JP2009109285A - Thermal flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal flowmeter whose S/N ratio can be raised in regions where the flow rate of a flowing fluid becomes high and the flow rate of the flowing fluid becomes low. <P>SOLUTION: The thermal flowmeter for controlling the temperature of a liquid flowing in a flow channel, and measuring its flow rate on the basis of the difference between the temperature of the fluid on the upstream side of the temperature controlling portion and that on the downstream side, is provided with the flow channel whose liquid touching portions are entirely constituted of glass, a heat transmission means provided in this flow channel, an upstream-side and a downstream-side temperature detecting means provided on the flow channel at positions being at equal intervals from the heat transmission means, and a drive calculation mean which drives the heat transmission means with a periodic driving signal, performs synchronous detection of detected temperature signals of the upstream-side and downstream-side temperature detecting means on the basis of the driving signal, calculates the upstream-side temperature and the downstream-side temperature, and finds the flow rate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermal flow meter that controls the temperature of a liquid flowing through a flow path and measures a flow rate based on a temperature difference between upstream and downstream fluids of a temperature control portion, and particularly to improve the S / N ratio. It relates to a thermal flow meter capable of

  Prior art documents related to a thermal flow meter that controls the temperature of the liquid flowing through the conventional flow path and measures the flow rate based on the temperature difference between the upstream and downstream fluids of the temperature control portion include the following. is there.

Japanese Patent Laid-Open No. 05-077975 Japanese Patent Laid-Open No. 07-159215 JP-A-10-082678 JP 2002-168668 A JP 2006-010322 A JP 2006-226996 A

  FIG. 6 is a block diagram showing an example of such a conventional thermal flow meter. In FIG. 6, 1 is a flow path composed of a thin metal tube, 2 is a heat transfer means such as a heater that heats the temperature of the fluid flowing through the flow path 1 to a constant temperature, and 3 and 4 are thermistors and platinum temperature measuring devices. Temperature detection means 5 such as a resistor is an arithmetic control means such as a CPU (Central Processing Unit) for obtaining a flow rate based on the temperature difference between the upstream and downstream fluids.

  As shown by “FL01” in FIG. 6, a heat transfer means 2 is provided in the central portion of the flow path 1 through which the liquid to be measured flows, and is located on the flow path 1 at equal intervals from the heat transfer means 2. Temperature detection means 3 and 4 are provided.

  The outputs of the temperature detection means 3 and 4 are connected to the calculation control means 5, respectively, and a control signal for temperature control from the calculation control means 5 is connected to the heat transfer means 2.

  Here, the operation of the conventional example shown in FIG. 6 will be described with reference to FIG. FIG. 7 is a characteristic curve diagram showing an example of the temperature distribution of the liquid to be measured in the flow path with respect to the position of the flow path. The arithmetic control unit 5 controls the heat transfer unit 2 so that the liquid to be measured has a constant temperature that is about several degrees higher than the temperature of the liquid to be measured that has been measured in advance.

  In such a state, when the flow rate is zero, as shown by “CH11” in FIG. 7, the temperature distribution is symmetrical about the installation position of the heat transfer means 2 indicated by “HT11” in FIG. For this reason, the temperatures at the installation positions of the temperature detecting means 3 and 4 indicated by “TS11” and “TS12” in FIG. 7 are equal. In other words, the temperature difference is zero.

  On the other hand, when the fluid in the flow path 1 flows, the peak of the temperature distribution shifts to the downstream side as shown by “CH12” in FIG. For this reason, the temperatures at the installation positions of the temperature detecting means 3 and 4 indicated by “TS11” and “TS12” in FIG. 7 are different, and a temperature difference as indicated by “DT11” in FIG. 7 is generated. .

  Since such a temperature difference becomes a signal depending on the flow rate of the liquid to be measured, the flow rate of the liquid to be measured flowing through the flow path 1 can be obtained by the arithmetic control unit 5 based on such a temperature difference.

  As a result, the temperature of the liquid to be measured flowing through the flow path 1 is controlled by the heat transfer means 2, the temperature of the fluid upstream and downstream of the heat transfer means 2 is measured by the two temperature detection means 3 and 4, and the arithmetic control is performed. By obtaining the flow rate based on the temperature difference of the temperature by means 5, it becomes possible to measure the flow rate of the liquid to be measured.

  However, the conventional example shown in FIG. 6 has a problem that the flow rate of the liquid corroding the metal cannot be measured because a metal thin tube or the like is used as the flow path 1.

  For this reason, the above-mentioned “Patent Document 2” describes a thermal flow meter (mass flow sensor) in which a flow path is formed on a glass substrate having excellent corrosion resistance.

  8 and 9 are a perspective view and a sectional view showing another example of the conventional thermal flow meter described in “Patent Document 2”. 8 and 9, 6 is a glass substrate, 7 and 9 are silicon substrates, 8 is a heat transfer means, and 10 is a flow path formed in the glass substrate 6.

