JP5260436B2 - Thermal flow meter with diagnostic function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To overcome the problem in a conventional thermal type flowmeter that is lacking in consideration related to a failure of a control circuit, although it can determine the failure of a detecting element. <P>SOLUTION: A heating element temperature control system is composed of a heating element 3, a heating element temperature detection means 5, a subtraction unit 9, an integrator 10, a subtraction unit 7 and a heating element driving means 6, and disturbance generated by a disturbance generator 8 is input to the heating element temperature control system in such a manner that the disturbance is subtracted from an output of the integrator 10 by the subtraction unit 7. A failure of the heating element temperature control system is determined in a failure decision means 11 by comparing an output of the disturbance generator 8 with the output of the integrator 10. When the failure decision means 11 determines the failure, a flow rate signal is fixed to the ground potential by a switching circuit 13. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a thermal flow meter, and more particularly to a thermal flow meter that can detect a failure of a control system (a heating element temperature control system) that controls the temperature of a heating element.

  As a conventional example capable of detecting a failure of the heating element temperature control system, there is a heating resistor type flow meter described in Japanese Patent Application Laid-Open No. 2005-308665. In this conventional example, the output voltage of the heating element driving means is observed, and a failure of the heating element temperature control system is detected based on whether or not the output voltage is within a predetermined range.

JP 2005-308665 A

  In a thermal flow meter that heats a heating element to a certain temperature and detects the flow rate from the temperature difference between the upstream and downstream, if the heating element temperature control system that heats the heating element to a certain temperature fails, the sensitivity of the flow meter becomes zero. On the contrary, the sensitivity becomes abnormally large. In order to cope with this, in the conventional example, the output voltage of the heating element driving means is observed, and it is determined whether or not the output voltage is within a predetermined range, thereby determining the failure of the heating element temperature control system. If it is determined, the system can notify the system side of the failure by fixing the flow rate output to the ground potential.

  However, in the above conventional example, although it is possible to determine the failure of the detection element, there is a lack of consideration regarding the failure of the control circuit.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thermal flow meter that can detect a failure of a detection element and a control circuit with high accuracy.

In order to solve the above problems, a heating element that is disposed in a fluid and generates heat by flowing current, heating element temperature detection means for detecting the temperature of the heating element, and output of the heating element temperature detection means Based on heating element driving means for supplying current to the heating element, upstream and downstream temperature detection means provided on the upstream side and downstream side of the heating element, respectively, and outputs of the upstream and downstream temperature detection means And a flow rate detection means for outputting a fluid flow rate signal, wherein a disturbance is superimposed on a heating element temperature control system comprising the heating element, the heating element temperature detection means, and the heating element drive means. providing a disturbance superimposing means, and a failure determination means for determining a failure by the disturbance superimposing means is for comparing the internal signal of the heating element temperature control system with the disturbance signal to be superimposed on the heating element temperature control system for

  ADVANTAGE OF THE INVENTION According to this invention, the thermal type flow meter which can detect the failure of the detection element and control circuit of a thermal type flow meter with high precision can be provided.

The block diagram of the thermal type flow meter of a 1st Example. The internal signal waveform of the thermal type flow meter of the first embodiment. The top view of the detection element 14 of the thermal type flow meter of a 2nd Example. The block diagram of the thermal type flow meter of a 2nd Example. The top view of the detection element 14 of the thermal type flow meter of a 3rd Example. The block diagram of the thermal type flow meter of a 3rd Example. The block diagram of the thermal type flow meter of a 4th Example. The block diagram of the thermal type flow meter of a 5th Example. The block diagram of the thermal type flow meter of a 6th Example. The block diagram of the thermal type flow meter of a 7th Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  A thermal flow meter according to a first embodiment of the present invention will be described with reference to FIGS. 1 is a block diagram of the thermal flow meter of the first embodiment, and FIG. 2 is an internal signal waveform of the thermal flow meter of the first embodiment.

