JPH03295418A - Thermal type mass flowmeter sensor - Google Patents

Abstract

PURPOSE:To improve a response characteristic to transient variation in flow rate by forming a sensor pipe of a single-layer pipe made of a metallic material which is richer in anticorrosiveness than stainless steel and has higher thermal conductivity than stainless steel. CONSTITUTION:The sensor pipe 1 is made nearly of nickel to, for example, a 0.6mm external diameter and a 0.52mm internal diameter and its thermal conductivity (k) is 94W/m/K and about 3.8 times as large as k=24.5W/m/K of stainless steel. This sensor can expand a measurable flow rate range and also improves response performance and anticorrosiveness performance to corrosive gas.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention involves winding a heater around a sensor pipe in which a fluid to be measured is suspended, and measuring the flow of the fluid flowing through the sensor pipe based on the temperature of the heater itself or before and after the heater. This invention relates to improvements in thermal mass flowmeter sensors that measure flow rates.

[Prior Art and Problems to be Solved by the Invention] As disclosed in Japanese Patent Application Laid-Open No. 1-107114, there is an example of a small flow rate measuring device that cools a sensor pipe through which fluid flows, but in general, Heating is simpler than cooling, so a typical configuration of a heating-type residue meter that uses a heated quality meter is to heat a part of the sensor pipe through which the fluid to be measured flows. Detect the temperature difference between the upstream and downstream sides, or wrap a heat-sensitive resistance wire around the upstream and downstream sides of the sensor pipe to heat the sensor pipe and at the same time detect the temperature difference between the upstream and downstream sides based on the change in resistance of the heat-sensitive resistance wire. The temperature difference between the two sides is detected and the flow rate of the fluid to be measured is measured from that temperature difference.

Detection of temperature differences is normally carried out using a Wheatstone bridge circuit, but the technology disclosed in Japanese Patent Publication No. 1983-702 utilizes changes in electrical resistance due to temperature changes, but because the sensor pipe itself has electrical resistance. In this case, the bridge circuit cannot be a normal Wheatstone bridge, and therefore the output of the bridge circuit may not vary linearly with the flow rate. However, there is also a technology in which the inner layer is made of stainless steel and the outer layer is made of silver or copper, which has high thermal conductivity, to create a two-layer tube (Refer to Utility Model Publication No. 1-25295). When using a halogen-based gas such as F2, corrosion is likely to occur even if the inner layer is made of stainless steel.

In particular, the wall thickness of the sensor pipe is generally extremely thin, so even a small amount of corrosion may impair reliability.7 Also, since heated mass flowmeters heat the fluid, However, the corrosion resistance of stainless steel deteriorates when halogen gas reaches high temperatures, which is a problem.

To explain the operation of a thermal flowmeter here, the temperature of the fluid at the positions corresponding to the temperature measurement positions on the upstream and downstream sides is 0 when the flow rate is 0.
When , they are equal to each other, that is, the temperature difference is O. If you then increase the flow rate, what is the temperature of the fluid at the 2nd upstream position? i
However, the temperature of the fluid at the downstream position does not decrease as the temperature of the fluid at the upstream position decreases, and depending on the positional relationship between the heating position and the temperature measurement position, the temperature of the fluid at the downstream position increases. However, the temperature difference between the two increases from O, and generally this temperature difference increases linearly with the flow rate of the fluid. If the flow rate of the fluid is further increased, there is a limit to the decrease in the temperature of the fluid at the upstream position, and at the same time, the fluid reaches the downstream position before it is sufficiently heated in the heating section, so the temperature difference between the fluid at both positions is decreases again, and therefore there is a limit to the measurement range of the flow rate.

Next, focusing on the temperature of the sensor pipe, if heat conduction in the longitudinal direction is poor, the temperature difference in the fluid at the upstream and downstream positions will be directly reflected in the temperature difference in the sensor pipe, so the sensitivity of the flowmeter will not be high. However, on the other hand, heat is not supplied from the higher temperature downstream sensor pipe to the lower temperature upstream side, so the upper limit of the flow rate measurement range is reached early.6 The stainless steel has a low thermal conductivity among metal materials. Therefore, in a configuration in which stainless steel is used as the sensor pipe or stainless steel is used as the inner layer, there is a problem that the flow rate measurement range is narrow.