  A flow path 10 having a long hole is formed in the central portion of the glass substrate 6 by ultrasonic processing, laser processing, sand blast processing, wet etching, or the like. A silicon substrate 7 is bonded to the upper surface of the glass substrate 6 by anodic bonding.

  Further, a silicon substrate 9 is bonded to the lower surface of the glass substrate 6 by anodic bonding, and “HL21” and “HL22” in FIG. 8 are attached to the silicon substrate 9 adjacent to both ends of the flow path 10 formed in the glass substrate 6. Are formed, which function as inflow holes or discharge holes for the liquid to be measured, respectively.

  Further, a heat transfer means 8 (also serving as a temperature detection means) such as a heater made of a metal having a large resistance temperature coefficient such as platinum or nickel is formed on the silicon substrate 7, and is formed on the silicon substrate 7 and the glass substrate 6. The wiring is appropriately formed.

  Here, in the conventional example shown in FIGS. 8 and 9, although the flow path 10 is formed on the glass substrate 6, the silicon substrates 7 and 9 are used on the upper and lower surfaces of the flow path 10. Again, there is a problem with corrosion resistance.

  On the other hand, by replacing the silicon substrates 7 and 9 with the glass substrate in the conventional example shown in FIGS. 8 and 9, all the wetted parts become glass and the corrosion resistance is improved, but the glass has a low thermal conductivity. When the flow rate of the liquid flowing through the flow path is large, the liquid immediately below the heat transfer means 8 is not sufficiently warmed.

  For this reason, when the temperature immediately below the heat transfer means 8 is not sufficiently warmed, the temperature difference between the upstream side and the downstream side changes as the flow rate increases.

  On the other hand, when the flow rate is small and the temperature just below the heat transfer means 8 is sufficiently warm, the temperature difference between the upstream side and the downstream side increases as the flow rate increases.

  That is, FIG. 10 is a characteristic curve diagram showing the relationship between the temperature difference between the upstream side and the downstream side and the flow rate. As shown in “TD31” in FIG. 10, the temperature difference between the upstream side and the downstream side is a peak. There was a problem that the measurable flow rate range becomes extremely narrow.

  For example, although the corrosion resistance is improved by replacing the silicon substrates 7 and 9 with the glass substrate in the conventional example shown in FIGS. 8 and 9, the flow rate as shown by “AR31” in FIG. There is a problem that the flow rate can be measured only under the condition that the temperature immediately below the means 8 is sufficiently warm.

  In order to solve such problems, “Patent Document 5” related to the application of the present applicant has been devised. 11 is a configuration block diagram showing another example of the thermal type flow meter described in “Patent Document 5”, and FIG. 12 is a plan view and a sectional view showing a specific example of the sensor part of another example of the thermal type flow meter. It is.

  11 and 12, 11 and 12 are glass substrates, 13 is a heat transfer means such as a heater, 14 and 15 are temperature detection means such as a thermistor and a platinum resistance temperature detector, 16 is a flow path through which the liquid to be measured flows, 17 Is a calculation control means such as a CPU for obtaining a flow rate based on the temperature difference between the upstream and downstream fluids.

  As shown by “FL41” in FIG. 11, a heat transfer means 13 is provided in the central portion of the flow path 16 through which the liquid to be measured flows, and is located on the flow path 16 at equal intervals from the heat transfer means 13. Temperature detection means 14 and 15 are provided.

  Further, as indicated by “TU41” and “TD41” in FIG. 11, the outputs of the temperature detecting means 14 and 15 are respectively connected to the arithmetic control means 17, and from the arithmetic control means 17 as indicated by “CT41” in FIG. A control signal for temperature control is connected to the heat transfer means 13.

  Furthermore, the specific example of the sensor part of another example of a thermal type flow meter is demonstrated in detail using FIG.

  A rectangular groove is formed along the longitudinal direction of the glass substrate 12 at the central portion in the short direction of the glass substrate 12 by ultrasonic processing, laser processing, sandblasting, wet etching, or the like. In addition, the glass substrate 11 is bonded to the glass substrate 12 on the side where the rectangular groove is formed by bonding, thermocompression bonding, or the like, and a flow path 16 is formed in which the liquid contact portion is entirely made of glass.

  Further, a heat transfer means 13 such as a heater is formed on the glass substrate 11 on the side not in contact with the flow path 16 and on the central portion of the flow path 16 by vapor deposition, sputtering, or the like. Temperature detecting means 14 and 15 are formed by vapor deposition, sputtering or the like on the glass substrate 11 on the upper side and not in contact with the flow path 16 and at equal intervals from the heat transfer means 13.

  That is, since the heat transfer means 13 and the temperature detection means 14 and 15 are formed on the glass substrate 11 on the side not in contact with the flow path 16, they are in a non-wetted state.

  Here, the operation of another example of the thermal flow meter shown in FIGS. 11 and 12 will be described with reference to FIG. FIG. 13 is a characteristic curve diagram showing the relationship between the temperature difference between the upstream side and the downstream side with respect to the flow rate, the temperature sum, and the value obtained by dividing the temperature difference by the temperature sum. However, description of operations similar to those of the conventional example shown in FIG.

