JP3273892B2 - Flow velocity detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the use of a flow rate sensor comprising a heater element and a temperature-measuring resistance element for changing a resistance value by heat transfer caused by a fluid moving on the heater element. The present invention relates to a flow velocity detecting device that detects a flow velocity, and more particularly to a flow velocity detecting device that can constantly detect whether or not a flow velocity sensor has failed during measurement of a flow velocity.

[0002] A flow rate sensor for measuring the flow rate of a fluid requires extremely high reliability when used in a combustion control system or the like. From now on, construction of a configuration that can always detect whether or not the flow velocity sensor has failed during measurement of the flow velocity has been called for.

[0003]

2. Description of the Related Art The applicant of the present invention has disclosed in Japanese Patent Application No. 3-106528 a flow rate sensor having a semiconductor diaphragm structure which realizes high-accuracy and high-speed response.

In this flow rate sensor, as shown in FIG. 9, an opening 101 not communicating with the front side is formed in the center of the back side of the silicon substrate 100 by using anisotropic etching, so that the silicon substrate 100 has a thin wall. Diaphragm 102
Is formed, a thin-film heater element 103 is disposed at the center of the surface of the diaphragm 102, and thin-film resistance measuring elements 104 and 105 are disposed on both sides of the heater element 103. The configuration adopts a configuration in which an ambient temperature measuring resistance element 106 for measuring an ambient temperature is provided in a portion.

[0005] S shown in the figure is a diaphragm 102
Through the heater element 103
And the temperature measuring resistance elements 104 and 105 are provided so as to be thermally insulated. The material of the diaphragm 102 is silicon nitride.

[0006] The flow velocity sensor disclosed by the assignee of the present invention uses the resistance element 10 to measure the heat transfer caused by the fluid moving on the heater element 103 to be heated.
4,105 is used to detect the flow velocity of the fluid. Since it is formed on a very thin diaphragm 102 which is thermally insulated, it has an extremely fast response speed and high accuracy. It is characterized in that it can detect the flow velocity of the fluid and operates with extremely low power consumption.

When such a flow rate sensor is driven in accordance with the prior art, as shown in FIG. 10, a heater element 103, an ambient temperature measuring resistor element 106, and fixed resistors R1 and R2 constitute a Whiston bridge circuit. do it,
When the heating value of the heater element 103 is higher than a specified value determined by the ambient temperature resistance element 106, the amount of current supplied to the heater element 103 is reduced, and when it is lower, the amount of current supplied is increased. Then, the heater element 103 is heated so as to show a constant temperature rise with respect to the ambient temperature.

As shown in FIG. 11, a Whiston bridge circuit is formed by the temperature measuring resistance elements 104 and 105 and the fixed resistances R3 and R4, and a DC voltage is applied to the circuit to increase the temperature. Temperature measuring resistance element 104,10
A configuration is adopted in which the resistance change of No. 5 is taken out as a loss of the voltage balance of the Whiston bridge circuit, and a configuration is adopted in which the flow rate of the fluid is detected by amplifying it by a differential amplifier.

[0009]

However, if the flow rate sensor is driven in accordance with such a circuit configuration, even if the heater element 103 or the ambient temperature resistance element 106 fails (disconnection or short circuit), However, there was a problem that it could not be detected. And even if the temperature measuring resistance elements 104 and 105 fail (disconnection or short circuit),
There was a problem that it could not be detected.

Therefore, according to the prior art, there is a problem that the flow velocity sensor disclosed by the present applicant cannot be used where high reliability is required. The present invention has been made in view of such circumstances, and has a flow rate that includes a heater element that generates heat and a resistance temperature element that changes a resistance value by heat transfer caused by a fluid moving on the heater element. When adopting a configuration that detects the flow velocity of a fluid using a sensor, the purpose is to provide a new flow velocity detection device that can constantly detect whether or not the flow velocity sensor has failed during measurement of the flow velocity. I do.

[0011]

FIG. 1 illustrates the principle configuration of a flow velocity detecting device constructed according to the present invention. In the figure, reference numeral 1 denotes a flow rate sensor constituting the flow velocity detecting device of the present invention, and 2 denotes a sensor control device constituting the flow velocity detecting device of the present invention.

