Fluid sensor and method for controlling the fluid sensor

Abstract

To improve the measurement accuracy of a fluid sensor by reducing noise components generated during an on-period of a heater.SOLUTION: A fluid sensor has a sensor portion that includes a heater and a temperature detecting portion including a pair of thermosensitive elements disposed on both sides of the heater, and a detection control portion that controls the on / off state of the heater, and detects the velocity of a fluid on the sensor portion, on the basis of a temperature difference signal indicating the difference of temperature detected by the pair of thermosensitive elements outputted from the temperature detecting portion. The detection control portion obtains a first signal value of the temperature difference signal before turning on the heater, obtains a second signal value of the temperature difference signal after turning on the heater, obtains a third signal value of the temperature difference signal after turning off the heater, interpolates a correction value at a generation timing of the second signal value with the first signal value and the third signal value, and calculates the velocity of the fluid on the basis of the difference between the second signal and the correction value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a fluid sensor and a method for controlling a fluid sensor. [Background technology]

[0002] A known technique for measuring gas flow velocity is to place resistor elements functioning as temperature-sensing elements on both sides of a heater and measure the flow velocity based on the difference in the resistance values of the resistor elements, which change in response to the airflow. This type of fluid sensor creates a pseudo-no-airflow state by temporarily turning off the heater, and stores the output voltage from the resistor element pair at this time as an error voltage such as an offset voltage. Then, by subtracting the error voltage from the output voltage during normal measurement with the heater turned on, noise components such as offsets contained in the flow velocity data are reduced (see, for example, Patent Document 1 and Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Publication No. 5-35289 [Non-patent literature]

[0004] [Non-Patent Document 1] Sensor Interface Circuit, Savingmation Review "Micro Flow Sensor" Special Issue, pp.42-48, Yamatake Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned method can detect offsets between resistor elements at a certain point when the heater is off. Furthermore, by periodically repeating this operation, it is possible to detect and remove offsets between resistor elements that change over time and 1 / f noise components. However, the above-mentioned method has difficulty removing noise components such as drift noise or 1 / f noise that occur while the heater is on.

[0006] The disclosed technology aims to improve the measurement accuracy of the fluid sensor by reducing the noise components that occur while the heater is on. [Means for solving the problem]

[0007] In order to solve the above technical problems, one form of the fluid sensor of the present invention has a sensor unit including a heater and a temperature detection unit including a pair of temperature-sensitive elements arranged on both sides of the heater, and a detection control unit that controls the on / off of the heater and detects the speed of a fluid above the sensor unit based on a temperature difference signal output from the temperature detection unit indicating the difference in temperature detected by the pair of temperature-sensitive elements, wherein the detection control unit acquires a first signal value of the temperature difference signal before turning on the heater, acquires a second signal value of the temperature difference signal after turning on the heater, and acquires a third signal value of the temperature difference signal after turning off the heater, interpolates a correction value at the timing of generation of the second signal value from the first signal value and the third signal value, and calculates the speed of the fluid based on the difference between the second signal value and the correction value. [Effects of the Invention]

[0008] By reducing the noise components that occur during the heater on period, the measurement accuracy of the fluid sensor can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a circuit block diagram showing an example of a fluid sensor according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating an example of the configuration of the sensor chip of FIG. [Figure 3] FIG. 10 is an explanatory diagram showing an example of a temperature change on a sensor chip due to an airflow. [Figure 4] 3 is a timing chart showing an example of the operation of detecting wind speed by the fluid sensor of FIG. 1. FIG. [Figure 5] 3 is a timing chart showing an example of repeatedly calculating wind speed and wind direction using the fluid sensor of FIG. 1. FIG. [Figure 6] FIG. 5 is a circuit block diagram showing an example of a fluid sensor according to a second embodiment of the present invention. [Figure 7] 3 is a timing chart showing an example of the operation of detecting wind speed by the fluid sensor of FIG. 1. FIG. [Figure 8] FIG. 10 is a timing chart showing an example of the wind speed detection operation by the fluid sensor according to the third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes the embodiments with reference to the drawings. Hereinafter, the voltage lines, terminals, and nodes through which voltages are transmitted are designated by the same reference numerals as the voltage names, and the signal lines, terminals, and nodes through which signals are transmitted are designated by the same reference numerals as the signal names. In each drawing, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0011] (First embodiment) Fig. 1 is a circuit block diagram showing an example of a fluid sensor according to a first embodiment of the present invention. The fluid sensor 10 shown in Fig. 1 has a sensor chip 20 and a controller 30. Although not particularly limited, the fluid sensor 10 may be installed outdoors as an anemometer, or may be installed indoors, such as in a clean room, to detect wind movement indoors.

