JPH11281448A - Thermal flow velocity sensor for liquid material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive current meter capable of accurately measuring the flow rate of highly corrosive liquid or a highly polishable liquid material even if the rate is small. SOLUTION: This thermal flow velocity sensor for a liquid material has a structure where a resistance heat generator 21 is covered with a protective coating layer made of ceramic mainly made of one or more selected from the corrosion or wear resistant group of alumina, silicon carbide, silicon nitride and zirconia, or corrosion resistant fluorine resin. Thus, the durability of a flow velocity detecting element is increased, and even for measuring the flow rate of highly corrosive liquid such as acid, alkali or the like, or a highly polishable liquid material such as a slurry of ceramic raw material powder or abrasive grains, the life of the element is secured for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow rate sensor for detecting a flow rate of a liquid such as a liquid or a slurry.

[0002]

2. Description of the Related Art Conventionally, the flow rate (or flow rate) of a liquid has been known.
An area type flow meter, a Karman vortex flow meter, a turbine type flow meter, an electromagnetic type flow meter, an ultrasonic type flow meter, or the like is used as a flow sensor for detecting the flow rate. The application fields of these flowmeters are extremely diverse, such as highly corrosive liquids such as acids and alkalis, ceramic raw material powders and granules (for example, used for polishing semiconductor silicon wafers, etc.), etc. When it is desired to measure the flow rate of a highly abrasive liquid such as the slurry described above, various restrictions often arise.

For example, in an area type flow meter or a turbine type flow meter, a movable portion such as a float or an impeller (turbine) is in constant contact with a fluid to be measured, and the movable portion is damaged by corrosion or polishing. There are drawbacks such as a shortened life, or a decrease in measurement accuracy due to hindrance to smooth movement of the movable part due to abrasive powder or the like. On the other hand, such a problem does not occur in a Karman vortex flow meter, an electromagnetic flow meter, or an ultrasonic flow meter having no movable portion, but they have the following other disadvantages. The Karman vortex flowmeter has a drawback that accuracy cannot be ensured when measuring a small flow rate (for example, about 500 ml / min). For example, it is not suitable for the purpose of precisely controlling the supply amount of an abrasive slurry or the like at a small flow rate, such as precision polishing of a semiconductor silicon wafer or the like. An electromagnetic flow meter or an ultrasonic flow meter can accurately measure a small flow rate, but is very expensive and has a drawback that its use is limited for economic reasons.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive flow rate sensor which can accurately measure the flow rate of a highly corrosive liquid or a highly abrasive liquid even at a small flow rate. .

[0005]

Means for Solving the Problems The invention described in the claims of the present specification for solving the above problems is as follows. (Claim 1) It has a main body in which a resistance heating element is covered with a protective coating layer made of ceramic or fluororesin mainly composed of one or more selected from alumina, silicon carbide, silicon nitride and zirconia, A thermal flow sensor for a liquid material, comprising: a flow rate detecting element for detecting a flow rate of the liquid material based on a change in an electric resistance value of the resistance heating element due to contact between the main body portion and the liquid material. (Claim 2) It has a main body covered with a protective coating layer made of an inorganic material such as ceramic or glass or a fluorine resin and having a thickness of 100 μm or more, and the main body and the liquid material come into contact with each other. A flow rate detecting element for detecting a flow rate of the liquid material based on a change in an electric resistance value of the resistance heating element. (Claim 3) In the main body of the flow velocity detecting element, the resistance heating element is a resistance metal winding, and the resistance metal winding is embedded in a base made of an inorganic material such as ceramic or glass or a fluororesin. 3. The thermal flow sensor for a liquid material according to claim 1, wherein a portion of the base covering the outside of the resistance metal winding portion forms a protective coating layer. (4) A detecting element mounting means for detachably mounting the flow velocity detecting element to a flow path forming member forming a flow path of a liquid material, with the main body positioned in the flow path. The thermal type flow rate sensor for a liquid material according to any one of the above. (Claim 5) A temperature compensation element in which the outside of a temperature-sensitive resistor whose electric resistance value changes in response to a temperature change of a liquid material is covered with a protective coating layer made of an inorganic material such as ceramic or glass or a fluororesin. 5. The thermal flow sensor for a liquid material according to claim 1, wherein the thermal flow sensor is provided separately from the flow rate detecting element. (Claim 6) The thermal flow sensor for a liquid material according to any one of claims 1 to 5, wherein the temperature compensating element is mounted upstream of the flow velocity detecting element in the flow path of the liquid substance to be subjected to flow velocity detection. (Claim 7) The flow velocity detecting element is formed in a rod shape extending in one axial direction, and is a non-directional detecting element that exhibits substantially equivalent detection characteristics in an arbitrary direction orthogonal to the axis thereof. 7. The thermal flow sensor for a liquid material according to claim 4, wherein the rod-shaped flow rate detecting element is attached to the flow path forming member so as to protrude inward from an inner surface of the flow path. (Claim 8) The flow path forming member is a pipe member, and the detection element mounting means is detachably mounted on the pipe member, and in the mounted state, forms a tubular support that forms a part of the flow path together with the pipe member. The flow rate detecting element is integrally attached to the tubular support so as to protrude inward from an inner surface thereof, and is attached to and detached from the pipe member together with the tubular support. 7. A thermal flow sensor for a liquid material according to any one of 7. (Claim 9) The flow velocity detecting element and the temperature compensating element are each formed in a rod shape, and the flow velocity detecting element and the temperature compensating element are arranged on the tubular support in the axial direction of the tubular support. 9. The thermal flow rate sensor for a liquid material according to claim 8, wherein the thermal flow sensors are arranged so as to protrude from their inner surfaces. (Claim 10) The thermal flow velocity for a liquid material according to claim 8 or 9, wherein the tubular support has a built-in resistance bridge circuit for detecting a change in an energized state of the flow velocity detecting element corresponding to the flow velocity of the liquid substance. Sensor. (Claim 11) The liquid according to any one of claims 8 to 10, wherein an intermediate portion of the tubular support is an enlarged diameter portion whose diameter is enlarged from both end portions, and the flow velocity detecting element is attached to the enlarged diameter portion. Thermal flow sensor for objects. (Claim 12) A flow velocity in a pipe member to which a tubular support is attached by correcting flow velocity information in an enlarged diameter portion based on a detection output of a flow velocity detecting element so as to correct a decrease in flow velocity in the enlarged diameter portion. The thermal flow rate sensor for a liquid material according to claim 11, further comprising a correction output unit that converts and outputs the information. (Claim 13) The flow velocity information based on the detection output of the flow velocity detection element is corrected according to the type of the liquid to be measured.
13. The thermal flow sensor for a liquid material according to claim 1, further comprising flow velocity information correction / output means for outputting the flow velocity information after the correction.