Here, the flow velocity detecting device detects the flow velocity of the fluid, and is used for detecting the flow rate of the fluid depending on the application. That is, since the flow path in which the flow velocity detecting device is installed is formed of a sufficiently durable material so that the fluid does not cause corrosion or wear, the cross-sectional area is considered to be substantially unchanged. May be. from now on,
By measuring the flow velocity, the flow rate represented by the product of the cross-sectional area and the flow velocity can also be uniquely determined, so that it is used for the flow rate detection of the fluid for the application point where the flow rate detection is required .

The flow rate sensor 1 is composed of a bridge circuit having a heater element, and changes a resistance value by a heater heating circuit 10 for heating the heater element and heat transfer caused by a fluid moving on the heater element. A sensor detection circuit 11 configured by a bridge circuit having one or a plurality of resistance temperature elements and generating a measurement signal corresponding to the resistance value of the resistance temperature element is provided.

On the other hand, the sensor control device 2
And detects the flow rate of the fluid flowing over the flow rate sensor 1 from the detection value of the flow rate sensor 1, and applies a drive signal having a specified period to the heater heating circuit 10, An application means 20 for applying a drive signal having a specified period to the sensor detection circuit 11;
Detecting means 21 for detecting whether or not the measurement signal generated by the measurement has a specified period, and outputting an abnormality when the measurement signal does not have the specified period; and using the measurement signal generated by the sensor detection circuit 11 for flow velocity measurement. Obtaining means 22 for obtaining a signal value;
Calculating means 23 for calculating the flow velocity of the fluid from the signal value obtained by the obtaining means 22;

When this configuration is adopted, the application means 2
When 0 applies a drive signal having a specified period to the heater heating circuit 10, a DC level drive signal is applied to the sensor detection circuit 11, and the application unit 20 applies a specified period to the sensor detection circuit 11. Is applied, a heater signal at a DC level is applied to the heater heating circuit 10.

The application means 20 comprises switching means for switching the DC power applied to the element to which the drive signal is applied, and driver means for switching the switching means using a clock signal generated by the CPU. May be done.

In the flow velocity detecting device according to the present invention, when the application means 20 applies a drive signal having a specified period to the heater heat generating circuit 10, the heater element responds to the drive signal. In response to this, the sensor detection circuit 11 generates a measurement signal having the same cycle as the drive signal applied by the application unit 20.

In response to the measurement signal having the periodicity, the detection means 21 detects whether the measurement signal has the same period as the drive signal applied by the application means 20 or not.
It detects whether the flow velocity sensor 1 is normal. Then, the obtaining unit 22 obtains a signal value used for the flow velocity measurement from the measurement signal while taking into account the cycle of the measurement signal. Calculate the flow velocity.

On the other hand, the application means 20 is connected to the sensor detection circuit 11
When a drive signal having a prescribed cycle is applied to the sensor signal, the sensor detection circuit 11 generates a measurement signal having the same cycle as the drive signal by periodically changing the measurement state in response to the drive signal.

Receiving the measurement signal having the periodicity, the detection means 21 detects whether the measurement signal has the same cycle as the drive signal applied by the application means 20 or not.
It detects whether the flow velocity sensor 1 is normal. Then, the obtaining unit 22 obtains a signal value used for the flow velocity measurement from the measurement signal while taking into account the cycle of the measurement signal. Calculate the flow velocity.

As described above, according to the flow velocity detecting device of the present invention, when the flow velocity of the fluid is measured using the flow velocity sensor 1, it can always be detected whether or not the flow velocity sensor 1 is out of order. Become like

The application means 20 comprises switching means for switching the DC power applied to the element to which the drive signal is applied, and driver means for switching the switching means using a clock signal generated by the CPU. In this case, even when the CPU fails, the sensor detecting circuit 11 does not generate a measurement signal having a specified period.
The failure of U can be detected.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail according to an embodiment applied to a combustion control system. FIG. 2 illustrates an example of a system configuration of a combustion control system to which the flow velocity detecting device of the present invention is applied.