[0012] The sensor chip 20 is an example of a sensor unit having a heater resistor Rh that functions as a heater and temperature-sensing elements Ru and Rd (a pair of temperature-sensing elements). For example, the heater resistor Rh is made of platinum (Pt), nichrome (NiCr), molybdenum silicide (MoSi2), tungsten silicide (WSi2), polysilicon, or the like. For example, the temperature-sensing elements Ru and Rd are resistor elements having a vanadium oxide film whose resistance value changes with temperature.

[0013] For example, the size and thickness of the vanadium oxide films forming the temperature sensors Ru and Rd are equal, and the resistance values of the temperature sensors Ru and Rd are equal. Furthermore, by using vanadium oxide to form the temperature sensors Ru and Rd, the temperature detection sensitivity can be improved compared to when other materials are used. On the other hand, vanadium oxide is known to have larger 1 / f noise than other materials.

[0014] The heater resistor Rh generates heat while receiving the heater voltage Vh. The thermosensors Ru and Rd are connected in series between the drive voltage line VREF and the ground line GND via the node Vsig. The resistance values of the thermosensors Ru and Rd, to which the drive voltage VREF is applied, change in response to changes in the ambient temperature due to heat generation by the heater resistor Rh, and generate an output signal Vsig at the node Vsig, which is a voltage division node. The output signal Vsig is an example of a temperature difference signal that indicates the difference in temperature detected by the thermosensors Ru and Rd. The thermosensors Ru and Rd are an example of a temperature detection unit that generates the output signal Vsig, which indicates the difference in resistance values, as a temperature difference signal.

[0015] The controller 30 includes a central processing unit (CPU) 31, a read-only memory (ROM) 32, a random access memory (RAM) 33, and an analog-to-digital converter (ADC) 34. For example, the controller 30 is a one-chip microcomputer. The controller 30 may also be designed using an application-specific integrated circuit (ASIC) or a field-programmable gate array (FGPA).

[0016] The ADC 34 converts the analog voltage indicated by the output signal Vsig into a digital value Vsigd at each sampling period and outputs the converted digital value Vsigd to the CPU 31. For example, the CPU 31 executes a control program stored in the ROM 32 to implement a control method for the fluid sensor 10 and control the overall operation of the fluid sensor 10.

[0017] For example, the CPU 31 controls the generation of the heater voltage Vh and the drive voltage VREF, and calculates the airflow velocity (wind speed) on the heater resistor Rh (i.e., on the fluid sensor 10) based on the digital value Vsigd output from the ADC 34. The CPU 31 then outputs data DT indicating the calculated wind speed to the outside of the fluid sensor 10. The CPU 31 is an example of a detection control unit that detects the airflow velocity based on the output signal Vsig (temperature difference signal). Note that the CPU 31 may supply a heater current to the heater resistor Rh instead of the heater voltage Vh.

[0018] Fig. 2 is a schematic diagram showing an example of the configuration of the sensor chip 20 of Fig. 1. Fig. 2(A) shows a plan view of the sensor chip 20, and Fig. 2(B) shows a cross-sectional view taken along line A-A' in Fig. 2(A). For example, the sensor chip 20 is formed using semiconductor manufacturing technology.

[0019] For example, the heater resistor Rh is provided in the center of the sensor chip 20, which is square in plan view. Thermosensitive elements Ru(1) and Rd(1) are provided on both sides of the sensor chip 20 in the X direction. Thermosensitive elements Ru(2) and Rd(2) are provided on both sides of the sensor chip 20 in the Y direction. In other words, the sensor chip 20 has two pairs of thermosensitive elements, in which the arrangement directions of the thermosensitive elements Ru(1) and Rd(1) and the arrangement directions of the thermosensitive elements Ru(2) and Rd(2) are different.

