JP2008241318A - Gas flow meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas flow meter which can detect a wind direction and a wind amount in an extensive wind amount range from a breeze range up to a strong wind range with high precision, and has high resistance to soiling. <P>SOLUTION: Along with forming a thermocouple 11 using a heating wire 13 and a copper foil 14 as a pair on a printed circuit board 10, a thermistor 12 is arranged on the circuit board 10, and the thermocouple 11 and the thermistor 12 are connected to a control circuit 21. Along with controlling passage of current through the heating wire 13 by an energization control circuit 16, a thermoelectromotive force according to the temperature difference between junctions 15a, 15b of the heating wire 13 with the copper foil 14 are detected along with its polarity together by a thermoelectromotive-force detection circuit 17. Thereby a wind direction and a wind amount in the breeze range can be obtained. Moreover, as to the strong wind range, a wind direction is detected with the thermocouple 11, and a wind amount is detected with the thermistor 12. It is desirable that many thermocouples are connected in series on the circuit board 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas flow meter, and more particularly to a thermal gas flow meter that measures a mass flow rate of gas that is disposed in a pipe line between a boiler combustion chamber and a blower and passes through the pipe line.

  Conventionally, for example, a wind pressure sensor as disclosed in Patent Document 1 has been widely used as means for detecting the amount of air blown into a boiler combustion chamber.

  This wind pressure sensor measures the pressure at both ends of a throttle provided in the pipe and detects the differential pressure to detect the air volume.

  As this type of air volume detection means, many techniques using a thermal mass flow meter have been proposed.

  For example, in Patent Document 2, gas or liquid is guided through a first temperature sensor, a heating element, and a second temperature sensor, respectively, and the mass flow rate is determined from the temperature signals of the two temperature sensors. In order to save energy, the heating element is operated in cycles, in the first cycle phase, the heating element is operated at a higher temperature than in the second cycle phase, and the first cycle phase is more than in the second cycle phase. A method of measuring the mass flow rate in a short time has been proposed.

  This patent document 2 is called a so-called flow sensor type mass flow meter, and uses a MEMS (Micro Electro Mechanical System) technology to form a fine temperature sensor on a semiconductor substrate, and two temperature sensors. The mass flow rate can be determined from the temperature difference.

  Patent Document 3 includes a flow rate measuring element formed on a substrate with a heating resistor and a temperature compensating resistor, and a casing that supports the flow rate measuring element and accommodates at least a drive circuit for the flow rate measuring element, The thermal air flow meter in which the flow rate measuring element is arranged in the air passage to be measured for flow rate through the casing has first and second temperature sensors for measuring temperature, and the first temperature sensor is the flow rate. There has been proposed a thermal air flow meter that is provided on a substrate of a measuring element and in which the second temperature sensor is provided inside the casing.

  In Patent Document 3, the air flow rate is calculated based on the output signal of the flow rate measuring element and the output signals of the first and second temperature sensors, and the air volume is obtained from these air flow rates.

  Further, in Patent Document 4, a thermal type including a main passage through which a fluid flows, a sub-passage for introducing a part of the fluid flowing through the main passage, and a sensor that is disposed in the sub-passage and detects the flow rate of the fluid. In the flow rate measuring device, a thermal flow rate measuring device provided with a capturing unit formed on the inner surface of the sub-passage and capturing and moving the liquid contained in the fluid has been proposed.

  In Patent Document 4, a capturing means for liquid material such as water droplets or oil droplets is formed in the sub-passage or main passage, and the captured fluid is separated from the flow rate detection sensor element by the capturing device. Through this, the liquid material such as water droplets is prevented from adhering to the sensor element for detecting the flow rate.

  Moreover, in patent document 5, the attachment of the hot-wire type wind speed sensor which outputs the signal according to the ventilation volume of the said ventilation gas from the circuit containing the resistance heating element for temperature detection and the temperature compensation resistance arrange | positioned in the flow path of ventilation gas A hot wire wind speed sensor having a structure in which the resistance heating element and the temperature compensation resistor are arranged in parallel along the flow direction of the blown gas has been proposed.