  The configuration of the thermal flow meter will be described with reference to FIG. The detection element 1 of the present thermal flow meter includes a heating element 3 that generates heat by flowing current, heating element temperature detection means 5 that detects the temperature of the heating element 3, and upstream that detects the temperature upstream of the heating element 3. The side temperature detecting means 2 and the downstream temperature detecting means 4 for detecting the temperature on the downstream side of the heating element 3 are configured. The control circuit includes a subtractor 9 for obtaining a difference between the output of the heating element temperature detecting means 5 and a reference value, an integrator 10 for integrating the output of the subtractor 9, a disturbance generator 8 for generating a disturbance, an integration A subtractor 7 for obtaining a difference between the output of the generator 10 and the disturbance generator 8, heating element driving means 6 for passing a current to the heating element 3 in accordance with the output of the subtractor 7, and an output and integration of the disturbance generator 8 Failure of the heating element temperature control system constituted by the heating element 3, the heating element temperature detecting means 5, the subtractor 9, the integrator 10, the subtractor 7, and the heating element driving means 6 by comparing the outputs of the generator 10 A failure determination unit 11 for determining the flow rate, a flow rate detection unit 12 for detecting a flow rate from outputs of the upstream temperature detection unit 2 and the downstream temperature detection unit 4, and a flow rate signal when the failure determination unit 11 determines a failure. The switching circuit 13 is fixed to a potential.

  In the thermal flow meter of the present embodiment, a disturbance is generated by the disturbance generator 8 in order to determine a failure of the heat generating body control system, and a signal in which the disturbance is superimposed on the output of the integrator 10 is generated by the subtractor 7. Then, a signal in which this disturbance is superimposed is applied to the heating element driving circuit 6. The internal signal waveform at this time is shown in FIG. In this embodiment, the disturbance generator 8 generates a trapezoidal wave disturbance as shown in FIG. 2 and applies it to the heating element driving means 6 via the subtractor 7. At this time, when the frequency of the trapezoidal wave is lower than the response frequency of the heating element temperature control system, the output signal of the heating element driving means 6 and the temperature of the heating element 3 hardly change by the action of the heating element temperature control system. This is because the influence of the disturbance is reduced by the loop gain of the heating element temperature control system. For this reason, the output of the integrator 10 becomes a signal having the same magnitude as the output of the disturbance generator 8. In other words, if some part of the heating element temperature control system fails, the output of the integrator 10 and the output of the disturbance generator 8 do not become the same. Therefore, the failure of the heating element temperature control system can be determined by comparing the output of the disturbance generator 8 and the output of the integrator 10. The failure determination means 11 synchronously detects the output of the integrator 10 with a trapezoidal wave that is an output signal of the disturbance generator 8 in order to determine the failure with higher accuracy, and this synchronous detection output is within a predetermined range. Confirmed that there was a failure. Note that if a repetitive signal such as a trapezoidal wave, a square wave, a triangular wave, or a sine wave is used as the output signal of the disturbance generator 8, synchronous detection of the output of the integrator 10 can be easily performed.

  Further, the frequency component of the output signal of the disturbance generator 8 was made sufficiently lower than the response frequency of the heating element temperature control system. By doing so, the temperature change of the heating element 3 can be made sufficiently small. This is because the temperature change of the heating element 3 due to the output signal of the disturbance generator 8 can be suppressed by the action of the heating element temperature control system up to the response frequency of the heating element temperature control system. The output signal of the disturbance generator 8 is preferably a trapezoidal wave, a triangular wave, a sine wave or the like with a small number of high frequency components. By doing so, the temperature change of the heating element 3 can be further suppressed.

  Further, in the present embodiment, there is no influence on the flow rate output because there is no change in the temperature of the heating element 3 even if a disturbance is superimposed. That is, the flow rate signal can be normally output in a state where the disturbance is superimposed. For this reason, it is possible to carry out failure determination of the heating element temperature control system by always superimposing disturbances.