[0020] The distances between each of the temperature sensing elements Ru(1), Rd(1), Ru(2), and Rd(2) and the heater resistance Rh are the same. Hereinafter, when the temperature sensing elements Ru(1) and Ru(2) are not distinguished from each other, they will also be referred to as the temperature sensing element Ru. When the temperature sensing elements Rd(1) and Rd(2) are not distinguished from each other, they will also be referred to as the temperature sensing element Rd. In addition, a temperature sensor TSNS formed by meandering a thin, long wire is provided on the sensor chip 20.

[0021] The sensor chip 20 has a semiconductor substrate SUB provided on the periphery of the sensor chip 20 in a plan view, and a membrane MEMB (thin film) provided on the semiconductor substrate SUB. For example, the semiconductor substrate SUB is a silicon substrate or an SOI (Silicon On Insulator) substrate. The membrane MEMB may have a multilayer wiring structure. In the center of the sensor chip 20, a space SP is provided on the back surface of the membrane MEMB facing the semiconductor substrate SUB. The heater resistor Rh and the temperature sensitive elements Ru and Rd are disposed on the membrane MEMB facing the space SP. A protective film PASF is provided on the membrane MEMB to cover the heater resistor Rh and the temperature sensitive elements Ru and Rd. Pads PAD exposed from the protective film PASF are provided on the protective film PASF.

[0022] The heater resistor Rh has a square shape with a meandering, elongated wiring. This allows the relative positional relationships between the thermosensors Ru(1), Rd(1), Ru(2), and Rd(2) and the heater resistor Rh to be the same. As a result, for example, the CPU 31 in FIG. 1 can use a common calculation method to calculate the wind speed over the heater resistor Rh for each pair of thermosensors Ru and Rd based on the output signal Vsig, which changes depending on changes in the resistance value.

[0023] For example, the CPU 31 can calculate the wind speed in the X direction based on the change in the resistance values of the thermosensitive elements Ru(1) and Rd(1), and calculate the wind speed in the Y direction based on the change in the resistance values of the thermosensitive elements Ru(2) and Rd(2). Furthermore, the CPU 31 can calculate the direction of the airflow (wind direction) from the two wind velocities calculated based on the change in the resistance values of the two thermosensitive element pairs Ru and Rd.

[0024] The temperature sensing element pair Ru and Rd shown in FIG. 1 is either the temperature sensing element pair Ru(1) and Rd(1) or the temperature sensing element pair Ru(2) and Rd(2). An ADC 34 is provided for each temperature sensing element pair Ru and Rd. A multiplexer may be provided in front of the ADC 34 to selectively switch the output signal Vsig received from the temperature sensing element pair Ru(1) and Rd(1) or the temperature sensing element pair Ru(2) and Rd(2), respectively, so that a single ADC 34 can be used in a time-division manner. In the following description, the temperature sensing element pair Ru and Rd in FIG. 1 will be described as the temperature sensing element pair Ru(1) and Rd(1).

[0025] Both ends of the heater resistor Rh, the thermosensitive elements Ru(1), Rd(1), Ru(2), and Rd(2), and the temperature sensor TSNS are connected to pads PAD provided on the periphery of the sensor chip 20 via wiring W. Each pad PAD is connected to a terminal provided on a printed circuit board or the like on which the sensor chip 20 is mounted via a bonding wire or bump (not shown). The two wirings not connected to the pads PD are dummy wiring DMY. By providing the dummy wiring DMY, the layout of the wiring around the heater resistor Rh and the thermosensitive elements Ru and Rd can be made symmetrical. This reduces variation in the shape of the thermosensitive elements Ru and Rd during the semiconductor manufacturing process of the sensor chip 20, and thus reduces deviations in the electrical characteristics of the thermosensitive elements Ru and Rd.

[0026] 3 is an explanatory diagram showing an example of temperature change on the sensor chip 20 due to airflow. Note that the protective film PASF is not shown in FIG. 3. When a heater voltage Vh is supplied to the heater resistor Rh and the heater resistor Rh generates heat, the temperature of the membrane MEMB increases as it approaches the heater resistor Rh, and the temperature of the air above the membrane MEMB increases depending on the temperature of the membrane MEMB. The air flowing above the sensor chip 20 is an example of a fluid.