[0006]

According to the thermal flow sensor for liquid material of the present invention, the liquid material is detected based on a change in the electric resistance of a resistance heating element incorporated in the main body of the sensing element. Since the flow velocity is detected, the flow velocity can be accurately measured even when the flow rate is small, and the cost is low. In addition, the resistance heating element is made of a ceramic mainly composed of one or more selected from alumina, silicon carbide, silicon nitride, and zirconia, which is excellent in corrosion resistance or abrasion resistance, or a fluorine resin having good corrosion resistance. The structure covered by the coating layer enhances the durability, so that highly corrosive liquids such as acids and alkalis, ceramic raw material powders and abrasives (for example, used for polishing semiconductor silicon wafers, etc.), etc. Even when measuring the flow rate of a highly abrasive liquid such as slurry, the life of the flow velocity detecting element (hereinafter, also simply referred to as the detecting element) can be ensured for a long time.

If the cross-sectional area of a flow path portion (for example, a pipe line) for measuring the flow velocity is known, the flow rate can be measured based on the cross-sectional area and the flow velocity. Therefore, in the present invention, "measurement of flow velocity" includes not only literal measurement of flow velocity but also measurement of flow rate.

Next, according to the flow rate sensor of the second aspect, the flow rate of the liquid material is detected based on a change in the electric resistance value of the resistance heating element incorporated in the detection element main body. The flow rate can be measured accurately even when the amount is small, and the cost is low. The resistance heating element is made of an inorganic material such as ceramic or glass or a fluororesin.
The structure covered with a protective coating layer of 00 μm or more enhances the durability of the sensing element, and highly corrosive liquids such as acids and alkalis, ceramic raw material powders and granules (for polishing semiconductor silicon wafers, etc.) Even when a flow rate of a liquid material having high abrasiveness such as a slurry such as used slurry is measured, the life can be ensured for a long time. If the thickness of the protective coating layer is less than 100 μm, the durability of the sensing element may not be sufficiently secured when the flow rate of the corrosive or abrasive liquid is measured.

Further, if the thickness of the protective coating layer exceeds 500 μm, the responsiveness of detection or the accuracy of detection may be impaired. Therefore, the thickness is preferably adjusted within the range below this value. Also in this case, it is desirable that the protective coating layer is made of a ceramic mainly composed of one or more selected from alumina, silicon carbide, silicon nitride and zirconia, or a fluororesin.

In a particularly preferred aspect of the first or second aspect of the present invention, the resistance heating element is a resistance metal winding portion, which is embedded in a base made of an inorganic material such as ceramic or glass or a fluororesin. 3 can be exemplified. In this configuration, the portion of the base that covers the outside of the resistance metal winding forms the protective coating layer. For example, when the base is made of ceramic, the sensing element can be manufactured very efficiently by burying the resistance metal winding in the ceramic raw material powder compact and firing it integrally. The ceramic base is desirably made of, for example, an alumina-based ceramic. Alumina-based ceramics are inexpensive, have extremely good corrosion resistance and abrasion resistance, and have high thermal conductivity, so that they have excellent responsiveness to heat. This makes it possible to provide a sensing element having high performance and excellent durability at a low price.

