JP2008014729A - Fluid flow velocity measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid flow velocity measuring instrument used not only for performing efficient measurement with a measurement down period eliminated but for performing measurement even if flow velocity is zero. <P>SOLUTION: A heater 3 starts heat generation by its power application to raise the temperature of the heater. Heat transfer takes place in temperature sensing elements 1 and 2. An output voltage 10 owing to a temperature rise of the sensing element 1 reaching V2 causes a trigger signal to be output from a comparator 6. An output of a logic element 8 becomes Low to cause a heater control circuit 9 to stop the power application to the heater 3. Because of this, heat transferring to the temperature sensing elements 1 and 2 decreases. An output voltage of the sensing element 2 reaching V1 causes a trigger signal to be output from a comparator 7. The output of the logic element 8 becomes High to start the power application to the heater 3. This operation is repeated to cause output pulses to be output from the logic element 8. Pulse intervals T1 and T2 are measured of these output pulses. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fluid flow velocity measuring apparatus, and more particularly to a fluid flow velocity measuring apparatus that measures a fluid flow velocity by measuring a speed at which a heater generates heat and heat generated by the heater is moved by the fluid.

Conventionally, a technique for measuring the flow velocity of a fluid by heating the heater in the fluid and measuring the speed and amount of heat transferred by the fluid from the heater is known. Using a flow sensor with a thermopile on the downstream side, measure the heat propagation time by measuring the time from when the heater heat starts to when a predetermined output difference occurs between the upstream thermopile and the downstream thermopile. A method has been proposed for measuring. (For example, refer to Patent Document 1).
Japanese Patent No. 3381831

In the method described in Patent Document 1, the heater is heated at the timing of the oscillator, and the flow rate is measured by the time until the heat reaches the thermopile. Therefore, from the time when the heat from the heater is detected by the thermopile. Next, the time until the heater generates heat is a measurement suspension period. Not only is the measurement efficiency not good, but there is no difference in thermopile output at a flow velocity of 0, so it is impossible to measure around the flow velocity of 0. There's a problem.
The present invention has been made in view of the above circumstances, and provides a fluid flow velocity measuring apparatus that not only eliminates the measurement suspension period but enables efficient measurement, but also enables measurement even at a flow velocity of zero. For the purpose.

  In order to solve the above-mentioned problem, the invention described in claim 1 includes a heater, a flow sensor including a first temperature sensor and a second temperature sensor arranged with the heater interposed therebetween, and a first sensor. A first comparing means for comparing the output voltage detected by the temperature sensing element with the first reference voltage and outputting a signal when the output voltage exceeds the first reference voltage; A second comparison means for comparing the output voltage detected by the body with a second reference voltage and outputting a signal when the output voltage exceeds the second reference voltage; and a first comparison means; A logic element that generates an output pulse based on a signal obtained from the second comparison means; and a heater control circuit that applies a current to the heater in accordance with the output pulse output from the logic element. The circuit uses the output signal from the first comparison means to generate the heater. By stopping or decreasing the current supply, starting or increasing the current supply to the heater according to the output signal from the second comparison means, and measuring the pulse interval of the output pulse supplied to the heater control circuit. It is characterized by a fluid flow velocity measuring device that measures the flow velocity of the fluid flowing on the flow sensor.

According to a second aspect of the present invention, there is provided the fluid flow velocity measuring device according to the first aspect, wherein the first temperature sensing body and the second temperature sensing body are a first temperature sensing resistor and a second temperature sensing resistor. The flow sensor includes a third temperature-sensitive resistor for detecting a fluid temperature, and a first fixed resistor and a second fixed resistor are connected in series with the third temperature-sensitive resistor, First, first, and second current flowing through the first temperature-sensitive resistor, the second temperature-sensitive resistor, and the first fixed resistor, the second fixed resistor, and the third temperature-sensitive resistor, respectively. 2 and a third constant current source are connected, and the first comparison means uses the voltage generated by the first fixed resistance, the second specific resistance, and the third temperature sensitive resistor as the first reference voltage. The second comparison means compares the voltage generated in the first fixed resistor and the third temperature sensitive resistor with the second reference voltage. Comparing the second voltage generated by the temperature sensing resistor and said as.
According to a third aspect of the present invention, in the fluid flow velocity measuring device according to the second aspect, the heater control circuit includes an integration circuit, and controls energization to the heater with a time constant determined by the integration circuit. Features.
According to a fourth aspect of the present invention, in the fluid flow velocity measuring device according to the third aspect, the voltage at the first and second temperature sensitive resistors, which is caused by the decrease and increase in energization to the heater, is obtained by the integration circuit. The heater control circuit is controlled to coincide with a predetermined time constant.
Further, the invention according to claim 5 is the fluid flow velocity measuring device according to any one of claims 1 to 4, wherein the first is generated when the energization of the heater is stopped or decreased and the energization of the heater is started or increased. A detection circuit for detecting a voltage difference between the temperature sensitive resistor and the second heat sensitive resistor is provided.