[0027] When there is no airflow, the temperature distribution around the heater resistor Rh is uniform around the heater resistor Rh, and the temperatures of the thermosensitive elements Ru and Rd are equal. Therefore, the output signal Vsig in Figure 1 is set to a voltage value that indicates there is no temperature difference between the thermosensitive elements Ru and Rd.

[0028] On the other hand, for example, if there is an airflow from the temperature sensor Ru toward the temperature sensor Rd, the heated air on the membrane MEMB moves to the temperature sensor Rd, causing the temperature of the temperature sensor Rd to become higher than the temperature of the temperature sensor Ru. Therefore, the output signal Vsig is set to a voltage value indicating that the temperature of the temperature sensor Rd is higher than the temperature of the temperature sensor Ru. The CPU 31 then detects the wind speed according to the change in the voltage value of the output signal Vsig.

[0029] FIG. 4 is a timing diagram showing an example of the wind speed detection operation by the fluid sensor 10 of FIG. 1. That is, FIG. 4 shows an example of a method of controlling the fluid sensor 10 by the CPU 31. In the diagram, ON of the heater resistor Rh indicates that the heater voltage Vh is supplied to the heater resistor Rh and the heater resistor Rh generates heat, and hereinafter this will also be referred to as heater ON. OFF of the heater resistor Rh indicates that the heater voltage Vh is not supplied to the heater resistor Rh and the heater resistor Rh does not generate heat, and hereinafter this will also be referred to as heater OFF. The heater ON and heater OFF are controlled by the CPU 31 by supplying and stopping the supply of the heater voltage Vh.

[0030] The curve showing the output signal Vsig indicates the change in the voltage value input to the ADC34. The triangles indicate the digital values Vsigd(hoff0, hoff1) obtained by converting the voltage value of the output signal Vsig by the ADC34 during the heater's off period. The circles indicate the digital values Vsigd(hon) obtained by converting the voltage value of the output signal Vsig by the ADC34 during the heater's on period. The digital value hoff0 is an example of a first signal value that the CPU31 acquires before turning on the heater. The digital value hon is an example of a second signal value that the CPU31 acquires after turning on the heater. The digital value hoff1 is an example of a third signal value that the CPU31 acquires after turning off the heater.

[0031] The square marks indicate the correction value ofs_hat at the timing of generation of the digital value hon, which is interpolated from the digital values hoff0 and hoff1 during the heater's off period. In the example shown in Fig. 4, the correction value ofs_hat is the value at the point where the imaginary line (two-dot chain line) connecting the digital values hoff0 and hoff1 intersects with the timing of generation of the digital value hon. The correction value ofs_hat is an estimated value of the noise component during the heater's on period, inferred from the digital values hoff0 and hoff1 during the heater's off period.

[0032] For example, the difference t0 between the timing at which the CPU 31 acquires the digital value hoff0 and the timing at which the digital value hon is acquired is set equal to the difference t1 between the timing at which the digital value hon is acquired and the timing at which the digital value hoff1 is acquired. In other words, the timing at which the digital value hon is acquired is set midway between the timing at which the digital value hoff0 is acquired and the timing at which the digital value hoff1 is acquired. In this case, the CPU 31 can set the average value of the digital values hoff0 and hoff1 as the digital value ofs_hat, and can easily calculate the digital value ofs_hat using the imaginary straight line.

[0033] When the heater is off and there is no heat generation from the heater resistor Rh, the ambient temperatures of the temperature sensors Ru and Rd are equal, regardless of the presence or absence of airflow. Therefore, the resistance values of the temperature sensors Ru and Rd are equal, and the CPU 31 does not detect a temperature difference between the temperature sensors Ru and Rd. However, for example, due to the 1 / f noise of each of the temperature sensors Ru and Rd, the voltage generated according to the resistance values of the temperature sensors Ru and Rd may differ from the actual voltage value. It has been found that the 1 / f noise of temperature sensors Ru and Rd made of vanadium oxide is larger than the 1 / f noise of temperature sensors Ru and Rd made of other materials. Furthermore, even if there is no difference in the resistance values of the temperature sensors Ru and Rd, the CPU 31 may detect a difference in the resistance values (i.e., a temperature difference) due to temperature drift or aging drift in the measurement system including the controller 30.