This combustion control system supplies a burner 30 for burning gas, a flame detection sensor 31 for detecting whether or not the burner 30 is burning, an igniter 32 for igniting the burner 30, and a burner 30. A gas proportional valve 33 for adjusting the gas flow rate, an air proportional valve 34 for adjusting the air flow rate supplied to the burner 30, and a main pressure regulating valve 35 for adjusting the pressure of the gas supplied to the gas proportional valve 33 When,
A pilot pressure regulating valve 36 for regulating the pressure of the ignition gas supplied to the pilot burner of the burner 30, a dual shutoff valve 37 for shutting off the gas supplied to the gas proportional valve 33, and an ignition supplied to the burner 30 A pilot shut-off valve 38 having a dual configuration for shutting off a gas for use, a gas flow rate sensor 39 having a semiconductor diaphragm configuration disclosed in Japanese Patent Application No. 3-106528 by the present applicant for detecting the flow rate of gas supplied to the burner 30. , Which detects the flow rate of air supplied to the burner 30 and has a semiconductor diaphragm structure disclosed in Japanese Patent Application No. 3-106528 by the present applicant.
A combustion control device 41 that controls the combustion control system;
A temperature controller 42 that issues a heat request to the combustion control device 41 from the temperature value of the control target and the set temperature value corresponding thereto.
It is composed of

In the combustion control system shown in FIG. 2, the combustion control device 41 uses the gas flow rate obtained from the gas flow rate detected by the gas flow rate sensor 39 to make the gas proportional valve 33 mechanically different from the air proportional valve 34. The proportional valve 34 for air is mechanically and structurally separated from the proportional valve 33 for gas by using the air flow rate obtained from the air flow rate detected by the air flow rate sensor 40 while controlling the air proportionally and structurally separately. By controlling, a configuration that realizes high-precision air-fuel ratio control is adopted.

In order to realize the air-fuel ratio control, it is necessary to measure the flow rates of gas and air at high speed and with high accuracy. It is indispensable to use the above-described flow rate sensor having a semiconductor diaphragm configuration disclosed in Japanese Patent Application No. 3-106528.

FIG. 3 shows an embodiment of the control structure of the gas flow rate sensor 39 and the air flow rate sensor 40 constructed according to the present invention. In the following, the gas flow rate sensor 39 and the air flow rate sensor 40 will be referred to as fluid flow rate sensors 50 for convenience of description.

In the embodiment shown in FIG. 3, the fluid flow rate sensor 50 includes a heater bridge circuit 51a and a sensor bridge circuit 52a. And the combustion control device 41
A buffer 413 for transmitting a clock signal generated by the CPU 410 to the fluid flow rate sensor 50 in order to control the fluid flow rate sensor 50 in addition to the CPU 410, the A / D converter 411, and the combustion control mechanism 412. A failure detection circuit 414 for detecting an abnormality in the fluid flow rate sensor 50 and the CPU 410; and a relay contact 415 provided between the CPU 410 and the combustion control mechanism 412 and opened when the failure detection circuit 414 detects an abnormality. And

The failure detection circuit 414 is specifically,
A comparator OP that outputs a high level when the measurement signal sent from the sensor bridge circuit 52a indicates a high level, and outputs a low level when the measurement signal indicates a low level.
1, a transistor Q1 that turns on when the comparator OP1 outputs a high level and turns off when the comparator OP1 outputs a low level, and turns off when the transistor Q1 turns on and turns on when the transistor Q1 turns off Transistor Q2 and the transistor Q1 are turned on when the transistor Q1 is turned on, and turned off when the transistor Q1 is turned off.
When the transistor Q3 is activated, the relay K1 having the relay contact 415, and the transistor Q2 are turned on, the transistor Q3 is charged via the diode D1. When the transistor Q3 is turned on, the transistor Q3 is charged via the diode D2 and the relay K1. It comprises a discharging capacitor C1 and a capacitor C2 which charges the capacitor C1 via a diode D2 when the transistor Q3 turns on and discharges via a relay K1 when the transistor Q3 turns off. Is done.