  The arithmetic control means 17 controls the heat transfer means 13 so that the liquid under measurement has a constant temperature that is several degrees higher than the temperature of the liquid under measurement measured in advance.

  In such a state, the temperature difference between the temperatures detected by the upstream temperature detection means 14 and the downstream temperature detection means 15 becomes a signal that depends on the flow rate of the liquid to be measured. The flow rate of the liquid to be measured flowing through the flow path 16 can be obtained by the arithmetic control means 17.

  However, as described in the above-described conventional example, when the liquid contact portion of the flow path is all made of glass, for example, the temperature difference is indicated by “TD51” in FIG. 13 because of the small thermal conductivity of the glass. Thus, there is a problem that the characteristic has a peak and the measurable flow rate range becomes extremely narrow.

  For this reason, the arithmetic control means 17 obtains the temperature difference between the temperatures detected by the upstream temperature detection means 14 and the downstream temperature detection means 15 and at the upstream temperature detection means 14 and the downstream temperature detection means 15. The temperature difference is normalized by finding the temperature sum of the detected temperatures and dividing the temperature difference by the temperature sum.

  For example, the temperature sum of the temperatures detected by the upstream temperature detecting means 14 and the downstream temperature detecting means 15 is a characteristic curve as shown by “TA51” in FIG. By dividing the temperature difference indicated by “TD51” in FIG. 13, a normalized temperature difference characteristic curve as indicated by “NT51” in FIG. 13 is obtained.

  Since the normalized temperature difference as indicated by “NT51” in FIG. 13 shows a monotonic increase in a wide flow range, it can be seen that a wide flow range can be measured.

  As a result, the temperature of the liquid to be measured flowing through the channel 16 whose liquid contact part is entirely made of glass is controlled by the heat transfer means 13, and the upstream side and the downstream side of the heat transfer means 13 by the two temperature detection means 14 and 15. The temperature of the fluid is measured, the temperature difference of the temperature is calculated by the arithmetic control means 17 to obtain a normalized temperature difference, and the flow rate is obtained on the basis of the normalized temperature difference. This makes it possible to measure a wide flow rate range of the liquid to be measured.

However, in another example of the thermal flow meter shown in FIGS. 11 and 12, when the flow path is made of glass and the heat transfer means 13 and the temperature detection means 14 and 15 are installed outside the flow path, the thermal flow rate is measured. When the flow rate of the fluid flowing through the meter increases, the temperature sum signal decreases, and when the flow rate of the fluid flowing through the thermal flow meter decreases, the temperature difference signal decreases, and the fluid in which the standardized S / N ratio of the temperature difference signal flows. However, there is a problem that the error and the variation increase in the region where the flow rate of the fluid increases and the region where the flow rate of the flowing fluid decreases.
Therefore, the problem to be solved by the present invention is to realize a thermal flow meter capable of improving the S / N ratio in a region where the flow rate of flowing fluid is large and a region where the flow rate of flowing fluid is small. .

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In the thermal flow meter that controls the temperature of the liquid flowing through the flow path and measures the flow rate based on the temperature difference between the upstream and downstream fluids of the temperature control part,
A flow path in which the liquid contact part is entirely made of glass, a heat transfer means provided in the flow path, and an upstream side and a downstream side provided on the flow path at equal intervals from the heat transfer means Temperature detection means, and the heat transfer means are driven by a periodic drive signal, and the temperature detection signals of the upstream and downstream temperature detection means are synchronously detected based on the drive signal to detect the upstream and downstream temperatures. By providing the drive calculation means for calculating the flow rate by calculating the flow rate, the S / N ratio of the thermal flow meter can be improved in a region where the flow rate of the flowing fluid is large and a region where the flow rate of the flowing fluid is small. .

The invention according to claim 2
In the thermal type flow meter which is the invention according to claim 1,
The drive calculation means is
The temperature detection signal of the temperature detecting means is synchronously detected based on the 0 degree phase shift signal and the 90 degree phase shift drive signal, and the square root of the sum of squares is calculated to obtain the temperature on the upstream side or the downstream side. The S / N ratio of the thermal type flow meter can be improved in a region where the flow rate is large and a region where the flow rate of the flowing fluid is small.

The invention described in claim 3
In the thermal flow meter that controls the temperature of the liquid flowing through the flow path and measures the flow rate based on the time difference of temperature detection on the downstream side of the temperature control part,
A flow path in which the liquid contact part is entirely made of glass, a heat transfer means provided in the flow path, and an upstream side and a downstream side provided on the flow path at equal intervals from the heat transfer means The temperature detection means and the heat transfer means are driven by a periodic drive signal, and the temperature detection signal of the downstream temperature detection means is synchronously detected based on the drive signal to drive the downstream temperature detection means. Drive calculating means for calculating the phase lag with respect to the flow rate to obtain the flow rate improves the S / N ratio of the thermal flow meter in the region where the flow rate of the flowing fluid is large and the region where the flow rate of the flowing fluid is small. be able to.

The invention according to claim 4
In the thermal flow meter that controls the temperature of the liquid flowing through the flow path and measures the flow rate based on the time difference of temperature detection on the downstream side of the temperature control part,
A flow path in which the liquid contact part is entirely made of glass, a heat transfer means provided in the flow path, and an upstream side and a downstream side provided on the flow path at equal intervals from the heat transfer means Temperature detecting means, a temperature detecting means provided outside the downstream temperature detecting means, and driving the heat transfer means with a periodic drive signal and detecting the temperature of the two downstream temperature detecting means A region in which the flow rate of the flowing fluid is increased by providing drive calculation means for synchronously detecting the signal based on the drive signal and calculating the difference in phase lag between the two temperature detection means on the downstream side to obtain the flow rate The S / N ratio of the thermal flow meter can be improved in a region where the flow rate of the flowing fluid is small.

The invention according to claim 5
In the thermal type flow meter which is invention of Claim 3 or Claim 4,
The drive calculation means is
The temperature detection signal of the temperature detection means is synchronously detected based on the drive signal of 0 degree phase shift and 90 degree phase shift, and the arc tangent of the ratio of the synchronous detection signal is calculated to calculate the phase lag with respect to the drive signal, or the phase lag By obtaining the difference, the S / N ratio of the thermal flow meter can be improved in the region where the flow rate of the flowing fluid is large and the region where the flow rate of the flowing fluid is small.

The invention described in claim 6
In the thermal type flow meter which is the invention according to any one of claims 1 to 5,
The drive calculation means is
Drive waveform generating means for supplying a periodic drive signal to the heat transfer means, two buffer amplifiers for shifting the drive signal by 0 degrees and 90 degrees, a temperature detection signal from the temperature detection means, and 0 Two mixers for multiplying the drive signals of the phase shift and the phase shift of 90 degrees, two low-pass filter means to which the outputs of these two mixers are input, and the upstream side based on the outputs of these two low-pass filter means And a calculation control means for calculating the phase lag with respect to the downstream temperature or the drive signal, so that the thermal flow meter can be used in a region where the flow rate of the flowing fluid is large and a region where the flow rate of the flowing fluid is small. The S / N ratio can be improved.

The invention described in claim 7
In the thermal type flow meter which is the invention according to any one of claims 1 to 6,
The drive calculation means is
By synchronously detecting the temperature detection signal based on the drive signal and simultaneously obtaining the upstream and downstream temperatures and the phase lag with respect to the drive signal, the flow rate measurement range can be expanded, and in addition to the flow rate, the fluid thermal Physical property values can be measured.

The invention described in claim 8
In the thermal type flow meter which is the invention according to claim 7,
The drive calculation means is
Calibrate while measuring the flow rate by measuring the flow rate using the upstream and downstream temperature or phase lag and performing the flow rate calibration process using the phase lag or upstream and downstream temperature. Processing can be performed.

The present invention has the following effects.
According to the first, second and sixth aspects of the invention, the heat transfer means is driven by a periodic drive signal such as a sine wave, and the temperature detection signal of the temperature detection means is driven by a drive signal (0 degree phase shift and 90 degrees). Based on the phase shift), the square root of the sum of squares is calculated, and the temperatures of the upstream and downstream temperature detecting means are obtained, whereby the flow rate of the flowing fluid is increased and the flow rate of the flowing fluid is decreased. The S / N ratio of the thermal flow meter can be improved in the region.

  According to the third, fourth, fifth and sixth aspects of the invention, the heat transfer means is driven by a periodic drive signal such as a sine wave, and the temperature detection signal of the downstream temperature detection means is driven by the drive signal ( (Synchronous detection based on 0 degree phase shift and 90 degree phase shift) to calculate the arc tangent of the ratio to obtain the phase lag (flow velocity) or phase lag difference with respect to the drive signal, and the phase lag or each By measuring the flow rate based on the phase lag difference in the temperature detection means, the S / N ratio of the thermal flow meter can be improved in the region where the flow rate of the flowing fluid is large and the region where the flow rate of the flowing fluid is small. .

  According to the invention of claim 7, the flow rate measurement range can be expanded by synchronously detecting the temperature detection signal based on the drive signal and simultaneously obtaining the upstream and downstream temperatures and the phase delay with respect to the drive signal. In addition to the flow rate, the thermal property value of the fluid can be measured.

  According to the eighth aspect of the present invention, the flow rate is measured using the upstream and downstream temperatures or the phase delay, and the flow rate is corrected using the phase delay or the upstream and downstream temperatures. By performing this, it becomes possible to perform the calibration process while measuring the flow rate.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration block diagram showing an embodiment of a thermal flow meter according to the present invention, and FIG. 2 is a plan view and a cross-sectional view showing a specific example of a sensor portion of an embodiment of the thermal flow meter according to the present invention. is there.

  1 and 2, 18 is a glass substrate, 19 is a flow path formed in the glass substrate 18, 20 is a heat transfer means such as a heater that heats the temperature of the fluid flowing through the flow path 19 to a constant temperature, 21 Reference numerals 22 and 22 denote temperature detection means such as a thermistor and a platinum resistance temperature detector, and 23 denotes a drive calculation means for driving the heat transfer means and obtaining the flow rate based on the temperature difference between the upstream and downstream fluids. Further, 18, 19, 20, 21, and 22 constitute a flow meter chip 50.

  The fluid to be measured is injected from the inflow hole indicated by “IN51” in FIG. 1, and the fluid to be measured is discharged from the outflow hole indicated by “OT51” in FIG. Therefore, the fluid to be measured flows in the flow path 19 in the direction indicated by “FL51” in FIG.

  As shown by “FL51” in FIG. 1, a heat transfer means 20 is provided in the central portion of the flow path 19 through which the liquid to be measured flows, and is located on the flow path 19 at equal intervals from the heat transfer means 20. Temperature detection means 21 and 22 are provided.

  The outputs of the temperature detection means 21 and 22 are connected to the drive calculation means 23, and the drive signal for temperature control from the drive calculation means 23 is connected to the heat transfer means 20.

  Furthermore, the specific example of the flowmeter chip | tip 50 of one Example of the thermal type flow meter which concerns on this invention is demonstrated in detail using FIG. In FIG. 2, 24 is a glass substrate, and 18, 19, 20, 21 and 22 are assigned the same reference numerals as in FIG.

  A rectangular groove is formed along the longitudinal direction of the glass substrate 18 at the central portion in the short direction of the glass substrate 18 by ultrasonic processing, laser processing, sandblasting, wet etching, or the like. In addition, the glass substrate 24 is bonded to the glass substrate 18 on the side where the rectangular groove is formed, by bonding, thermocompression bonding, or the like, and the flow path 19 in which the liquid contact portion is entirely made of glass is formed.

  A heat transfer means 20 such as a heater is formed on the glass substrate 24 on the side not in contact with the flow path 19 and on the central portion of the flow path 19 by vapor deposition or sputtering. Temperature detecting means 21 and 22 are formed by vapor deposition, sputtering, or the like on the glass substrate 24 located on the upper side and not in contact with the flow path 19 and at equal intervals from the heat transfer means 20.

  That is, since the heat transfer means 20 and the temperature detection means 21 and 22 are formed on the glass substrate 24 on the side not in contact with the flow path 19, they are in a non-wetted state.

  FIG. 3 is a block diagram showing a specific example of the drive calculation means. In FIG. 3, reference numeral 25 denotes drive waveform generation means for generating a periodic drive signal such as a sine wave, and 26 denotes the phase of the drive signal. The buffer amplifier 27 shifts the phase of the drive signal, 27 is a buffer amplifier that shifts the phase of the drive signal by 0 degree, 28 and 29 are mixers, 30 and 31 are low-pass filter means, 32 is arithmetic control means such as a CPU, and 33 is heat transfer means. 34 are temperature detection means on either the upstream side or the downstream side.

  Reference numerals 25, 26, 27, 28, 29, 30, 31, and 32 constitute the drive calculation means 22.

  One end of the drive waveform generating means 25 is connected to the input terminals of the buffer amplifiers 26 and 27 and one end of the heat transfer means 33, respectively. The output of the buffer amplifier 26 is connected to one input terminal of the mixer 28, and the output of the buffer amplifier 27 is connected to one input terminal of the mixer 29.

  One end of the temperature detecting means 34 is connected to the other input terminals of the mixers 28 and 29, respectively, and the outputs of the mixers 28 and 29 are connected to the two input terminals of the arithmetic control means 32 via the low-pass filter means 30 and 31, respectively. The Finally, the other end of the drive waveform generating means 25, the other end of the heat transfer means 33, and the other end of the temperature detecting means 34 are grounded.

  Here, the operation of the embodiment shown in FIG. 1 will be described. However, the description of the operation similar to that of the conventional example shown in FIG.

  The drive calculation means 22 applies a periodic drive signal such as a sine wave to the heat transfer means 20. Specifically, a periodic drive signal such as a sine wave that is the output of the drive waveform generating means 25 is applied to the heat transfer means 33. For this reason, the heat transfer means 20 periodically heats the temperature of the fluid flowing through the flow path 19.

  On the other hand, the temperature detection signals of the temperature detection means 21 and 22 are supplied to the drive calculation means 23 and synchronously detected based on the drive signal for driving the heat transfer means 20.

  Specifically, the temperature detection signal from the temperature detection means 34 (temperature detection means 21 or temperature detection means 22) is multiplied by a signal obtained by shifting the phase of the drive signal by 90 degrees by the mixer 28, and the low-pass filter means. The high frequency component is removed at 30 and synchronous detection is performed based on the drive signal (90-degree phase shift).

  Similarly, the temperature detection signal from the temperature detection means 34 (temperature detection means 21 or temperature detection means 22) is multiplied by a signal obtained by shifting the phase of the drive signal by 0 degrees by the mixer 29, and then the low-pass filter means 31. The high frequency component is removed, and synchronous detection is performed based on the drive signal (0 degree phase shift).

  Then, the calculation control means 32 calculates the temperature in the temperature detection means 34 (temperature detection means 21 or temperature detection means 22) by calculating the square root of the square sum of the two synchronous detection signals obtained in this way. Ask.

  However, in FIG. 3, for the sake of simplicity of explanation, either the upstream or downstream temperature detection means is illustrated, but in the actual drive calculation means 22, both upstream and downstream temperature detection means. The temperature detection signals 21 and 22 are synchronously detected based on the drive signals (0 degree phase shift and 90 degree phase shift), and the temperatures in the temperature detection means 21 and 22 are obtained, respectively.

  Finally, the calculation control unit 32 obtains the flow rate based on the temperature difference between the temperature detection units 21 and 22, thereby measuring the flow rate of the liquid to be measured.

  In the conventional example shown in FIG. 6 and the like, the heat transfer means is controlled in a direct current manner. By periodically driving the heat transfer means and synchronously detecting the temperature detection signal with the drive signal, Noise components can be removed, and the S / N ratio can be improved.

  As a result, the heat transfer means is driven by a periodic drive signal such as a sine wave, and the temperature detection signal of the temperature detection means is synchronously detected based on the drive signal (0 degree phase shift and 90 degree phase shift) to calculate the sum of squares. By calculating the square root and obtaining the temperatures of the temperature detection means on the upstream side and downstream side, the S / N ratio of the thermal flow meter is calculated in the region where the flow rate of the flowing fluid is large and the region where the flow rate of the flowing fluid is small. Can be improved.

  In addition, as in the conventional example, a standardized temperature difference obtained by dividing the temperature difference by the temperature sum is obtained, and the flow rate is obtained based on the standardized temperature difference, thereby enabling more accurate and broadband flow rate measurement. become.

  In the embodiment shown in FIG. 1 and the like, the temperature is obtained by synchronously detecting the temperature detection signal based on the driving signal (0 degree phase shift and 90 degree phase shift) and calculating the square root of the sum of squares. The phase lag may be measured from the ratio of the two synchronous detection signals, and the flow rate may be measured by the TOF (Time of Flight) method.

  For example, the temperature detection signal from the temperature detection means 34 on the downstream side is multiplied by a signal obtained by shifting the phase of the drive signal by 90 degrees by the mixer 28, the high frequency component is removed by the low-pass filter means 30, and the drive signal (90 degrees) Synchronous detection based on phase shift).

  Similarly, the temperature detection signal from the temperature detection means 34 on the downstream side is multiplied by a signal obtained by shifting the phase of the drive signal by 0 degrees by the mixer 29, the high frequency component is removed by the low pass filter means 31, and the drive signal (0 Synchronous detection based on phase shift).

  Then, the calculation control means 32 calculates the arc tangent (arc tangent) of the ratio of the two synchronous detection signals obtained in this way, thereby obtaining a phase delay with respect to the drive signal. It corresponds to the time carried by the above, in other words, it corresponds to the flow velocity, so that the flow rate can be obtained by the TOF method.

  For example, FIG. 4 is an explanatory diagram for explaining the TOF method. In FIG. 4, “HT61” is a heat transfer means, and in FIG. 4, “TS61” and “TS62” are temperature detection means provided on the downstream side. When the liquid to be measured flows through the flow path as indicated by “FL61” in FIG. 4, the temperature heated by the heat transfer means at time “T0” propagates through the flow path at time “T1” in FIG. It is detected by the temperature detecting means indicated by “TS61”.

  Here, “L1 = T1−T0” is the flow velocity (phase delay) of the fluid to be measured. If the flow velocity is known, the flow rate can be measured from the known cross-sectional area of the flow path.

  As a result, the heat transfer means is driven by a periodic drive signal such as a sine wave, and the temperature detection signal of the downstream temperature detection means is synchronously detected based on the drive signal (0 degree phase shift and 90 degree phase shift). By calculating the arc tangent of the ratio and calculating the phase lag (flow velocity) with respect to the drive signal, the S of the thermal type flow meter is used in a region where the flow rate of the flowing fluid is large and a region where the flow rate of the flowing fluid is small. / N ratio can be improved.

  Further, a plurality of temperature detection means may be provided as in the conventional TOF method, and the flow rate may be measured based on the difference in phase delay between the two temperature detection means.

  FIG. 5 is a block diagram showing the configuration of another embodiment of the thermal type flow meter according to the present invention. In FIG. 5, 35 is a glass substrate, 36 is a flow path formed in the glass substrate 35, 37 is a heat transfer means such as a heater for heating the temperature of the fluid flowing through the flow path 36 to a constant temperature, 38, 39, Reference numerals 40, 41, 42, and 43 denote temperature detection means such as a thermistor and a platinum resistance temperature detector, and 44 denotes a drive calculation means that drives the heat transfer means and obtains a flow rate based on the difference in phase delay between the two temperature detection means. . Further, 35, 36, 37, 38, 39, 40, 41, 42, 43 and 44 constitute a flow meter chip 51.

  The fluid to be measured is injected from the inflow hole indicated by “IN71” in FIG. 5, and the fluid to be measured is discharged from the outflow hole indicated by “OT71” in FIG. Therefore, the fluid to be measured flows in the flow path 36 in the direction indicated by “FL71” in FIG.

  As shown by “FL71” in FIG. 5, a heat transfer means 37 is provided in the central portion of the flow path 36 through which the liquid to be measured flows, and is located on the flow path 36 at equal intervals from the heat transfer means 37. Temperature detection means 40 and 41 are provided.

  Similarly, temperature detection means 39 and 42 and temperature detection means 38 and 43 are sequentially provided on the flow path 36 and outside the temperature detection means 40 and 41 (the side where the heat transfer means 37 is not provided).

  Further, the outputs of the temperature detection means 38, 39, 40, 41, 42 and 43 are connected to the drive calculation means 44, respectively, and the drive signal for temperature control from the drive calculation means 44 is connected to the heat transfer means 37. .

  Here, the operation of the embodiment shown in FIG. 1 will be described. However, the configuration of the drive calculation means is the same as in FIG. 3, and the description of the operation similar to that of the embodiment shown in FIG.

  In the drive calculation means 44, the heat transfer means 37 is driven by a periodic drive signal such as a sine wave, and the temperature detection signals of the downstream temperature detection means 41 to 43 are drive signals (0 degree phase shift and 90 degree shift). The phase lag with respect to the drive signal in each of the temperature detecting means 41 to 43 on the downstream side is obtained by calculating the arctangent of the ratio of the synchronous detection signals.

  And the drive calculating means 44 measures a flow volume based on the difference of the phase delay between each temperature detection means 41-43 of downstream.

  For example, when the liquid to be measured flows through the flow path as indicated by “FL61” in FIG. 4, the temperature heated by the heat transfer means at time “T0” propagates through the flow path and is shown at time “T1”. 4 is detected by the temperature detecting means indicated by “TS61” in FIG. 4 and further detected by the temperature detecting means indicated by “TS62” in FIG. 4 at time “T2”.

  Here, “L2 = T2−T1” is the flow velocity (phase delay) of the fluid to be measured. If the flow velocity is known, the flow rate can be measured from the known cross-sectional area of the flow path.

  As a result, the heat transfer means is driven by a periodic drive signal such as a sine wave, and the temperature detection signal of the downstream temperature detection means is synchronously detected based on the drive signal (0 degree phase shift and 90 degree phase shift). By calculating the arc tangent of the ratio to obtain the phase lag (flow velocity) with respect to the drive signal and measuring the flow rate based on the phase lag difference in each temperature detection means, the flow rate of the flowing fluid increases. The S / N ratio of the thermal flow meter can be improved in a region where the flow rate of the flowing fluid is small.

  In addition, temperature (square root of sum of squares of synchronous detection signal) and phase lag (inverse tangent of ratio of synchronous detection signal) can be obtained at the same time, so the flow rate measurement range can be expanded by using both together. It becomes possible.

  For example, when the measurable flow rate range between the method based on the temperature difference and the TOF method is different, the flow rate can be measured by one method, and the flow rate cannot be measured by the other method. For this reason, it becomes possible to extend the flow rate measurement range by combining both methods.

  Moreover, since the temperature (square root of the sum of squares of the synchronous detection signal) and the phase delay (inverse tangent of the ratio of the synchronous detection signal) can be obtained at the same time, the thermal characteristic value of the fluid ( It is possible to measure thermal conductivity and the like.

  In other words, the TOF method can obtain information depending only on the flow rate, whereas the method based on the temperature difference (hereinafter referred to as the temperature difference method) has a flow characteristic and a thermal characteristic value (thermal conductivity, etc.) of the fluid. Therefore, if the thermal characteristic value of the fluid is unknown, the flow rate is measured by the TOF method, and the thermal characteristic value is calculated based on the measurement result and the signal obtained by the temperature difference method. be able to.

  In addition, temperature (square root of sum of squares of synchronous detection signal) and phase lag (inverse tangent of ratio of synchronous detection signal) can be obtained at the same time. It becomes possible to do.

  For example, flow rate measurement is performed using temperature (or phase delay) and flow rate calibration processing is performed using phase delay (or temperature).

It is a block diagram showing the configuration of an embodiment of a thermal flow meter according to the present invention. It is the top view and sectional drawing which show the specific example of the sensor part of one Example of the thermal type flow meter which concerns on this invention. It is a block diagram showing a specific example of the drive calculation means. It is explanatory drawing explaining TOF method. It is a block diagram which shows the other Example of the thermal type flow meter which concerns on this invention. It is a block diagram showing an example of a conventional thermal flow meter. It is a characteristic curve figure which shows an example of the temperature distribution of the to-be-measured liquid in a flow path with respect to the position of a flow path. It is a perspective view which shows another example of the conventional thermal type flow meter. It is sectional drawing which shows another example of the conventional thermal type flow meter. It is a characteristic curve figure which shows the relationship between the temperature difference of an upstream and a downstream, and flow volume. It is a block diagram which shows another example of a thermal type flow meter. It is the top view and sectional drawing which show the specific example of the sensor part of another example of a thermal type flow meter. It is a characteristic curve figure which shows the relationship of the value which divided the temperature difference of the upstream and downstream with respect to flow volume, a temperature sum, and the temperature difference divided by the temperature sum.

Explanation of symbols

1,10,16,19,36 Flow path 2,8,13,20,33,37 Heat transfer means 3,4,14,15,21,22,34,38,39,40,41,42,43 Temperature detection means 5, 17, 32 Operation control means 6, 11, 12, 18, 24 Glass substrate 7, 9, 35 Silicon substrate 23, 44 Drive operation means 25 Drive waveform generation means 26, 27 Buffer amplifier 28, 29 Mixer 30 31 Low pass filter means,
50,51 Flow meter chip

Claims (8)

In the thermal flow meter that controls the temperature of the liquid flowing through the flow path and measures the flow rate based on the temperature difference between the upstream and downstream fluids of the temperature control part,
A channel in which the wetted parts are all made of glass,
A heat transfer means provided in the flow path;
Upstream and downstream temperature detection means provided on the flow path at equal intervals from the heat transfer means;
The heat transfer means is driven by a periodic drive signal, and the temperature detection signals of the upstream and downstream temperature detection means are synchronously detected based on the drive signal, and the upstream and downstream temperatures are calculated to calculate the flow rate. A thermal type flow meter comprising a drive calculation means to be obtained. The drive calculation means is
The temperature detection signal of the temperature detection means is synchronously detected based on a drive signal having a phase shift of 0 degrees and a phase shift of 90 degrees, and the square root of the sum of squares is calculated to determine the upstream or downstream temperature. Item 2. The thermal flow meter according to Item 1. In the thermal flow meter that controls the temperature of the liquid flowing through the flow path and measures the flow rate based on the time difference of temperature detection on the downstream side of the temperature control part,
A channel in which the wetted parts are all made of glass,
A heat transfer means provided in the flow path;
Upstream and downstream temperature detection means provided on the flow path at equal intervals from the heat transfer means;
The heat transfer means is driven by a periodic drive signal, and the temperature detection signal of the temperature detection means on the downstream side is synchronously detected based on the drive signal to calculate a phase delay with respect to the drive signal in the temperature detection means on the downstream side. A thermal flow meter comprising a drive calculation means for obtaining a flow rate. In the thermal flow meter that controls the temperature of the liquid flowing through the flow path and measures the flow rate based on the time difference of temperature detection on the downstream side of the temperature control part,
A channel in which the wetted parts are all made of glass,
A heat transfer means provided in the flow path;
Upstream and downstream temperature detection means provided on the flow path at equal intervals from the heat transfer means;
Temperature detection means provided outside the downstream temperature detection means;
The heat transfer means is driven by a periodic drive signal, and the temperature detection signals of the two temperature detection means on the downstream side are synchronously detected based on the drive signal, and the phase delay between the two temperature detection means on the downstream side is detected. A thermal flow meter comprising a drive calculation means for calculating a difference to obtain a flow rate. The drive calculation means is
The temperature detection signal of the temperature detection means is synchronously detected based on the drive signal of 0 degree phase shift and 90 degree phase shift, and the arc tangent of the ratio of the synchronous detection signal is calculated to calculate the phase lag with respect to the drive signal, or the phase lag The thermal flow meter according to claim 3 or 4, wherein a difference is obtained. The drive calculation means is
Drive waveform generating means for supplying a periodic drive signal to the heat transfer means;
Two buffer amplifiers for shifting the drive signal by 0 degrees and 90 degrees;
Two mixers for multiplying the temperature detection signal from the temperature detection means by a drive signal of 0 degree phase shift and 90 degree phase shift, respectively;
Two low-pass filter means to which the outputs of these two mixers are input;
6. An arithmetic control means for calculating upstream and downstream temperatures or a phase delay with respect to a drive signal based on outputs of the two low-pass filter means. The thermal flow meter according to Crab. The drive calculation means is
7. The thermal flow meter according to claim 1, wherein the temperature detection signal is synchronously detected based on the drive signal to simultaneously obtain the upstream and downstream temperatures and the phase delay with respect to the drive signal. . The drive calculation means is
8. The flow rate is measured using upstream and downstream temperatures or phase delay, and the flow rate is calibrated using phase delay or upstream and downstream temperatures. Thermal flow meter.

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