The material of the resistance metal winding portion is a Pt or Pt alloy (hereinafter referred to as a Pt-based metal) wire in consideration of both the ease of wire winding and the possibility of firing integrally with alumina. It is good to comprise. In this case, the P
The wire diameter of the t-based metal wire is preferably adjusted in the range of 20 to 50 μm in consideration of securing a necessary resistance value and ease of wire manufacture and wire winding. Further, the thickness of the alumina-based ceramic layer covering the winding portion is preferably at least larger than the diameter of the Pt-based metal wire, and desirably 100 mm.
The thickness is preferably from 500 to 500 µm, more preferably from 200 to 400 µm.

Next, in the structure of the fourth aspect, since the detecting element mounting means for detachably mounting the detecting element to the flow path forming member (for example, the pipe member) is provided, the mounting and replacement of the detecting element can be easily performed. It can be carried out.

According to the fifth aspect of the present invention, the temperature compensating element in which the outside of the temperature-sensitive resistor is covered with a protective coating layer made of an inorganic material such as ceramic or glass or a fluorine resin is provided separately from the flow velocity detecting element. The configuration was provided. By providing the temperature compensating element, it is possible to correct the influence of the temperature change of the liquid on the flow velocity measurement value, and it is possible to measure the flow velocity with higher accuracy. Further, since the temperature compensating element is provided separately from the detecting element, a problem that the heat generated by the resistance heating element of the detecting element is erroneously recognized as a rise in the temperature of the liquid is less likely to occur, and more accurate measurement can be performed. And since the temperature-sensitive resistor is covered with the same protective coating layer as the sensing element, even if the flow rate of a liquid substance having high corrosiveness or abrasiveness is measured, its life is ensured for a long time. be able to.

In this case, the thickness of the protective coating layer of the temperature compensation element is set to 100 to 5 for the same reason as in the case of the detection element.
It is preferable to adjust the thickness in the range of 00 μm, preferably 200 to 400 μm. It is also desirable that the material is made of a ceramic mainly composed of one or more selected from alumina, silicon carbide, silicon nitride and zirconia, or a fluororesin. In a particularly desirable embodiment, the temperature-sensitive resistor is a resistance metal winding similar to the resistance heating element of the detection element, and the protective coating layer is an alumina-based ceramic base in which the resistance metal winding is embedded. Examples can be given.

The temperature compensating element is mounted on the upstream side of the flow velocity detecting element in the flow path of the liquid material to be subjected to the flow velocity detection so as to reduce the influence of the heat generated by the resistance heating element of the detecting element. Further, the measurement becomes more difficult, and more accurate measurement can be performed.

Further, the flow velocity detecting element is a rod-shaped non-directional detecting element, and the rod-shaped detecting element is directed inward from the inner surface of the flow path to the flow path forming member by the detecting element mounting means. The structure is such that the liquid material hits the rod-shaped sensing element from the side, and the structure other than the sensing element (for example, the support of the sensing element) is less likely to project into the flow path. Therefore, the flow is hardly hindered, and a decrease in detection accuracy due to the occurrence of turbulence or the like is suppressed.

Preferably, the flow path forming member is a pipe member.
The sensing element mounting means is configured to include a tubular support detachably attached to the tubular member as described above, and the sensing element is integrally attached to the tubular support, and the tubular support and the tubular support are attached to the tubular member. If it is configured to be attached and detached,
Attachment or replacement of the sensing element is further facilitated.
In addition, it is easy to secure a seal between the tubular support and the tubular member.

In this case, if the detection element and the temperature compensation element are integrally provided on the tubular support, the attachment of the temperature compensation element together with the detection element can be performed at a time. The replacement work becomes easier. When the sensing element and the temperature compensating element are each formed in a rod shape in the form of an omnidirectional element or the like, the sensing element and the temperature compensating element are connected to the axis of the tubular support. Protruding from their inner surfaces in a line in a direction (for example, protruding in the radial direction)
By arranging, the influence of the turbulence of the flow by the element on the upstream side is less likely to be exerted on the element on the downstream side, and more accurate measurement can be performed. In this case as well, it is desirable that the temperature compensating element be arranged upstream of the sensing element, but this is not the case in a situation where the influence of heat generation from the sensing element can be reduced.

If the tubular support is provided with a resistance bridge circuit for detecting a change in the energization state of the flow velocity detecting element corresponding to the flow velocity of the liquid material, the flow velocity detecting element (or the flow velocity detecting element) can be provided. Since the wiring distance between the element and the temperature compensating element) and the resistance bridge circuit is shortened, attenuation of the flow velocity detection output in the wiring and the influence of noise can be reduced.
Measurement accuracy can be improved.

[0020] According to the eleventh aspect, the middle portion of the tubular support is an enlarged diameter portion whose diameter is larger than both end portions, and the flow velocity detecting element is attached to the enlarged diameter portion. Can be easily measured even in a small-diameter tube member where it is difficult to directly dispose. Further, by providing the enlarged diameter portion, the flow velocity is reduced, and turbulence is less likely to occur, so that an effect of increasing the measurement accuracy can be obtained. In this case, as in claim 12,
The flow velocity information in the enlarged diameter portion based on the detection output of the flow velocity detection element is converted into flow velocity information in the pipe member to which the tubular support is attached, in a form that corrects the decrease in the flow velocity in the enlarged diameter portion. By providing the correction output means for outputting, the influence of the decrease in the flow velocity due to the formation of the enlarged diameter portion is automatically corrected, and the flow velocity in the flow path can be accurately grasped.

