow rate from a pressure. Fig. 2 is an enlarged view of the pressure sensor and the flow path 50 in Fig. 1 and their vicinity. In Fig. 2, a fluid flows in the flow path 50 in the positive direction of the X-axis. Fig. 2 is a cross-sectional view of the flow path 50 in a direction parallel to the flow direction. The flow path 50 is a pipe formed by a cylindrical housing 52 such as a cylinder.

[0032] One method for calculating the flow rate from pressure is to compare the pressure before and after a different-diameter pipe called an orifice or a Venturi tube, and calculate the flow rate from the pressure difference. The flow path 50 in FIG. 2 is also a different-diameter pipe. The pressure P １ and the pressure P at the second position ２ The flow rate Q can be calculated by measuring the pressure difference and solving the simultaneous equations of the following equations (1) and (2) according to Bernoulli's theorem. Here, ρ is the density of the fluid, v is the flow velocity of the fluid, S is the cross-sectional area of ​​the flow path 50, g is the gravitational acceleration, h is the height of the flow path 50, and the subscript 1 or 2 indicates the value at the first position or the second position.

[0033] One method for measuring the pressure difference between two locations is to connect the two locations with a separate route such as a bypass and insert a relative pressure sensor between them (relative pressure measurement method). In this case, a separate route must be provided to measure the pressure difference, which makes the flow path 50 complicated.

[0034] Another method for measuring the pressure difference between two locations is to install a pressure sensor at each of the two locations and calculate the pressure difference (two-point measurement method). The two-point measurement method does not require a complex flow path 50 and is easy to install in existing equipment. In this embodiment, the two-point measurement method is used in the cooling system 100 to calculate the flow rate of the fluid.

[0035] The measuring device 20 measures the pressure difference of the fluid between a first position and a second position in the flow path 50. The first pressure sensor 21 is provided at the first position and outputs a first potential corresponding to the pressure of the fluid. The second pressure sensor 22 is provided at the second position and outputs a second potential corresponding to the pressure of the fluid. The first pressure sensor 21 and the second pressure sensor 22 are, for example, semiconductor piezo-resistance pressure sensors.

[0036] 3 is a diagram showing the circuit configuration of a measurement device 20 in this embodiment. In addition to a first pressure sensor 21 and a second pressure sensor 22, the measurement device 20 includes a potential difference detection unit 24 and a flow rate calculation unit 26. The first pressure sensor 21 outputs a first potential to the potential difference detection unit 24, and the second pressure sensor 22 outputs a second potential to the potential difference detection unit 24.

[0037] The potential difference detection unit 24 detects the potential difference between the first potential and the second potential and converts the potential difference into a pressure difference. The output terminal of the first pressure sensor 21 and the output terminal of the second pressure sensor 22 may be directly connected to the input terminal of the potential difference detection unit 24. Direct connection may mean connection without any other circuit elements between them, or may mean no AD converter between them. The potential difference detection unit 24 outputs the converted pressure difference to the flow rate calculation unit 26. One example of the potential difference detection unit 24 is an AD converter.

[0038] The flow rate calculation unit 26 is an electronic computer that acquires the pressure difference output from the potential difference detection unit 24 and calculates the flow rate of the fluid from the pressure difference. The flow rate calculation unit 26 may calculate the flow rate using the above-mentioned formulas (1) and (2). The flow rate calculation unit 26 may display the calculation results on a monitor or the like, or may transmit them to another device.

[0039] The first potential and the second potential may be analog signals. The potential difference detection unit 24 may detect a potential difference between a first potential analog signal indicating the first potential and a second potential analog signal indicating the second potential, and convert the potential difference into a pressure difference digital signal.

[0040] 4 is a diagram illustrating the timing at which the potential difference detection unit 24 detects the output of the pressure sensor. Fig. 4 shows the output (first potential) of the first pressure sensor 21 and the output (second potential) of the second pressure sensor 22. The horizontal axis of Fig. 4 represents time.

[0041] The fluid flowing through the flow path 50 has a pulsating component. Pulsation is a phenomenon in which the flow rate or flow velocity of a fluid changes periodically. For example, pulsation occurs due to the rotation of a pump. Therefore, pulsating components also appear in the outputs of the first pressure sensor 21 and the second pressure sensor 22. FIG. 4 shows only the pulsating components of the outputs of the first pressure sensor 21 and the second pressure sensor 22.

[0042] According to the measuring device 20 of the embodiment shown in FIG. 3, since the potential difference between the first potential and the second potential is detected, the timing of detecting the first potential and the second potential is simultaneous or the timing difference is negligibly small. In other words, the pulsating components contained in the first potential and the second potential are equal. In FIG. 4, the timing of detecting the potential difference is indicated by a dotted line, and the respective pulsating components at that timing are indicated by thick arrows. Then, since the difference between the first potential and the second potential is detected, the respective pulsating components are canceled out. Therefore, even if the fluid is pulsating, the pressure difference value is stable, improving measurement accuracy.

[0043] Fig. 5 is a diagram showing the circuit configuration of a measuring device 200 in a comparative example. The measuring device 200 of this example differs from the measuring device 20 shown in Fig. 3 in that a potential difference detection unit 24 is provided for each pressure sensor. The measuring device 200 includes a potential difference detection unit 24-1 and a potential difference detection unit 24-2.

[0044] The potential difference detection unit 24-1 detects the output (first potential) of the first pressure sensor 21, compares the first potential with a reference potential, and converts it into a pressure value at a first position (first pressure value). Similarly, the potential difference detection unit 24-2 detects the output (second potential) of the second pressure sensor 22, compares the second potential with a reference potential, and converts it into a pressure value at a second position (second pressure value). The reference potential may be ground potential. The flow rate calculation unit 26 obtains the above-mentioned pressure difference by taking the difference between the first pressure value and the second pressure value. Calculation of the flow rate from the pressure difference is similar to the case of FIG. 3.

[0045] 6 is a diagram showing the circuit configuration of a measuring device 200 in another comparative example. The measuring device 200 in this example includes one potential difference detection unit 24. The potential difference detection unit 24 in this example is a multi-channel A / D conversion circuit having an A / D converter 32 and a multiplexer 34.

[0046] In a multi-channel A / D conversion circuit, simultaneous conversion requires an A / D converter 32 for each channel, which results in a large circuit scale and high cost. Therefore, a typical multi-channel A / D conversion circuit uses a single A / D converter 32 and a multiplexer 34 to switch inputs to convert multiple channels. The potential difference detection unit 24 in FIG. 6 illustrates a typical multi-channel A / D conversion circuit. Specifically, the multiplexer 34 selects channel 1, and the A / D converter 32 converts the first potential. Channel 2 is then selected, and the second potential is converted. In other words, the first potential and the second potential are not converted simultaneously.

[0047] FIG. 7 is a diagram illustrating the timing at which the potential difference detection unit 24 in the comparative example detects the output of the pressure sensor. In both the comparative examples shown in FIGS. 5 and 6, there is a discrepancy in the timing at which the output of the pressure sensor is detected. FIG. 7 illustrates the example shown in FIG. 6. The dotted lines indicate the timing at which the output of the first pressure sensor 21 is converted in channel 1 and the timing at which the output of the second pressure sensor 22 is converted in channel 2. Because the two timings are different, the pulsating components contained in the output of the first pressure sensor 21 and the output of the second pressure sensor 22 are not equal. As a result, errors occur due to the pulsating components, deteriorating measurement accuracy.

[0048] Fig. 8 is a diagram showing the results of flow rate calculations using the measuring device 20 of the embodiment. Fig. 9 is a diagram showing the results of flow rate calculations using the measuring device 200 of the comparative example. The horizontal axis of the graphs in Figs. 8 and 9 represents time, and the vertical axis represents the calculated flow rate. The solid lines in the diagrams represent the results of flow rate calculations using the measuring device 20. For comparison, the flow rate was also measured using a flow meter. The constant values ​​indicated by the dotted lines and arrows in the diagrams indicate points where the flow rate values ​​measured using the flow meter are stable.