On the other hand, the heater bridge circuit 51a
As shown in FIG. 10A, in addition to the conventional heater bridge circuit 60 shown in FIG. 10, a transistor Q4 for controlling whether a DC voltage is supplied to the heater bridge circuit 60, and a combustion control device 41 Of the transistor Q4 according to a control signal sent from the
And a driver DR1 for controlling the / OFF operation. Here, as shown in FIG. 9, reference numeral 103 denotes a heater element formed on the diaphragm 102, and reference numeral 106 denotes an ambient temperature measuring resistance element formed on the silicon substrate 100.

Further, the sensor bridge circuit 52a is configured as shown in FIG.
As shown in (b), it is constituted by the conventional sensor bridge circuit 61 shown in FIG. Here, as shown in FIG. 9, reference numerals 104 and 105 denote temperature measuring resistance elements formed on the diaphragm 102.

In the embodiment of FIG. 3 configured as described above,
The CPU 410 of the combustion control device 41 generates a specified periodic signal by dividing the clock signal, and transmits the periodic signal via the buffer 413 to the driver DR1 of the heater bridge circuit 51a of the fluid flow rate sensor 50. To send to.

In response to the transmission of the periodic signal, the heater bridge circuit 51a turns on / off the transistor Q4 in accordance with a prescribed cycle, whereby the transistor Q4
While the transistor Q4 is in the OFF operation, the heater element 103 is heated so as to show a constant temperature rise from the ambient temperature detected by the ambient temperature measuring resistance element 106, and while the transistor Q4 is in the OFF operation. Then, the heating operation is stopped.

As shown in FIG. 9, the heater element 1
03 is formed on the diaphragm 102 made of a thin film of silicon nitride, and can be heated to a desired temperature in a very short time. It can be achieved.

In response to the temperature rise of the heater element 103, the temperature measuring resistance elements 104 and 105 are caused by the flow of the fluid when the heater element 103 is heated to show a constant temperature rise from the ambient temperature. The resistance value is changed according to the heat transfer, and in response thereto, the sensor bridge circuit 52a outputs a voltage corresponding to the change in the resistance value while the heater element 103 is being heated, and is not heated. During this time, this voltage output is stopped.

In this way, the sensor bridge circuit 52a of the fluid flow rate sensor 50 outputs a measurement signal having the same cycle as the cycle signal sent by the CPU 410.

Upon receiving the measurement signal output from the sensor bridge circuit 52a, the CPU 410, as shown in FIG. 5, sets the A / D at the time when a specified time has elapsed from the edge of the periodic signal sent to the heater bridge circuit 51a. Converter 4
By reading the digital value of the measurement signal output by the sensor 11, a normal voltage output output by the sensor bridge circuit 52 a is obtained, and the obtained voltage output is used by using the voltage output.
Is calculated.

On the other hand, upon receiving the measurement signal output from the sensor bridge circuit 52a, the measurement signal is transmitted to the CPU 410.
If the measurement signal indicates a high level, the charge of the capacitor C1 is determined by the failure detection circuit 414 of the combustion control device 41 to
The relay K1 is turned on by discharging on the route of the diode D2, the relay K1, and the transistor Q3, and the capacitor C2 is charged by discharging on the route of the diode D2, the capacitor C2, and the transistor Q3. Indicates that the capacitor C2
Is discharged through the route of the capacitor C2 and the relay K1, thereby turning on the relay K1 and repeating the process of the power supply charging the capacitor C1 through the route of the transistor Q3, the diode D1, and the capacitor C1. Therefore, the relay K1 always operates ON.

On the other hand, as shown in FIG. 6, when the heater element 103 and the temperature measuring resistance elements 104 and 105 fail (disconnection or short circuit), the fluid flow rate sensor 50 fails or the CPU 410 fails. The measurement signal output from the sensor bridge circuit 52a is
10 does not have the same cycle as the periodic signal issued by the relay K1, the repetitive operation is interrupted, and the relay K1 is turned off.
Is turned off, whereby the relay contact 415 is opened, and the combustion control mechanism 412 enters a prescribed fail-safe operation.

As described above, according to the present invention, when measuring the flow velocity of the fluid using the fluid flow velocity sensor 50, it is determined whether the fluid flow velocity sensor 50 is out of order. This makes it possible to always detect whether the CPU 410 of the combustion control device 41 is out of order.