Further, when it is attempted to detect the flow velocities of different kinds of liquids using the same flow velocity detecting element, even if the detection output levels of the flow velocity detecting elements are the same, the detection output levels are different depending on the type of the liquid substance. Corresponding flow velocity levels may be different. In this case, the flow velocity information based on the detection output of the flow velocity detection element is corrected by the flow velocity information correction / output means according to the type of the liquid to be measured, and the corrected flow velocity information is output. If output is configured, the flow rates of various liquid materials can be measured more accurately.

[0022]

Embodiments of the present invention will be described below with reference to the embodiments shown in the drawings. FIG. 1 shows a thermal flow sensor for liquid material (hereinafter simply referred to as a flow sensor) 1 according to an embodiment of the present invention, and a flow measuring system 1 using the same.
It is an external appearance perspective view which shows 00. The flow rate sensor 1 includes pipe members 150 and 15 that form a flow path of a liquid to be measured.
It is designed to be removable between 1
Tubular support 5 and flow velocity detecting element 6 disposed therein
And a temperature compensating element 7, and a circuit accommodating portion 8 integrated with the outer peripheral surface of the tubular support 5 and accommodating a resistance bridge circuit (described later) to which the flow velocity detecting element 6 and the temperature compensating element 7 are connected. It has. The flow velocity measuring system 100 includes the flow velocity sensor 1, a detection control unit 3, and a cable 2 connecting the two.

As shown in FIG. 2, the flow velocity detecting element 6 and the temperature compensating element 7 are each formed in a rod shape and penetrate the wall of the tubular support 5 having a substantially circular cross section from the outside in the through hole 5b. And is arranged to protrude radially from its inner surface. The two elements 6 and 7 have their base ends fixed to the circuit housing portion 8, respectively.
Is connected to the resistance bridge circuit section 101 housed inside the circuit. On the other hand, the circuit accommodating portion 8 is adhered to the outer peripheral surface of the tubular support 5 by an adhesive layer 8a, and is integrated.

The tubular support 5 is made of a metal or plastic having excellent corrosion resistance, for example, Ti, Zr, T
a, Nb, Ni, or other metal or stainless steel, or a fluororesin, or a ceramic such as an alumina-based ceramic, and external thread portions 5a for mounting are formed at both ends of the outer peripheral surface. , Pipe members 150, 151
Female threaded portions 150a, 1a formed on the inner surface of each connection end side of
By being screwed with 51a, it can be attached to this. Then, in the attached state, the inner surfaces of the pipe members 150 and 151 and the tubular support 5 become the flow path P, and the liquid F flows in the axial direction thereof (in the drawing,
The flow direction is indicated by arrows). Here, the liquid material F is
For example, it is a highly corrosive liquid such as an acid or alkali, or a highly abrasive liquid such as a slurry of ceramic raw material powder or granules (for example, used for polishing a semiconductor silicon wafer). It should be noted that the female screw portions 150a and 151a of the pipe members 150 and 151 and the male screw portions 5a of the tubular support 5 are provided.
In some cases, a sealing material (not shown) such as a fluororesin-based sealant is disposed between them.

As a result, the flow velocity detecting element 6 and the temperature compensating element 7 are arranged such that each axis is perpendicular to the flow direction of the liquid material F. Further, the flow velocity detecting element 6 and the temperature compensating element 7 are arranged so that the temperature compensating element 7 is located on the upstream side along the flow direction of the liquid material F (that is, the central axis direction of the tubular support 5). .

The flow rate detecting element 6 and the temperature compensating element 7
As shown in FIG. 3, each of the resistance metal winding portions 21 is formed by winding a Pt fine wire having a wire diameter of 20 to 50 μm.
Has a main body 9 buried in a base 10 made of ceramic such as alumina ceramic, glass, or fluororesin. The resistance metal winding part 21 functions as a resistance heating element in the flow velocity detecting element 6 and functions as a temperature-sensitive resistance element in the temperature compensation element 7. As shown in FIG. 3B, the resistance metal winding portion 21 is formed into a U-shape by, for example, bending a helical winding back at an intermediate portion.
The terminal portions 21a and 21b formed on the opening side of the
Project from the base end surface of the base member. Then, as shown in FIG. 3C, the resistance metal winding portion 21 of the base 10 is formed.
A portion covering the outside of the protective layer 12 becomes the protective coating layer 12. The thickness of the protective coating layer 12 is at least equal to or greater than the wire diameter of the resistance metal winding portion 21, and is preferably 100 to 50.
It is preferable to adjust the thickness in a range of 0 μm, and more preferably in the range of 200 to 400 μm.

The resistance metal wire used for the temperature compensating element 7 has a large resistance change due to a temperature change. If the temperature coefficient of the resistance metal wire is a positive metal, it is possible to use a material other than Pt, such as Ni. It is possible.