  According to the present invention, it is possible to provide a fluid flow velocity measuring device that not only eliminates the measurement suspension period and enables efficient measurement, but also enables measurement even at a flow velocity of 0 by adopting the above configuration.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Example 1]
FIG. 1 is a circuit diagram showing a schematic configuration of a fluid flow velocity measuring apparatus according to an embodiment of the present invention.
In the figure, 1 and 2 are a first temperature sensor and a second temperature sensor made of a thermopile, 3 is a heater made of a temperature sensor that generates heat when energized, and 4 and 5 have a predetermined voltage V1 and A power supply for supplying V2 to the second comparator 7 and the first comparator 6, 8 is a flip-flop circuit for generating an output pulse by a trigger signal from the first comparator 6 and the second comparator 7, etc. A logic element, 9 is a heater control circuit that controls energization of the heater in accordance with the output pulse, 34 is an arithmetic circuit that measures the pulse interval of the output pulse and calculates the flow velocity of the fluid, and 35 is an arithmetic circuit 34 It is a display means which displays the flow velocity of the fluid output from.

Next, the operation of the fluid flow velocity measuring apparatus according to this embodiment will be described with reference to FIG. FIG. 2 is a time chart for explaining the operation of the fluid flow velocity measuring apparatus according to the present embodiment. FIG. 2 shows the operation timing when the power is turned on in this configuration when the fluid is flowing in the positive direction. It is. The direction (arrow X) in which the fluid flows from the first temperature sensing element 1 to the second temperature sensing element 2 in FIG. 1 is positive.
Although not shown in the drawing, this fluid flow velocity measuring device is started by applying a power ON reset signal (b) or the like to the logic element 8, whereby the output (e) of the logic element 8 becomes High, and the heater control circuit 9 starts energizing the heater 3. When energized, the heater 3 starts to generate heat, the temperature of the heater rises, and the heat that moves to the first temperature sensor 1 and the second temperature sensor 2 through the space increases. With this heat transfer, the trigger voltage (c) is output from the first comparator 6 when the output voltage 10 due to the temperature rise of the first temperature sensing element 1 reaches V2 (see FIG. 2 (a)). The output of the logic element 8 becomes Low, and the heater control circuit 9 stops energizing the heater 3. As a result, the temperature of the heater 3 decreases and the heat transferred to the first temperature sensing body 1 and the second temperature sensing body 2 through the going space is reduced, and the output voltage of the second temperature sensing body 2 is V1. , The trigger signal (d) is output from the second comparator 7, the output of the logic element 8 becomes High, and energization of the heater 3 is started. This operation is repeated, and an output pulse is output from the logic element 8. By calculating the pulse interval T1 (ON time) and T2 (OFF time) of the output pulse, the calculation circuit 34 calculates from the relationship line (calibration curve) between the pulse interval T1 and T2 obtained in advance and the fluid flow velocity. Thus, the flow velocity is measured, and the flow velocity is displayed by the display means 35.

Further, the heater control method in the present embodiment is controlled at a heat generation temperature sufficient to provide a temperature rise detected by the first temperature sensing element 1 and the second temperature sensing element 2, and has been described above. A series of operations is performed in the process where the heater temperature rises and falls. The temperature increase / decrease rate of the heater is determined by the heat capacity of the heater, and the temperature increase / decrease rate of the heater serves as a reference. In such a case, at the time of heater heat generation control, in the first temperature sensing element 1, the movement of heat accompanying the rise in heater temperature is hindered by the flow of fluid, the temperature rise rate becomes slow, and the second temperature sensing element 2. Then, since the heat accompanying the temperature rise of the heater moves to the second temperature sensing body 2, the temperature rise speed is increased. On the other hand, during the heater non-heat generation control, the lowering speed of the first temperature sensing element 1 is increased, and in the second temperature sensing element 2, the heat accompanying the temperature drop of the heater moves to the second temperature sensing element 2. Therefore, the temperature drop rate becomes slow.
In this embodiment, the high time of the output pulse is defined by the temperature rise speed of the first temperature sensing element 1 during the heater heat generation control, and the temperature drop speed of the second temperature sensing element 2 during the heater non-heat generation control. Since it defines the low time of the output pulse, measuring the pulse period of the output pulse makes it possible to measure the flow velocity without a measurement pause period.