[0049] The flow rate values ​​calculated by the measuring device 20 of the embodiment are stable near the flow rate value of the flowmeter, and no large errors are observed. On the other hand, the measuring device 200 of the comparative example has a large error due to the pulsating component, and the calculated flow rate values ​​are not stable. In other words, it was confirmed that the measuring device 20 of the embodiment improves measurement accuracy by removing the pulsating component.

[0050] 10 is a diagram showing the circuit configuration of a modified example of the measuring device 20. The measuring device 20 of this example further includes a differential amplifier 28 in addition to the components shown in FIG. 3. The differential amplifier 28 amplifies the potential difference between the first potential output from the first pressure sensor 21 and the second potential output from the second pressure sensor 22, and outputs the amplified potential difference to the potential difference detection unit 24.

[0051] In this example, the first potential and the second potential may also be analog signals. That is, the differential amplifier 28 amplifies the difference between a first potential analog signal indicating the first potential and a second potential analog signal indicating the second potential, and outputs a potential difference analog signal indicating the potential difference. The output terminal of the first pressure sensor 21 and the output terminal of the second pressure sensor 22 may be directly connected to two input terminals of the differential amplifier 28. The output terminal of the differential amplifier 28 may be directly connected to the input terminal of the potential difference detection unit 24. Even with this configuration, the outputs of the pressure sensors are detected at the same time, which allows the pulsating component to be canceled out and improves measurement accuracy.

[0052] FIG. 11 is a diagram showing an example of a process for converting a potential difference into a pressure difference in the measurement device 20. The horizontal axis of FIG. 11 represents the potential difference, and the vertical axis represents the pressure difference. The potential difference detection unit 24 may acquire in advance a relational expression that represents the relationship between the pressure difference and the potential difference. In this example, the relational expression is a linear function with a slope a and an intercept b. When the potential difference detection unit 24 in this example detects a certain potential difference, it multiplies the potential difference by the slope a and adds the intercept b to obtain the pressure difference.

[0053] The slope a is a parameter determined by the sensitivity of the pressure sensor and is calibrated before shipping. On the other hand, the intercept b is an offset value that represents the potential difference when no fluid is flowing through the flow path 50. The potential difference detection unit 24 may acquire the slope a and the intercept b in advance. The potential difference detection unit 24 may correct the pressure difference using the intercept b. This further improves measurement accuracy.

[0054] Here, intercept b changes due to, for example, relaxation of adhesive stress when attaching the pressure sensor. Therefore, the potential difference detection unit 24 may periodically acquire intercept b and update the value of intercept b. This further improves measurement accuracy.

[0055] 12 is a diagram illustrating an example of the configuration and installation of a pressure sensor according to an embodiment of the present invention. The pressure sensor in this example is installed in a flow path 50. While the first pressure sensor 21 is used as an example in FIG. 12, the second pressure sensor 22 and other pressure sensors may be similarly configured. The first pressure sensor 21 has a housing 62, a coating agent 64, and a sensor portion 66.

[0056] The housing 62 is a housing for the first pressure sensor 21. A coating agent 64 and a sensor portion 66 are provided inside the housing 62. The housing 62 and the housing 52 of the flow path 50 may be attached with an adhesive. The housing 52 of the flow path 50 is provided with a hole 54 for allowing the fluid to flow into the inside of the housing 62. The sensor portion 66 is protected from the fluid flowing into the inside of the housing 62 by the coating agent 64 such as gel.

[0057] The sensor unit 66 detects the pressure of the fluid. As an example, the sensor unit 66 is provided with a semiconductor piezo-resistive pressure sensor formed on a semiconductor chip. However, as an example, the sensor unit 66 may also be provided with a diode or a resistance element formed on the semiconductor chip for temperature detection. This allows the sensor unit 66 to detect the pressure and temperature of the fluid.