  In Patent Document 5, as shown in FIG. 15, various electronic components 102 to 106 necessary for measurement control are mounted on the upper surface of the circuit board 101, and at the lower right edge of the circuit board 101. A rectangular notch 107 is formed, and a resistance heating element 108 and a temperature compensating resistor 109 are arranged in parallel in the notch 107 so as to be separated from each other in the front-rear direction. That is, the resistance heating element 108 and the temperature compensation resistor 109 are wired in the air and fixed to the circuit board 101, and the resistance heating element 108 and the temperature compensation resistance 109 are exposed to the air to directly contact the blown gas, thereby reducing the air volume. Detected.

JP 2003-336838 A JP 2002-533663 A JP 2005-9965 A JP 2006-162631 A JP-A-8-15296

  By the way, in a boiler, combustion air is blown from the blower to the boiler combustion chamber, thereby performing a combustion operation. However, when the blower is stopped, air may flow backward from the boiler combustion chamber to the blower side. In particular, in the case of a multi-can boiler, exhaust gas from an adjacent boiler may flow from the boiler combustion chamber to the blower side through the flue. Such an exhaust gas amount is a slight air amount of about 0.01 to 0.1 m / s in terms of wind speed, but even such a small air amount can be detected together with the wind direction to protect the blower and the like. It is desirable to do.

  At the start of operation, pre-purge is performed to scavenge the boiler combustion chamber for a predetermined time. In this pre-purge, an air volume of about 5 to 10 m / s in terms of the wind speed is sent to the boiler combustion chamber. There is a risk of being aroused. In addition, it is desirable to measure not only the air volume but also the wind direction during pre-purge or combustion, so as to prevent boiler and blower malfunctions.

  However, in any of the above Patent Documents 1 to 5, even if the air volume can be detected, the wind direction cannot be detected.

  On the other hand, dust and dust are floating in the air, and such dust and dust may be directly sucked into the blower. Further, when the boiler is started, the condensed water adhering to the impeller or casing of the blower may be scattered as water droplets. Therefore, the flow meter arranged in the pipe line is required to withstand a harsh environment.

  However, in the wind pressure sensor as shown in Patent Document 1, since a throttle is provided in the pipe, it is difficult to accurately detect the air volume if the throttle is closed by dust or dust.

  In addition, in the flow sensor type mass flow meter as in Patent Document 2, the sensitivity is improved by minimizing the measurement element, but when the dust, dust, water droplets, etc. adhere to the minimum measurement element, an accurate air flow measurement is performed. I can't do that.

  The thermal air flow meter of Patent Document 3 is also vulnerable to dust, dust, water droplets, etc., as in Patent Document 2, and it is difficult to accurately detect the air volume if these dust, dust, water droplets, etc. adhere to the temperature sensor. become.

  Moreover, although the thermal flow measuring device of patent document 4 can prevent water droplet adhesion, the vulnerability of the sensor element itself does not change. That is, it is vulnerable to external factors such as dust and dust other than water droplets, and when these dust and dust adhere to the sensor element, it becomes difficult to accurately detect the air volume.

  On the other hand, as shown in FIG. 15, the hot wire type wind speed sensor disclosed in Patent Document 5 has an extremely fine resistance heating element 108 and a temperature compensation resistor 109 that are wired in the air. Requires a high level of skill and is not easy to handle during assembly due to its low mechanical strength. In addition, expensive equipment investment is required for manufacturing without manual processing, which may increase the economic burden.

  This invention is made | formed in view of such a situation, The 1st objective of this invention is to provide the gas flowmeter which can detect a wind direction at low cost. A second object of the present invention is to provide a gas flow meter with good dirt resistance that eliminates the influence of dust, dirt, water droplets and the like as much as possible. Furthermore, the third object of the present invention is to provide a gas flow meter capable of detecting the air direction and the air flow with high accuracy in a wide air flow region from a light air region to a strong air region such as pre-purge.

  In order to achieve the first object, a gas flow meter according to the present invention is a thermal gas flow meter that measures the mass flow rate of a gas that is arranged in a pipe and passes through the pipe, A sensor for generating a thermoelectromotive force between the junction points of the heating wire and the copper foil, wherein a thermocouple is formed on the substrate as a pair of heating wire that generates heat by the heating wire and the copper foil joined to the heating wire. A main body, and a control means for controlling the sensor main body, wherein the control means controls the energization control means for controlling the energization state of the heating wire, and the temperature between the junction points of the heating wire and the copper foil. A thermoelectromotive force detecting means for detecting the thermoelectromotive force according to the difference together with the polarity; and a wind direction / air volume detecting means for detecting the wind direction and the air volume based on the detection result of the thermoelectromotive force detecting means. It is a feature.

  In order to achieve the second object, the gas flow meter according to the present invention is the above-described gas flow meter, wherein the sensor body is configured such that a number of the thermocouples are connected in series on the substrate. It is a feature.

  In the gas flowmeter of the present invention, the control means has switching means for switching between an output from the heating control means and an input to the thermoelectromotive force detection means, and the heating operation to the heating wire and the The thermoelectromotive force detection operation is alternately repeated.

  Furthermore, the gas flowmeter of the present invention includes a storage unit that stores a plurality of types of energization patterns to the heating wire, and an energization pattern change unit that changes the energization pattern according to the detected thermoelectromotive force. It is characterized by having.

  Furthermore, in order to achieve the third object, the gas flow meter according to the present invention is the above gas flow meter, wherein the temperature detecting means for detecting the temperature of the substrate is arranged on the substrate. It is a feature.

  Moreover, the gas flowmeter of this invention is interposed between the boiler combustion chamber and the air blower which ventilates gas to this boiler combustion chamber.

  According to the gas flow meter, the thermoelectromotive force according to the temperature difference between the junctions of the thermocouple is detected by the thermoelectromotive force detecting means together with the polarity, and not only the air volume but also the wind direction is detected by the wind direction / air volume detecting means. Therefore, it is possible to detect the flow direction of the air in the pipe line, and to detect a slight back wind to protect the blower. In addition, since the thermocouple is formed on the substrate, it is possible to obtain a gas flowmeter having a small number of parts that is excellent in assemblability without requiring air wiring and at low cost.

  In addition, since the sensor body has a large number of thermocouples connected in series on the substrate, even if a substance that hinders measurement, such as dust, dust, or water droplets, is attached to a part of the thermocouple, Measurement errors can be suppressed, and dirt resistance can be improved.

  Further, the control means has switching means for switching between an output from the heating control means and an input to the thermoelectromotive force detection means, and the heating operation to the heating wire and the thermoelectromotive force detection operation are performed. Since it is repeated alternately, the wind direction and the air volume can be detected with high accuracy and efficiency.

  Moreover, since it has the memory | storage means which memorize | stored multiple types of electricity supply patterns to the said heating wire, and the electricity supply pattern change means which changes the said electricity supply pattern according to the said detected thermoelectromotive force, according to the air volume An energization pattern can be selected, and it is possible to avoid as much as possible that the heating wire is heated and burned out or that the heating wire is excessively cooled and the temperature difference between the thermocouple junctions is not proportional to the air volume.

  Further, since the temperature detecting means for detecting the temperature of the substrate is arranged on the substrate, the temperature difference and the air volume are generated as a result of the heating wire being supercooled in a strong wind region such as pre-purge or combustion. Even if it is not proportional, the air volume can be detected from the substrate temperature detected by the temperature detecting means. In addition, since the wind direction can always be detected by the thermoelectromotive force detection means by energizing the heating wire, the wind direction and the air volume can be detected even in a strong wind region. Furthermore, it can be monitored by the temperature detection means that the heating wire is excessively heated and burns out.

  Furthermore, since it is interposed between the boiler combustion chamber and a blower that blows gas to the boiler combustion chamber, it is possible to detect the wind direction and the amount of air with the thermoelectromotive force in a light wind region such as when the blower is stopped. In the strong wind region at the time of combustion, it is possible to detect the wind direction and the air volume by using both the heating wire energization and the substrate temperature detection by the temperature detection means. It is possible to prevent the occurrence of abnormalities.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an overall configuration diagram schematically showing an embodiment of a boiler provided with an air flow meter as a gas flow meter according to the present invention.

  That is, this boiler includes a boiler combustion chamber 2 provided with a burner 1, a chimney 3 that discharges exhaust gas from the boiler combustion chamber 2, a blower 4 that blows air as combustion gas into the boiler combustion chamber 2, and A throttle valve 5 that controls the amount of air supplied to the boiler combustion chamber 2 is provided, and a thermal air flow meter 7 is disposed in a pipe line 6 that connects the blower 4 and the throttle valve 5.

  FIG. 2 is a system configuration diagram showing a first embodiment of the air flow meter 7, and the air flow meter 7 includes a sensor main body 8 and a control unit 9 for controlling the sensor main body 8. .

  The sensor body 8 includes a thermocouple 11 formed on a printed circuit board 10 and a thermistor (temperature detection means) 12 disposed on the printed circuit board 10 in the vicinity of the thermocouple 11.

  The thermocouple 11 includes a heating wire 13 that generates heat when energized and a pair of copper foils 14 and 14 joined to the heating wire 13. Specifically, a pair of copper foils 14 is formed on the printed circuit board 10 in a pattern, and both ends of the heating wire 13 are joined to the copper foils 14 and 14. It is comprised so that a thermoelectromotive force may generate | occur | produce between the junction points 15a and 15b of the heating wire 13 and the copper foils 14 and 14. FIG.

  The metal material used for the heating wire 13 is not particularly limited as long as it generates a thermoelectromotive force with copper, but has a high resistivity and a large thermoelectromotive force with copper. It is preferably generated, and constantan (Cu: 55%, Ni: 45%), which is a kind of Cu—Ni alloy, is preferably used.

  Further, the control unit 9 controls the energization control circuit 16 that controls the energization of the heating wire 13, the thermoelectromotive force detection circuit 17 that detects the thermoelectromotive force between the junctions 15 a and 15 b together with the polarity, and the heating wire 13. Switching circuit 18 for switching input to the thermoelectromotive force detection circuit 17 from the thermocouple 11, temperature measuring circuit 19 to which the output from the thermistor 12 is input, thermoelectromotive force detection circuit 17 and measurement An A / D converter 20 that converts an analog signal from the temperature circuit 19 into a digital signal and a control circuit 21 that controls each of the above components are provided. The thermoelectromotive force detection circuit 17 incorporates a voltage amplifier (not shown) that amplifies the detection signal.

  The control circuit 21 includes an input unit 21a to which an output signal from the A / D converter 20 is input, a storage unit 21b in which a predetermined conversion map, a predetermined calculation program, and the like are stored, and a storage unit 21b. An arithmetic unit 21c that reads out a stored arithmetic program and the like and performs arithmetic processing, and an output unit 21d that outputs a predetermined signal to the energization control circuit 16 and the switching circuit 18 based on the arithmetic result of the arithmetic unit 21c. .

  In the air flow meter 7 configured as described above, when the wind speed is reduced, such as when the blower is stopped, between the junction points 15a and 15b in the thermocouple 11 in the case of a light wind region of about 0.01 to 0.1 m / s. The thermoelectromotive force according to the temperature difference ΔT is detected together with the polarity, and the wind direction and the air volume can be calculated.

  On the other hand, in the case of a strong wind range of about 5 to 10 m / s in terms of wind speed, such as during pre-purge or combustion, the heating wire 13 is exposed to strong wind and cooled. Although a temperature difference ΔT occurs, the temperature difference ΔT is no longer proportional to the earliest air volume, making it difficult to accurately measure the air volume.

  Therefore, in the strong wind region, the polarity of the thermoelectromotive force is detected based on the temperature difference ΔT, the wind direction is detected, the substrate temperature T of the printed circuit board 10 is detected by the thermistor 12, and the air volume is determined based on the detection result. Calculated.

  That is, the air flow meter 7 calculates the wind direction and the air volume by detecting the polarity and the thermoelectromotive force by the thermoelectromotive force detection circuit 17 in the light wind region, and detects the polarity by the thermoelectromotive force detection circuit 17 in the strong wind region. At the same time, the temperature measuring circuit 19 detects the substrate temperature T from the thermistor 12, thereby calculating the wind direction and the air volume.

  FIG. 3 is a diagram for explaining the detection principle of the thermoelectromotive force and polarity in the light wind region.

  FIG. 3A shows a standby state in which both the energization control circuit 16 and the thermoelectromotive force detection circuit 17 are not driven. That is, in the present embodiment, as will be described later, three kinds of energization patterns are appropriately selected according to the air blowing state, but a standby state is provided as an adjustment section for making the energization / measurement cycle constant.

  FIG. 3B shows a state in which the heating wire 13 is energized from the energization control circuit 16. The heating wire 13 exposed to the wind direction in the arrow A direction is energized in the arrow B direction, and the heating wire 13 generates heat. To do. Then, after the heating wire 13 is heated for a certain time, the switching circuit 18 switches from the energization control circuit 16 to the thermoelectromotive force detection circuit 17 as shown in FIG. 3C, and the temperature difference between the junctions 15a and 15b. A thermoelectromotive force according to ΔT is detected. That is, when the wind direction is the direction of arrow A, a positive thermoelectromotive force is generated in the direction of arrow C. On the other hand, when the wind direction is opposite to the direction of arrow A, the polarity of the thermoelectromotive force is reversed and the direction of arrow D is Negative thermoelectromotive force is generated. When a temperature difference ΔT occurs between the junction points 15a and 15b, a thermoelectromotive force proportional to the temperature difference ΔT is detected by the thermoelectromotive force detection circuit 17 together with the polarity.

  Thus, when the thermoelectromotive force according to the temperature difference ΔT is detected together with the polarity, the detection signal (analog signal) is converted into a digital signal by the A / D converter 20 and input to the control circuit 21. In this control circuit 21, the air volume is converted based on the thermoelectromotive force-air volume conversion map stored in the storage section 21c, and is transferred to the main controller of the boiler together with the wind direction for processing.

  As described above, in the present embodiment, energization to the heating wire 13 and measurement / detection of the thermoelectromotive force are alternately and repeatedly performed, and even when a small amount of air flows into the pipeline 6, The wind direction can also be detected.

  In the present embodiment, the storage unit 21b of the control circuit 21 stores three types of energization patterns as described above, and the calculation unit 21c stores the energization patterns according to the detected thermoelectromotive force. Any one of the energization patterns is selected.

  FIG. 4 is a diagram showing the relationship between the air volume, the temperature difference ΔT between the junction points 15a and 15b, and the substrate temperature T of the printed circuit board 10.

  When the air volume is in the region indicated by E in the figure, it is possible to obtain an air volume (thermal electromotive force) corresponding to the temperature difference ΔT.

  However, as described above, when the heating wire 13 is energized, the heating wire 13 generates heat. However, if the energization time is always constant, if the air flow is extremely small, the heating wire 13 may become hot and burn out. There is. On the other hand, if the air volume is relatively large even in the light wind region, the heating wire 13 is cooled, the temperature difference ΔT and the air volume are not proportional, and there is a possibility that the accurate air volume cannot be measured.

  In this way, even in the light wind region, depending on the air volume, it may be possible to cause an obstacle to the measurement of the wind direction and the air volume, and the energization pattern can be appropriately changed according to the detection signal of the thermoelectromotive force.

  FIG. 5 is a time chart of energization / measurement time in the case of moderate air volume in the light wind region, and one cycle t is constituted by the standby time t1, the energization time t2, and the measurement time t3.

  In this case, as shown in FIG. 6A, the energization time t2 is set so that the substrate temperature T does not exceed the upper limit temperature Tmax and the heating wire 13 is not excessively cooled. By setting the energization time t2 as described above, the air volume and the temperature difference ΔT can maintain a proportional relationship as shown in FIG. 6B, and the air volume (heat generation) corresponding to the temperature difference ΔT can be maintained. Power) can be detected with high accuracy together with polarity.

  FIG. 7 is a time chart of energization / measurement time when the air volume is smaller than the above-mentioned medium air volume in the light wind region. One cycle t is represented by the standby time t1 ′, the energization time t2 ′, and the measurement time t3. It is composed.

  In this case, since the air volume is extremely small, if the energization time t2 ′ is increased, the substrate temperature T may rise and the heating wire 13 may be burned as shown in FIG.

  Therefore, the energization time t2 ′ is set to a time shorter than the energization time t2 of FIG. 5 so that the heating wire 13 does not burn out. As a result, the air volume and the temperature difference ΔT can maintain a proportional relationship as shown in FIG. 8B, and the heating wire 13 is not burned out, and the air volume (thermoelectromotive force) corresponding to the temperature difference ΔT is maintained. ) Can be detected with high accuracy together with the polarity. In this case, since the energization / measurement cycle t and the measurement time t3 are set to the same time as in FIG. 5, the standby time t1 ′ is set to t1 ′> t1.

  Further, FIG. 9 shows a time chart of energization / measurement time when the air volume is slightly larger than the above-mentioned medium air volume in the light wind region, and one cycle t at standby time t1 ″, energization time t2 ″, and measurement time t3. Is configured.

  In this case, as shown in FIG. 10A, the energization time t2 ″ is set to a time longer than the energization time t2 of FIG. 5 so that the substrate temperature T is not excessively lowered and the heating wire 13 is not overcooled. As a result, the air volume and the temperature difference ΔT can maintain a proportional relationship, as shown in Fig. 10B, and the air volume (thermal electromotive force) corresponding to the temperature difference ΔT can be accurately detected together with the polarity. In this case, the energization / measurement cycle t and the measurement time t3 are set to the same time as in FIG. 5, and therefore the standby time t1 ′ is set to t1 ″ <t1.

  As described above, in the present embodiment, since the energization pattern is variably controlled according to the air volume, the air volume in the slight wind area can be detected with high accuracy along with the wind direction.

  On the other hand, in a strong wind region such as pre-purge or combustion, the air flow rate of about 5 to 10 m / s is sent to the boiler combustion chamber by the blower 4 in terms of wind speed, so the heating wire 13 is excessively cooled and the junction points 15a and 15b The temperature difference ΔT becomes smaller and the temperature difference ΔT is not proportional to the air volume. That is, a slight temperature difference ΔT occurs between the junctions 15a and 15b, so that the polarity can be detected, and therefore the wind direction can be detected. However, since the temperature difference ΔT is not proportional to the air volume, the accurate air volume cannot be obtained from the thermoelectromotive force obtained from the thermocouple 11.

  FIG. 11 is a diagram showing the relationship between the air volume in the strong wind region, the substrate temperature T, and the temperature difference ΔT, and the region indicated by F in the drawing is the strong wind region.

  That is, in the strong wind region, even when the energization time is increased to t2 ″ as shown in FIG. 9, the heating wire 13 is exposed to the strong wind, so that the substrate temperature T decreases as shown in FIG. As shown in FIG. 11B, although the temperature difference ΔT occurs, the temperature difference ΔT and the air volume are not proportional to each other, and it is difficult to accurately detect the air volume even if the wind direction can be measured only by the thermoelectromotive force method.

  Thus, as described above, in the strong wind region, the heating wire 13 is energized with the same energization pattern as in FIG. 9 and the polarity is detected by the thermoelectromotive force detection circuit 17, thereby obtaining the wind direction, while on the printed circuit board 10. The temperature of the printed circuit board 10 is detected by the thermistor 12 arranged in the circuit board. The circuit board temperature T is input to the control circuit 21 through the temperature measuring circuit 19, thereby calculating the air volume in a strong wind region such as pre-purge. .

  Thus, the air volume and direction from the light wind region to the strong wind region can be obtained. Moreover, the thermocouple 11 does not require an aerial wiring, is easy to assemble, has a small number of parts, and can provide an inexpensive air flow meter.

  FIG. 12 is a system configuration diagram showing a second embodiment of the air flow meter.

  In the second embodiment, in the sensor main body 23 of the air flow meter 22, a large number of thermocouples composed of heating wires 24 and copper foils 25 are connected in series on the printed circuit board 26, whereby the thermocouple group 27 is formed. Is formed.

  Specifically, in the thermocouple group 27, the copper foil 25 is formed in a fixed pattern on the printed circuit board 26, and the heating wires 24 are formed on the printed circuit board 26 so that a large number of thermocouples are connected in series. Many are arranged in the vertical direction in the figure. And thereby, the thermoelectromotive force according to the temperature difference of both ends will be detected between each joining point 28a, 28b of the copper foil 24 and the heating wire 24. FIG.

  In the second embodiment, the thermoelectromotive force is detected between the junction points 28a and 28b of the thermocouple group 27 in which many copper foils 25 and the heating wires 24 are connected in series on the printed circuit board 26. The output can be increased, and even if dust, dust, water droplets, etc. adhere to a part of the thermocouple group 27, the measurement error can be suppressed, and the dirt resistance can be improved. That is, when there is one thermocouple as in the first embodiment or in Patent Documents 2 to 4, measurement errors are likely to occur if dust, dust, water droplets, etc. adhere to the measurement element. In the second embodiment, since many thermocouples composed of heating wires 24 and copper foils 25 are connected in series on the printed circuit board 26 to constitute the thermocouple group 27, one of the thermocouple groups 27. Even if dust, dirt, water droplets, or the like adhere to the thermocouple of the part, the stain resistance can be improved because the joint points 28a and 28b are provided. For example, when the thermocouple group 27 is composed of n rows of serially connected thermocouples, the influence on the thermoelectromotive force is suppressed to 1 / n even if dust, dust, water droplets, etc. adhere to one thermocouple. And the dirt resistance can be improved.

  The present invention is not limited to the above embodiment.

  In the above embodiment, the energization pattern changing process is performed by the control circuit 21, but it may be configured to be variably controlled by a command from the outside, such as a boiler main controller, and the number of energization pattern switching stages. Needless to say, the number of stages is not limited to three, and may be two or more than four.

  Moreover, in the said embodiment, although air is used as medium gas, it cannot be overemphasized that it can apply also to gas flowmeters other than air.

  Furthermore, in the said embodiment, although the air flowmeter is mounted in the boiler, it is applicable also to apparatuses other than a boiler.

  Next, examples of the present invention will be described.

  The experimental apparatus shown in FIG. 13 was prototyped and the relationship between wind speed and temperature difference was examined.

  In this experimental apparatus, a gas flow meter 32 of the present invention is mounted on a polyvinyl chloride pipe 31 having a diameter of 100 mm, and the gas flow meter 32 is connected to a personal computer 36. A commercially available air flow meter 34 is interposed between the variable air volume blower 33 and the pipe line 31, and the variable air volume air blower 33 is connected to an inverter 35.

  Then, the frequency was adjusted by operating the inverter 35 while visually observing the air flow meter 34, various air volumes were sent from the variable air volume blower 33 to the pipe 31, and the air volume characteristics of the gas flow meter 32 were measured.

  In addition, the gas flowmeter used what connected 20 thermocouples which consist of copper foil and constantan (electric heating wire) in series on the printed circuit board. In addition, the energization time to the constantan is set to 0.13 seconds, the measurement time is set to 0.05 seconds, the standby time is set to 0.01 seconds, and these are set as one cycle to detect the air volume and the thermoelectromotive force at that time A temperature difference ΔT was calculated.

  FIG. 14 is a characteristic diagram, in which the horizontal axis indicates the wind speed (m / s) obtained from the air volume, and the vertical axis indicates the temperature difference ΔT (K). Further, in the figure, ♦ indicates the forward direction (G direction in FIG. 13), and ■ indicates the reverse direction (H direction in FIG. 13).

  As apparent from FIG. 14, the polarity is reversed between the forward direction and the reverse direction, and it was confirmed that the wind direction can be detected by the polarity.

  In addition, in the light wind region where the wind speed is low, the temperature difference ΔT increases in proportion to the wind speed, but it has also been found that the proportional relationship between the wind speed and the temperature difference ΔT cannot be maintained when the wind speed exceeds a certain level. This is presumably because the cooling effect of the thermocouple increases as the wind speed increases, and as a result, the wind speed and the temperature difference ΔT are not proportional.

It is a lineblock diagram showing one embodiment of a boiler provided with a gas flow meter of the present invention. It is a system configuration figure showing a 1st embodiment of an air flow meter as a gas flow meter concerning the present invention. It is a figure explaining the detection principle of the thermoelectromotive force and polarity in a light breeze area. It is the figure which showed the general relationship with air volume, temperature difference (DELTA) T, and heating wire temperature T. FIG. It is a time chart of the energization / measurement time in the case of moderate air volume in the light wind region. It is a figure which shows an example of the relationship between the air volume, temperature difference (DELTA) T, and board | substrate temperature T in the case of medium air volume in a light breeze region. 6 is a time chart of energization / measurement time when the air volume is smaller than the medium air volume in the light air region. It is a figure which shows an example of the relationship between the air volume, temperature difference (DELTA) T, and board | substrate temperature T in the case of an air volume smaller than the said medium air volume in a light breeze region. 6 is a time chart of energization / measurement time when the air volume is slightly larger than the medium air volume in the light air region. It is a figure which shows an example of the relationship between the air volume, temperature difference (DELTA) T, and board | substrate temperature T in the case of a slightly larger air volume than the said medium air volume in a light breeze region. It is a figure which shows an example of the relationship between the air quantity in a strong wind area, temperature difference (DELTA) T, and board | substrate temperature T. It is a system configuration figure showing a 2nd embodiment of an air flow meter. It is a schematic block diagram of the experimental apparatus used in the Example. It is the airflow characteristic figure obtained in the Example. It is a front view of the hot-wire type wind speed sensor described in Patent Document 5.

Explanation of symbols

2 Boiler combustion chamber 4 Blower 6 Pipe line 8 Sensor body 9 Control unit (control means)
10 Printed circuit board (board)
DESCRIPTION OF SYMBOLS 11 Thermocouple 13 Heating wire 14 Copper foil pattern 15a, 15b Joint 16 Energization control circuit (energization control means)
17 Thermoelectromotive force detection circuit (thermal electromotive force detection means)
18 Switching circuit (switching means)
19 Thermistor (temperature detection means)
21b Storage unit (storage unit)
21c Calculation unit (wind direction / air volume detection means, energization pattern change means)
23 Printed circuit board 24 Heating wire 25 Copper foil 26 Sensor body 27 Thermocouple group 28a, 28b Junction point

Claims (6)

A thermal gas flow meter that measures the mass flow rate of a gas that is arranged in a pipeline and passes through the pipeline,
A thermocouple is formed on the substrate, and a thermoelectromotive force is generated between the joining points of the heating wire and the copper foil. A sensor body;
Control means for controlling the sensor body,
The control means detects the electromotive force with the polarity of the energization control means for controlling the energization state of the heating wire and the temperature difference between the junction points of the heating wire and the copper foil. And a wind direction / air volume detection means for detecting a wind direction and an air volume based on a detection result of the thermoelectromotive force detection means.   The gas flowmeter according to claim 1, wherein the sensor body has a large number of thermocouples connected in series on a substrate.   The control means includes switching means for switching between an output from the heating control means and an input to the thermoelectromotive force detection means, and heating operation to the heating wire and detection operation of the thermoelectromotive force are alternately performed. The gas flowmeter according to claim 1 or 2, wherein the gas flowmeter is repeated.   2. A storage unit storing a plurality of types of energization patterns for the heating wire, and an energization pattern changing unit for changing the energization pattern according to the detected thermoelectromotive force. The gas flowmeter according to claim 3.   The gas flowmeter according to any one of claims 1 to 4, wherein temperature detecting means for detecting the temperature of the substrate is arranged on the substrate.   The gas flowmeter according to any one of claims 1 to 5, wherein the gas flowmeter is interposed between a boiler combustion chamber and a blower that blows gas into the boiler combustion chamber.

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