  Further, the frequency of the output signal of the disturbance generator 8 was set higher than the response frequency of the flow rate detection means 12. By doing so, even if the temperature change of the heating element 3 occurs, the influence on the flow rate output can be eliminated. In order to enhance this effect, it is also possible to arrange a low-pass filter at the output of the flow rate detection means 12, and even if a temperature change of the heating element 3 occurs by arranging the low-pass filter, it will affect the flow rate output. Can be eliminated. Note that the cutoff frequency of the low-pass filter needs to be sufficiently lower than the frequency of the output signal of the disturbance generator 8.

  In the present embodiment, the switching circuit 13 is provided, and the flow rate signal is fixed to the ground potential when the failure determination unit 11 determines that a failure has occurred, but may be fixed to the power supply voltage. This is because when the flow signal of the thermal flow meter is fixed to the ground potential or the power supply voltage, the receiving system of the flow signal of the thermal flow meter can determine that the thermal flow meter has failed. Because.

  Next, a thermal type flow meter according to a second embodiment of the present invention will be described with reference to FIGS. 3 is a plan view of the detection element 14 of the thermal flow meter of the second embodiment, and FIG. 4 is a configuration diagram of the thermal flow meter of the second embodiment.

  The detection element 14 of the present thermal flow meter will be described with reference to FIG. The detection element 14 has a diaphragm 15 disposed on a flat substrate made of a material having good thermal conductivity such as silicon or ceramic, and a heating resistor 19 heated to a predetermined temperature difference on the surface of the diaphragm 15 and a heating resistor. A heating element temperature detection resistor 18 for detecting the temperature of the heating resistor 19 in the vicinity of the body 19, and temperature detection resistors 16, 17, 20, 21 as temperature detection means on both sides (upstream and downstream) of the heating resistor 19. Is forming. The heating resistor 19 is a resistor made of a polysilicon thin film, a platinum thin film, a nickel alloy thin film or the like, and generates heat when a current is passed. The heating element temperature detection resistor 18 and the temperature detection resistors 16, 17, 20, and 21 are resistors made of a polysilicon thin film, a platinum thin film, a nickel alloy thin film, etc., and the resistance value of these resistors is the temperature. The heating element temperature detection resistor 18 detects the temperature of the heating resistor 19, and the temperature detection resistors 16, 17, 20, and 21 detect the temperatures upstream and downstream of the heating resistor 19. To detect. Further, the heating resistor 19 is electrically connected to the outside through connection terminals 27 and 28. The heating element temperature detection resistor 18 is electrically connected to the outside through connection terminals 26 and 29, and the temperature detection resistors 16, 17, 20, and 21 are connected to the connection terminals 22, 23, 24, 25, 30, It can be electrically connected to the outside via 31, 32, 33.

  Next, the configuration of the thermal flow meter will be described with reference to FIG. This thermal type flow meter includes a heating element temperature detection resistor 18 and resistance elements 35, 36, and 37, and a bridge circuit 34 that detects the temperature of the heating resistor 19, and an amplification circuit 39 that amplifies the output voltage of the bridge circuit 34. A subtractor 9 for obtaining a difference between the output of the amplifier circuit 39 and the reference value, an integrator 10 for integrating the output of the subtractor 9, a disturbance generator 8 for generating a disturbance, and an output of the integrator 10 And subtractor 7 for obtaining the difference between disturbance generator 8 and heating element drive circuit 6 for passing a current to heating resistor 19 in accordance with the output of subtractor 7, the output of disturbance generator 8 and the output of integrator 10 The failure determination means 11 for determining the failure of the heating element temperature control system and the temperature detection resistors 16, 17, 20, 21 are detected, and the temperature difference between the upstream side and the downstream side of the heating resistor 19 is detected. To output a signal corresponding to the flow rate. 38, an amplifier circuit 40 for amplifying the output of the bridge circuit 38 constituted by a switching circuit 13 for fixing the flow rate signal to the ground potential when the failure determining means 11 determines that the failure.

  In the present embodiment, as in the first embodiment, the failure of the heating element temperature control system can be determined by comparing the output of the disturbance generator 8 and the output of the integrator 10. That is, the failure determination means 11 can be configured by a comparison circuit that compares the output of the disturbance generator 8 and the output of the integrator 10. Moreover, since the temperature of the heating resistor 19 does not change even if a disturbance is superimposed, there is no influence on the flow rate output. That is, the flow rate signal can be normally output in a state where the disturbance is superimposed. For this reason, it is possible to carry out failure determination of the heating element temperature control system by always superimposing disturbances.

  Next, a thermal flow meter according to a third embodiment of the present invention will be described with reference to FIGS. 5 is a plan view of the detection element 14 of the thermal flow meter of the third embodiment, and FIG. 6 is a configuration diagram of the thermal flow meter of the third embodiment.

  The detection element 14 of the present thermal flow meter is obtained by adding a sub-heating resistor 41 and connection terminals 42 and 43 of the sub-heating resistor 41 to the detection element 14 of the thermal flow meter of the second embodiment. The sub-heating resistor 41 generates heat when an electric current flows, and this heat generation causes a disturbance as a heat flow to the heating resistor 19.

  Next, the configuration of the thermal flow meter will be described with reference to FIG. This thermal flow meter is obtained by changing the connection destination of the disturbance generator 8 with respect to the second thermal flow meter, and the disturbance generator 8 is connected to the auxiliary heating resistor 41. The disturbance generator 8 applies a disturbance signal to the sub-heating resistor 41, and overheats the sub-heating resistor 41 with the disturbance signal, thereby giving a disturbance to the heating resistor 19. Since the output signal of the integrator 10 is changed by this disturbance signal, the failure determination means 11 can determine the failure of the heating element temperature control system by comparing the output of the disturbance generator 8 and the output of the integrator 10. .

  Even in the present embodiment, even if a disturbance is superimposed, the temperature of the heating resistor 19 does not change, so there is no influence on the flow rate output. That is, the flow rate signal can be normally output in a state where the disturbance is superimposed. For this reason, it is possible to carry out failure determination of the heating element temperature control system by always superimposing disturbances.

  Next, a thermal flow meter according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a configuration diagram of the thermal type flow meter of the fourth embodiment.

  This thermal flow meter is obtained by changing the connection destination of the disturbance generator 8 with respect to the thermal flow meter of the second embodiment, and the disturbance generator 8 is connected to the power source of the bridge circuit 34. Since the bridge circuit 34 includes the heating element temperature detection resistor 18 and the resistance elements 35, 36, and 37, the self-heating of the heating element temperature detection resistor 18 changes by applying a disturbance signal to the power supply of the bridge circuit 34. . In other words, the disturbance generator 8 changes the self-heating of the heating element temperature detection resistor 18 by applying a disturbance signal to the power supply of the bridge circuit 34, and gives a disturbance to the heating resistor 19 by this self-heating. Since the output signal of the integrator 10 is changed by this disturbance signal, the failure determination means 11 can determine the failure of the heating element temperature control system by comparing the output of the disturbance generator 8 and the output of the integrator 10. .

  Even in the present embodiment, even if a disturbance is superimposed, the temperature of the heating resistor 19 does not change, so there is no influence on the flow rate output. That is, the flow rate signal can be normally output in a state where the disturbance is superimposed. For this reason, it is possible to carry out failure determination of the heating element control system by always superimposing disturbances.

  Next, a thermal flow meter according to a fifth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a configuration diagram of the thermal flow meter of the fifth embodiment.