When the base 10 is made of a fluororesin, the fluororesin may be a polytetrafluoroethylene resin, a tetrafluoroethylene-perfluoroalkylvinyl ether resin, a tetrafluoroethylene-
Hexafluoropropylene copolymer, polytrichlorotrifluoroethylene, tetrafluoroethylene-ethylene copolymer, chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, polyvinyl fluoride and the like can be used.

Further, as shown in FIG. 4 (a), the main body 9 may be configured so as to cover the outside of the base 10 such as ceramics with a protective coating layer 12 of another material such as fluororesin. It is. As shown in FIG. 2B, the main body 9 is formed by winding a resistance metal wire around a rod-shaped ceramic base material 11 made of a weather-resistant material such as ceramic or glass to form a winding portion 21. However, a configuration in which the outside is covered with a protective coating layer 12 made of glass, a fluorine-based resin, or the like can also be adopted.

FIG. 5A is a circuit diagram showing an example of an electrical configuration of the flow velocity measuring system 100. Hereinafter, the configuration and operation will be described. In this circuit, the resistance change due to the cooling of the resistance metal winding 21 of the flow velocity detecting element 6 is detected by the resistance metal winding 21, the temperature compensation unit 7 ′ including the temperature compensation element 7, and the electric resistance. Resistance R of known value
1 and a variable resistor R2 on each side. In this circuit, portions incorporated in the detection control unit 3 in FIG. 1 are indicated by dashed-dotted lines with corresponding reference numerals, and a portion to be connected to the resistance bridge circuit unit 101 is a cable in FIG. They are bundled in the form of 2.

The circuit accommodating section 8 includes a transistor 105 and an operational amplifier 102 in addition to the bridge circuit section 101.
The portion enclosed by the frame indicated by the reference numeral 300 in FIG. However, connection cable 2
If the length can be specified to a predetermined value,
It is also possible to incorporate all of the components within the frame 00 except for the flow velocity detecting element 6 and the temperature compensating element 7 into the detection control unit 3 side. In this case, the circuit housing section 8 may be omitted.

In the resistance bridge circuit section 101, the connection point c between the flow velocity detecting element 6 and the temperature compensating unit 7 'is grounded. The connection point d between the resistor R1 and the flow velocity detecting element 6 and the connection point b between the variable resistor R2 and the temperature compensation unit 7 'are connected to input terminals of the operational amplifier 102, respectively.

On the other hand, the output side of the operational amplifier 102 has a resistor R
3 is connected to the base of the transistor 105. A power supply (voltage + Vcc) (not shown) is connected to the collector side of the transistor 105, and the resistor bridge circuit section 101 is connected to the emitter side. Note that R
Reference numeral 3 denotes a resistor for adjusting the input voltage to the base of the transistor 105.

When detecting the flow velocity of the liquid using such a flow velocity measurement system 100, the operational amplifier 102 is set in an operating state. First, in a state where the flow velocity is almost zero (hereinafter, referred to as a reference state), the point d is set. The resistance value of the variable resistor R2 is adjusted so that the voltage value between the ground and the ground becomes, for example, a known predetermined voltage (for example, about 3 to 4 V).
Set as The operational amplifier 102 outputs an output corresponding to a difference voltage between the connection points d and b of the resistance bridge circuit section 101 to the resistance bridge circuit section. This output is current-amplified by the transistor 105, and
01 is supplied.

In the resistance bridge circuit section 101, a temperature compensation unit 7 'is arranged on a side where the temperature compensation element 7 should be arranged. This is constituted by a sub-bridge circuit incorporating the temperature compensation element 7 in order to prevent an excessive current from flowing through the temperature compensation element 7 to generate resistance heating. FIG. 5B shows an example of a circuit configuration of the temperature compensating unit 7 ', in which a temperature compensating element 7 is provided on one side of the bridge. That is, in order to avoid overheating of the temperature compensating element 7 due to the current, it is necessary to use an element having a large resistance value. Since a difference easily occurs in the responsiveness with the element 6 (FIG. 2), it is difficult to perform temperature compensation when the liquid temperature changes suddenly. Therefore, by incorporating the temperature compensating element 7 into the bridge circuit, even if the temperature compensating element is not so high in resistance, the apparent resistance can be increased.

This bridge includes a temperature compensating element 7 (electric resistance value R), a transistor 201 (an FET or an indirectly heated thermistor can be used as long as the resistance changes depending on voltage or current), a resistor 202, 203 (electrical resistance values are r1 and r2, respectively) and an operational amplifier 204
It is composed of Note that 205 is a transistor 201
This is a resistor for adjusting the base input voltage to the power supply. Here, when feedback is applied by the operational amplifier 204 so that the bridge is always balanced, the following equation (1) is established. r1 · rT = r2 · R ‥‥‥ (1) rT is the resistance value of the transistor. Here, if the resistor 202 whose electric resistance value r1 is sufficiently larger than the electric resistance value R of the temperature compensation element 7 is selected, then r1 >> R ＞ (2). And the combined resistance of the whole bridge is
Is represented by

[0037]

(Equation 1)

From equation (1), rT = R · (r2 / r1) ‥‥‥ (3) By substituting equation (3) into equation 1, the following equation 2 is obtained.

