JPH0989620A - Thermal type flow-rate sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal type flow-rate sensor with a high sensitivity regardless of a low-speed flow rate and a high-speed flow rate. SOLUTION: A sensor comprises two hot wires 21 and 22 which are aligned in parallel at the upstream and downstream sides of the flow of a fluid, resistors 31, 32, and 33 for constituting the hot wires and a bridge, and an operation means 4, where switching means 5 and 6 for connecting the two hot wires 21 and 22 in series or in parallel are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate sensor for detecting a flow rate of a fluid, and more particularly to a thermal type flow rate sensor for detecting a flow rate according to an amount of a fluid flowing in contact with a heat ray to cool the heat ray.

[0002]

2. Description of the Related Art A thermal type semiconductor flow rate sensor for detecting the flow rate of a fluid is
There are single-line type, two-line type, and three-line type. As shown in FIG. 4, the single wire type flow rate sensor is composed of one heating wire 21, and the effect of cooling the heating wire 21 by the fluid is the resistance value R of the heating wire.
The heat wire 21 and the resistors 31, 32, which are detected as a decrease in h,
This is a method of electrically detecting using a bridge circuit composed of 33 and an amplifier 4. As shown in FIG. 5, the two-wire flow sensor is composed of two heating wires 21 and 22 arranged at a distance in a direction orthogonal to the flow, and the temperature difference between the upstream and downstream heating wires caused by the flow This is a method of electrically detecting the difference in resistance value using a bridge circuit composed of the heat wires 21 and 22 and the resistors 31 and 32 and the amplifier 4. The three-wire flow sensor is composed of a heating wire for heat generation and resistance wires for temperature detection arranged at both ends of the heating wire, and the temperature difference between the upstream and downstream resistance wires caused by the flow is electrically determined as a difference between resistance values of the resistance wires. It is a method to detect.

However, the above conventional techniques have the following drawbacks. That is, the two-line type flow sensor and the three-line type flow sensor have the following methods for detecting a low flow rate:
Although it is advantageous in that the sensitivity can be increased, the output tends to be saturated when detecting a flow rate having a high flow rate. On the contrary, the method of the single-line type flow sensor has an advantage that it can detect a high flow rate, but has a drawback that it cannot have a higher sensitivity than the method of the two-wire type and the three-line type flow sensor when detecting a low flow rate. .

[0004]

In view of the above problems, the present invention provides a two-wire hot wire type flow sensor having a high sensitivity to a low flow rate and a single wire hot wire type flow sensor having a high sensitivity to a high flow rate. It is an object of the present invention to provide a new type hot wire type flow sensor having both of the above features.

[0005]

In order to solve the above-mentioned problems, a thermal type flow sensor according to the present invention comprises a heating wire 21 arranged on the upstream side of the flow, a heating wire 22 arranged on the downstream side, and a resistor 31. , 32, and 33, an amplifier 4, and two switching means 5 and 6 for switching between a high flow rate side and a low flow rate side. As a circuit suitable for high flow rate flow rate detection, the heat wire 21 and the heat wire 21 are provided. A series connection body of 22 is used as one side, and resistors 31, 32, 33 are respectively used as the remaining three sides to form a bridge circuit, and a connection point P1 between the resistance 31 and the heating wire 21 and a connection point P4 between the resistance 32 and the resistance 33 are formed. The flow rate was detected by detecting the degree of imbalance.

Further, according to the present invention, as a circuit suitable for low flow rate flow rate detection, the heating wire 21 and the heating wire 22 are each one side, and the resistors 31 and 32 are the other two sides to form a bridge circuit. The flow rate is detected by detecting the degree of imbalance between the connection point P1 of the heating wire 21 and the connection point P4 of the resistor 32 and the heating wire 22. At this time, the resistance value of the heating wire 21 is Ru, the resistance value of the heating wire 22 is Rd, and the resistance values of the resistors 31, 32, and 33 are R1 and R, respectively.
2 and R3, the resistance values are set to R1 = R2 and Ru = Rd = 0.5R3 in consideration of the balance condition of the bridge circuit.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the circuit configuration of a thermal type flow sensor according to the present invention. The thermal type flow sensor of the present invention includes a bridge circuit 1 including a heating wire 21 and a heating wire 22, and resistors 31, 32, and 33, a calculation unit 4 including an operational amplifier,
Two switching means 5, 6 for changing the configuration of the bridge circuit
And a control means 7. Switch means 5, 6
By switching to the high speed side when high flow velocity is detected and switching to the low flow velocity side when low flow velocity is detected, a single line type or 2
It can act as a linear thermal flow sensor.

The bridge circuit 1 is constructed by connecting a series connection body of a resistance 31 and a heating wire 21 and a series connection body of a resistance 32, a resistance 33 and a heating wire 22 in parallel. Here, the resistance 32 and the resistance 33 are connected in series via the contact 5a of the first changeover switch 5 and the high flow velocity side contact 5h, and the connection point P3 of the resistance 33 and the heat wire 22 is the first changeover means 5. Is connected to the low flow velocity side contact 5l and the high flow velocity side contact 6h of the second switching means 6, is grounded when the high flow velocity is detected, and is connected to the resistor 32 and the resistor 33 is disconnected from the circuit when the low flow velocity is detected. . The connection point P1 between the resistor 31 and the heating wire 21, and the resistor 32
And the connection point P4 of the contact 5a of the first switching means 5 is connected to the two input terminals of the amplifier 4. Heat wire 21 and heat wire 22
Is connected to the low flow velocity side contact point 6l of the second switching means 6.
Is connected to and is grounded when low flow velocity is detected.

The first switching means 5 and the second switching means 6 are
The control means 7 simultaneously switches to the high flow rate side or the low flow rate side. Further, these switching means 5 and 6 may be mechanical switches or electric switches (semiconductor switches or the like).

