JP2017120197A - Thermal flow rate sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal flow rate sensor capable of suppressing generation of drift of an output value even under high temperature and humidity.SOLUTION: A thermal flow rate sensor for measuring a flow rate of a fluid flowing in a pipe by using a resistor includes: a sensor chip 2 including a resistor (heat source 22); and a soft adhesive 4 for bonding the sensor chip 2 to a pipe 1. The soft adhesive 4 contains a fluororesin or silicone as a main component, and has a Young's modulus of 20 MPa or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thermal flow sensor in which a sensor chip is attached to a pipe.

  2. Description of the Related Art Conventionally, a thermal flow sensor that measures a flow rate of a fluid flowing through a pipe using a resistor is known (see, for example, Patent Document 1). This thermal flow sensor includes a sensor chip in which the resistor is disposed in a diaphragm portion, and the diaphragm portion of the sensor chip is attached to a pipe.

International Publication No. 2001/088407

When the sensor chip is bonded to a pipe with an epoxy-based adhesive, if the thermal flow sensor is left under high temperature and high humidity, the output value of the sensor chip drifts as shown in FIG. As a result, we found the problem of exceeding the allowable range and affecting the detection.
On the other hand, this thermal flow sensor is used in various fields for measuring a flow rate. Therefore, if the output value drifts in the measurement environment, the product has low reliability. Therefore, there is a need for a thermal flow sensor with high reliability even in long-term use.

  The present invention has been made to solve the above-described problems, and can suppress the occurrence of drift of the output value even when the apparatus is placed under high temperature and high humidity compared to the conventional configuration. The object is to provide a thermal flow sensor.

  A thermal flow sensor according to the present invention includes a sensor chip having a resistor and a soft adhesive that bonds the sensor chip to a pipe.

  According to this invention, since it comprised as mentioned above, generation | occurrence | production of the drift of an output value can be suppressed even if it is a case where it is placed under high temperature and high humidity with respect to the conventional structure.

1A is a side sectional view showing a configuration example of a thermal flow sensor according to Embodiment 1 of the present invention, and FIG. 1B is a sectional view taken along line AA in FIG. 1A. FIG. 2A is a diagram showing a characteristic example of a soft adhesive used in the thermal flow sensor according to Embodiment 1 of the present invention, and FIG. 2B is a diagram showing a characteristic example of an epoxy-based adhesive. It is a figure which shows the effect of the thermal type flow sensor which concerns on Embodiment 1 of this invention, and is a figure which shows the resistance value fluctuation | variation of a sensor chip when it is placed under high temperature and high humidity. It is a figure which shows the subject at the time of adhere | attaching a sensor chip to piping with an epoxy-type adhesive agent, and is a figure which shows the resistance value fluctuation | variation of a sensor chip when a thermal type flow sensor is put under high temperature and high humidity.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
1 is a diagram showing a configuration example of a thermal flow sensor according to Embodiment 1 of the present invention.
A thermal flow sensor measures the flow volume of the fluid (liquid or gas) which flows through the piping 1 using a resistor. As shown in FIG. 1, the thermal type flow sensor includes a pipe (capillary) 1 through which a fluid flows, and sensor chips 2 and 3 attached to the pipe 1. The sensor chip 2 is provided with a single heat source (resistor) 22 that applies heat to the fluid in the pipe 1 in a diaphragm portion 21 that is a part attached to the pipe 1. The sensor chip 3 is provided with a temperature sensor (resistor) 31 that measures the temperature of the fluid in the pipe 1.

  In the present invention, the diaphragm portion 21 of the sensor chip 2 is bonded to the pipe 1 using the soft adhesive 4. Here, as shown in FIG. 2A, the soft adhesive 4 is an adhesive having a fluororesin or silicone as a main component when defined by components, and an adhesive having a Young's modulus of 20 MPa or less when defined by characteristics.

  In the thermal type flow sensor configured as described above, when the fluid in the pipe 1 is stationary, the amount of heat when the heat source 22 applies heat so as to be a constant temperature higher than the surroundings, When the fluid flows from the upstream side to the downstream side, a difference occurs in the amount of heat when heat is applied by the heat source 22 so that the temperature is higher than the surroundings by a certain temperature. This difference in the amount of heat has a correlation with the flow rate of the fluid in the pipe 1. Therefore, the flow rate of the fluid flowing through the pipe 1 can be measured from the difference in the amount of heat.

Next, the effect of the thermal flow sensor of the present invention will be described. FIG. 3 is a diagram showing the effect of the thermal flow sensor according to Embodiment 1 of the present invention, and shows the resistance value fluctuation of the sensor chip 2 when the thermal flow sensor is left under high temperature and high humidity. FIG.
In a conventional thermal flow sensor, the sensor chip 2 is bonded to the pipe 1 using an epoxy adhesive. As shown in FIG. 2B, the Young's modulus of the epoxy adhesive is about several GPa. If this conventional thermal flow sensor is placed under high temperature and high humidity, as shown in FIG. 4, the output value of the sensor chip 2 drifts and exceeds the allowable range. This is because, as the adhesive absorbs and swells under high temperature and high humidity, the stress applied to the diaphragm portion 21 on which the resistor (heat source 22) of the sensor chip 2 is mounted gradually changes. This is probably because the amount of distortion changes.

  In contrast, in the present invention, the sensor chip 2 is bonded to the pipe 1 using the soft adhesive 4. Thereby, as shown in FIG. 3, generation | occurrence | production of the drift of the output value of the sensor chip 2 can be suppressed, and it can be in the tolerance | permissible_range. That is, the soft adhesive 4 has a low Young's modulus even if it absorbs and swells under high temperature and high humidity, so that the stress is absorbed and the change in stress applied to the resistor (heat source 22) of the sensor chip 2 can be reduced. Therefore, the influence on the amount of strain on the resistor can be reduced.

  As described above, according to the first embodiment, the sensor chip 2 having the resistor (heat source 22) and the soft adhesive 4 for bonding the sensor chip 2 to the pipe 1 are provided. Even when it is placed under high temperature and high humidity, it is possible to suppress the occurrence of drift of the output value.

  In the above description, the sensor chip 2 provided with the resistor (heat source 22) in the diaphragm portion 21 is bonded to the pipe 1 using the soft adhesive 4. However, the present invention is not limited to this, and the sensor chip 3 in which the resistor (temperature sensor 31) is provided on the substrate is also affected by the stress caused by the adhesive. Therefore, the sensor chip 3 may be bonded to the pipe 1 using the soft adhesive 4 as in the case of the sensor chip 2. Thereby, the stress change applied to the resistor of the sensor chip 3 can be relaxed, and the influence on the amount of strain on the resistor can be reduced.

  Further, in the present invention, any constituent element of the embodiment can be modified or any constituent element of the embodiment can be omitted within the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Piping 2, 3 Sensor chip 4 Soft adhesive 21 Diaphragm part 22 Heat source 31 Temperature sensor

Claims (3)

In a thermal flow sensor that measures the flow rate of fluid flowing through a pipe using a resistor,
A sensor chip having the resistor;
A thermal flow sensor comprising: a soft adhesive that bonds the sensor chip to the pipe. The thermal flow sensor according to claim 1, wherein the soft adhesive is an adhesive mainly composed of fluororesin or silicone. The thermal flow sensor according to claim 1, wherein the soft adhesive is an adhesive having a Young's modulus of 20 MPa or less.

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