[0058] 13 is a diagram showing an example of the configuration of a portion of a measurement device 20 according to an embodiment of the present invention. In this example, a first pressure sensor 21 will be used as an example of a pressure sensor. The measurement device 20 of this example includes a temperature sensor 71 in addition to the first pressure sensor 21. The first pressure sensor 21 is attached on the opposite side of the temperature sensor 71 from the flow path 50.

[0059] The temperature sensor 71 detects the temperature of the fluid. A thermistor 72 is provided near the tip of the temperature sensor 71. The temperature sensor 71 is fixed by penetrating the housing 52 of the flow path 50, and the tip where the thermistor 72 is provided is located inside the flow path 50. A resistance temperature detector (RTD) or a thermocouple may be used instead of the thermistor 72.

[0060] A detailed description of the inside of the temperature sensor 71 will be omitted, but the temperature sensor 71 has a hollow interior near where the thermistor 72 is provided, allowing fluid to flow into the temperature sensor 71 in the positive direction of the Z axis. As a result, the fluid reaches the first pressure sensor 21, and the pressure of the fluid is measured by the sensor unit 66. With this configuration, it is possible to measure the pressure and temperature of the fluid.

[0061] The first pressure sensor 21 may have an output terminal 31. The first pressure sensor 21 may output a first potential from the output terminal 31 to the potential difference detection unit 24. The temperature sensor 71 may also have an output terminal 31. The temperature sensor 71 may output a potential of a thermistor 72 or the like from the output terminal 31 to the outside.

[0062] The potential difference detection unit 24 may acquire the above-mentioned offset value (intercept b in FIG. 11 ) for each temperature of the fluid. For example, the temperature of the fluid changes depending on the operating conditions of the object to be cooled 16 and the liquid pump 10. This causes the offset value to change. Therefore, acquiring an offset value for each temperature allows for more accurate correction of the pressure difference. The potential difference detection unit 24 may select the offset value to use depending on the measurement results of the temperature sensor 71.

[0063] Furthermore, the liquid density ρ generally has temperature dependency. Therefore, the flow rate calculation unit 26 may use or acquire data on the liquid density ρ for each temperature of the liquid being used, and solve the simultaneous equations of Equation (1) and Equation (2) using the liquid density ρ corresponding to the temperature acquired by the temperature sensor 71. This allows for more accurate calculation of the flow rate. Note that the liquid density ρ corresponding to the temperature can also be used in Equation (3) and Equation (4), which will be described later.

[0064] FIG. 14A is a diagram illustrating the placement of a pressure sensor at a connection point 80 of a flow path 50. The flow path 50 in this example has a connection point 80 to which three or more branch paths 82 connect. In this example, branch paths 82-1, 82-2, and 82-3 are connected at the connection point 80. In this specification, the branch paths 82 refer to all flow paths including the main flow at the connection point 80. That is, at a connection point 80 to which three or more flow paths 50 connect, each flow path 50 is referred to as a branch path 82. When four or more branch paths 82 are provided at the connection point 80, all of the branch paths 82 may branch from the same branch position or may branch from different branch positions. The connection point 80 may be an area including multiple branch positions. The connection point 80 may refer to a branch housing to which multiple branch paths 82 are connected. The branch paths 82 may be connected within the branch housing. A set of consecutive branch positions where the spacing between the branch positions is within five times the diameter of the branch path 82 may be defined as one connection point 80. The range of the connection point 80 may be, for example, within a range of five times the diameter of the flow path 50 from the point where the extension directions of the branch paths 82 intersect. The diameter of the flow path 50 may be the inner diameter of the pipe that constitutes the flow path 50.