FIG. 3 shows output signals 10 and 11 (refer to A1, B1, and C1) and heater control signals (A2, A1, B2) of the first temperature sensor 1 and the second temperature sensor 2 when the fluid flows are different. B2 and C2) are shown. (A) is a state where the fluid is flowing in the positive direction, as described above. (B) is the state of the flow velocity 0 where the fluid is not flowing. In the state where the flow velocity is 0, the temperature increasing speed and the temperature decreasing speed of the first temperature sensing element 1 and the second temperature sensing element 2 are the same, and the first temperature sensing element 1 and the first temperature sensing element 1 in a state where there is a flow. The temperature rise speed and the temperature fall speed are located in the middle of the two temperature sensing bodies 2. (C) is a state in which the fluid is flowing in the opposite direction. In this case, the first temperature sensing element 1 is on the downstream side, and the temperature rise rate is faster than the second temperature sensing element 2, and the temperature drop rate. Will be late. Therefore, the operation shown in FIG. As described above, in this method, measurement can be performed without a pause period in the range of flow velocity from − to +.
In this embodiment, the heater heat generation is controlled by the detection levels V1 and V2 of the temperature sensor output. By setting the voltage levels of V1 and V2 to the minimum necessary levels, A minute heat transfer from the heater to the temperature sensing element can be measured, and thereby, a high flow rate at which the reaction of the upstream temperature sensing element becomes small can be measured.

[Example 2]
FIG. 4 is a circuit diagram showing a schematic configuration of a fluid flow velocity measuring device according to another embodiment of the present invention. The same components as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted.
In FIG. 4, reference numerals 13 and 14 denote temperature sensing elements made of a temperature sensing resistor, respectively, a first temperature sensing resistor and a second temperature sensing resistor, and 15 a temperature sensing resistor for detecting the fluid temperature. The third temperature-sensitive resistor, 16 and 17 are a first specific resistance and a second specific resistance having a predetermined resistance value, and 18, 19 and 20 are the first temperature-sensitive resistor 13 and the second specific resistance, respectively. The constant current source is supplied to the temperature sensitive resistor 14, the third temperature sensitive resistor 15, and the first and second specific resistors 16 and 17.
This example is different from Example 1 described above in that a temperature sensitive resistor is used instead of the thermopile as the temperature sensitive material. In the flow sensor using a temperature sensitive resistor, the heater and the temperature detection element can be created in the same process, and can be made into the same shape, thereby making the temperature response speed between the elements the same, The feature of the present embodiment is that a fluid temperature reference is made by using a temperature sensitive resistor having the same shape as the temperature sensing resistor for measuring the flow velocity, and further, a fixed resistor is connected in series to the reference temperature sensitive resistor. The temperature compensation is performed by using the resistance value of the fixed resistance as the temperature detection level of the temperature sensing resistor for measuring the flow velocity.

Moreover, the suitable structure of the flow sensor which consists of a temperature sensitive resistor used for a present Example is shown in FIG.5 and FIG.6. The flow sensor shown in FIG. 5 and FIG. 6 is manufactured using a semiconductor process. Openings 21a, 21b, 21c, 21d, and 21e are formed on a base 22 made of silicon wafer in order from the fluid flow direction X. The openings 21a, 21b, 21c, 21d, and 21e are connected to each other through gaps 21f, and connection terminals 15a, 15b, 13a, 13b, 3a, 3b, 14a, and 14b are provided at both ends. Temperature sensitive resistors 15, 13, 3, and 14 connected to the base 22 are provided, and are formed so that variations in resistance values between adjacent elements are small. The first temperature-sensitive resistor 13, the second temperature-sensitive resistor 14, and the third temperature-sensitive resistor 15 conduct temperature detection by passing a weak constant current that does not generate heat. In the case of the present embodiment, the currents supplied to the three temperature sensitive resistors 13, 14 and 15 have the same current value. With this configuration, when the heater 3 is in a non-heated state, the resistance values of the temperature sensitive resistors 13, 14, and 15 show substantially the same resistance value even when the temperature of the fluid changes. The voltage generated at both ends is substantially the same.
Fixed resistors 16 and 17 are connected in series to the temperature sensitive resistor 15, and the voltage V 1 generated by the temperature sensitive resistor 15 and the fixed resistor 16 is compared with the voltage 11 generated by the temperature sensitive resistor 14. The temperature is set so that the temperature-sensitive resistor 14 has a temperature that is higher than the fluid temperature by a value defined by the resistance value of the fixed resistor 16. The voltage V2 generated by the temperature sensitive resistor 15, the fixed resistor 16, and the fixed resistor 17 is a voltage for comparison with the voltage 10 generated by the temperature sensitive resistor 13, and the temperature sensitive resistor 13 is compared with the fluid temperature. Thus, the temperature is set to be higher by the amount defined by the total resistance value of the fixed resistors 16 and 17. Here, when the voltage generated in the temperature sensitive resistor 15 is considered as the GND level (reference) in the first embodiment, the operation of the present embodiment is the same as that in FIG. 3 of the first embodiment.

In addition, the fixed resistors 16 and 17 described above determine the temperature detection level of the temperature sensitive resistors 13 and 14, but the flow sensor as shown in FIG. The resistance value can be very small.
Furthermore, an adjustment circuit is added to the constant current sources 18, 19, 20 to reduce the voltage difference caused by variations in the temperature sensitive resistors 13, 14, 15, and the fixed resistors 16, 17 can be set to a minimum resistance value. good. As a result, the temperature detection level of the temperature sensitive resistors 13 and 14 can be made slightly higher than the fluid temperature, and a slight amount of heat moving from the heater 3 can be detected.
Further, since the temperature at the temperature sensitive resistor 13 does not rise above the temperature defined by the fixed resistors 16 and 17, the temperature sensitive resistor 15 is further provided as a temperature sensitive resistor 13 as shown in FIG. By placing it upstream, it is almost unaffected by the heat of the heater. The temperature sensitive resistor 15 is provided for temperature compensation of the temperature sensitive resistor whose resistance value changes depending on the ambient temperature, and all the temperature sensitive resistors including the temperature sensitive resistor 15 for temperature compensation are the same. Since the shape can be made to have the same heat capacity, and the temperature response speeds are all the same, the flow velocity can be measured without error even when a sudden temperature change occurs in the fluid.

As can be seen from the configuration shown in FIG. 4, the present embodiment can be configured with a very small number of parts, and all measurements are made by comparing resistance values. Therefore, the constant current sources 18, 19, and 20 whose details are not described need not have a relative error, so that they can be easily made based on one simple constant voltage source. In recent years, high-performance and low-priced metal film resistors on chips have become widespread, so it does not increase the cost of the circuit. The only expensive parts are the comparators 6 and 7, but the required flow rate measurement performance You can also choose cheaper ones.
Also, since the output in this configuration is a pulse output, it can be converted into a flow velocity without the need for parts such as an AD converter, so the flow velocity measuring device using this embodiment is inexpensive.

[Example 3]
FIG. 7 is a circuit diagram showing a schematic configuration of a fluid flow velocity measuring device according to another embodiment of the present invention. The same components as those in Example 2 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 7, 23 is a reference power supply for the ramp integration circuit, 24 is a fixed resistor for the ramp integration circuit, 25 is a capacitor for the ramp integration circuit, 26 is an operational amplifier for the ramp integration circuit, and 27 is an analog switch.
In the present embodiment, an integration circuit is used as the heater control circuit 9 of the second embodiment described above, and the rate of increase in the heat generation temperature of the heater is defined by a circuit time constant. The integrating circuit in the present embodiment is a ramp integrating circuit, whereby the voltage applied to the heater 3 changes linearly with time. The operation in FIG. 7 is shown in FIG. In FIG. 8, (A1), (A2), and (A3) respectively indicate (A) the voltage applied to the heater when there is a flow in the positive direction, the voltage 10 detected by the temperature-sensitive resistor 13, and the sensitivity. The voltage 11 detected by the temperature resistor 14 and the heater control signal output signal output from the logic element 8 are shown. Similarly, (B1), (B2), (B3), (C1), (C2) , (C3) is (B) when there is no flow, (C) the voltage applied to the heater when there is flow in the reverse direction, the voltage 10 detected by the temperature sensitive resistor 13, and the temperature sensitive resistor 14 2 shows the voltage 11 detected at 1 and the heater control signal output signal output from the logic element 8.

In the present embodiment, the heater control signal is set to low when the voltage 10 generated at the temperature sensitive resistor 13 reaches the voltage V2, and the heater 11 when the voltage 11 generated at the temperature sensitive resistor 14 reaches the voltage V1. Let the control signal be High. In the above operation, since the repetition period of the heating temperature rise / fall of the heater 3 is determined by the time constant determined by the ramp integration circuit, the power consumption due to the heat capacity of the heater can be suppressed by increasing the time constant.
Further, in this embodiment, the amount of temperature rise in the temperature sensitive resistor 13 is fixed to the minimum amount of heat that can detect the flow velocity (the voltage value of V2), thereby determining the upper limit value of the heater heat generation temperature. . In other words, the heater heat generation temperature is controlled to the minimum heat generation temperature that can be measured according to the flow velocity. Thus, in this embodiment, it is possible to realize flow velocity measurement with low power consumption without causing the heater to generate heat unnecessarily.

[Example 4]
FIG. 9 is a circuit diagram showing a schematic configuration of a fluid flow velocity measuring apparatus according to another embodiment of the present invention. The same components as those in Example 3 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 9, 28 is an operational amplifier, 29 is a fixed resistor, 30 and 31 are differential amplifiers, 36, 37, 38, 39 and 40 are fixed resistors for adders, and 41 is an operational amplifier for adders.
The present embodiment is basically the same as that described in the third embodiment, but the signals detected by the temperature sensitive resistors 13 and 14 are input through the differential amplifiers 30 and 31. Is added to the operational amplifier 28, and the output of the ramp integrating circuit is controlled, and the temperature rise and fall speeds of the temperature sensitive resistors 13 and 14 for measuring the flow velocity are determined by the ramp integrating circuit. It is characterized by controlling the heater 3 so as to be the same.
More specifically, the voltages 10 and 11 generated by the temperature sensitive resistors 13 and 14 are compared and amplified with the voltage 12 generated by the temperature sensitive resistor 15 and the fixed resistor 29, so that the heater 3 generates the temperature sensitive resistor 13. , 14 is used to take out the voltage change caused by the temperature rise / drop caused by the heat transferred to the differential amplifiers 30 and 31. This signal is synthesized by an adder and compared with the voltage ramp signal 42 to control the heater 3. Since the voltage ramp signal 42 is controlled by the temperature of the temperature sensitive resistors 13 and 14, the swing range of the lamp voltage 42 is naturally stabilized at a level that matches the output signal from the adder. By this operation, the temperature rise and fall speeds of the temperature sensitive resistors 13 and 14 change linearly with time.

FIG. 10 shows the operation timing according to this configuration. In the figure, (A1) and (A2) respectively represent (A) the voltage 10 detected by the temperature sensing resistor 13 and the voltage 11 detected by the temperature sensing resistor 14 when there is a flow in the positive direction, and the logic. The heater control signal output signal output from the element 8 is shown. Similarly, (B1), (B2), (C1), and (C2) flow in the reverse direction when (B) there is no flow. The voltage 10 detected by the temperature-sensitive resistor 13 and the voltage 11 detected by the temperature-sensitive resistor 14 and the heater control signal output signal output from the logic element 8 are shown.
According to this configuration, the composition of the temperature increasing speed and the composition of the temperature decreasing speed of the temperature sensitive resistors 13 and 14 are always constant, and this condition is fixed regardless of the flow speed and the ambient temperature. Therefore, heat is supplemented from the heater 3 in accordance with the amount of heat flowing out from the temperature sensitive resistors 13 and 14 to the base 22 of the flow sensor, a flow rate is generated, and the temperature sensitive resistors 13 and 14 are heated. Even when there is a temperature difference, since the ratio of the amount of heat supplied from the heater 3 depends on the flow velocity, the same amount of heat that flows out to the base 22 is supplied from the heater. Therefore, the influence of the heat flowing out to the base 22 is not affected at all.