  This thermal flow meter is obtained by changing the connection destination of the disturbance generator 8 with respect to the thermal flow meter of the second embodiment, and the disturbance generator 8 is connected to the power source of the bridge circuit 38. Since the bridge circuit 38 is composed of the temperature detection resistors 16, 17, 20, and 21, the self-heating of the temperature detection resistors 16, 17, 20, and 21 is changed by applying a disturbance signal to the power supply of the bridge circuit 38. . That is, the disturbance generator 8 changes the self-heating of the temperature detection resistors 16, 17, 20, and 21 by applying a disturbance signal to the power supply of the bridge circuit 38, and gives a disturbance to the heating resistor 19 by this self-heating. . Since the output signal of the integrator 10 is changed by this disturbance signal, the failure determination means 11 can determine the failure of the heating element temperature control system by comparing the output of the disturbance generator 8 and the output of the integrator 10. .

  Even in the present embodiment, even if a disturbance is superimposed, the temperature of the heating resistor 19 does not change, so there is no influence on the flow rate output. That is, the flow rate signal can be normally output in a state where the disturbance is superimposed. For this reason, it is possible to carry out failure determination of the heating element control system by always superimposing disturbances.

  Next, a thermal flow meter according to a sixth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a configuration diagram of the thermal flow meter of the sixth embodiment.

  This thermal flow meter is different from the thermal flow meter of the second embodiment in that a subtractor 44 is added between the subtractor 9 and the integrator 10, and the disturbance generator 8 is added to the subtractor 44. Connected. Since the thermal flow meter superimposes a disturbance signal on the input of the integrator 10, the temperature of the heating resistor 19 changes according to the disturbance signal, so the failure determination means 11 causes the output of the disturbance generator 8 and the subtractor. The failure of the heating element temperature control system can be determined by comparing the outputs of 9.

  In this embodiment, since the temperature of the heating resistor 19 changes according to the disturbance signal, the frequency of the disturbance signal is made sufficiently higher than the response frequency of the amplifier circuit 40 so as not to affect the flow rate output. Thus, the temperature change of the heating resistor 19 due to the disturbance signal is prevented from affecting the flow rate signal due to the high frequency attenuation effect of the amplifier circuit 40. Note that the same effect can be obtained by adding an opus filter to the output of the amplifier circuit 40. Thus, in the present embodiment, the flow rate signal can be normally output in a state where the disturbance is superimposed. For this reason, it is possible to perform failure determination of the heating element temperature control system by always superimposing disturbances.

  Next, a thermal flow meter according to a seventh embodiment of the present invention will be described with reference to FIG. FIG. 10 is a configuration diagram of the thermal flow meter of the seventh embodiment.

  This thermal flow meter is configured so that the failure determination means 11 can determine whether or not the input signal of the integrator 10 is within a predetermined range as compared with the thermal flow meter of the second embodiment. In this embodiment, it is confirmed that the input of the integrator 10 is 0 if the body temperature control system is operating normally. In this embodiment, a zero-fixed failure of the amplifier circuit 39 cannot be detected, but a failure of the integrator 10, the heating element driving means 6, and the heating resistor 19 can be detected.

DESCRIPTION OF SYMBOLS 1,14 Detection element 2 Upstream temperature detection means 3 Heating body 4 Downstream temperature detection means 5 Heating body temperature detection means 6 Heating body drive means 7, 9 Subtractor 8 Disturbance generator 10 Integrator 11 Failure judgment means 12 Flow rate Detection means 13 Switching circuit 15 Diaphragm 16, 17, 20, 21 Temperature detection resistor 18 Heating element temperature detection resistor 19 Heating resistor 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 33 , 42, 43 Connection terminals 34, 38 Bridge circuits 35, 36, 37 Resistance elements 39, 40 Amplifying circuit 41 Sub heating resistor 44 Subtractor

Claims (14)