[0065] At the connection point 80, multiple pressure sensors may be attached to at least three branch paths 82, one for each. The multiple pressure sensors include the first pressure sensor 21 and second pressure sensor 22 described above. In this example, the first pressure sensor 21 is attached to the branch path 82-1, the second pressure sensor 22 is attached to the branch path 82-2, and the third pressure sensor 23 is attached to the branch path 82-3. The third pressure sensor 23 may have a configuration similar to the first pressure sensor 21 and the second pressure sensor 22. The third pressure sensor 23 is provided at a third position and outputs a third potential corresponding to the pressure of the fluid. Pressure sensors may be attached to all of the branch paths 82 at the connection point 80.

[0066] The potential difference detection unit 24 may detect potential differences between the multiple pressure sensors. In this example, the potential difference detection unit 24 detects the potential difference between the first potential and the second potential, the potential difference between the first potential and the third potential, and the potential difference between the second potential and the third potential.

[0067] The pressure P at the first location of the connection point 80１ , pressure P at the second position ２ , and the pressure P at the third position ３ The flow rate Q can be calculated by measuring the pressure difference between the two pressures and solving the simultaneous equations of the following equations (3) to (5) according to Bernoulli's theorem. The letters and the like in the formula are the same as those in formula (1) and formula (2).

[0068] In this example, the potential difference is also detected and converted into a pressure difference, so the influence of the pulsating component can be eliminated. Furthermore, according to this example, there is no need to narrow the flow path 50 for measurement, so clogging and pressure loss in the flow path 50 can be suppressed. In addition, the flow rates of all branch paths 82 can be calculated. Furthermore, since the connection points 80 in existing equipment can be used as they are, installation is easy.

[0069] At the connection point 80 shown in Figure 14A, the fluid flowing through the branch path 82-1 branches into the branch path 82-2 and the branch path 82-3, but at the connection point 80, the fluid flowing through two branch paths 82 may merge into one branch path 82. Furthermore, the connection point 80 is not limited to a point where all the branch paths 82 are connected. For example, a case where another branch path 82 branches off at the branch path 82-2 downstream of the branch point of the branch path 82-3 in Figure 14A is also included in the connection point 80.

[0070] 14B is a diagram showing another example of the connection point 80. The branch path 82 in this example has a main flow path 92 of the flow path 50 and a bypass path 94. The main flow path 92 is the main flow path of the flow path 50 through which the fluid flows. The main flow path 92 may be the flow path 50 that connects the components of the cooling system 100. The bypass path 94 branches off from the main flow path 92 at a connection point 80-1 and merges with the main flow path 92 at a connection point 80-2. At each connection point 80, the main flow path 92 and the bypass path 94 become the above-mentioned branch path 82.

[0071] 14B, the pressure of the main flow 92 before and after the connection point 80-1 and the pressure of the bypass path 94 are measured. In this example, the flow rate can be calculated in the same way as in the case of FIG. 14A by measuring the pressure of each flow path 50. The same is true for the connection point 80-2. Furthermore, since the provision of the bypass path 94 eliminates the need to throttle the main flow 92, clogging of the main flow 92 due to the addition of the measurement device 20 can be prevented.

[0072] The diameter of the main flow 92 upstream of the connection point 80 (negative side of the X-axis in the figure) is D1, the diameter of the main flow 92 downstream of the connection point 80 (positive side of the X-axis in the figure) is D2, and the diameter of the bypass path 94 is D3. Diameter D3 may be smaller than diameter D1. By making the diameter of the bypass path 94 smaller than the diameter of the main flow 92, the flow rate of the bypass path 94 increases, making it easier to reduce pressure (static pressure). As a result, a pressure difference occurs even at low flow rates, making measurement easier.

[0073] The diameter D2 may be the same as the diameter D1 or may be smaller than the diameter D1. The diameter D3 may be smaller than the diameter D2. A valve 90 may be provided at the connection point 80-1 between the main flow 92 and the bypass path 94. The valve 90 may open and close depending on the fluid flow rate to adjust the flow rate of the bypass path 94. For example, when the flow rate of the main flow 92 is high, a sufficient differential pressure is generated due to the difference between the diameters D1 and D2, so the valve 90 is closed. When the flow rate of the main flow 92 is low, the above differential pressure may not be sufficient, so the valve 90 is opened to use the bypass path 94, which is more likely to generate a differential pressure. This allows the range of flow rates that can be measured by the measurement device 20 to be expanded. The ratio of the diameters D3 and D1 (throttle ratio) may be adjusted depending on the range of flow rates to be measured.

[0074] 14C is a diagram showing another example of the connection point 80. The connection point 80 in this example is provided with a multi-way valve 96 that controls the flow rate of the fluid flowing in the branch paths 82. The multi-way valve 96 may be an electronic valve or a solenoid valve. In the connection point 80 in this example, the branch paths 82-1 to 82-5 are connected via the multi-way valve 96. The multi-way valve 96 may include a variable valve that controls the flow rate or the direction of the fluid flow in each branch path 82.

[0075] A pressure sensor is provided in each branch path 82. The fourth pressure sensor 124 provided in branch path 82-4 and the fifth pressure sensor 125 provided in branch path 82-5 may also have the same configuration as the first pressure sensor 21. Even with this configuration, there is no need to narrow the flow path 50 to measure the flow rate, so clogging and pressure loss in the flow path 50 can be suppressed. In addition, the flow rates of all branch paths 82 can be calculated. Furthermore, the multi-way valve 96 in existing equipment can be used as is, making installation easy.

[0076] 1, the first pressure sensor 21 and the second pressure sensor 22 may be attached to the flow path 50 between the intake port 11 of the liquid pump 10 and the object 16 to be cooled. In other words, the pressure sensors may be attached to the return system of the cooling system 100. Because the fluid pressure is lower downstream of the cooling system 100, the measurement range of the pressure sensors can be narrowed. This improves measurement accuracy. The same applies when other pressure sensors, such as the third pressure sensor 23, are used.

[0077] However, the distance D4 (see FIG. 1 ) from the suction port 11 of the liquid pump 10 to the first pressure sensor 21 and the second pressure sensor 22 may be 10 times or more the diameter of the flow path 50. The fluid pressure is unstable near the suction port 11 of the liquid pump 10 due to turbulence in the flow path. By placing the pressure sensor at a certain distance from the suction port 11, it is possible to measure a stable pressure. The distance D4 may be 20 times or more, or even 30 times or more the diameter of the flow path 50. The same applies when using other pressure sensors such as the third pressure sensor 23.

[0078] 15 is a diagram showing the circuit configuration of a measuring device 20 according to a second embodiment of the present invention. Description of components similar to those described in FIGS. 3 and 5 will be omitted where appropriate. The measuring device 20 of this example includes a potential difference detection unit 24, a first low-pass filter 30-1, and a second low-pass filter 30-2.

[0079] The potential difference detection unit 24 calculates the pressure of the fluid at a first position from the first potential, and calculates the pressure of the fluid at a second position from the second potential. The potential difference detection unit 24 in this example has a first potential difference detection unit 24-1 and a second potential difference detection unit 24-2. The first potential difference detection unit 24-1 calculates the pressure of the fluid at the first position from the first potential. The second potential difference detection unit 24-2 calculates the pressure of the fluid at the second position from the second potential. In other words, the connections between each pressure sensor and the potential difference detection unit 24 are the same as in the example shown in FIG. 5. Therefore, the timing at which the first potential difference detection unit 24-1 calculates the pressure and the timing at which the second potential difference detection unit 24-2 calculates the pressure may differ.

[0080] The first low-pass filter 30-1 is provided between the first pressure sensor 21 and the potential difference detection unit 24. The first low-pass filter 30-1 filters the first potential. The second low-pass filter 30-2 is provided between the second pressure sensor 22 and the potential difference detection unit 24. The second low-pass filter 30-2 filters the second potential.