[0039]

(Equation 2)

Here, from the equation (2), the first term of the denominator of the equation (2) is very small and can be neglected, so that the combined resistance can be approximately obtained by the following equation. R (1 + r2 / r1) ‥‥‥ (4) That is, the electric resistance value of the temperature compensation unit 7 ′ becomes equivalently large, and the resistance value is large even if the shape of the temperature compensation element 7 is small, and the response is high. Functions as a compensation edge.

As a result, in FIG. 5A, the current amplified by the transistor 105 mainly flows to the flow velocity detecting element 6 to generate resistance heat, and then flows to the ground at the point c. The electric resistance value of the flow velocity detecting element 6 changes due to the heat generation. The operational amplifier 102 outputs a feedback output to the resistance bridge circuit unit 101 so that the voltage difference between the connection points d and b becomes as small as possible. Since the voltage is adjusted, as long as the reference state is maintained, the resistance bridge circuit 10
1 is maintained, and a substantially constant voltage is applied to the resistance metal winding 21.

In this state, when the liquid material F (FIG. 2) hits the heated flow velocity detecting element 6 and is cooled, the resistance value of the resistance metal winding portion 21 decreases and the resistance bridge circuit portion 10
The equilibrium of 1 is broken. However, since the unbalanced voltage is fed back to the resistance bridge circuit section 101 via the operational amplifier 102 and the transistor 105, the resistance metal winding section 21 approaches the original electric resistance value, that is, further generates heat. As described above, the current If is supplied. As a result, an extra current corresponding to the amount of heat taken by the liquid F flows through the flow velocity detecting element 6 compared to the case of the reference state, and an extra voltage corresponding to the increased current is applied. . Here, the current If corresponds to the heat generated by the resistance metal winding portion 21 deprived by the liquid F (FIG. 2), and the amount of heat deprived increases as the flow rate increases. The flow rate can be detected by measuring the increment of. In this case, for example, the voltage at point d as viewed from the ground level of the resistance bridge circuit unit 101 can be extracted as a flow velocity signal. In FIG. 2, by multiplying the flow rate value ρ by the flow path cross-sectional area S of the tubular support 5,
The flow rate λ can be known.

Although there are various possible circuit configurations for the portion for extracting the flow velocity signal, the present embodiment is, for example, as follows. That is, the voltage at the point d indicates the reference voltage V0 even when the flow velocity is almost zero, but the flow velocity is reflected in the increment from the reference voltage V0, so that the reference voltage V0 is subtracted from the d-point voltage Vd to output the flow velocity signal. And Specifically, the peripheral resistor 1
If the voltage Vd at the d point is input to one terminal of the operational amplifier 103 constituting the differential amplifier together with the reference voltage V0 from the power supply 103e to the other terminal, the output of the operational amplifier 103 becomes the difference Vd between the two. -V0, which can be extracted as a flow velocity signal output. In this embodiment, Vd-V0 is set to the operational amplifier 1
03, inverts and amplifies with unity gain, takes out, and further inverts and amplifies with unity gain again by the operational amplifier 104 to return the output voltage polarity to the original.
Note that the circuit can be provided with a linearization circuit 106 that linearizes the flow velocity signal obtained as described above.
Note that the absolute value of the gain of at least one of the operational amplifier 103 and the operational amplifier 104 may be set to a value other than 1 as necessary.

Now, in the flow velocity sensor 1 of the present invention,
As described above, since the flow velocity of the liquid material F is detected based on the change in the electric resistance value of the resistance metal winding portion 21 of the flow velocity detection element 6, even when the flow rate is small, the flow velocity can be accurately measured. Yes, and cheap. FIG.
As shown in the figure, in the main body 9 of the flow velocity detecting element 6 to the temperature compensating element 7, the outside of the resistance metal winding 21 is made of alumina ceramic, glass or fluororesin.
Since it is covered with the protective coating layer 12 having a thickness of 0 μm or more, a highly corrosive liquid such as an acid or an alkali, a slurry of a ceramic raw material powder or an abrasive (for example, used for polishing a semiconductor silicon wafer or the like), etc. Even in the case of the liquid material F having a high abrasive property, the life can be ensured for a long time.

The flow velocity detecting element 6 and the temperature compensating element 7 may be arranged on both sides of the central axis O of the tubular support 5 as shown in FIG. 6, for example.

As shown in FIG. 7, an enlarged diameter portion 5d is formed at an intermediate portion of the tubular support 5 so as to be larger in diameter than both end portions thereof. The compensating element 7 may be provided. Thereby, the flow in the small-diameter tube member can also be easily measured. In this embodiment, connecting portions 5c each having an inner surface tapered are formed between the male screw portions 5a, 5a at both ends and the enlarged diameter portion 5d. The taper surface angle θ inside the connection portion 5c
Is preferably adjusted in the range of 6 to 10 ° or less. If the angle θ exceeds 10 °, turbulence is likely to occur, and the accuracy of measuring the flow velocity may not be secured. On the other hand, if the angle is less than 6 °, the length of the connecting portion 5c required for forming the desired enlarged diameter portion 5d becomes too large, which may lead to an undesired increase in the size of the tubular support 5.