A heating element that is disposed in the fluid and generates heat by flowing an electric current, a heating element temperature detection means for detecting the temperature of the heating element, and a heating element that passes current to the heating element based on the output of the heating element temperature detection means A flow rate of outputting a flow rate signal of the fluid based on outputs of the drive means, upstream and downstream temperature detection means provided on the upstream side and downstream side of the heating element, and the upstream side and downstream temperature detection means, respectively. In a thermal flow meter having detection means,
Disturbance superimposing means for superimposing a disturbance on a heating element temperature control system constituted by the heating element, the heating element temperature detecting means, and the heating element driving means, and the disturbance superimposing means are superimposed on the heating element temperature control system . A thermal flow meter with a diagnostic function, comprising failure determination means for determining failure by comparing a disturbance signal and an internal signal of the heating element temperature control system. In the thermal type flow meter with a diagnostic function according to claim 1,
A thermal flow meter with a diagnostic function, comprising means for fixing the output of the flow rate detection means to a ground potential or a power supply voltage in accordance with the output of the failure determination means. In the thermal type flow meter with a diagnostic function according to claim 1 or 2,
The thermal flow meter with a diagnostic function, wherein the disturbance superimposing unit superimposes a disturbance on the input of the heating element driving unit. In the thermal type flow meter with a diagnostic function according to claim 1 or 2,
A sub-heating element that is arranged adjacent to the heating element and generates heat by flowing current;
The thermal flow meter with a diagnostic function, wherein the disturbance superimposing means superimposes a disturbance on the auxiliary heating element. In the thermal type flow meter with a diagnostic function according to claim 1 or 2,
The heating element temperature detecting means is constituted by a resistance bridge disposed adjacent to the heating element, and the disturbance superimposing means superimposes a disturbance on a power supply terminal of the resistance bridge of the heating element temperature detecting means. Thermal flow meter with diagnostic function. In the thermal type flow meter with a diagnostic function according to claim 1 or 2,
The upstream side and downstream side temperature detection means are constituted by a resistance bridge disposed adjacent to the heating element,
The thermal flow meter with a diagnostic function, wherein the disturbance superimposing unit superimposes a disturbance on a power supply terminal of a resistance bridge of the upstream and downstream temperature detecting units. In the thermal type flow meter with a diagnostic function according to claim 1 or 2,
The thermal flow meter with a diagnostic function, wherein the disturbance superimposing unit superimposes a disturbance on the output of the heating element temperature detecting unit. The thermal flow meter with a diagnostic function according to any one of claims 1 to 7,
The thermal flow meter with a diagnostic function, wherein the failure determining means determines a failure by comparing a disturbance signal superimposed by the disturbance superimposing means and an input signal to the heating element driving means. The thermal flow meter with a diagnostic function according to any one of claims 1 to 7,
The thermal flow meter with a diagnostic function, wherein the failure determining means determines a failure by comparing a disturbance signal superimposed by the disturbance superimposing means and a signal corresponding to an output of the heating element temperature detecting means. The thermal flow meter with a diagnostic function according to any one of claims 1 to 9,
The thermal flow meter with a diagnostic function, wherein the disturbance signal superimposed by the disturbance superimposing means is a repetitive signal. The thermal flow meter according to claim 10,
A thermal flow meter with a diagnostic function, wherein the disturbance signal superimposed by the disturbance superimposing means is a trapezoidal wave, a square wave, a triangular wave, or a sine wave. The thermal flow meter according to any one of claims 1 to 11,
A thermal flow meter with a diagnostic function, wherein a frequency of a disturbance signal superimposed by the disturbance superimposing means is lower than a response frequency of the heating element temperature control system. The thermal flow meter according to any one of claims 1 to 12,
A thermal flow meter with a diagnostic function, wherein a frequency of a disturbance signal superimposed by the disturbance superimposing unit is higher than a response frequency of the flow rate detecting unit. The thermal flow meter according to any one of claims 1 to 13,
A thermal flow meter with a diagnostic function, characterized by having a low-pass filter at the output of the flow rate detecting means so as to remove the frequency of the disturbance signal superimposed by the disturbance superimposing means.

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