JP3380345B2 - Thermal flow sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow velocity sensor used for detecting fluidic oscillation in a fluidic flowmeter, for example.

[0002]

2. Description of the Related Art As a flow meter used in a gas meter or the like, there is a flow meter using a thermal type flow velocity sensor (hereinafter referred to as a flow sensor). The flow sensor is a sensor that obtains the flow velocity of the fluid flowing through the pipe, and has the advantage of high sensitivity and fast response. In the flow meter using this flow sensor, the flow rate corresponding to the flow velocity is obtained from the output of the flow sensor and displayed.

As a flow sensor, for example, Japanese Unexamined Patent Publication No.
As shown in Japanese Patent No. 259527, two temperature measuring resistance elements that emit heat by themselves are arranged along the direction of the fluid flow, or two temperature measuring resistive elements are disclosed, for example, in Japanese Unexamined Patent Publication No. 4-58111. For example, a resistance element (sensor resistor) and a heater element (heater resistor) provided between the two temperature measuring resistance elements are arranged along the direction of fluid flow. In such a flow sensor, heat moves due to the flow of fluid and the resistance values of the two resistance temperature elements change. Therefore, a bridge circuit is used to respond to the imbalance of the resistance values of the two resistance temperature elements. A signal is generated and the flow velocity is obtained from this signal.

A fluidic flow meter is known as another type of flow meter used for a gas meter or the like. This fluidic flow meter forms a flow path expansion part by a pair of side walls on the downstream side of the nozzle part for generating a jet flow, and a return guide provided on the outside of the side wall allows the fluid passing through the nozzle part to be separated from each other. A phenomenon in which a pair of feedback flow paths that lead to the ejection port side of the nozzle section is formed along the outside of the side wall, and the fluid that has passed through the nozzle section alternately flows through the pair of feedback flow paths (this is referred to as fluidic oscillation in the present application. ) Is used to measure the fluid flow rate based on the frequency and period of fluidic oscillation. A pressure sensor is often used as a sensor for detecting fluidic oscillation in this fluidic flow meter, but it is also possible to use a flow sensor as disclosed in Japanese Patent Laid-Open No. 4-58111.

However, since the flow sensor is an active sensor that emits heat and requires a large amount of electric power, it cannot be continuously used when it is used in a battery-driven device such as a gas meter. There was a problem. To solve this problem, for example, there is a method of reducing the magnitude of the supply current. However, since the output voltage of the flow sensor is proportional to the cube of the consumption current, if the consumption current is simply reduced, the sensor output voltage will decrease, and the S / N ratio will deteriorate. Therefore, an expensive circuit is required to improve the S / N ratio, and the effect of the improvement is limited. Therefore, conventionally, in a flow sensor used for a gas meter, intermittent measurement is performed by performing so-called intermittent drive in which the flow sensor is driven only when necessary, instead of continuously driving the flow sensor.

FIG. 26 is a circuit diagram showing a main part of a flow sensor configured to be driven intermittently. This flow sensor includes an upstream temperature measuring resistance element 501 and a downstream temperature measuring resistance element 50 arranged along the direction of fluid flow.
2 and. These resistance elements (sensor resistors) 501 and 502 have the same resistance value when the temperatures are the same. One end of the upstream temperature measuring resistance element 501 is connected to the constant current circuit 504 via the switch 503.
The other end of the upstream temperature measuring resistance element 501 is connected to one end of the downstream temperature measuring resistance element 502, and the other end of the downstream temperature measuring resistance element 502 is grounded. At both ends of the two temperature measuring resistance elements 501 and 502 connected in series,
Reference resistors 505, 5 connected in series and having the same resistance value
06 is connected to these temperature measuring resistance elements 501,
A bridge circuit is constituted by 502 and the reference resistors 505 and 506. RTD element 501,
The connection point of 502 and the connection point of the reference resistors 505 and 506 are connected to the input terminals of the amplifier 507, respectively. The switch 503 is controlled to be turned on and off by the drive control circuit 508.

As shown in FIG. 27A, in this flow sensor, the drive control circuit 508 intermittently operates at a constant cycle (T) and a constant duty ratio (the ratio of the switch-on time T _{on to} the cycle T). Then, the switch 503 is turned on, and the constant current circuit 504 supplies the current to the bridge circuit. In this case, the current consumption is reduced to T _on / T as compared with the case of continuous driving. The temperature measuring resistance elements 501 and 502 generate heat by themselves by this current. Here, when the flow velocity is zero, the temperature measuring resistance elements 501, 5
Since the resistance values of 02 are equal, the output of the amplifier 507 (detection signal 518) is zero. On the other hand, when the flow velocity has a certain magnitude, a difference occurs in the resistance values of the temperature measuring resistance elements 501 and 502, and this difference increases as the flow velocity increases. Therefore, the detection signal 51 output from the amplifier 507
8 has a size corresponding to the flow velocity.

[0008]

In such a conventional flow sensor, the temperature measuring resistance elements 501 and 502 are used.
Generates heat during the time (T _on ) when the switch 503 is on, and the temperature gradually rises with a thermal time constant determined by the shape of the sensor. Then, a predetermined time (hereinafter referred to as thermal response time τ) is required from the start of heat generation to the equilibrium temperature.

Therefore, under a certain flow velocity, the temperature difference between the temperature measuring resistance elements 501 and 502 is as shown in FIG.
, And the output 518 of the amplifier 507 changes as shown in FIG. 27C. Therefore,
In order to sample the output accurately, the switch-on period (T _on ) needs to be at least the time (τ) for the output 518 of the amplifier 507 to stabilize. on the other hand,
To reduce current consumption, switch off period (T _off )
is necessary. Therefore, the measurement sampling period must be at least (τ + T _off ) or more. here,
The time τ during which the output voltage of the sensor stabilizes is about tens of msec even in the case of a microflow sensor having a fast thermal response. Therefore, for example, if it is attempted to reduce the current consumption to 1/10, T _on : T = 1: 10, and it is necessary to set the sampling period to about several hundred msec.

On the other hand, in the case of intermittent driving, measurement is not possible while the switch is off. Therefore, in order to measure a flow whose flow velocity fluctuates at a high frequency like a fluidic flow meter, a response of about 100 Hz is required. It is said that That is, it is necessary to set the sampling period to about 10 msec. Therefore, it is difficult to apply the above intermittent driving method to the fluidic flowmeter. In order to improve this, it is conceivable to further reduce the shape of the flow sensor to shorten the thermal response time τ, but this is accompanied by manufacturing difficulties, and the reduction in shape also causes it to be affected by dust. Since the adverse effect becomes large, there is a practical problem.

When the flow sensor is used as a sensor for detecting the fluidic oscillation in the fluidic flow meter, as shown in FIG. 28, the oscillation frequency 511 of the fluidic oscillation increases as the flow rate increases, and The output signal 512 of the flow sensor also increases. However, the absolute value of the flow velocity is not necessary to detect the fluidic oscillation, and it is sufficient if the direction of the fluid flow is known. Therefore, in a region where the output signal 512 of the flow sensor exceeds the minimum output level 513 capable of detecting the flow velocity, useless power is consumed.

The present invention has been made in view of the above problems, and a first object thereof is to provide a thermal type flow velocity sensor capable of reducing power consumption while enabling continuous or sufficiently short period measurement. To provide.

A second object of the present invention is, in addition to the above object, a thermal type flow velocity sensor capable of further reducing power consumption when used as a sensor for detecting fluidic oscillation in a fluidic flowmeter. To provide.

[0014]

A thermal type flow velocity sensor according to claim 1 has a temperature measuring resistor which generates heat when energized and whose resistance value changes according to temperature. A sensor circuit that outputs a detection signal according to the flow velocity of the fluid based on the change in the resistance value of the temperature measuring resistor caused by the movement of the heat emitted from the resistor by the fluid, and the temperature measuring resistor. On the other hand, an intermittent heating current is supplied so that the minimum amount of heat necessary to output the minimum detection signal capable of recognizing the flow velocity from the sensor circuit is generated, and the detection signal is output. the calling of the measurement for the current required
And a current supply means for supplying the heating current in a superimposed manner .