In this case, the cross-sectional area of the flow path in the enlarged diameter portion 5d is S
1. The flow velocity is ρ1, the flow path cross-sectional area of a pipe member (corresponding to 150 and 151 in FIG. 1) connected before and after the tubular support 5 is S2,
Assuming that the flow rate is ρ2 and the pressure loss at the connecting portion 5c is almost negligible, the flow rates of the enlarged diameter portion 5d and the pipe member become equal to each other. S1 × ρ1 = S2 × ρ2 ‥‥‥ (1) , Ρ1 = (S2 / S1) × ρ2 ‥‥ (1) ′. Therefore, the flow velocity ρ1 in the pipe member to be measured is (S2 / S1) times the flow velocity in the enlarged diameter portion 5d.

In FIG. 5, for example, if the gain of the inverting amplifier by the operational amplifier 104 is not unity gain and the output is amplified by the gain corresponding to (S2 / S1), the flow rate measurement corresponding to the flow rate ρ1 can be performed. The output is obtained. For this purpose, for example, assuming that the resistance value of the resistor 111 on the input side of the operational amplifier 104 is RA and the resistance value of the resistor 110 of the negative feedback unit is RB, (RB / RA) = (S2
/ S1), the values of RA and RB may be set. In this case, the operational amplifier 104 (inverting amplifier) constitutes a correction output unit.

Next, when an attempt is made to detect the flow velocities of different types of liquids using the same flow velocity detecting element, even if the detection output levels of the flow velocity detecting elements are the same, the detection output level depends on the type of liquid substance. May correspond to different flow velocity levels. In this case, if the flow velocity information based on the detection output of the flow velocity detection element is corrected according to the type of the liquid substance to be measured, and the corrected flow velocity information is output, the flow velocity of various liquid substances can be increased. Be able to measure accurately. FIG. 8 shows a circuit configuration in that case (note that parts common to those in FIG. 5 are denoted by the same reference numerals and detailed description is omitted).

Here, a plurality of output correction circuits 250 having substantially the same configuration as that of the detection control section 3 in FIG. 5 are provided in accordance with the type of the liquid material to be measured. Selectively bridge circuit 1
01 is connected. The analog switch circuit 251 has an analog switch corresponding to each output correction circuit 250. The switch operation unit 254 is used to specify an output correction circuit 250 to be connected, and includes a push button operation unit or a dial operation unit. Then, the switch control signal generation unit 253 recognizes the operation state of the switch operation unit 254, and transmits a switch control signal for turning on the corresponding analog switch to the analog switch circuit 251.

Further, in each output correction circuit 250, the voltage of the power supply 103e is set to a different value so that a reference voltage V0 optimal for linearizing the flow velocity signal is given to the corresponding kind of liquid. . Also, the linearization circuit 106
Also, the circuit constants are set to be different from each other so that the gradient of the flow velocity-output curve after linearization gives the correct flow velocity value of the corresponding liquid material.

At the time of measurement, the switch operation unit 25
By setting 4 to the operation state corresponding to the type of the liquid to be measured, the corresponding output correction circuit 250 is selected by the switch circuit 251 and connected to the bridge circuit 101. As a result, the difference between the output Vd from the bridge circuit 101 and the reference voltage V0 specific to the selected liquid material is amplified by the operational amplifier 103, and further the linearization circuit 106 having a circuit constant specific to the liquid material. Linearization is performed, and the flow velocity signal after the linearization is output as a corrected flow velocity signal.

The output correction circuit 250 can be mainly composed of a microprocessor as shown in FIG. The microprocessor includes an I / O port 251 and a CPU 252, a RAM 253, and a ROM 2 connected thereto.
54. The output Vd from the bridge circuit 101 is A
The data is input to the microprocessor via the / D converter 255, and the CPU 252 performs a correction output process of the flow velocity value corresponding to the Vd input using the RAM 253 as a work area based on the control program 254a stored in the ROM 254. The ROM 254 stores the value of Vd (Vd1, Vd2, ‥‥) and the value of the flow velocity ρ (ρ11, ρ12, に 対 し て for fluid 1; ρ21, ρ22,
And the like (hereinafter, referred to as voltage-flow rate relationship information) 254b. Then, after selecting the type of the liquid material to be measured according to the input content from the input unit 257 (keyboard, mouse, etc.), when the value of Vd is captured, the voltage corresponding to the selected liquid material is reduced.
The flow velocity value ρ corresponding to Vd is calculated using the flow velocity relation information 254b, and is output as a flow velocity signal via the D / A converter 256 (in the case of digital output, the D / A converter is used). 256 becomes unnecessary).

[Brief description of the drawings]

FIG. 1 is an external exploded perspective view showing an example of a thermal flow rate sensor for a liquid material of the present invention and a flow rate measuring system using the same.

FIG. 2 is a cross-sectional view showing the internal structure of the thermal flow sensor for a liquid material in an attached state.

FIG. 3 is an external perspective view of a main body of a flow velocity detecting element and a temperature compensating element, a schematic diagram showing an internal structure thereof, and an explanatory diagram showing an enlarged main part thereof.