FIG. 7 shows another embodiment of the control structure of the fluid flow rate sensor 50 constructed according to the present invention. In the embodiment shown in FIG. 7, the fluid flow rate sensor 50 includes a heater bridge circuit 51b and a sensor bridge circuit 52b.

Then, the combustion control device 41 includes a CPU 41
0, the A / D converter 411, and the combustion control mechanism 412, as well as the CPU 4 for controlling the fluid flow rate sensor 50.
The apparatus includes a buffer 413 for sending the clock signal generated by 10 to the flow rate sensor for fluid 50, and a failure detection circuit 416 for detecting an abnormality of the flow rate sensor for fluid 50 and the CPU 410.

The failure detection circuit 416 is, specifically,
A comparator OP that outputs a high level when the measurement signal sent from the sensor bridge circuit 52b indicates a high level, and outputs a low level when the measurement signal indicates a low level.
1; a transistor Q1 which is turned on when the comparator OP1 outputs a high level; and a transistor Q1 which is turned off when the comparator OP1 outputs a low level. The timer is cleared when the transistor Q1 is turned on. The watchdog timer circuit 417 notifies the combustion control mechanism 412 of an abnormal state when the timer value exceeds a specified value.

On the other hand, the heater bridge circuit 51b
As shown in (a), it is constituted by the conventional heater bridge circuit 60 shown in FIG. Here, as shown in FIG. 9, reference numeral 103 denotes a heater element formed on the diaphragm 102, and reference numeral 106 denotes an ambient temperature measuring resistance element formed on the silicon substrate 100.

Further, the sensor bridge circuit 52b is configured as shown in FIG.
As shown in FIG. 11B, in addition to the conventional sensor bridge circuit 61 shown in FIG. 11, a transistor Q2 for controlling whether a DC voltage is supplied to the sensor bridge circuit 61, and a combustion control device 41 ON / OFF of the transistor Q2 in accordance with the control signal sent from the buffer 413 of FIG.
And a driver DR1 for controlling the OFF operation.
Here, as shown in FIG. 9, reference numerals 104 and 105 denote temperature measuring resistance elements formed on the diaphragm 102.

In the embodiment of FIG. 7 configured as described above,
The CPU 410 of the combustion control device 41 generates a specified periodic signal by dividing the frequency of the clock signal, and transmits the periodic signal via the buffer 413 to the driver DR1 included in the sensor bridge circuit 52b of the fluid flow rate sensor 50. To send to.

In response to the transmission of the periodic signal, the sensor bridge circuit 52b turns on / off the transistor Q2 in accordance with the specified cycle, thereby the transistor Q2
While the 2 is ON, enter the regular measurement mode,
A normal voltage corresponding to the flow velocity of the fluid is output, and while the transistor Q2 is in the OFF operation, the measurement mode for checking is entered and the output of this voltage is stopped.

In this way, the sensor bridge circuit 52b of the fluid flow rate sensor 50 outputs a measurement signal having the same cycle as the cycle signal sent by the CPU 410.

In response to the measurement signal output from the sensor bridge circuit 52b, the CPU 410, as in the embodiment of FIG. By reading the digital value of the measurement signal output from the / D converter 411, a normal voltage output output from the sensor bridge circuit 52b is obtained, and using this, the fluid flow rate sensor 5 is used.
The flow velocity of the fluid flowing over zero is calculated.

On the other hand, upon receiving the measurement signal output from the sensor bridge circuit 52b, the measurement signal is transmitted to the CPU 410.
In the failure detection circuit 416 of the combustion control device 41, the timer value of the watchdog timer circuit 417 is cleared without exceeding the specified value in accordance with the periodic ON operation of the transistor Q1 when the periodic signal issued by Since the process is repeated, the abnormal state is not notified to the combustion control mechanism 412.

On the other hand, the heater element 103 and the temperature measuring resistance elements 104 and 105 are out of order (disconnection or short circuit).
Doing so may cause the fluid flow rate sensor 50 to fail,
If the sensor 410 fails, the sensor bridge circuit 5
When the measurement signal output from 2b does not have the same cycle as the cycle signal issued by the CPU 410, this repetitive operation is interrupted, and the timer value of the watchdog timer circuit 417 exceeds a specified value, so that the combustion control mechanism 412 Abnormal condition is notified.