In this thermal type flow velocity sensor, heat is released from the temperature measuring resistor, and based on a change in the resistance value of the temperature measuring resistor caused by the movement of the heat by the fluid, the fluid is discharged from the sensor circuit. A detection signal corresponding to the flow velocity of is output. Further, the current supply means intermittently generates heat to the temperature measuring resistor so that the minimum amount of heat necessary for causing the sensor circuit to output the minimum detection signal capable of recognizing the flow velocity is generated. with use current is supplied, the heating
Measurement current required for output of the detection intelligence signals supplied is overlapped with the use current. As a result, it is possible to reduce power consumption for heat generation of the temperature measuring resistor while always enabling measurement by the sensor circuit.

According to a second aspect of the present invention, there is provided a thermal type flow rate sensor according to the first aspect, wherein the current supply means supplies an intermittent heat generation current to the temperature measuring resistor. Is less than twice the thermal time constant of the temperature measuring resistor. Generally, the heater has an inherent thermal time constant (that is, the time from the start of heat generation to the equilibrium temperature) due to the heat capacity. Therefore, by intermittently supplying electric power at a cycle that is equal to or less than this thermal time constant, the temperature gradually rises and eventually reaches a certain temperature when heat generation and heat dissipation are in equilibrium. As a result, the temperature (heat generation amount) of the heater can be made substantially constant despite the intermittent power supply. The supply cycle of the intermittent heating current supplied to the temperature measuring resistor is preferably equal to or less than the thermal time constant of the temperature measuring resistor.

[0017]

[0018]

[0019]

[0020]

The thermal type flow velocity sensor according to claim 3 is provided in a flow path of the fluidic flow meter whose flow velocity changes in accordance with the fluidic oscillation, and the thermal flow velocity sensor detects the flow velocity to detect the fluidic oscillation. A sensor,
It has a temperature measuring resistor that generates heat when energized and changes its resistance value depending on the temperature.The temperature measuring resistor is generated by the movement of the heat released from this temperature measuring resistor by the fluid. Based on the change in resistance value, a sensor circuit that outputs a detection signal according to the flow velocity of the fluid, and a temperature measuring resistor are supplied with a heating current necessary for heat generation and a measurement current necessary for outputting the detection signal. The temperature measuring resistor is supplied so that the minimum amount of heat necessary to output the minimum detection signal capable of recognizing the flow velocity from the sensor circuit is generated according to the detection signal of the sensor circuit. and a current supply means for controlling the supply of heating current, the current supply means
Intermittently supplies at least the heating current to the temperature measuring resistor.
Is supplied to the sensor circuit and measured according to the detection signal from the sensor circuit.
Measured by changing the voltage applied to the temperature resistor.
It controls the supply of current to the temperature resistor .

In this thermal type flow velocity sensor, heat is released from the temperature measuring resistor, and the flow velocity of the fluid from the sensor circuit is based on the change in the resistance value of the temperature measuring resistor caused by the movement of this heat by the fluid. A detection signal corresponding to is output. Also,
By means of current supply, at least
Also, the heating current is intermittently supplied and the sensor circuit
Change the voltage applied to the temperature measuring resistor according to the detection signal of
Control the current supply to the temperature measuring resistor
To be done . When fluidic oscillation is detected by the thermal type flow velocity sensor, the absolute value of the flow velocity is not necessary, and it is sufficient if the direction of the fluid flow is known. Therefore, as described above, it is possible to further reduce the power consumption by controlling the current supplied to the temperature measuring resistor in accordance with the detection signal of the sensor circuit so that the minimum amount of heat is transferred. it can

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a cross section of a fluidic flowmeter equipped with a thermal type flow sensor according to an embodiment of the present invention. The present embodiment is an example of a fluidic flow meter used as a gas meter.

As shown in FIG. 1, this fluidic flowmeter comprises a main body 10 having an inlet portion 11 for introducing gas and an outlet portion 12 for discharging gas. A partition wall 13 is provided in the main body 10, and a gas flow path 14 is formed between the partition wall 13 and the inlet portion 11.
A gas flow path 15 is formed between the partition wall 13 and the outlet portion 12. An opening 16 is provided in the partition wall 13, and a shutoff valve 17 capable of closing the opening 16 is provided in the gas flow path 14. A solenoid 18 is fixed to the outside of the body 10, and a plunger 19 of the solenoid 18 is attached to the body 1
It penetrates the side wall of No. 0 and is joined to the shutoff valve 17. A spring 20 is provided around the plunger 19 between the shutoff valve 17 and the main body 10, and the spring 20 biases the shutoff valve 17 toward the opening 16.

In the gas passage 15, there is provided a nozzle portion 21 which allows the gas introduced from the inlet portion 11 to pass therethrough and arranges a jet flow. A rectifying member 22 for regulating the flow of gas is provided on the upstream side of the nozzle portion 21.
On the downstream side of the nozzle portion 21, a pair of side walls 23 and 24 that form an enlarged flow path are provided. This side wall 2
A predetermined space is provided between the No. 3 and No. 24, and the first No.
The target 25 and the second target 26 are disposed on the downstream side, respectively. A pair of feedback flow paths 27, 28 are formed outside the side walls 23, 24 to return the gas passing through the nozzle part 21 to the ejection port side of the nozzle part 21 along the outer circumferences of the side walls 23, 24. Guide 29
Is provided. A return guide 29 is provided between each outlet of the feedback flow paths 27 and 28 and the outlet 12.
A pair of discharge paths 31, 32 are formed by the back surface of the body and the main body 10.
Are formed. In the vicinity of the ejection port of the nozzle portion 21,
A pressure guide hole 33 leading to a thermal type flow velocity sensor for detecting switching of the flow direction of the gas passing through the nozzle portion 21,
34 are provided.

FIG. 2 is an enlarged view of a cross section including the pressure guiding holes 33 and 34 and the thermal type flow velocity sensor in FIG. As shown in this figure, on the outside of the bottom of the main body 10,
A pressure guiding tube 37 is provided which connects the pressure guiding hole 33 and the pressure guiding hole 34. The difference between the pressure in the pressure guiding hole 33 and the pressure in the pressure guiding hole 34 (hereinafter, simply referred to as the differential pressure) is detected as the flow velocity of the gas flowing in the pressure guiding tube 37 on the inner wall surface of the pressure guiding tube 37 substantially at the center. Then, by detecting the change in the flow direction, the flow direction of the gas passing through the nozzle portion 21 is switched (that is, fluidic oscillation).
A thermal type flow velocity sensor 38 for detecting is detected. Further, the pressure guiding tube 37 is covered with a case 39 fixed to the outside of the bottom of the main body 10.

FIG. 3 shows a cross section of the pressure guiding tube 37 of FIG. 2 taken along a plane parallel to the bottom of the main body 10. As shown in this figure, the flow sensor 38 disposed on the inner wall of the pressure guiding tube 37 includes a semiconductor base 40, a thin film layer (not shown) formed on the semiconductor base 40, and a thin film on the thin film. And two sensor resistors 41 and 42 for temperature measurement which are formed on the. These two resistors are connected in the direction of gas flow (arrow A
Alternatively, they are arranged along B) and are isolated from each other so that large heat transfer due to heat conduction does not occur.

Next, the general operation of the fluidic flow meter having the above-mentioned structure will be described. The gas introduced from the inlet portion 11 has a gas flow passage 14, an opening 16, a gas flow passage 15,
After passing through the flow regulating member 22 in order, it enters the nozzle portion 21. The gas that has passed through the nozzle portion 21 becomes a jet stream and is jetted from the jet outlet. The gas ejected from the ejection port flows along one side wall due to the Coanda effect. Here, first, the side wall 2
Flow along line 3. The gas flowing along the side wall 23 is further returned to the ejection port side of the nozzle portion 21 via the feedback flow passage 27, and is discharged to the outlet portion 1 via the discharge passage 31.
It is discharged from 2. At this time, the gas ejected from the nozzle portion 21 is changed in direction by the gas flowing through the feedback flow path 27, and now flows along the other side wall 24. This gas is further returned to the ejection port side of the nozzle portion 21 via the feedback flow path 28,
It is discharged from the outlet 12 through the discharge passage 32. Then,
The gas ejected from the nozzle portion 21 is changed in direction by the gas flowing through the feedback channel 28, and then flows again along the side wall 23 and the feedback channel 27. By repeating the above operation, the gas that has passed through the nozzle portion 21 performs fluidic oscillation that alternately flows through the pair of feedback flow paths 27 and 28.