[0034] In this embodiment, the CPU 31 acquires digital values hoff0 and hoff1 before and after the heater is turned on, respectively, and calculates their average as the digital value ofs_hat. The digital value ofs_hat, which is interpolated from the digital values hoff0 and hoff1 when the heater is off, does not include changes in resistance value due to temperature increases caused by turning the heater on, but includes noise components such as 1 / f noise, temperature drift, and drift over time that are independent of wind speed. By subtracting the digital value ofs_hat from the digital value hon, the CPU 31 can acquire a digital value ΔVsig1 with reduced noise components as a signal indicating the temperature difference. The CPU 31 can then accurately calculate the wind speed over the heater resistor Rh based on the digital value ΔVsig1 with reduced noise components.

[0035] The CPU 31 can detect changes in wind speed with high accuracy by repeatedly calculating the wind speed at every predetermined cycle CYC. The CPU 31 can also calculate the average wind speed within a predetermined period with high accuracy by averaging the repeatedly calculated wind speeds.

[0036] Note that if the temperature coefficients of resistance TCR of the temperature sensors Ru and Rd are even slightly different, the amount of change in the resistance values of the temperature sensors Ru and Rd will be different even if the amount of change in the ambient temperature of the temperature sensors Ru and Rd is the same. Therefore, to reduce the effect of fluctuations in the characteristics of the temperature sensors Ru and Rd due to the temperature coefficient of resistance TCR, the offset in a windless state may be acquired as a digital value hon_ofs, and this may be subtracted from the digital value Δsig1 to obtain a signal indicating the temperature difference. For example, the digital value ofs_ofs may be acquired during a testing process during the manufacture of the sensor chip 20 and stored in the ROM 32.

[0037] Note that the digital value ΔVsig0 calculated by subtracting the digital value hoff0 from the digital value hon without using the digital value hoff1 includes the digital value ofs_hat, which is a noise component. For this reason, the wind speed data calculated using the digital value ΔVsig0 is less accurate than the wind speed data calculated using the digital value hoff2.

[0038] 5 is a timing diagram showing an example of repeated calculation of wind speed and wind direction by the fluid sensor 10 of FIG. 1. For example, in FIG. 5, the cycle CYC shown in FIG. 4 is 250 ms. The CPU 31 calculates instantaneous wind speed data every 250 ms, and calculates instantaneous wind direction data based on two wind speed data calculated from two output signals Vsig from two resistor pairs Ru and Rd. Note that for ease of explanation, the pulse width of the waveform indicating the timing of AD conversion is shown larger than it actually is.

[0039] Furthermore, CPU 31 calculates average wind speed data for one second from four pieces of wind speed data calculated per second, and calculates average wind direction data for one second from four pieces of wind direction data calculated every 250 ms. Furthermore, CPU 31 may calculate average wind speed data and average wind direction data for 10 seconds using 40 pieces of wind speed data and 40 pieces of wind direction data calculated every 250 ms. The average wind speed data and average wind direction data for 10 seconds may be calculated using 10 pieces of wind speed data and 10 pieces of wind direction data calculated every second.

[0040] As described above, in this embodiment, the CPU 31 subtracts the digital value ofs_hat, which is interpolated from the digital values hoff0 and hoff1 acquired before and after the heater is turned on, from the digital value hon acquired during the heater is turned on. This allows the CPU 31 to acquire the digital value ΔVsig1, in which noise components have been reduced, as a signal indicating the temperature difference, and to accurately calculate the wind speed over the heater resistor Rh based on the acquired digital value ΔVsig1.

[0041] By setting the timing for acquiring the digital value hon to be midway between the timing for acquiring the digital value hoff0 and the timing for acquiring the digital value hoff1, the CPU 31 can set the average value of the digital values hoff0 and hoff1 as the digital value ofs_hat.

[0042] By arranging each of the resistor elements Ru and Rd of the plurality of resistor element pairs across the heater resistor Rh, the CPU 31 can calculate wind speeds in a plurality of directions based on changes in the resistance values of the plurality of thermosensitive element pairs Ru and Rd, thereby enabling the CPU 31 to calculate wind direction.

[0043] The CPU 31 can detect changes in wind speed with high accuracy by repeatedly calculating the wind speed at each predetermined cycle CYC. Furthermore, the CPU 31 can calculate the average wind speed within a predetermined period with high accuracy by averaging the repeatedly calculated wind speeds. Similarly, the CPU 31 can detect changes in wind direction with high accuracy by repeatedly calculating the wind direction at each predetermined cycle CYC. Furthermore, the CPU 31 can calculate the average wind direction within a predetermined period with high accuracy by averaging the repeatedly calculated wind direction.

[0044] By forming the temperature sensors Ru and Rd from vanadium oxide, it is possible to improve the temperature detection sensitivity compared to when other materials are used. Furthermore, even when the 1 / f noise caused by the temperature sensors Ru and Rd made of vanadium oxide is large, it is possible to accurately detect wind speed and direction based on the digital value ΔVsig1 with reduced noise components.

[0045] (Second embodiment) Figure 6 is a circuit block diagram showing an example of a fluid sensor according to a second embodiment of the present invention. Detailed descriptions of elements similar to those in Figure 1 will be omitted. The fluid sensor 10A shown in Figure 6 adds a filter 35 that removes high-frequency components from the output signal Vsig to the controller 30 of Figure 1. The other configurations and functions of the fluid sensor 10A are similar to those of the fluid sensor 10 shown in Figure 1, except that the control program executed by the CPU 31 is different.

[0046] The filter 35 generates a digital value Vsig_flt by removing high-frequency components from the digital value Vsigd output from the ADC 34, and outputs the generated digital value Vsig_flt to the CPU 31. As a result, even if the output signal Vsig received by the ADC 34 contains high-frequency noise components, the CPU 31 can obtain a digital value ΔVsig1 in which the noise components have been reduced, as will be described later, and calculate the wind speed with high accuracy.

[0047] The ADC 34 outputs the digital value Vsigd at a cycle shorter than the AD conversion cycle shown in Fig. 4. Although not particularly specified, the filter 35 is, for example, a digital filter such as a moving average filter, an FIR (Finite Impulse Response) filter, or an IIR (Infinite Impulse Response) filter.

[0048] The CPU 31 calculates the wind speed on the heater resistor Rh using the filtered digital value Vsig_flt received from the filter 35. Then, the CPU 31 outputs data DT indicating the calculated wind speed to the outside of the fluid sensor 10A. The CPU 31 may also calculate the wind direction from the two wind speeds calculated based on the changes in the resistance values of the two pairs of temperature sensitive elements Ru and Rd shown in Figure 2, and output this together with the data DT indicating the wind speed to the outside of the fluid sensor 10A.

[0049] The function of the filter 35 may be realized by a program executed by the CPU 31. Alternatively, a low-pass filter connected to the input of the ADC 34 may be provided instead of the filter 35. In this case, the low-pass filter removes high-frequency components from the output signal Vsig and outputs the signal to the ADC 34.

[0050] FIG. 7 is a timing diagram showing an example of the wind speed detection operation by the fluid sensor 10A of FIG. 1. That is, FIG. 7 shows an example of a method of controlling the fluid sensor 10A by the CPU 31. Detailed description of elements similar to those in FIG. 4 will be omitted. In this embodiment, the CPU 31 obtains digital values hoff0 and hoff1 before the heater is turned on and a predetermined period after the heater is turned off from the filtered digital value Vsig_flt received from the filter 35. As in FIG. 4, the CPU 31 uses an imaginary line (two-dot chain line) connecting the digital values hoff0 and hoff1 to calculate the average value of the digital values hoff0 and hoff1 as the digital value ofs_hat.

[0051] The CPU 31 then subtracts the digital value ofs_hat from the digital value hon to obtain a digital value ΔVsig1 with reduced noise components as a signal indicating the temperature difference. Thus, even if the output signal Vsig received by the ADC 34 contains high-frequency noise components, the CPU 31 can average the noise components by filtering and extract the digital value ofs_hat. The CPU 31 then subtracts the extracted digital value ofs_hat from the digital value hon to obtain a digital value ΔVsig1 with reduced noise components. Furthermore, the CPU 31 can calculate the wind speed over the heater resistor Rh with high accuracy based on the digital value ΔVsig1 and output it to the outside of the fluid sensor 10A. As shown in FIG. 5, the CPU 31 may repeatedly calculate the wind speed at predetermined cycles CYC.

[0052] As described above, this embodiment can also achieve the same effects as the above-described embodiment. For example, the CPU 31 can obtain a digital value ΔVsig1 with reduced noise components as a signal indicating the temperature difference by subtracting the digital value ofs_hat, which is interpolated from the digital values hoff0 and hoff1, from the digital value hon. The CPU 31 can then accurately calculate the wind speed over the heater resistor Rh based on the obtained digital value ΔVsig1.

[0053] Furthermore, in this embodiment, even if the output signal Vsig received by the ADC 34 contains high-frequency noise components, the CPU 31 can obtain a digital value ΔVsig1 in which the noise components are reduced, and can calculate the wind speed with high accuracy.

[0054] (Third embodiment) FIG. 8 is a timing diagram showing an example of the wind speed detection operation by a fluid sensor according to a third embodiment of the present invention. Detailed descriptions of elements similar to those in FIGS. 4 and 7 will be omitted. The configuration and functions of the fluid sensor of this embodiment are similar to those of the fluid sensor 10 shown in FIG. 1, except that the control program executed by the CPU 31 is different. In the following description, the same reference numerals as those in FIGS. 2 and 6 will be used. FIG. 8 shows an example of a method for controlling the fluid sensor 10 by the CPU 31.

[0055] In this embodiment, the CPU 31 removes high-frequency components from the digital value Vsigd received from the ADC 34 only while the heater is off. For example, the CPU 31 obtains, as the digital value hoff0, the average value of a predetermined number of digital values Vsigd received from the ADC 34 during a predetermined period before the heater is turned on. In the example shown in FIG. 8, the CPU 31 removes high-frequency components by calculating the average value of seven digital values Vsigd from time t=k-3 to k+3. The symbol k indicates a predetermined time before the heater is turned on.

[0056] Furthermore, the CPU 31 obtains, as a digital value hoff1, the average value of a predetermined number of digital values Vsigd received from the ADC 34 during a predetermined period after the heater is turned off. In the example shown in Fig. 8, the CPU 31 removes high frequency components by calculating the average value of seven digital values Vsigd from time t = j-3 to j+3. The symbol j indicates a predetermined time after the heater is turned on.

[0057] 4, the CPU 31 uses the virtual line (two-dot chain line) connecting the digital values hoff0 and hoff1 to calculate the average of the digital values hoff0 and hoff1 as the digital value ofs_hat. For example, the period t0 from time t=k to the acquisition of the digital value hon is equal to the period t1 from the acquisition of the digital value hon to time t=j. Therefore, the CPU 31 can use the average of the digital values hoff0 and hoff1 as the digital value ofs_hat.

[0058] The CPU 31 subtracts the digital value ofs_hat from the digital value hon to obtain a digital value ΔVsig1 with reduced noise components as a signal indicating the temperature difference. Here, the CPU 31 does not filter the digital value Vsigd while the heater is on. Therefore, the CPU 31 can obtain the digital value ΔVsig1 using the unfiltered digital value Vsigd that is AD converted from the output signal Vsig generated by the resistor elements Ru and Rd.

[0059] Then, the CPU 31 calculates the wind speed on the heater resistor Rh based on the digital value ΔVsig1 and outputs the calculated value to the outside of the fluid sensor 10. Note that, as shown in Fig. 5, the CPU 31 may repeatedly calculate the wind speed at every predetermined cycle CYC.

[0060] As described above, this embodiment also achieves the same effects as the above-described embodiment. Furthermore, in this embodiment, the CPU 31 filters the output signal Vsig generated by the resistor elements Ru and Rd only during the heater-off period. Therefore, the CPU 31 can obtain the digital value ΔVsig1 using the digital value Vsigd equivalent to the output signal Vsig. As a result, even when the output signal Vsig contains high-frequency noise components, the CPU 31 can obtain the digital value ΔVsig1 with the noise components reduced, thereby enabling the wind speed to be calculated with high accuracy.

[0061] Although the present invention has been described above based on the embodiments, the present invention is not limited to the requirements shown in the above embodiments. These requirements can be changed without departing from the spirit of the present invention, and can be appropriately determined depending on the application form. [Explanation of symbols]

[0062] 10, 10A...fluid sensor, 20...sensor chip, 30...controller, 31...CPU, 32...ROM, 33...RAM, 34...ADC, 35...filter, CYC...cycle, DMY...dummy wiring, hoff0, hoff1...digital value, hon...digital value, MEMB...membrane, PAD...pad, PASF...protective film, Rd...thermosensitive element, Rh...heater resistor, Ru...thermosensitive element, SP...space, SUB...semiconductor substrate, TSNS...temperature sensor, Vh...heater voltage, VREF...drive voltage, Vsig...output signal, Vsigd...digital value, Vsig_flt...digital value, W...wiring, ΔVsig0, ΔVsig1...digital value

Claims

1. a sensor unit including a heater and a temperature detection unit including a pair of temperature-sensing elements disposed on both sides of the heater; a detection control unit that controls on / off of the heater and detects the velocity of the fluid above the sensor unit based on a temperature difference signal that indicates a difference in temperature detected by the pair of temperature-sensitive elements output from the temperature detection unit, The detection control unit obtaining a first signal value of the temperature difference signal before turning on the heater; obtaining a second signal value of the temperature difference signal after turning on the heater; obtaining a third signal value of the temperature difference signal after turning off the heater; interpolating a correction value at a generation timing of the second signal value from the first signal value and the third signal value; Calculating the velocity of the fluid based on the difference between the second signal value and the correction value Fluid sensor.

2. the detection control unit performs filtering to remove high-frequency components of the temperature difference signal; The first signal value, the second signal value, and the third signal value are obtained from the filtered temperature difference signal. The fluid sensor according to claim 1 .

3. The detection control unit an average of a plurality of signal values of the temperature difference signal acquired before turning on the heater is set as the first signal value; The average of a plurality of signal values of the temperature difference signal obtained after the heater is turned off is set as the third signal value. The fluid sensor according to claim 1 .

4. The timing of acquiring the second signal value is midway between the timing of acquiring the first signal value and the timing of acquiring the third signal value.

4. The fluid sensor according to claim 1.

5. The detection control unit repeatedly executes a calculation operation of acquiring a first signal value, a second signal value, and a third signal value and calculating a velocity of a fluid.

5. The fluid sensor according to claim 1.

6. The detection control unit calculates an average velocity of the fluid based on the plurality of fluid velocities calculated by the plurality of calculation operations. The fluid sensor according to claim 5 .

7. the temperature detection unit has a plurality of pairs of temperature-sensing elements, the arrangement directions of the temperature-sensing elements of which are different, The detection control unit calculates the direction of the fluid from the velocity of the fluid calculated based on the first signal value, the second signal value, and the third signal value from each of the plurality of temperature sensitive element pairs. The fluid sensor according to any one of claims 1 to 6.

8. The temperature-sensitive element is formed using vanadium oxide.

8. The fluid sensor according to claim 1.

9. a sensor unit including a heater and a temperature detection unit including a pair of temperature-sensing elements disposed on both sides of the heater; a detection control unit that controls on / off of the heater and detects a velocity of a fluid above the sensor unit based on a temperature difference signal that indicates a difference in temperatures detected by the pair of temperature-sensitive elements output from the temperature detection unit, The detection control unit obtaining a first signal value of the temperature difference signal before turning on the heater; obtaining a second signal value of the temperature difference signal after turning on the heater; obtaining a third signal value of the temperature difference signal after turning off the heater; interpolating a correction value at a generation timing of the second signal value from the first signal value and the third signal value; Calculating the velocity of the fluid based on the difference between the second signal value and the correction value A method for controlling a fluid sensor.

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