[Example 5]
FIG. 11 is a circuit diagram showing a schematic configuration of a fluid flow velocity measuring apparatus according to another embodiment of the present invention. The same components as those in Example 4 are denoted by the same reference numerals, and description thereof is omitted.
In this embodiment, the basic operation is the same as that of the above-described fourth embodiment, and the temperature rise / fall rate of the temperature sensitive resistor 13 is fixed by a time constant determined by the ramp integration circuit of the heater control circuit 9. It is. As a result, the temperature-sensitive resistor 13 is used as a reference, and the temperature increase / decrease rate of the temperature-sensitive resistor 14 changes depending on the flow velocity. As a result, the temperature increase / decrease rate of the temperature sensitive resistors 13 and 14 is defined by the time constant of the ramp integration circuit, so there is no influence of the heater heat generation temperature, thereby eliminating the temperature dependence and the heat conduction of the fluid. The error due to the difference in the rate is eliminated, and the influence due to aging deterioration of the temperature sensitive resistor is also eliminated. Thus, since the heater heat generation temperature changes according to the flow rate, a stable output from a low flow rate to a high flow rate can be obtained. Furthermore, although the circuit scale of this embodiment is smaller than that of Embodiment 4, the temperature rise / fall speed of the temperature sensitive resistor 13 is fixed, so that the change of the output pulse with respect to the flow velocity is small. Become.

[Example 6]
FIG. 12 is a circuit diagram showing a schematic configuration of a fluid flow velocity measuring apparatus according to another embodiment of the present invention. The same components as those in Example 3 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 12, 33 is a differential amplifier.
In the present embodiment, attention is paid to the fact that the outputs of the upstream and downstream temperature sensing elements do not intersect except when the flow velocity is 0. In this configuration, a differential amplifier 33 detects a voltage difference generated at 13 and 14. By adding this configuration, it is possible to detect adhesion of dust to the temperature sensitive resistors 13 and 14.
This dust detection will be described with reference to FIG. In FIG. 13, (A1) and (A2) are (A) a voltage 10 detected by the temperature-sensitive resistor 13 and a voltage 11 detected by the temperature-sensitive resistor 14 when there is a flow in the positive direction, respectively. Similarly, (B1), (B2), (C1), (C2), (D1), and (D2) indicate the output (B) flow from the differential amplifier 33. When there is no flow, (C) when there is a flow in the reverse direction, and (D) when the dust is attached to the temperature sensing resistor 13 and there is no flow, the voltage 10 detected by the temperature sensing resistor 13 and the temperature sensing resistor 14 shows the voltage 11 detected at 14 and the output (flow velocity 0 output) 43 from the differential amplifier 33.

  As is clear from this figure, the flow rate 0 output 43 does not swing when the output of the temperature sensitive resistors 13 and 14 sandwiches 0V when no dust is attached, but the dust does not swing. , 14, when it is attached to either of them, as shown in (D2), it swings across 0V. This is a phenomenon that occurs when dust is attached even if the same amount of heat is supplied from the heater 3 to the temperature sensitive resistors 13 and 14, because the heat capacity increases and the temperature rise rate and the temperature fall rate become slow. is there. Therefore, by monitoring the flow velocity 0 output 43 according to the present embodiment, it is possible to reliably detect that dust has adhered to the temperature sensitive resistor without being affected by the type of fluid. With regard to the treatment at the time of adhering to dust, it is removed by eliminating the adhesive force by flowing a large current through the temperature sensitive resistor to which dust is adhering to carbonize the dust, or predicting the size of dust from the flow rate 0 output 43 A plurality of means are conceivable, such as correcting the flow velocity signal or issuing an alarm signal to prompt cleaning.

1 is a circuit diagram illustrating a schematic configuration of a fluid flow velocity measuring apparatus according to a first embodiment of the present invention. It is a time chart which shows operation | movement of the fluid flow velocity measuring apparatus which concerns on Example 1 by this invention. In the waveform diagram of the signal showing the operation of the fluid flow velocity measuring device according to the first embodiment of the present invention, (A) when there is a fluid flow in the positive direction, (B) when there is no flow, (C) is a waveform diagram when there is a flow in the reverse direction. It is a circuit diagram which shows schematic structure of the flow velocity measuring apparatus of the fluid based on Example 2 by this invention. It is a top view of the flow sensor used with the flow velocity measuring device of the fluid concerning Example 2 by the present invention. It is sectional drawing cut | disconnected on the AA line of FIG. It is a circuit diagram which shows schematic structure of the flow velocity measuring apparatus of the fluid which concerns on Example 3 by this invention. In the waveform diagram of the signal showing the operation of the fluid flow velocity measuring device according to the third embodiment of the present invention, (A) when there is a fluid flow in the positive direction, (B) when there is no flow, (C) is a waveform diagram when there is a flow in the reverse direction. It is a circuit diagram which shows schematic structure of the flow velocity measuring apparatus of the fluid which concerns on Example 4 by this invention. In the waveform diagram of the signal showing the operation of the fluid flow velocity measuring device according to the fourth embodiment of the present invention, (A) when there is a fluid flow in the positive direction, (B) when there is no flow, (C) is a waveform diagram when there is a flow in the reverse direction. It is a circuit diagram which shows schematic structure of the flow velocity measuring apparatus of the fluid which concerns on Example 5 by this invention. It is a circuit diagram which shows schematic structure of the flow velocity measuring apparatus of the fluid based on Example 6 by this invention. In the waveform diagram of the signal showing the operation of the fluid flow velocity measuring device according to the sixth embodiment of the present invention, (A) when there is a fluid flow in the positive direction, (B) when there is no flow, (C) is a waveform diagram when there is a flow in the reverse direction, and (D) is a waveform diagram when dust is attached to the temperature sensitive resistor and there is no flow.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... 1st temperature sensor, 2 ... 2nd temperature sensor, 3 ... Heater, 4 ... 2nd reference voltage source, 5 ... 1st reference voltage source, 6 ... 1st comparator, 7 ... 2nd comparator, 8 ... logic element, 9 ... heater control circuit, V1 ... second reference voltage, V2 ... first reference voltage, 10 ... voltage detected by second temperature sensor, 11 ... first Detected voltage by temperature sensing element, 13 ... first temperature sensing resistor, 14 ... second temperature sensing resistor, 15 ... third temperature sensing resistor, 16 ... first fixed resistance, 17 ... second Specific resistance, 18 ... first constant current source, 19 ... second constant current source, 20 ... third constant current source, 34 ... arithmetic circuit, 35 ... display means

Claims (5)

A flow sensor including a heater, and a first temperature sensor and a second temperature sensor disposed between the heaters;
A first comparing means for comparing the output voltage detected by the first temperature sensing element with the first reference voltage and outputting a signal when the output voltage exceeds the first reference voltage;
A second comparison means for comparing the output voltage detected by the second temperature sensor with a second reference voltage and outputting a signal when the output voltage exceeds the second reference voltage;
A logic element for generating an output pulse by signals obtained from the first comparison means and the second comparison means;
A heater control circuit for applying a current to the heater in response to an output pulse output from the logic element,
The heater control circuit stops or decreases energization to the heater according to an output signal from the first comparison means, and starts or increases energization to the heater according to an output signal from the second comparison hand. An apparatus for measuring a flow velocity of fluid, wherein the flow velocity of the fluid flowing on the flow sensor is measured by measuring a pulse interval of the output pulse supplied to the heater control circuit. In the fluid flow velocity measuring device according to claim 1,
The first temperature sensor and the second temperature sensor are a first temperature sensor and a second temperature sensor,
The flow sensor includes a third temperature sensing resistor for fluid temperature detection,
Connecting a first fixed resistor and a second fixed resistor in series with the third temperature sensitive resistor;
First, first, and second current flowing through the first temperature-sensitive resistor, the second temperature-sensitive resistor, and the first fixed resistor, the second fixed resistor, and the third temperature-sensitive resistor, respectively. Connecting the second and third constant current sources,
The first comparison means uses the voltage generated by the first fixed resistor, the second specific resistance, and the third temperature sensitive resistor as the first reference voltage, and the voltage generated by the first temperature sensitive resistor. Compared to
The second comparing means compares the voltage generated by the first fixed resistor and the third temperature sensitive resistor with the voltage generated by the second temperature sensitive resistor as the second reference voltage. Fluid velocity measuring device. In the fluid flow velocity measuring device according to claim 2,
The heater control circuit includes an integration circuit, and controls the energization of the heater with a time constant determined by the integration circuit. In the fluid flow velocity measuring device according to claim 3,
The heater control circuit is controlled so that the voltage at the first and second temperature sensitive resistors, which is caused by the decrease and increase in energization to the heater, coincides with the time constant determined by the integration circuit. Fluid velocity measuring device. In the fluid flow velocity measuring device according to any one of claims 1 to 4,
A detection circuit is provided for detecting a voltage difference between the first temperature-sensitive resistor and the second heat-sensitive resistor that is generated when the energization of the heater is stopped or reduced and when the energization of the heater is started or increased. Fluid velocity measuring device.

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