JPH071184B2 - Thermal flow sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive flow sensor for detecting the flow rate of a fluid by using a heat-sensitive resistor (heating resistor).

[0002]

2. Description of the Related Art As a flow rate sensor of a type which detects a flow rate from a thermal equilibrium state of a bridge circuit including a heat sensitive resistor arranged in a fluid, for example, there is a flow rate sensor disclosed in Japanese Utility Model Laid-Open No. 61-108930. This is a heating resistor which is a thermosensitive resistor having a platinum thin film resistor formed on a ceramic substrate.

FIG. 2 shows the structure of a heat-sensitive flow sensor, in which a base portion 2 is provided at a predetermined position in a housing 1 which serves as a main passage for a fluid.
Is provided, the thermosensitive resistor 3 and the air temperature sensor 4 are provided at predetermined positions on the base 2, and a bridge circuit is configured with the resistors R ₁ and R ₂ . Both inputs of the differential amplifier 101 are connected to the connection points b and f of the bridge circuit,
The output of 01 is connected to the base of the transistor 102,
The emitter of the transistor 102 is one end a of the bridge circuit.
And the collector is connected to the positive electrode of the power supply 103.

FIG. 3 shows a support structure for the heat sensitive resistor 3, in which the support member 5 is attached to the base portion 2, and the heat sensitive resistor 3 is supported on the support member 5 so that the plane is substantially along the flow direction of the fluid. To be done. Further, the support member 5 has a lead 6 for electrical connection.
Is supported, and the lead 6 is connected to the thermal resistor 3 via the lead wire 34.

In the above structure, when the voltages at the connection points b and f become equal, the bridge circuit reaches the equilibrium state. At this time, the current I _H corresponding to the flow rate flows through the thermal resistor 3, and the voltage at the point b. V ₀ is represented by I _H × R ₁ , and this voltage V ₀ is used as a flow rate signal.

[0006]

However, the above-mentioned conventional heat-sensitive flow rate sensor has a problem that an error occurs in the voltage V ₀ as a flow rate signal. The factors include the size and shape of each part and the constant error of each resistance forming the bridge circuit. Further, there is a temperature distribution variation of the heat generating part of the heat-sensitive resistor 3, and the error due to the temperature distribution variation is relatively small. It was a big one.

The present invention has been made to solve the above problems, and an object thereof is to obtain a heat-sensitive flow rate sensor with high accuracy.

[0008]

In the heat-sensitive flow sensor according to the present invention, the trimming region of the resistance film trimmed so that the resistance value of the heat-sensitive resistor becomes a predetermined value is defined as the end portion of the heat-sensitive resistor on the side of the supporting member. It is provided near the end on the opposite side.

[0009]

According to the present invention, the trimming region of the resistance film of the heat-sensitive resistor is provided near the end of the heat-sensitive resistor opposite to the support member side end, and the temperature of the support member side end is the trimming amount of the trimming region. Does not change, and the ratio of the amount of heat transfer from the heat sensitive resistor to the fluid and the amount of heat transfer to the support member does not change.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a front view of a heat-sensitive resistor 3 according to this embodiment. The heat-sensitive resistor 3 has a temperature-dependent resistance film 36 on a substantially rectangular insulating substrate 35 as in the conventional case, and the temperature-dependent resistance film 36 in One end is supported by the support member 5 so that the longitudinal direction thereof is substantially perpendicular to the flow direction of the fluid in the fluid. Reference numeral 31 is a heat generating portion, 32 is an electrode portion, 33 is a supporting portion which is closer to the end portion than the one-dot chain line or is embedded in the supporting member 5, and 34 is a lead wire which is electrically connected to the electrode portion 32.
The heat generating portion 31 is formed of the resistance film 36, and in order to make the resistance value of the resistance film 36 constant, a trimming region b is generally provided. The trimming area b is trimmed to the same shape as the non-trimming area a or not trimmed at all in order to adjust the material variation and thickness variation of the resistor. Now, assuming that the trimming area b is trimmed to have the same shape as the non-trimming area a, the temperature distribution of the heat generating portion 31 during energization becomes substantially uniform. However, if the trimming area b is not trimmed at all, It is clear that the temperature distribution of 31 has a low value in the trimming area b.

FIG. 4 shows this temperature distribution. (A) shows the case where the entire trimming area (b) of the thermosensitive resistor 3 is completely trimmed, and (b) shows the case where it is not trimmed at all. 4. h ₀ to h _{6 in} FIG. 4 indicate the axial positions of the heat sensitive resistor 3, which coincides with h ₀ to h ₆ in FIG. The point of interest in FIG. 4 is the temperature t ₀ at the h ₀ position which is the end position on the support member side.
Is the size of. That is, the temperature t _{01 in the} completely trimmed state shown in FIG. 4A and the temperature t _{02 in the} completely untrimmed state shown in FIG. 4B are t ₀₁ = t ₀₂ .
On the other hand, when the trimming area b and the non-trimming area a are replaced in FIG. 1, the temperature distribution when the trimming area b is not trimmed at all is shown in FIG.
As shown in (c), t ₀₁ = t ₀₂ > t ₀₃ . Here, h temperature t ₀ of the _zero point represents a heat transfer to the support member 5, the ratio of heat transfer from the t ₀ value is different from the heat generation unit 31 to the supporting member 5 and the heat transfer to the fluid As a result, the voltage V ₀ with respect to the flow rate changes. In this embodiment, FIG.
Is provided at a portion close to the end opposite the crop region b and the support member side end portion as shown in, no change of the voltage V ₀ by the trimming amount, if provided at a position closer to the supporting member-side end portion Therefore, the voltage V ₀ changes greatly.

[0012]

As described above, according to the present invention, since the trimming region of the resistance film of the heat-sensitive resistor is provided at the portion far from the end of the heat-sensitive resistor on the side of the supporting member, the temperature of the end on the side of the supporting member is increased. Does not change depending on the trimming amount, and the flow rate characteristics do not change. Therefore, a highly accurate heat-sensitive flow sensor can be obtained.

[Brief description of drawings]

FIG. 1 is a front view of a heat-sensitive resistor according to the present invention.

FIG. 2 is a configuration diagram of a thermal flow sensor.

FIG. 3 is a support structure diagram of a heat-sensitive resistor.

FIG. 4 is a temperature distribution diagram of a heat sensitive resistor.

[Explanation of symbols]

 3 Heating Resistor 5 Supporting Member 35 Insulating Substrate 36 Resistive Film b Trimming Area

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Tanimoto 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Industrial Systems Research Center, Sanryo Electric Co., Ltd. (72) Yuji Ariyoshi 8-chome Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture No. 1 Sanrishi Electric Co., Ltd. Industrial Systems Research Center

Claims (1)

[Claims] 1. A thermosensitive resistor having a temperature-dependent resistance film on a substantially rectangular insulating substrate is supported at one end in the longitudinal direction such that the longitudinal direction is substantially perpendicular to the flow direction of the fluid in the fluid. In a heat-sensitive flow sensor that is supported by a member and detects the flow rate by the amount of heat released when the heat-sensitive resistor is heated, the trimming area of the resistance film is trimmed so that the resistance value of the heat-sensitive resistor becomes a predetermined value. A heat-sensitive flow sensor, wherein the heat-sensitive resistor is provided in a portion near an end of the heat-sensitive resistor opposite to a supporting member side end.