As described above, according to the present invention, when the flow velocity of the fluid is measured using the flow velocity sensor for fluid 50, it is determined whether or not the flow velocity sensor for fluid 50 is out of order. Therefore, it is possible to always detect whether or not the CPU 410 of the combustion control device 41 is out of order.

Although the present invention has been disclosed in accordance with the illustrated embodiment,
The present invention is not limited to this. For example, in the embodiments, the present applicant has disclosed the present invention in accordance with a flow rate sensor having a semiconductor diaphragm structure disclosed in Japanese Patent Application No. 3-106528, but the present invention is applicable to a flow rate sensor having a semiconductor diaphragm structure. It is not limited.

[0054]

As described above, according to the present invention,
When adopting a configuration in which a flow rate of a fluid is detected using a flow rate sensor composed of a heater element and a temperature measuring resistance element that changes a resistance value by heat transfer caused by a fluid moving on the heater element. ,
During the measurement of the flow velocity, it is possible to always detect whether or not the flow velocity sensor is out of order.

When the CPU is mounted, it is possible to always detect whether or not the CPU has failed.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a system configuration example of a combustion control system to which the present invention is applied.

FIG. 3 is an embodiment of the present invention.

FIG. 4 is an embodiment of a bridge circuit.

FIG. 5 is an operation explanatory diagram of the embodiment.

FIG. 6 is an operation explanatory diagram of the embodiment.

FIG. 7 is another embodiment of the present invention.

FIG. 8 is an embodiment of a bridge circuit.

FIG. 9 is an explanatory diagram of a flow rate sensor disclosed by the present applicant.

FIG. 10 is an explanatory diagram of a flow rate sensor disclosed by the present applicant.

FIG. 11 is an explanatory diagram of a flow rate sensor disclosed by the present applicant.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 flow velocity sensor 2 sensor control device 10 heater heating circuit 11 sensor detection circuit 20 applying means 21 detecting means 22 obtaining means 23 calculating means

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-230808 (JP, A) JP-A-4-113228 (JP, A) JP-A-2-22514 (JP, A) JP-A-2-230 213767 (JP, A) JP-A-3-172716 (JP, A) JP-A-3-33619 (JP, A) JP-A-64-28522 (JP, A) JP-A-64-25722 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/68-1/699 G01F 25/00

Claims (3)

(57) [Claims] 1. A flow rate sensor comprising: a heater element that generates heat; and one or a plurality of resistance temperature elements that change a resistance value by heat transfer caused by a fluid moving on the heater element, A flow rate detecting device for detecting a flow rate of a fluid based on a resistance value of the temperature measuring resistance element, an applying means for applying a drive signal for heat generation having a specified period to the heater element; Detecting means for receiving, as an input, a measurement signal generated in accordance with the resistance value, detecting whether or not the cycle of the measurement signal matches the cycle of the drive signal, and outputting an abnormality when the cycle does not match. The flow rate is measured from the measurement signal while taking into account the period of the measurement signal, with the measurement signal generated according to the resistance value of the resistance temperature element as an input. And a means for obtaining a signal value for use in the flow rate detection. 2. A flow rate sensor comprising: a heater element that generates heat; and one or more temperature-measuring resistance elements that change a resistance value by heat transfer caused by a fluid moving on the heater element. A flow rate detecting device for detecting a flow rate of a fluid based on a resistance value of the resistance temperature element, an application unit configured to apply a drive signal for measurement having a specified period to the resistance temperature element; The measurement signal generated according to the signal level of the resistance element and the resistance value of the resistance element is input, and it is detected whether or not the cycle of the measurement signal matches the cycle of the drive signal. Detection means for outputting an abnormality when not performed, and a measurement signal generated according to a signal level of the drive signal and a resistance value of the temperature measuring resistance element as an input. Obtaining means for obtaining a signal value used for flow rate measurement from the measurement signal while taking into account the cycle of the measurement signal. 3. The flow velocity detecting device according to claim 1, wherein the applying means switches a DC power supply applied to an element to which the drive signal is applied, and a CP.
A flow rate detection device, comprising: driver means for performing a switching operation of the switching means using a clock signal generated by U.