[0010]

As described above, according to the present invention, when the flow velocity is high, the heating wire 21 and the heating wire 22 are connected in series to form one side of the bridge circuit 1. Therefore, the detection sensitivity of the flow velocity can be increased. Therefore, when the flow velocity is low, the two heat wires form each one side of the bridge circuit 1, so that the flow velocity detection sensitivity can be increased.

[0011]

EXAMPLE An example of a schematic structure of the flow velocity detecting element 1 will be described below with reference to FIG. FIG. 2 is a conceptual diagram of the flow velocity detecting element 2 as viewed from above. In the flow velocity detecting element 2, two heat rays 2
1, 22 are arranged so as to be respectively positioned on the upstream side and the downstream side of the flow of the fluid, and are connected in series and are manufactured using a material such as polycrystalline silicon on a semiconductor substrate 28 made of silicon or the like. Has been done. An electrode pad 23 is provided at one end 21a, 22b of each heating wire 21, 22.
25 is configured, and the other ends 21b of the heat wires 21 and 22,
22a are commonly connected and provided with an electrode pad 24 for extraction. A concave portion 26 for heat insulation is provided below each of the heating wires 21 and 22, and the upper surface of the flow velocity detecting element 2 is formed of a protective film such as silicon oxide except for the electrode pads 23, 24 and 25. Covered.
The electrode pads 23, 24, 25 correspond to the connection points P1, P2, P3 shown in FIG. 1, respectively.

The schematic structure of the sensor chip 10 installed in the flow channel will be described with reference to FIG. Sensor chip 10
Has a flow rate detecting element 2 attached on a glass substrate 13, and the electrode pads 23, 24, 25 of the detecting element 2 are connected to three gold wirings 14 provided on the glass plate 13 by aluminum bonding 15 respectively. Has been done.
A conductor 16 is connected to the gold wiring 14 and is connected to the bridge circuit 1 of the flow rate detecting means.

The operation of detecting the flow rate using the flow rate detecting means having the sensor chip 10 will be described. First, the flow rate detection when the flow velocity is slow, that is, when the flow rate is small will be described. In this case, the first switching means 5
The second switching unit 6 and the second switching unit 6 are switched to the low flow velocity side by the control unit 7. Therefore, the bridge has a configuration in which the series connection body of the resistance 31 and the heating wire 21 and the series connection body of the resistance 32 and the heating wire 22 are connected in parallel, and the connection point P2 is grounded. Therefore, the flow rate detecting means is 2
It works linearly and can increase the detection sensitivity even when the flow velocity is low. Next, flow rate detection when the flow velocity is fast, that is, when the flow rate is large will be described. In this case, the first switching unit 5 and the second switching unit 6 are switched to the high flow velocity side by the control unit 7. Therefore, the bridge is composed of the resistor 31, the heating wire 21, and the heating wire 22 connected in series.
The resistor 32 and the resistor 33 are connected in parallel, and the connection point P3 is grounded. Therefore, the flow rate detecting means works as a single-line type, and the detection sensitivity can be increased even when the flow velocity is high. At this time, the resistance value of the heating wire 21 is Ru and the resistance value of the heating wire 22 is Rd.
When the resistance values of 2, 33 are R1, R2, R3, the resistance values of R, R2, and R3 are set in consideration of the equilibrium condition of the bridge circuit.
By setting 1 = R2 and Ru = Rd = 0.5R3, even if the connection is changed according to the change in the flow velocity, the balance condition does not change significantly, and the input signal of the amplifier 4 changes greatly. Never.

In the above description, the switching means 5 and 6 are switched according to the flow velocity, but the control means 7 is arranged to switch the switching means at a predetermined time interval.
Alternatively, the low flow velocity detection value and the high flow velocity detection value may be extracted at regular intervals, and the high sensor detection value may be used as the correct detection value.

[0015]

As described above, according to the present invention, it is possible to measure the flow velocity with high sensitivity from low flow velocity to high flow velocity by using one flow velocity sensor.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an outline of a flow sensor according to the present invention.

FIG. 2 is a conceptual plan view showing an outline of the structure of a flow velocity detecting element used in the flow rate sensor of the present invention.

FIG. 3 is a conceptual diagram showing an outline of the configuration of a sensor chip used in the flow sensor of the present invention.

FIG. 4 is a diagram showing a circuit configuration of a conventional single-wire flow sensor.

FIG. 5 is a diagram showing a circuit configuration of a conventional two-wire flow sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 bridge circuit 2 flow rate detection element 4 amplifier 5,6 switching means 7 control means 10 sensor chip 21,22 heat wire 23,24,25 electrode pad 26 adiabatic space 28 silicon substrate 31,32,33 resistance

Claims (4)

[Claims] 1. A thermal type flow sensor comprising: two heating wires arranged in parallel on the upstream side and the downstream side of a fluid flow; three resistances forming a bridge with the heating wires; and a computing means. A thermal flow sensor, comprising switching means for connecting and changing two heating wires in series or in parallel. 2. The bridge comprises a series connection body of a first resistance and a first heating wire, a second resistance, a first switching means, a third resistance and a series connection body of a second heating wire. And a first switching means for selecting whether to connect the second resistor and the third resistor in series or to connect the second resistor and the second heating wire in series,
Second switching means for selecting whether to connect the first heating wire and the second heating wire in series to ground or to connect the first heating wire and the second heating wire in parallel to ground the connection point is provided. The thermal type flow sensor according to claim 1. 3. The thermal flow sensor according to claim 1, wherein the first heating wire and the second heating wire are provided on the same semiconductor substrate. 4. The thermal type flow sensor according to claim 1, wherein the first switching means and the second switching means are simultaneously switched at a predetermined time interval.