The frequency (or cycle) of this fluidic oscillation has a correlation with the flow rate (flow velocity) and is detected by the flow sensor 38. That is, when the gas that has passed through the nozzle portion 21 alternately flows through the pair of feedback flow paths 27 and 28, a pressure difference is generated between the pressure guiding hole 33 and the pressure guiding hole 34 according to Bernoulli's law, and this difference is generated. The direction of pressure changes at a frequency corresponding to the flow rate (flow velocity). Therefore, in the pressure guiding tube 37, gas alternately flows in the directions of arrows A and B according to the change in the pressure difference direction. The fluidic oscillation frequency is obtained by detecting the change in the flow direction by the flow sensor 38, and the flow rate flowing through the nozzle portion 21 of the fluidic flowmeter is obtained from this.

FIG. 4 shows an outline of a sensor circuit configured to detect the fluidic oscillation frequency by using the flow sensor 38 of FIG. As shown in this figure,
The sensor resistor 41 and the sensor resistor 4 of the flow sensor 38
2 is connected in series, and constitutes a bridge circuit 50 together with the other two reference resistors 51 and 52 which are also connected in series. The sensor resistors 41 and 42 have the same resistance value under the same temperature, and the resistance value increases as the temperature rises. The reference resistors 51 and 52 are kept in the same temperature state so as to always have the same resistance value. Sensor resistor 4
Connection point a of 1, 42 and connection point b of reference resistors 51, 52
Are connected to the respective input terminals of the differential amplifier 53. The output terminal of the differential amplifier 53 is the sample and hold circuit 5.
5 and the output end of the sample hold circuit 55 is connected to the input end of the cycle detection circuit 56.
The potential difference between the connection points a and b of the bridge circuit 50 is amplified by the differential amplifier 53.

The other end of the sensor resistor 41 is connected to the reference resistor 51.
Is connected to the other end and is also connected to a current supply unit 60 which supplies a sensor drive current intermittently at a constant cycle.
The other end of the sensor resistor 42 is connected to the other end of the resistor 52 and is also grounded. Sensor resistors 41, 4
2 generates heat by itself by the current supplied from the current supply unit 60, changes its resistance value according to each temperature, and changes the resistance balance of the sensor resistors 41, 42 due to the change of the flow velocity. The potential of a is changed.

The current supply unit 60 outputs a constant sensor driving current, and a constant current circuit 61, and a switch 62 inserted and connected between the constant current circuit 61 and the bridge circuit 50.
And a switching control circuit 64 that outputs a switching signal 63 for on / off (closing / opening) control of the switch 64.

FIG. 5 shows a specific configuration of the switching control circuit 64 of the current supply section 60 shown in FIG. Further, FIG. 6 is a waveform diagram for explaining the operations of the switching control circuit 64 and the sensor resistors 41 and 42. As shown in FIG. 5, the switching control circuit 64 is
A pulse generating circuit 84 having resistors 81 and 82 and a capacitor 83 as external elements, and a monostable multivibrator 87 having a resistor 85 and a capacitor 86 as external elements are provided. The switching control circuit 64 operates as follows. That is, the pulse generator 84, the resistance value of the resistor 81 (R _A), the resistance value of the resistor 82 (R _B), and the capacitance value of the capacitor 83 (C)
A trigger pulse 88 (FIG. 6A) is generated at a period (T ₂ ) determined by the combination of the above, and is supplied to the monostable multivibrator 87. In the monostable multivibrator 87, a pulse signal having a pulse width (T ₁ ) determined by the resistance value (R _X ) of the resistor 85 and the capacitance value (C _X ) of the capacitor 86 is generated, and the switching control signal 63 ( Figure 6
(B)) is output. The switching signal 63 output from the switching control circuit 64 is applied to the base of a switch 62 composed of, for example, an NPN type transistor, and the switch 62 corresponds to the “1” and “0” levels of the switching signal 63. Turn it on and off. Thus, as shown in FIG. 6 (c), with respect to the bridge circuit 50 from the current supply unit 60, the sensor drive current (I _H) is supplied at a constant period (T ₂₎ predetermined time width for each (T ₁₎ It

Next, the operation of the sensor circuit (FIG. 4) having the above configuration will be described with reference to FIGS. 7 and 8. When the sensor drive current (I _H ) is intermittently supplied from the current supply unit 60 to the bridge circuit 50 according to the switching signal 63 (FIG. 7A), the sensor resistors 41 and 42 are in the current supply period. On the other hand, heat is stopped in the current non-supply period, and the temperature drops at a gradient determined by the thermal time constants of the sensor resistors 41 and 42. Therefore, the temperatures of the sensor resistors 41 and 42 fluctuate up and down according to the on / off state of the switch 62.

Here, the value of the period (T ₂ ) is set to the thermal time constant of 2
If the temperature is set to be equal to or less than twice or less, the temperature of the sensor resistors 41 and 42 rises stepwise as shown in FIG. It stabilizes at ₁ ). Here, the thermal time constant is 1 / e times (about 63%) of the time (thermal response time τ) from the start of heat generation to the time when a constant temperature is reached in the case of continuous energization. In this case, the temperature of the sensor resistors 41 and 42 is smoothed by the filter effect due to the heat capacity of the sensor itself, even though the power is intermittently supplied. As will be described later, this temperature (t ₁ ) is set to be equal to or higher than the minimum temperature (t _TH ) at which the minimum flow velocity in the pressure guiding tube 37 can be recognized by the output (detection signal 54) of the differential amplifier 53. Set it. Specifically, in order to satisfy this condition, the duty ratio of the switching signal 63 (that is,
The ratio of the pulse width (T ₁ ) to the period (T ₂ )) and the magnitude of the power output from the constant current circuit 61 (I _H ) are set appropriately. In addition, the power supply cycle is the sensor resistance 4
Considering the pulsation of the temperature of 1,42, it is preferable that the thermal time constant is equal to or less than the thermal time constant.

As described above, the flow velocity is measured while the sensor resistors 41 and 42 are stable at a constant temperature (t ₁ ). When there is no gas flow in the pressure guiding tube 37 of FIG. 3 (that is, when the flow rate (flow velocity) of the fluidic flow meter is zero), the heat generation amounts of the sensor resistors 41 and 42 are equal and the temperatures are equal. (FIGS. 7C and 7D). Therefore, the resistance values of the sensor resistors 41 and 42 are equal, and the potentials of the points a and b are equal (that is, the bridge circuit 5).
Since 0 becomes a balanced state), the output of the differential amplifier 53 becomes zero (FIG. 7 (e)).

On the other hand, when the gas flows in the fluidic flowmeter at a certain velocity, a fluidic oscillation occurs at a frequency corresponding to the velocity, and the gas passes through the pressure guiding tube 37 by the arrow A.
And B alternately flow (FIG. 7 (c)). Here, for example, if the direction of the gas flow at a certain moment is the direction of arrow A, the sensor resistor 42 on the leeward side.
Is higher than when the flow velocity is zero due to the heat carried by the gas flow from the sensor resistor 41 on the windward side, and the sensor resistor 41 on the windward side is cooled by the gas flow and is higher than when the temperature is zero. Also descends. Therefore, while the resistance value of the sensor resistor 41 decreases, the resistance value of the sensor resistor 42 increases, resulting in a difference between the resistance values.
This breaks the balance of the bridge circuit 50 (that is, the potential at the point a of the sensor resistors 41 and 42 becomes higher than the potential at the point b of the reference resistors 51 and 52), and the output of the differential amplifier 53 (sensing) The signal 54) increases. On the other hand, when the direction of the gas flow is in the direction of arrow B, the state is completely opposite to the above, and the potential of the connection point a of the sensor resistors 41 and 42 is the potential of the connection point b of the reference resistors 51 and 52. And the detection signal 54 decreases. Therefore, when the gas alternately flows through the pressure guiding tube 37 in the directions of arrows A and B by fluidic oscillation (FIG. 7C), the sensor resistor 4
The temperature difference between 1 and 42 fluctuates sinusoidally as shown in FIG. However, in this case, since the sensing current necessary to obtain the detection signal 54 is also intermittent, the detection signal 54 has a comb-shaped waveform as shown in FIG. The detection signal 54 (FIGS. 7 (e) and 8 (a)) is interpolated by the sample-hold circuit 55 at the missing portion of the signal to become a stepwise signal 57 as shown in FIG. Input to the detection circuit 56 to input the cycle (or frequency)
Is detected. The frequency detected here is a fluidic oscillation frequency and increases as the flow velocity of the gas flowing in the fluidic flow meter increases, as indicated by reference numeral 511 in FIG. Since the flow velocity in the pressure guiding tube 37 increases as the fluidic oscillation frequency increases, the potential difference between the connection points a and b also increases, and as shown by reference numeral 512 in FIG. The amplitude of signal 54) also increases.