FIG. 4 is a sectional view showing some modified examples of the main body.

FIG. 5 is a circuit diagram showing an example of an electrical configuration of the flow velocity measuring system of FIG.

FIG. 6 is an axial sectional view showing a modified example of the thermal flow sensor for a liquid material.

FIG. 7 is a perspective view showing another modified example.

FIG. 8 is a circuit diagram showing an example of a configuration in which a flow velocity signal is corrected and output according to the type of a liquid material to be measured.

FIG. 9 is a block diagram showing an example in which a correction output circuit is mainly configured by a microprocessor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal flow sensor for liquid materials 5 Tubular support (detection element mounting means) 6 Flow velocity detection element 7 Temperature compensation element 8 Circuit accommodating part 9 Main part 10 Base 12 Protective coating layer 21 Resistance metal winding part (resistance heating element, 150, 151 Tube member 250 Output correction circuit (flow velocity information correction / output means)

Claims (13)

[Claims] 1. A body having a resistance heating element covered with a protective coating layer made of a ceramic mainly composed of one or more kinds selected from alumina, silicon carbide, silicon nitride and zirconia, or a fluororesin. And a flow rate detecting element for detecting a flow rate of the liquid material based on a change in an electric resistance value of the resistance heating element due to the contact between the main body portion and the liquid material. Sensor. 2. A main body in which a resistance heating element is covered with a protective coating layer made of an inorganic material such as ceramic or glass or a fluororesin and having a thickness of 100 μm or more, wherein the main body and the liquid material come into contact with each other. A thermal flow rate sensor for a liquid material, comprising: a flow rate detecting element for detecting a flow rate of the liquid material based on a change in electric resistance of the resistance heating element. 3. In the main body of the flow velocity detecting element, the resistance heating element is a resistance metal winding, and the resistance metal winding is provided in a base made of an inorganic material such as ceramic or glass or a fluororesin. The thermal flow sensor for a liquid material according to claim 1, wherein a portion of the base that is embedded and covers the outside of the resistance metal winding portion forms the protective coating layer. 4. A detecting element mounting means for detachably mounting the flow rate detecting element to a flow path forming member for forming a flow path of the liquid material, with the main body positioned in the flow path. Item 4. A thermal flow sensor for a liquid material according to any one of Items 1 to 3. 5. A temperature compensation element in which the outside of a temperature-sensitive resistor whose electric resistance changes in response to a temperature change of the liquid material is covered with a protective coating layer made of an inorganic material such as ceramic or glass or a fluororesin. 5. The thermal flow sensor for a liquid material according to claim 1, wherein the thermal flow sensor is provided separately from the flow rate detecting element. 6. The thermal flow velocity for a liquid material according to claim 1, wherein the temperature compensating element is mounted upstream of the flow velocity detecting element in a flow path of the liquid material to be subjected to flow velocity detection. Sensor. 7. The non-directional sensing element is formed in a rod shape extending in one axial direction and has substantially equivalent sensing characteristics in an arbitrary direction orthogonal to the axis thereof. The thermal means for a liquid material according to any one of claims 4 to 6, wherein the means attaches the rod-shaped flow velocity detecting element to the flow path forming member so as to protrude inward from an inner surface of the flow path. Flow rate sensor. 8. The tubular member, wherein the flow path forming member is a tubular member, and the detecting element attaching means is detachably attached to the tubular member, and forms a part of a flow passage together with the tubular member in the attached state. The flow rate detecting element is integrally attached to the tubular support in a form protruding inward from an inner surface thereof, and is attached to and detached from the pipe member together with the tubular support. The thermal flow sensor for liquid material according to any one of claims 4 to 7, wherein: 9. The flow rate detecting element and the temperature compensating element are each formed in a rod shape, and the flow rate detecting element and the temperature compensating element are provided on the tubular support in an axial direction of the tubular support. 9. The thermal flow rate sensor for a liquid material according to claim 8, wherein the thermal flow sensors for a liquid material are arranged so as to protrude from the inner surfaces thereof in a lined-up manner. 10. A resistance bridge circuit for detecting a change in an energized state of the flow rate detecting element corresponding to a flow rate of the liquid material is incorporated in the tubular support.
4. A thermal flow sensor for a liquid material according to claim 1. 11. The tubular support according to claim 8, wherein an intermediate portion of the tubular support is an enlarged diameter portion whose diameter is larger than both end portions, and the flow velocity detecting element is attached to the enlarged diameter portion. Thermal flow sensor for liquids. 12. The pipe member to which the tubular support is attached, wherein the flow rate information in the enlarged diameter portion based on the detection output of the flow velocity detection element is corrected for the flow velocity decrease in the enlarged diameter portion. The thermal flow rate sensor for a liquid material according to claim 11, further comprising a correction output unit that converts and outputs the flow rate information in the inside. 13. A flow velocity information correction / output means for correcting flow velocity information based on the detection output of the flow velocity detection element according to the type of the liquid substance to be measured, and outputting the corrected flow velocity information. The thermal flow rate sensor for a liquid material according to any one of claims 1 to 12, wherein: