JPH08240462A - Flow-rate/flow-velocity sensor - Google Patents

Abstract

PURPOSE: To provide a heating temperature measuring type flow-rate/flow- velocity sensor which is excellent in a heat responsive sensitivity characteristic. CONSTITUTION: In the flow-rate/flow-velocity sensor which is provided with a case 8 in contact with a measuring object fluid, a heating source 2 which is arranged in the case 8 and whose heat is taken away by the measuring object fluid through the case 8 and a temperature measuring element 4 arranged in the vicinity of the heating source 2 in the case 8, and measures a flow rate or flow velocity of the measuring object fluid, a hollow layer 13 to substantially thermally cut off the heating source 2 and the temperature measuring element 4 from the other part on the opposite side of the measuring object fluid, is provided in the case 8. Air pressure in the hollow layer 13 is preferable to be not more than the atmospheric pressure. For example, the hollow layer 13 is arranged between a filler 10 filled in the case 8 or a cover of the case 8, the heating source 2 and the temperature measuring element 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exothermic temperature measuring type flow rate / flow rate sensor (thermal sensor) used for measuring the flow rate / flow rate of gas or liquid.

[0002]

2. Description of the Related Art In recent years, as a heat measuring temperature measuring type flow rate / flow velocity sensor, there has been proposed one having a structure having a cross section as shown in FIG. As shown in the figure, this sensor is provided with a case 41 in contact with the fluid to be measured flowing through the pipe 40, and a sensor element 42 arranged in the case 41. The sensor element 42 includes a heat source from which heat is removed by the fluid to be measured via the case 41, and a temperature measuring element arranged in the case 41 near the heat source. And case 4
The temperature measuring element outputs a signal according to the temperature in the vicinity of the heat source from which heat is taken away via the lead wire 43. Based on the difference between this temperature and the temperature of the fluid to be measured, the flow rate and flow velocity of the fluid to be measured can be obtained.

[0003]

However, this sensor is suitable for measuring a constant flow rate or flow velocity, but is not suitable for measurement when the flow rate or flow velocity changes in a short time. The reason is that the heat generated from the heating element in the element 42 is taken away by the fluid to be measured, but part of the heat is also conducted to the filler 44 filled on the element 42, so that the heating element can be used for a long time. When the flow rate and flow velocity are measured by energizing, the temperature of the filler 44 changes until the filler 44 reaches thermal saturation (thermal equilibrium state).
That's what it means. Since the filler 44 is arranged to block the influence of the outside air temperature, a material having poor heat conduction is selected, but such a material generally has a large heat capacity and is difficult to cool once it is heated. Therefore, if the flow rate / velocity is measured for a long time, it becomes impossible to follow a rapid change in the flow rate / velocity.

An object of the present invention is to provide a flow rate / flow velocity sensor of exothermic temperature measuring type which is excellent in thermal response sensitivity characteristics in view of the problems of the prior art.

[0005]

In order to achieve this object, according to the present invention, a case that comes into contact with a fluid to be measured, and a heat source that is disposed in the case and takes heat from the fluid to be measured through the case are provided. A flow rate / flow velocity sensor for measuring the flow rate or flow velocity of the fluid to be measured, the heat source and the temperature measuring element being the fluid to be measured. On the opposite side is provided with a hollow layer in the case, which is thermally insulated from the other part substantially.

The atmospheric pressure in the hollow layer is preferably below atmospheric pressure.

The hollow layer is provided, for example, between the filler filled in the case or the lid of the case and the heat source and the temperature measuring element.

[0008]

In this structure, when the heat source is heated, the heat is taken away by the fluid to be measured through the case, but after a lapse of a predetermined time, the heat near the heat source becomes saturated and the temperature reaches a constant value. . This temperature is measured via the temperature measuring element, and the flow rate and flow velocity of the fluid to be measured are obtained based on the temperature and the temperature of the fluid to be measured. At that time, since the heat source and the temperature measuring element are substantially thermally shielded from the other part on the side opposite to the fluid to be measured by the hollow layer, the predetermined time is shorter than that of the conventional one. Further, even if the flow rate / velocity of the fluid to be measured changes, the thermal saturation state corresponding to the changed flow rate / velocity is quickly reached. That is, the thermal response sensitivity characteristic is superior to the conventional one. Therefore, the measurement is performed according to the rapid changes in the flow rate and the flow velocity. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0009]

1 is a sectional view showing the structure of a flow rate / flow velocity sensor according to an embodiment of the present invention. In the figure, 1 is a substrate with good thermal conductivity such as alumina, 2 is a Ni / Cr alloy,
A heating element formed of a material such as tantalum nitride or cermet on the substrate 1, 3 is an interlayer insulating film formed on the heating element 2 of SiO ₂ or Si ₃ N ₄ , and 4 is an MnCo-based thermistor material. A thin film thermistor formed on the insulating film 3,
5 is an electrode connected to the heating element 2 and the thermistor 4, 6
Is a protective layer that covers and protects these heating elements 2 to electrodes 5. The heating element 2 to the electrode 5 are formed in a predetermined pattern by using a thin film forming method such as vacuum deposition or sputtering. It is effective in terms of thermal efficiency to arrange the pattern of the thermistor 4 on the pattern of the heating element 2. Reference numeral 7 is a lead wire connected to the electrode 5. Reference numeral 8 denotes a case attached to the pipe 14 so that the outside is in contact with the fluid to be measured flowing in the pipe 14 in the direction of the arrow 12, and the sensor element having the substrate 1 to the protective layer 6 and the like is attached to the case. An adhesive 11 fixes the substrate 1 to the sensor 8, and the heat generated by the heating element 2 is taken away by the fluid to be measured via the substrate 1 and the case 8.

Reference numeral 9 denotes a cover provided on the sensor element, which is provided with a sufficient clearance so as not to contact the sensor element, and the hollow layer 1 is provided between the sensor element and the cover.
3 is formed. The cover 9 is made of glass or a plastic material in terms of heat resistance and heat conduction. Reference numeral 10 denotes a filling material that is filled in the case 8 after the case 8 to which the sensor element and the cover 9 are attached is attached to the pipe 14.

In this structure, when an electric current is passed through the heating element 2 to generate heat, the heat is taken away by the fluid to be measured through the case 8. However, after a predetermined period of time, the heat near the heating element 2 is saturated. And the temperature reaches a certain value. This temperature is measured via the thermistor 4, and the flow rate and flow velocity of the fluid to be measured are measured based on the temperature and the temperature of the fluid to be measured.

FIG. 2 is a graph showing the relationship (response characteristic) between the elapsed time and the output ratio when the thermal saturation is reached by a solid line. The output is an output of the resistance value obtained through the thermistor 4 or a temperature corresponding to the resistance value, and the output ratio is a ratio of the output at each elapsed time to the output when the thermal saturation is reached. Note that the relationship in the conventional case in which the cover 9 is not provided and the filler 10 is all filled is shown by a broken line. As shown in this graph, the output ratio is 95
% (Response time τ (95%)) is 1.6 sec in the conventional case, and is 0.% in the case of the present embodiment.
It is 9 seconds, and it can be seen that the response characteristic is improved as compared with the conventional case.

Furthermore, in actual use, the time required to reach thermal saturation (the output ratio is 1) is about 2 seconds in the case of this embodiment, as can be seen from FIG. 2, whereas it is 10 in the conventional case. It takes about a second. Further, depending on the selection of the filler 10, it takes about 30 seconds in the conventional case, but it is 2 seconds or less in the case of the present embodiment regardless of the filler. Therefore, in the case of the conventional sensor without the hollow layer, the selection range of the filler is limited, and the use is limited depending on the application, whereas the sensor of the present example has the advantage of wide versatility. is there.

FIG. 3 shows a flow rate according to another embodiment of the present invention.
It is sectional drawing which shows the structure of a flow velocity sensor. This sensor omits the element cover 9 in that of FIG.
5 is used to seal the sensor element below atmospheric pressure. In this example, a hermetic seal is used as the seal between the case 8 and the lid, and the resistance welder is used for sealing.

That is, in the case 8 in which the lead portion 16 electrically insulated from the case 8 is formed in advance, the sensor element 17 having the same structure as in the above-mentioned embodiment is formed.
After bonding, the lead portion 16 and the electrode of the sensor element 17 are electrically coupled by forming a wire bonding 18 between them, and then the stem 15 serving as a lid is placed on the case 8 and the resistance is set. It is constructed by sealing using a welding machine. At this time, the inside of the case 8 is maintained at that pressure by keeping the inside of the seal chamber of the resistance welding machine at atmospheric pressure or lower by the vacuum pump. The lower the pressure, the more preferable, but it is usually preferable that the pressure is 1 Torr or less. Furthermore, it is preferable to coat the inside of the lid 15 or the case 8 with a resin 19 which serves as a heat insulating material, whereby the influence of the outside air temperature can be reduced and a more reproducible flow rate / flow velocity sensor can be realized.

[0016]

As described above, according to the present invention, since the heat source and the temperature measuring element are substantially thermally insulated from other portions on the side opposite to the fluid to be measured by the hollow layer, Even in a fluid in which the flow rate / velocity changes in a short time, the flow rate / velocity can be measured by following the change. Further, by making the hollow layer lower than atmospheric pressure, the influence of the outside air temperature can be reduced, the reproducibility of measurement can be improved, and more accurate measurement can be performed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a flow rate / flow velocity sensor according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship (response characteristic) between an elapsed time and an output ratio when the sensor of FIG. 1 reaches thermal saturation, in comparison with a conventional case.

FIG. 3 is a cross-sectional view showing the structure of a flow rate / flow velocity sensor according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a configuration of a flow rate / flow velocity sensor according to a conventional example.

[Explanation of symbols]

1: substrate, 2: heating element, 3: interlayer insulating film, 4: thin film thermistor, 5: electrode, 6: protective layer, 7: lead wire, 8: case, 11: adhesive, 9: cover, 13: hollow Layer, 1
0: filler, 16: lead part, 17: sensor element, 1
8: Wire bonding, 15: Lid, 19: Resin.

Claims (3)

[Claims] 1. A case which is in contact with a fluid to be measured, a heat source which is arranged in the case and heat is taken away by the fluid to be measured through the case, and a case which is arranged in the case near the heat source. A flow rate / flow velocity sensor for measuring the flow rate or flow velocity of a fluid to be measured, comprising a temperature element, wherein the heat source and the temperature measuring element are thermally separated from the other side substantially on the side opposite to the fluid to be measured. A flow rate / flow velocity sensor, comprising a hollow layer for blocking in the case. 2. The flow rate / velocity sensor according to claim 1, wherein the atmospheric pressure in the hollow layer is equal to or lower than atmospheric pressure. 3. The method according to claim 1, wherein the hollow layer is provided between a filling material filled in the case or a lid of the case and the heat source and the temperature measuring element. Flow rate / flow velocity sensor.