As described above, according to this embodiment, the heating current is intermittently supplied to the bridge circuit 50 at a cycle of twice the thermal time constant of the sensor resistance or less, thereby shortening the sampling cycle of measurement. At the same time, the power consumption can be reduced. Therefore, it is particularly effective when the sensor is configured by the battery drive system with the flow having a short fluctuation period of the flow velocity as the measurement target.

FIG. 9 shows another embodiment of the sensor circuit configured to detect the fluidic oscillation frequency by using the flow sensor 38 of FIG. In addition to the configuration of FIG. 4, this sensor circuit further includes a constant current circuit 65 for supplying a constant sensing current (I _S ) in the current supply unit 60. The output terminal of the constant current circuit 65 is directly connected to the connection point between the sensor resistor 41 and the reference resistor 51 of the bridge circuit 50 so that the bridge circuit 50 is always supplied with the sensing current (I _S ). There is. Further, this sensor circuit is not provided with the sample hold circuit shown in FIG. 4, and the detection signal 58 output from the differential amplifier 53 is directly input to the cycle detection circuit 55.

The operation of the sensor circuit having the above configuration will be described with reference to FIG. As in the case of FIG. 4, the constant current circuit 61 supplies a constant current I _H (hereinafter, heating current I _H) to the bridge circuit 50 via a switch 62 that is turned on / off by a switching signal 63 output from a switching control circuit 64. Is intermittently supplied (see FIG. 10).
(A)). On the other hand, the bridge circuit 50 includes a constant current circuit 65.
The sensing current (I _S ) is constantly supplied from the sensor (FIG. 10B). Therefore, the waveform of the sensor drive current supplied to the bridge circuit 50 is a superposition of the heating current I _H and the sensing current I _S as shown in FIG. 10C, and the peak value of the sensor drive current is obtained. I _D is the sum of I _S and I _H.

The sensor resistors 41 and 42 are provided with a heating current I
While heating only _H supply period, heating is stopped in the non-supply period of the heating current I _H, the sensor resistors 41 and 42
The temperature of 2 drops. Therefore, similarly to the above-described embodiment (FIG. 4), if the value of the period (T ₂ ) is set to be equal to or less than twice the thermal time constant, the temperatures of the sensor resistors 41 and 42 will be as shown in FIG.
As shown in, the temperature rises stepwise and stabilizes at a substantially constant temperature (t ₁ ) when heat generation and heat dissipation are in equilibrium. The value of the period (T ₂ ) is preferably equal to or less than the thermal time constant in consideration of the pulsation of the temperature of the sensor resistors 41 and 42.

The following operation is almost the same as in the case of FIG. However, in the present embodiment, since the sensing current I _S is constantly supplied to the bridge circuit 50, the differential amplifier 5
3 is always in the output state. Therefore, the detection signal 58 from the differential amplifier 53 does not become intermittent (comb-shaped),
A smooth sinusoidal shape is obtained as indicated by a broken line indicated by reference numeral 58 in FIG. Therefore, the sample hold circuit 55 in FIG. 4 becomes unnecessary.

As described above, according to this embodiment, the heating current is intermittently supplied to the bridge circuit 50 to reduce the power consumption due to the heating current, while the sensing current is constantly supplied. Therefore, if a minimum required supply duty of the heating current to the bridge circuit 50 is secured, the sensor output can be continuously obtained, and the flow rate can be constantly measured. Therefore, the sensor circuit of the present embodiment is particularly effective for applications in which the flow velocity fluctuates at a high frequency (short cycle) as in the flow velocity measurement associated with fluidic oscillation in a fluidic flow meter.

FIG. 11 shows another embodiment of the sensor circuit configured to detect the fluidic oscillation frequency by using the flow sensor 38 of FIG. In this figure,
The same parts as those in the above embodiment (FIG. 9) are designated by the same reference numerals,
Description is omitted as appropriate.

In addition to the circuit configuration of FIG. 9, this sensor circuit further includes a switch 66 provided between the constant current circuit 65 and the bridge circuit 50 in the current supply section 60, and on / off control of the switch 66. Switching signal 6
A switching control circuit 68 that outputs 7 and a sample hold circuit 55 that is provided between the differential amplifier 53 and the period detection circuit 55 and that interpolates a missing portion of the detection signal 59 output from the differential amplifier 53. ing. The switching signal 67 is a pulse signal having a frequency (cycle T ₃ ) higher than that of the switching signal 63, and the switch 66 is turned on / off corresponding to the “1” and “0” thereof. Other configurations are the same as those in FIG. 7.

The operation of the sensor circuit having such a configuration is shown in FIG.
2 will be described. In this circuit, the heat generation current I _H flowing through the bridge circuit 50 due to the on / off operation of the switch 63 is intermittent as shown in FIG.
On the other hand, when the switch 66 is turned on and off, the sensing current I _S flowing through the bridge circuit 50 is as shown in FIG.
As shown in (b). Therefore, the bridge circuit 50
The total current supplied to the circuit has a waveform as shown in FIG. In this case, since the sensing current is also intermittent, the detection signal 59 from the differential amplifier 53 is as shown in FIG.
It becomes intermittent as shown in. The detection signal 59 is interpolated by the sample hold circuit 57 at the missing portion of the signal to become a stepped signal 57 as shown in FIG. 8B, and is further input to the cycle detection circuit 56 to have a cycle (or frequency). To be detected.

Also in this embodiment, as shown in FIG. 7B, the supply duty of the heating current (cycle T ₂
To the pulse width T ₁ and the value of the heating current I _H )
Is set so that the temperature of the sensor resistors 41 and 42 at zero flow velocity always exceeds the threshold value t _TH . This ensures measurement sensitivity that enables the minimum flow velocity detection.

As described above, according to the present embodiment, by intermittently supplying the heating current to the bridge circuit 50, not only the power consumed for heating the sensor resistors 41, 42 can be reduced. By intermittently supplying the sensing current, the current consumption due to the sensing current can also be reduced, and power can be saved more than in the case of the embodiment of FIG. Moreover, in the present embodiment, the intermittent cycle of the sensing current is shorter than the intermittent cycle of the heating current, so that the measurement sampling frequency can be made higher than in the case of FIG. It becomes possible to measure. Therefore, there is an advantage that a smooth oscillation curve can be obtained even when the fluidic oscillation frequency is considerably high, and it is particularly suitable for use as a fluidic fluid meter.

When the flow rate is calculated by the fluidic flow meter, only the frequency (fluidic oscillation frequency) of the sensor output signal (detection signal 59) is required, and its absolute value (amplitude) is not required. Therefore, the frequency can be detected even if the temperature of the sensor resistors 41 and 42 fluctuates to some extent as long as the detection signal 59 having the minimum magnitude necessary for recognizing the gas flow is obtained.

FIG. 13 shows another embodiment of the sensor circuit configured to detect the fluidic oscillation frequency by using the flow sensor 38 of FIG. In this figure, the same parts as those in the above-described embodiment (FIG. 9) are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

In this sensor circuit, the constant current circuit 6 of FIG.
Instead of 5, a backup capacitor 69 is connected and arranged. The other configuration is the same as the circuit of FIG.