[0081] The cutoff frequencies of the first low-pass filter 30-1 and the second low-pass filter 30-2 may be smaller than the reciprocal of the rotation period of the liquid pump 10. When fluid pulsation is generated by the rotation of the liquid pump 10, the pulsation component can be removed by removing the rotation frequency component of the liquid pump 10. Therefore, even if the timing at which the first potential difference detection unit 24-1 calculates the pressure differs from the timing at which the second potential difference detection unit 24-2 calculates the pressure, errors due to the pulsation component can be suppressed. The cutoff frequency may be equal to or smaller than ½, ⅕, or 1 / 10 of the reciprocal of the rotation period of the liquid pump 10.

[0082] FIG. 16 is a diagram showing a modified example of the measuring device 20 according to the second embodiment of the present invention. The potential difference detection unit 24 of this example includes an A / D converter 32 and a multiplexer 34. In other words, the measuring device 200 shown in FIG. 6 is provided with a first low-pass filter 30-1 and a second low-pass filter 30-2. The other points are the same as those shown in FIG. 15. This makes it possible to suppress errors due to pulsating components, even when pressures are calculated sequentially using the multiplexer 34, as in the case of the potential difference detection unit 24 of this example.

[0083] 17A is a diagram showing the output after the first low-pass filter 30-1 in FIG. 16. FIG. 17B is a diagram showing the output after the second low-pass filter 30-2 in FIG. 16. The horizontal axis in FIGS. 17A and 17B represents time, and the vertical axis represents the potential output by each sensor. In FIGS. 17A and 17B, the flow rate is increased, so the output increases over time. No pulsating components were observed in the output of either sensor.

[0084] Figure 17C shows the output difference (potential difference) between Figures 17A and 17B. In the circuit shown in Figure 16, there is a 3 ms delay in channel switching in the multiplexer 34. However, because the low-pass filter removes pulsating components from each output, the pulsating components can also be removed from the output difference in Figure 17C.

[0085] FIG. 18A is a diagram showing the output of the first pressure sensor 21 in a comparative example. FIG. 18B is a diagram showing the output of the second pressure sensor 22 in a comparative example. The horizontal axis in FIGS. 18A and 18B represents time, and the vertical axis represents the potential output by each sensor. The comparative example is a configuration in which a low-pass filter is not provided in the measuring device 20 shown in FIG. 16 (the same configuration as the measuring device 200 shown in FIG. 6). In FIGS. 18A and 18B, the flow rate is increased, so the output increases over time. In FIGS. 18A and 18B, the output of both sensors includes a 160 Hz pulsating component.

[0086] 18C is a diagram showing the difference in output (potential difference) between Figures 18A and 18B. In the comparative example, there is also a 3 ms delay in channel switching in the multiplexer 34. As a result, the magnitude of the pulsating components contained in the output of each sensor differs (see Figure 7), and the sum of these components increases the error due to the pulsating components.

[0087] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0088] 10...liquid pump, 11...suction port, 12...chiller, 13...discharge port, 14...valve, 16...object to be cooled, 20...measuring device, 21...first pressure sensor, 22...second pressure sensor, 23...third pressure sensor, 24...potential difference detection unit, 26...flow rate calculation unit, 28...differential amplifier, 30...low-pass filter, 31...output terminal, 32...A / D converter, 34...multiplexer, 50...flow path, 52...housing, 54...hole, 62...housing, 64...coating agent, 66...sensor unit, 71...temperature sensor, 72...thermistor, 80...connection point, 82...branch path, 90...valve, 92...main flow, 94...bypass path, 96...multi-way valve, 100...cooling system, 124...fourth pressure sensor, 125...fifth pressure sensor, 200...measuring device

Claims

1. A measuring device for measuring the pressure difference of a fluid at a first position and a second position in a fluid flow path, A first pressure sensor provided at the first position and outputting a first potential corresponding to the pressure of the fluid, A second pressure sensor provided at the second position and outputting a second potential corresponding to the pressure of the fluid, A potential difference detection unit that detects the potential difference between the first potential and the second potential and converts the potential difference into a pressure difference. A measuring device equipped with the following features.

2. The potential difference detection unit detects the potential difference, which is the difference between the first potential analog signal representing the first potential and the second potential analog signal representing the second potential, and converts the potential difference into the pressure difference digital signal. The measuring device according to claim 1.

3. The system further includes a differential amplifier that amplifies the difference between a first potential analog signal indicating the first potential and a second potential analog signal indicating the second potential, and outputs a potential difference analog signal indicating the potential difference. The measuring device according to claim 1.

4. The potential difference detection unit first acquires an offset value, which is the potential difference when the fluid is not flowing through the flow path, and corrects the pressure difference using the offset value. The measuring device according to claim 1.

5. The system further includes a temperature sensor for detecting the temperature of the fluid, The potential difference detection unit acquires the offset value for each temperature of the fluid. The measuring device according to claim 4.

6. The aforementioned flow path has a connection point where three or more branch paths are connected. At the connection point, one pressure sensor, including the first pressure sensor and the second pressure sensor, is attached to each of the three branch paths, and the potential difference between the multiple pressure sensors is detected. The measuring device according to claim 1.

7. The aforementioned branching path includes the main channel of the flow path and a bypass path with a smaller diameter than the main channel. The measuring device according to claim 6.

8. The connection point is provided with an electronic valve or solenoid valve that controls the flow rate of the fluid flowing through the branch path. The measuring device according to claim 6.

9. The system further comprises a temperature sensor for detecting the temperature of the fluid. The measuring device according to claim 1.

10. The system further includes a flow rate calculation unit that calculates the flow rate of the fluid from the pressure difference. The measuring device according to claim 1.

11. The measuring device is used in a cooling system that cools an object to be cooled by flowing the fluid through the flow path using a liquid pump. The first pressure sensor and the second pressure sensor are installed in the flow path between the inlet of the liquid pump and the object to be cooled. The measuring device according to any one of claims 1 to 10.

12. The distance from the suction port of the liquid pump to the first pressure sensor and the second pressure sensor is 10 times or more the diameter of the flow path. The measuring device according to claim 11.

13. The plurality of pressure sensors include a third pressure sensor provided at a third position and outputting a third potential corresponding to the pressure of the fluid, The potential difference detection unit detects the potential difference between the first potential and the second potential, the potential difference between the first potential and the third potential, and the potential difference between the second potential and the third potential. The measuring device according to claim 6.

14. The bypass path merges with the main flow of the channel at another connection point. The measuring device according to claim 7.

15. The flow path is provided in a loop shape from the discharge port of the liquid pump, through the object to be cooled, to the suction port of the liquid pump, The first pressure sensor and the second pressure sensor are installed between the object to be cooled and the inlet of the liquid pump in the direction of fluid flow in the flow path. The measuring device according to claim 11.

16. A measuring device for measuring the pressure difference of a fluid at a first position and a second position in a fluid flow path, A first pressure sensor provided at the first position and outputting a first potential corresponding to the pressure of the fluid, A second pressure sensor provided at the second position and outputting a second potential corresponding to the pressure of the fluid, A potential difference detection unit calculates the pressure of the fluid at the first position from the first potential and the pressure of the fluid at the second position from the second potential, A first low-pass filter is provided between the first pressure sensor and the potential difference detection unit to filter the first potential, A second low-pass filter is provided between the second pressure sensor and the potential difference detection unit to filter the second potential. A measuring device equipped with the following features.

17. The measuring device is used in a cooling system that cools an object to be cooled by flowing the fluid through the flow path using a liquid pump. The cutoff frequencies of the first low-pass filter and the second low-pass filter are smaller than the reciprocal of the rotation period of the liquid pump. The measuring device according to claim 16.

18. The cutoff frequencies of the first low-pass filter and the second low-pass filter are less than or equal to 1 / 5 of the reciprocal of the rotation period of the liquid pump. The measuring device according to claim 17.