In this sensor circuit, while the switch 62 is on, the constant current circuit 61 to the bridge circuit 5
When the current is supplied to 0, the capacitor 69 is charged at the same time, the capacitor 69 is discharged while the switch 62 is off, and the current is supplied to the bridge circuit 50. Therefore,
The drive current supplied to the bridge circuit 50 has a triangular waveform as shown in FIG. 14B corresponding to “1” and “0” of the switching signal 63 (FIG. 14A). In this case, the drive cycle (T ₂ ), the pulse width (T ₁ ) and the peak value of the drive current (I _D = I _S + I _H ) are determined by the switch 62.
The sensing current (I _S ) to the bridge circuit 50 is secured and the sensor resistors 41 and 4 are secured even during the off period of
The temperature curve 70 of No. 2 is set so as to always exceed the threshold value t _TH when the flow velocity is zero (FIG. 14 (c)). As a result, the differential amplifier 53 always outputs the effective detection signal 58, and at the same time, the measurement sensitivity that enables the minimum flow velocity detection is secured.

As described above, according to the configuration of this embodiment, the capacitor 69 is used instead of the constant current circuit 65 (FIG. 9) as a means for always ensuring the supply of the sensing current to the bridge circuit 50. Therefore, continuous measurement is possible while simplifying the circuit configuration.

The above four embodiments (FIG. 4, FIG. 9,
11 and 13), the case where the intermittent drive control of the flow sensor is mainly applied to the special application of detecting the fluidic oscillation frequency in the fluidic flow meter has been described, but the present invention is not limited to this, and it is not limited to a certain condition. Below, the flow rate (flow velocity) of a steady flow flowing in a certain direction
It can also be applied to detection. That is, even when the temperature of the sensor resistors 41 and 42 at the zero flow velocity fluctuates cyclically in time, the timing at which the temperature at the zero flow velocity becomes constant (specifically, the operation of the switch 63). If the sensor output (detection signal 54, etc.) is sampled at the timing (synchronized with the timing), the time variation of temperature becomes almost no problem, and the absolute value of the flow velocity of the steady flow and its change are obtained at regular intervals. It can be detected relatively accurately.

Further, in consideration of the thermal time constants of the sensor resistors 41 and 42, the bridge circuit 50 of the bridge circuit 50 is controlled so that the fluctuation range of the temperature at the zero flow velocity falls within a certain allowable range required from the measurement accuracy of the flow rate. If the intermittent drive control is performed, it is also possible to detect the change in the absolute value of the flow rate (flow velocity) of the steady flow continuously or extremely finely.

FIG. 15 shows another embodiment of the sensor circuit configured to detect the fluidic oscillation frequency by using the flow sensor 38 of FIG. In this figure, the same parts as those in the above-described embodiment (FIG. 9) are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

This sensor circuit feeds back the detection signal 54 from the differential amplifier 53 to the switching control circuit 74, and according to the level or cycle (frequency) of the detection signal 58, the duty ratio of the switching signal 73 (cycle T ₂
The ratio of the pulse width T ₁ to the pulse width) is variably controlled. Thereby, automatic control is performed so that the duty of intermittent current supply to the sensor resistors 41 and 42 changes according to the flow velocity in the pressure guiding tube 37, that is, the flow rate of the fluidic flow meter. Specifically, the control is performed so as to decrease the power supply duty to the sensor resistors 41 and 42 as the flow rate increases. The other circuit configuration is the same as that of the embodiment shown in FIG.

FIG. 16 shows the switching control circuit 7 of FIG.
4 illustrates a configuration example of No. 4. This circuit compares the voltage level of the detection signal 58 from the differential amplifier 53 with a predetermined reference voltage (V _TH ) and outputs a digital signal “0” or “1” according to the comparison result. 90 and a duty determination circuit 100 that determines the duty of power supply to the sensor resistors 41 and 42 based on the comparison result signal from the comparison circuit 90. Then, in the present circuit, the duty ratio of the switching signal 73 (pulse width T _{1 with} respect to the period T ₂ is changed according to the level of the detection signal 58).
Ratio) is variably controlled.

The comparison circuit 90 includes a diode 91 to which the detection signal 58 is input to the anode and the diode 91.
Rectifier circuit 93 composed of a capacitor 92 connected between the cathode of the
And a comparator 96 having a constant voltage power supply 95 connected to the other input end. The comparator 96 outputs the output signal 94 of the rectifier circuit 93 and the constant voltage power source 9
5 is compared with the reference voltage (V _TH ), and a comparison result signal 97 of “0” when the output signal 94 is less than V _{TH and} “1 (= V _CC )” when the output signal 94 is V _TH or more. It is designed to output.

The duty determining circuit 100 switches the counting direction (up / down) according to the comparison result signal 97, and an up / down counter 101 for counting.
A counter 102 whose count value is reset by a reset signal 108 to start counting up, a count value 103 of the up / down counter 101, and a counter 1
The count value 104 of 02 is sequentially compared, and the comparator 105 that outputs the comparison result signal 109 of "0" or "1" according to the comparison result, the inverter 106 that inverts the comparison result signal 109, and the up / down The counter 101 and the counter 102 are provided with a clock supply circuit 107 that supplies a clock signal 109 of a predetermined frequency (cycle T ₀ ).

The operation of the switching control circuit 74 having the above configuration will be described with reference to FIGS. 17 and 18.

When the flow rate of the gas flowing through the fluidic flow meter changes from a low flow rate to a high flow rate, the frequency and amplitude of the fluidic oscillation detected by the sensor circuit (FIG. 15) in the pressure guiding tube 37 gradually increase, For example, the waveform of the detection signal 58 from the differential amplifier 53 changes as shown in FIG. The detection signal 58 is half-wave rectified by the rectification circuit 93 of the comparison circuit 90, and is input to one input end of the comparator 96 as an output signal 94 having a waveform as shown in FIG. The comparator 96 outputs the output signal 94 and the reference voltage (V _TH ).
And the output signal 94 as shown in FIG.
Is less than V _TH, a comparison result signal 97 of "0" is output, and when the output signal 94 is V _TH or more, "1 (= V _CC )" is output.

The up / down counter 101 of the duty determining circuit 100 performs a count-up operation when the comparison result signal 97 is "0", and the comparison result signal 97 is "1".
When, the countdown operation is performed. Therefore, at time t ₁ when the output signal 94 exceeds V _TH , the counting direction of the up / down counter 101 is switched from up to down (FIGS. 17C, 17D, and 18A). On the contrary, when the gas flow rate of the fluidic flow meter decreases, the frequency and amplitude of the fluidic oscillation gradually decrease, and when the output signal 94 falls below V _TH , the count direction of the up / down counter 101 goes down. Switches from up to up.

FIG. 18C shows an example of the operation of such an up / down counter 101. In this figure,
Count value 103 of the up-down counter 101, at the rising edge of the clock signal 109 (FIG. 18 (b)), after increasing "i-1" from to "j", the count direction is switched at time t _1, now Is “j”, “j
-1 ", ... and so on.

On the other hand, the counter 102 has the reset signal 1
At the falling timing of 08 (FIG. 18E), the count value up to that point is reset and the count operation is started. Then, at the timing of the rising edge of the clock signal 109 (FIG. 18 (b)), it counts up like "1", "2", ... And this count value 104 (FIG. 1).
8 (d)).

The comparator 105 includes the up / down counter 1
The count value 103 of 01 and the count value 104 of the counter 102 are compared. As a result, when the former is larger than the latter, “0” is output as the comparison result signal 110,
When the former is smaller than the latter, "1" is output. For example, in FIGS. 18C and 18D, the timing (t) at which the count value 103 decreases from “j-2” to “j-3” and the count value 104 increases from “n” to “n + 1”. _{In 2} ), the count value 103 is the count value 10
If it falls below 4, the comparison result signal 110 changes from "0" to "1" at this timing (FIG. 18).
(F)). In this case, n = j-3.

The comparison result signal 110 is the reset signal 10
It is reset to "0" level at the timing of 8 (FIG. 18 (e)) and is inverted by the inverter 106. Therefore, as shown in FIG. 18 (g), the switching signal 73 having a pulse width of nT ₀ is output from the inverter 106.
Is output.

In this case, assuming that the reset signal 108 is provided for every m clock signals 109, the pulse period of the reset signal 108 is mT ₀ . Therefore, the duty ratio of the switching signal 73 is n / m.

Here, the integer n is indirectly determined corresponding to the difference between the level (magnitude of amplitude) of the detection signal 58 and the reference voltage V _TH of the comparator 96. That is, as described above, every time the level of the detection signal 58 crosses the reference voltage V _TH due to the flow rate change, the up / down counter 10
Although the count direction of 1 is switched, when the level of the detection signal 58 is lower than the reference voltage V _TH , the up / down counter 101 continues to count up, and then the count value 103 is finally performed while alternately performing countdown and countup. Converges to a large value, so n also becomes a large value, and the pulse width of the switching signal 73 (T ₁ = nT
₀ ) increases. On the other hand, when the level of the detection signal 58 exceeds the reference voltage V _TH , the up / down counter 10
1 continues the countdown, and thereafter, the count value 103 converges to a small value while performing the countup and the countdown alternately, so that the value of n also becomes small and the pulse width of the switching signal 73 becomes (T ₁ = n
T ₀ ) Reduce.

In this way, when the level (amplitude) of the detection signal 58 from the differential amplifier 53 increases as the flow rate increases, the switch 62 is switched by the switching signal 73.
When the level (amplitude) of the detection signal 58 decreases as the flow rate decreases while the ON period of the switch 62 decreases, the switch 62
The ON period of becomes longer. That is, as shown in FIG. 19, the duty change curve 111 of the power supply to the sensor resistors 41 and 42 decreases with an increase in the flow rate. Therefore, the temperature curves 112 of the sensor resistors 41 and 42 are
Also decreases with increasing flow rate. At this time, the sensor output (detection signal 58) is proportional to the electric power applied to the bridge circuit 50. Therefore, assuming that the increase rate of the sensor output accompanying the flow velocity increase is k, duty control is performed so that the supplied electric power becomes 1 / k. Is preferred.

When the power supply to the sensor resistors 41 and 42 is reduced, the temperature difference between the sensor resistors 41 and 42 is suppressed from increasing. As a result, even when the flow velocity increases, the detection signal 58 from the differential amplifier 53 is indicated by reference numeral 120 in FIG.
As shown in, it is maintained at a substantially constant level regardless of the flow rate. However, at this time, the level 120 of the detection signal 58 needs to exceed the threshold value 121 that allows the cycle (frequency) to be detected by the cycle detection circuit 56.

As described above, according to this embodiment, as shown in FIG. 20, the output voltage of the sensor circuit (the level 120 of the detection signal 58) does not control the duty of the power supply to the sensor resistors 41 and 42. In comparison with the output voltage 122 in this case, the power supplied to the sensor resistors 41 and 42 can be saved by the amount corresponding to the output voltage difference 123. Therefore, it becomes easy to realize a fluidic flowmeter using such a flow sensor by a battery drive system. Incidentally, such a configuration is possible, in the fluidic flow meter, the flow rate can be obtained only by detecting the frequency of the sensor output voltage accompanying the fluidic oscillation,
This is because it has a characteristic that it is not necessary to detect the absolute value of the sensor output voltage.

The constant current circuit 6 is also used in this embodiment.
5, the sensing current I _S to the bridge circuit 50
Is continuously supplied, so continuous measurement is possible.

FIG. 21 shows another configuration example of the switching control circuit 74 in FIG. This circuit
A rectifying circuit 130 for rectifying the detection signal 58 from the differential amplifier 53 of FIG. 15, and an output signal 1 of the rectifying circuit 130.
The level detection circuit 140 that detects the level of 36 and outputs a control signal 145 corresponding to the detected level, and the switch control signal 68 that is a pulse signal having a pulse width corresponding to the control signal 145 from the level detection circuit 140. And a duty determining circuit 150 for outputting. And
In this circuit, the duty ratio (the ratio of the pulse width T _{1 to} the period T ₂ ) of the switching signal 73 is variably controlled according to the level of the detection signal 54.

The rectifier circuit 130 includes a diode 131 to which the detection signal 58 is input at the anode end, and a diode 13.
1 is composed of a capacitor 132 inserted and connected between the cathode and the ground, and the detection signal 58 input as an AC signal is half-wave rectified to form the diode 131 and the capacitor 13.
It is designed to output from the connection point with 2.

The level detection circuit 140 includes the rectification circuit 130.
The differential rectification signal 136 from is input to one of the input terminals via the resistor 141, and a differential amplifier (op-amp) 142 is provided. The other input end of the differential amplifier 142 is connected to a constant voltage power supply 144 that outputs a constant reference voltage V _TH . The output terminal of the differential amplifier 142 is connected to the resistor 141 via the resistor 143.
Is connected to the input end of. This level detection circuit 140
Is configured to amplify a difference between the reference voltage V _TH and the rectified signal 136 and output a control signal 145 having a level corresponding to the difference.

The duty determining circuit 150 includes a resistor 8
1, 82 and a capacitor 83 as external elements, and a N-type MOS (Metal-Oxide S).
emiconductor) transistor 151 and capacitor 8
6 as an external element, and a monostable multivibrator 87. A control signal 145 from the level detection circuit 140 is applied to the gate of the MOS transistor 151, and the source-drain resistance value (R _X ′) changes according to the level of the control signal 145.

The operation of the switching control circuit 74 having the above configuration will be described with reference to FIG. When the flow rate of the gas flowing through the fluidic flow meter changes from a low flow rate to a high flow rate, the frequency and amplitude of the fluidic oscillation detected by the sensor circuit (FIG. 15) in the pressure guiding tube 37 gradually increase. Detection signal 58 from the dynamic amplifier 53
Waveform changes as shown in FIG.

The detection signal 58 is half-wave rectified by the rectifier circuit 130, and the rectified signal 1 having a waveform as shown in FIG.
36 is input to the level detection circuit 140. The differential amplifier 142 of the level detection circuit 140 includes a resistor 141
The difference between the rectified signal 136 input to one of the input terminals through the reference voltage V _TH is amplified, and the control signal 145 as shown in FIG. 22C is output.

Control signal 14 from level detection circuit 140
5 is a MOS transistor 1 of the duty determination circuit 150
51 applied to the gate of the MOS transistor 15
The source-drain resistance value (R _X ′) of 1 is controlled.
Specifically, when the level of the control signal 145 increases, R
_X is increased 'decreases, R _X when the level of the control signal 145 is reduced'.

[0089] On the other hand, the pulse generator 84, the resistance value of the resistor 81 (R _A), the resistance value of the resistor 82 (R _B), and the period determined by combination of the capacitance value of the capacitor 83 (C) (T ₂ ), A trigger pulse 88 (FIG. 22D) is generated and supplied to the monostable multivibrator 87. The monostable multivibrator 87 includes a MOS transistor 151.
Source-drain resistance (R _X ′) and capacitor 8
Pulse width determined by the product of the 6 capacitance value (C _X) (T
The pulse signal of ₁ ) is generated and this is output as the switching control signal 73 (FIG. 22 (e)).

Here, the detection signal 58 increases as the flow rate increases.
When the amplitude of the control signal 145 increases, the level of the control signal 145 input from the differential amplifier 142 of the level detection circuit 140 to the duty determination circuit 150 also increases. This allows the MOS
Since the source-drain resistance value (R _X ′) of the transistor 151 decreases and the value of the product (R _X ′ × C _X ) decreases, the pulse width of the switching signal 73 output from the monostable multivibrator 87 is T ₁ to T ₁ ′, T
It gradually decreases to ₁ ″ (FIG. 22 (e)). At this time, since the cycle (T ₂ ) of the switching signal 73 is constant, the duty of the electric power supplied to the sensor resistors 41 and 42 is eventually It is decreasing as shown in FIG.

As described above, also with the circuit configuration of this embodiment, as in the case of the above-described embodiment (FIG. 16), the control for decreasing the duty of the power supply to the sensor resistors 41 and 42 according to the increase in the flow rate is performed. 16 can be performed, and the same effect as in the case of FIG. 16 can be obtained.

In the present embodiment, the duty ratio of the switching signal 73 is variably controlled according to the level of the detection signal 58. However, as described in the description of FIG. 15, the frequency of the detection signal 58 is changed. According to the above, the duty ratio of the switching signal 73 may be variably controlled. In this case, instead of the level detection circuit 140 of FIG. 21, a frequency / voltage conversion circuit for outputting a voltage according to the frequency of the detection signal 58 is provided, and the duty determination circuit is provided by the output of this frequency / voltage conversion circuit. The source-drain resistance (R _X ′) of the MOS transistor 150 of 150 may be changed.

The embodiment described above (see FIGS. 16 and 2)
In 1), in order to change the duty ratio of the switching signal 73, the pulse period is made constant and the pulse width is changed, but the present invention is not limited to this, and conversely, the pulse width is made constant and the pulse period is changed. Can be changed, or both the pulse period and the pulse width can be changed to change the duty ratio.

FIG. 23 shows another embodiment of the sensor circuit configured to detect the fluidic oscillation frequency by using the flow sensor 38 of FIG. In this figure, the same parts as those in the above embodiment (FIG. 9) are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

This sensor circuit includes sensor resistors 41 and 4
A variable voltage power supply 75 is provided instead of the constant current circuit 61 of FIG.
Is fed back to the variable voltage power supply 75. By changing the output level of the variable voltage power supply 75 according to the level of the detection signal 58, the duty of power supply to the sensor resistors 41 and 42 is variably controlled. That is, the duty of the power supply to the sensor resistors 41 and 42 is changed by increasing or decreasing the magnitude of the supplied power itself according to the change in the flow velocity in the pressure guiding tube 37 (that is, the change in the flow rate of the fluidic flow meter). Thus, automatic control is performed. Specifically, the control is performed so that the magnitude of the power supplied to the sensor resistors 41 and 42 is reduced as the flow rate increases. The other circuit configuration is the same as that of the embodiment shown in FIG. 9, and the circuit configuration of the switching control circuit 64 is also as shown in FIG.

FIG. 24 shows an example of the circuit configuration of the variable voltage power supply 75 shown in FIG. This circuit includes a rectifier circuit 160 for half-wave rectifying the detection signal 58 which is an AC signal,
A filter circuit 170 for smoothing the rectified signal 163 output from the rectifier circuit 160, and the filter circuit 1
The sensor voltage setting circuit 180 outputs a sensor drive voltage 186 having a magnitude corresponding to the level of the smoothed output signal 174 output from the digital camera 70.

The rectifier circuit 160 includes a diode 161 to which the detection signal 58 is input at the anode and a diode 161.
Capacitor 1 connected between the cathode of 61 and ground
62, and the detection signal 58 is half-wave rectified and output.

The filter circuit 170 includes a differential amplifier (op-amp) 171 having an output terminal fed back to a negative input terminal, and a resistor 172 connected to an output terminal of the differential amplifier 171.
And a capacitor 173 inserted and connected between the other end of the resistor 172 and the ground. Differential amplifier 17
The positive input terminal of 1 is connected to the connection point between the diode 161 and the capacitor 162 of the rectifier circuit 160, and the resistor 172
The connection point between the capacitor and the capacitor 173 is the sensor voltage setting circuit 1
Connected to 80. Then, the filter circuit 170
Smooths the rectified signal 163 from the rectifier circuit 160,
The smoothed output signal 174 is output.

The sensor voltage setting circuit 180 includes a differential amplifier (op amp) 182 whose output end is feedback-connected to a negative input end via a resistor 183, and a negative input end of the differential amplifier 182 and a resistance of the filter circuit 170. Resistor 181 connected between the connection point of the resistor 172 and the capacitor 172
Is connected in series between the power source V _CC and the ground, and outputs a predetermined reference voltage V _TH from the connection point.
185 and. The positive input terminal of the differential amplifier 182 is connected to the connection point of the voltage dividing resistors 184 and 185, and the reference voltage V _TH is input. Then, the sensor voltage setting circuit 180 inverts and amplifies the difference between the smoothed signal 174 input from the filter circuit 170 and the reference voltage V _TH, and outputs the sensor drive voltage 186 according to this difference. .

The operation of the variable voltage power supply 75 (FIG. 24) and the sensor circuit (FIG. 23) including the variable voltage power supply 75 having the above-described configuration will be described with reference to FIG.

When the flow rate of the gas flowing through the fluidic flow meter changes from a low flow rate to a high flow rate, the frequency and amplitude of the fluidic oscillation detected by the sensor circuit (FIG. 23) in the pressure guiding tube 37 gradually increase, For example, the waveform of the detection signal 58 from the differential amplifier 53 changes as shown in FIG.

The detection signal 58 is half-wave rectified by the rectification circuit 160, and the rectification signal 1 having a waveform as shown in FIG.
63 and input to the filter circuit 170. In the filter circuit 170, the rectified signal 163 is smoothed,
The smoothed signal 174 as shown in FIG. 25C is output. The differential amplifier 182 inverts and amplifies the difference between the smoothed signal 174 and the reference voltage V _TH, and outputs a sensor drive voltage 186 (FIG. 25 (d)) corresponding to the difference. On the other hand, the switch 62 of the sensor circuit (FIG. 23) is similar to the case of FIG.
Switching signal 63 from switching control circuit 64
Is turned on and off with a constant duty ratio (cycle T ₂ , pulse width T ₁ ). Therefore, the sensor resistors 41, 4
2 shows a constant period (T ₂ ) as shown in FIG.
With a period of time (T ₁₎ a current flows only every, its current value, I _H 'from I _H with the flow rate increased, I _H "
It will be gradually decreased.

As described above, according to the present embodiment, the magnitude of the power supplied to the sensor resistors 41 and 42 itself decreases as the flow rate increases, so that the sensor resistor 41 as shown in FIG. , 42, the temperature curve 112 decreases as the flow rate increases. As a result, the detection signal 58 from the differential amplifier 53 is suppressed from increasing in level, and is maintained at a substantially constant level regardless of the flow velocity, as indicated by reference numeral 120 in FIG. However, also in this case, the level 120 of the detection signal 58
Duty control is performed so as to exceed the threshold value 121 (FIG. 16) at which the cycle (frequency) can be detected by the cycle detection circuit 56.

As described above, also in this embodiment, FIG.
Sensor resistor 4 corresponding to the output voltage difference 123 of
The power supply to 1, 42 can be saved.

In this embodiment, the ON period (T ₂ ) and the ON period (T ₁ ) of the switch 63 are set to be constant, and the temporal duty ratio of the heater intermittent drive is set to be constant. The duty control of the heater intermittent drive and the current control for changing the supplied power value itself can be used together. In this case, the switching control circuit 74 of FIG. 15 (specifically, the circuit configuration of FIG. 16 or FIG. 21) is used in place of the switching control circuit 64 of FIG. 23, and the detection signal 58 from the differential amplifier 53 is used for this.
May be configured to be fed back.

Further, in this embodiment, the magnitude of the current supplied to the sensor resistors 41 and 42 is variably controlled according to the level of the detection signal 58, but it is supplied according to the frequency of the detection signal 58. The magnitude of electric power may be variably controlled. In this case, instead of the rectifier circuit 160 and the filter circuit 170 of FIG. 24, a frequency / voltage conversion circuit for outputting a voltage according to the frequency of the detection signal 58 is provided, and the output of this frequency / voltage conversion circuit is provided. The sensor voltage setting circuit 180 may be input.

In each of the above embodiments, the drive power source of the bridge circuit 50 (excluding the variable voltage power source 75 of FIG. 23) is the current source, but the same applies to the voltage source. Further, in each of the above embodiments, the two sensor resistors 41 and 42 are arranged along the gas flow, but the present invention is not limited to this, and only one sensor resistor 41 may be arranged. Good. In this case, for example, in FIG. 4, another reference resistor having the same resistance value as the reference resistors 51 and 52 is always provided instead of the sensor resistor 42, and the bridge circuit 50 is configured by these four resistors. You can do it. However, in the case of such a configuration, point a
Since the potential difference between the point b and the point b is smaller than that when two sensor resistors 41 and 42 are used, the sensitivity of the sensor circuit is lowered. Therefore, when the sensitivity is more important, the method using the two sensor resistors 41 and 42 is preferable.

[0108]

As described above, according to the thermal type flow velocity sensor of the first aspect, the minimum supply signal capable of recognizing the flow velocity is sent to the temperature measuring resistor by the current supply means. In addition to supplying an intermittent heating current so that the minimum amount of heat necessary to output from
Superimposes the measurement current required to output the detection signal with the heating current
Since the power is supplied by being supplied, there is an effect that power consumption can be reduced while enabling continuous measurement. Therefore, it is particularly effective when the sensor is configured by the battery drive system with the flow having a short fluctuation period of the flow velocity as the measurement target.

According to the thermal type flow velocity sensor of the second aspect, the supply cycle of the intermittent current supplied to the temperature measuring resistor by the current supplying means is set to the thermal time constant of the temperature measuring resistor. Since the amount is twice or less, the heat generation amount of the temperature-measuring resistor can be made substantially constant although the current supply is intermittent.

[0110] Further, according to the thermal flow rate sensor according to claim 3, the current supply means, small with respect to temperature-measuring resistor
Even if the heating current is intermittently supplied, the sensor
The voltage applied to the temperature measuring resistor according to the detection signal of the circuit
Supplying current to the temperature measuring resistor by changing
Since it was decided to control , in addition to the above effects, when used as a sensor to detect fluidic oscillation in a fluidic flow meter, it is possible to optimize the heat generation amount of the temperature measuring resistor according to the flow rate, There is an effect that the power consumption can be further reduced.

[0111]

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a fluidic flowmeter including a thermal type flow sensor according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a section including a pressure guiding hole and a thermal type flow velocity sensor in FIG.

FIG. 3 is a cross-sectional view showing a state in which the pressure guiding tube of FIG. 2 is cut along a plane parallel to the bottom of the main body.

FIG. 4 is a circuit diagram showing an embodiment of a sensor circuit configured to detect a fluidic oscillation frequency using the flow sensor of FIG.

5 is a circuit diagram showing a configuration of a switching control circuit of FIG.

FIG. 6 is a timing diagram showing the operation of the switching control circuit and the sensor resistor.

FIG. 7 is a signal waveform diagram for explaining the operation of the sensor circuit of FIG.

FIG. 8 is a signal waveform diagram for explaining the operation of the sensor circuit of FIG.

9 is a circuit diagram showing another embodiment of the sensor circuit configured to detect the fluidic oscillation frequency using the flow sensor of FIG.

FIG. 10 is a timing chart for explaining the operation of the sensor circuit of FIG.

11 is a circuit diagram showing another embodiment of a sensor circuit configured to detect a fluidic oscillation frequency using the flow sensor of FIG.

FIG. 12 is a timing chart for explaining the operation of the sensor circuit of FIG.

FIG. 13 is a circuit diagram showing another embodiment of the sensor circuit configured to detect the fluidic oscillation frequency by using the flow sensor of FIG.

FIG. 14 is a timing chart for explaining the operation of the sensor circuit of FIG.

15 is a circuit diagram showing another embodiment of the sensor circuit configured to detect the fluidic oscillation frequency using the flow sensor of FIG.

16 is a circuit diagram showing a configuration of the switching control circuit of FIG.

17 is a timing chart for explaining the operation of the switching control circuit of FIG.

FIG. 18 is a timing chart for explaining the operation of the switching control circuit of FIG.

FIG. 19 is an explanatory diagram showing a relationship between a flow rate, a power supply duty, and a sensor calorific value in a fluidic flow meter using the thermal type flow sensor of the present invention.

FIG. 20 is an explanatory diagram showing a relationship between a flow rate and a sensor output voltage in the fluidic flow meter.

21 is a circuit diagram illustrating another circuit configuration example of the switching control circuit of FIG.

22 is a timing chart for explaining the operation of the switching control circuit of FIG.

23 is a circuit diagram showing another embodiment of the sensor circuit configured to detect the fluidic oscillation frequency using the flow sensor of FIG.

FIG. 24 is a circuit diagram showing a circuit configuration of the variable current circuit of FIG.

FIG. 25 is a signal waveform diagram for explaining operations of the variable current circuit and the sensor resistor of FIG. 24.

FIG. 26 is a circuit diagram showing a main configuration of a sensor circuit configured to detect a fluidic oscillation frequency using a conventional flow sensor.

FIG. 27 is an explanatory diagram showing the operation of the sensor circuit of FIG. 26.

28 is an explanatory diagram showing operating characteristics of the sensor circuit of FIG. 26. FIG.

[Explanation of symbols]

10 body 11 Entrance 12 Exit 21 Nozzle part 33, 34 Pressure guide hole 37 Pressure guide tube 38 Flow sensor 41,42 Sensor resistor 50 bridge circuit 53 Differential amplifier 54,58 detection signal 55 Sample and hold circuit 56 cycle detection circuit 61,65 constant current circuit 62, 66 switch 63,73 switching signal 64,74 switching control circuit 69 Capacitor 75 Variable voltage power supply 84 pulse generator 87 Monostable multivibrator 90 Comparison circuit 93,130,160 Rectifier circuit 96 comparator 100,150 Duty determination circuit 101 up-down counter 102 counter 105 comparator 140 level detection circuit 142, 171, 182 Differential amplifier 151 MOS transistor 170 Filter circuit 180 sensor voltage setting circuit 186 Sensor drive voltage

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Hiyama 1-12-2 Kawana, Fujisawa-shi, Kanagawa Yamatake Honeywell Co., Ltd. Fujisawa Plant (72) Inventor Go Watanabe 1-12-2 Kawana, Fujisawa, Kanagawa Issue Yamatake Honeywell Co., Ltd. Fujisawa Plant (72) Inventor Mitsuhiko Nagata 1-12-2 Kawana, Fujisawa, Kanagawa Prefecture Yamatake Honeywell Co., Ltd. Fujisawa Plant (72) Inventor Shigeru Aoshima 1-12 Kawana, Fujisawa, Kanagawa Prefecture No. 2 Yamatake Honeywell Co., Ltd. Fujisawa Factory (72) Inventor Aiji Oishi 1-12-2 Kawana, Fujisawa City, Kanagawa Yamatake Honeywell Co., Ltd. Fujisawa Factory (56) Reference JP-A-2-259527 (JP) , A) Japanese Unexamined Patent Publication No. 4-58111 (JP, A) Actual Development No. 2-32062 (JP, U) Special Table 4-505211 (JP, A) Special Table 1-50 2392 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01F 1/00-9/02

Claims (3)

(57) [Claims] 1. A temperature measuring resistor which generates heat when energized and whose resistance value changes according to temperature, and which is generated by movement of heat released from the temperature measuring resistor by a fluid. A sensor circuit that outputs a detection signal according to the flow velocity of the fluid based on a change in the resistance value of the temperature resistor, and the minimum detection signal that can recognize the flow velocity with respect to the temperature measurement resistor. The intermittent heating current is supplied so that the minimum amount of heat required to output from the sensor circuit occurs, and the measurement current required to output the detection signal is supplied.
A thermal type flow velocity sensor, comprising: a current supply unit that supplies the heating current in an overlapping manner . 2. When electricity is applied, heat is generated.
It has a temperature measuring resistor whose resistance value changes according to temperature.
Of the heat released from the temperature measuring resistor of the
Based on the change in resistance value of the temperature measuring resistor caused by
For the sensor circuit that outputs a detection signal according to the body flow rate and the temperature measuring resistor, the minimum
The maximum necessary to output the detection signal from the sensor circuit.
Intermittent heating current is applied so that a low amount of heat transfer occurs.
In addition to supplying the measurement current required to output the detection signal
A current supply means for supplying the heating current by superimposing it
And a supply cycle of the intermittent heating current supplied to the temperature measuring resistor by the current supply means is not more than twice the thermal time constant of the temperature measuring resistor. And thermal type flow velocity sensor. 3. A thermal type flow velocity sensor, which is provided in a flow path of a fluidic flow meter whose flow velocity changes with fluidic oscillation, and which detects the flow velocity for detecting fluidic oscillation, and which is energized. The resistance value of the temperature measuring resistor changes due to the movement of the heat released from the temperature measuring resistor by the fluid. Based on the above, a sensor circuit that outputs a detection signal according to the flow velocity of the fluid, and a heating current necessary for heat generation and a measurement current necessary for outputting the detection signal are supplied to the temperature measuring resistor. With
According to the detection signal of the sensor circuit, for heat generation to the temperature measuring resistor so that the minimum amount of heat necessary to output the minimum detection signal capable of recognizing the flow velocity from the sensor circuit occurs. And a current supply means for controlling the supply of current
The current supply means is less than the temperature measuring resistor.
In addition, the heating current is intermittently supplied and
The voltage applied to the temperature measuring resistor according to the detection signal of the sensor circuit.
The current to the temperature measuring resistor is changed by changing the pressure.
A thermal type flow velocity sensor characterized by controlling the supply of air.