Next, looking at heat conduction in the radial direction of the sensor pipe, the temperature of the fluid reaches the inner surface of the sensor pipe, is transmitted through the wall thickness of the sensor pipe, and then reaches the temperature measuring means attached to the outer surface, so heat conduction in the radial direction If the quality is poor, the response characteristics to transient changes in flow rate will be slow.6 Stainless steel has low thermal conductivity, so in a configuration that uses stainless steel as the sensor pipe or stainless steel as the inner layer, the response to transient changes in flow rate will deteriorate. There is also the problem of doing so.

As a means to improve the radial heat conduction of the sensor pipe, there is a technique to reduce the wall thickness of the sensor pipe (
JP-A No. 62-192618), there is a risk that the strength of the sensor pipe will be unreliable.6 Similarly, if the wall thickness of the two-layer stainless steel is made thin, there is a risk that the strength of the sensor pipe will be unreliable.

Therefore, an object of the present invention is to provide a thermal mass flowmeter sensor that has excellent response characteristics to transient changes in flow rate, excellent corrosion resistance against halogen gas, and can be used over a wide maximum flow rate range.

[Means for Solving the Problems] The present invention achieves the above objects by forming the sensor pipe with a single-layer pipe made of a metal material that is more corrosion resistant than stainless steel and has higher thermal conductivity than stainless steel. This is what I did.

Examples of the metal material include nickel or platinum.

[Function] Since the sensor pipe of the present invention is made of a metal material with higher thermal conductivity than stainless steel, heat conduction between the inner and outer surfaces of the sensor pipe is improved, and the response to transient changes in flow rate is improved. Characteristics improve.

At the same time, heat is supplied from the higher-temperature downstream sensor pipe to the lower-temperature upstream side, and therefore, although the sensitivity of the flowmeter becomes lower, the flow rate measurement range becomes wider. As a result, when fluid flows through the sensor pipe and the bypass flow path that bypasses it, the flow rate in the bypass flow path can be small, so the structure of the bypass flow path can be simplified, and the measured flow rate relative to the total flow rate can be reduced. Since the ratio is high, the accuracy of the flowmeter as a whole improves.

Further, in the present invention, since the sensor pipe is made of a metal material that is more corrosion resistant than stainless steel, the sensor pipe has improved corrosion resistance compared to when the sensor pipe is made of stainless steel. In other words, the thermal quality 1FfLI meter is mainly used for controlling the flow rate of gas in semiconductor manufacturing equipment.
N2. Passes various gases such as Ar, He, Cl□6
Among them, halogen-based gases such as CI2, CIFq, and F2 are extremely corrosive, and corrode most metals, including stainless steel, especially in high-temperature ranges, but pure nickel has better corrosion resistance than stainless steel, such as It is hardly affected by CIFq up to about 600°C. Therefore, metals that are more corrosion resistant than stainless steel, such as nickel and platinum, have corrosion resistance even when used in high temperature ranges with halogen gases used in the semiconductor manufacturing field, ensuring a long service life.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is an external view of a thermal flowmeter sensor S according to an embodiment of the present invention, in which a pair of cases 4 and 4' are made of aluminum material and are formed almost symmetrically, and FIG. FIG. A heat insulating material 6 made of ceramic paper made of ceramic fibers formed into a vapor shape is installed in the dipper 5 formed on the mating surface 3 of the case 4.4', and is assembled to hold the sensor pipe 1. sensor pipe 1
is a thin tube bent into a roughly U-shape, with both ends of the sensor pipe 1
The 7-sensor pipe 1, which is fixed so that a and 1b pass through the substrate 2, has an outer diameter of 0.6 mm and an inner diameter of 0.52 mm, and is composed almost entirely of nickel, and its thermal conductivity is 194 W/m/ (Science Chronology 6
0 version), stainless steel = 24-5W/m/
It is approximately 3.8 times larger than K (same as before).

Both ends 1a and 1b of this sensor pipe are connected to a main pipe (not shown), and a bypass flow path is formed in the main pipe in parallel with this sensor pipe 1, and the flow rate Q of the sensor pipe 1 and the bypass flow are The flow rate Q of the sensor pipe 1 and the total flow rate of the main pipe can be determined in this way.

A pair of coils 7.8 are wound around the outer circumference of the sensor pipe 1, and are housed in a coil 5 within a case 4.4'. The coil 7.8 is both a heating element and a temperature-sensitive element, and is formed of a very fine enamelled metal wire with a core of platinum, iron-nickel, etc. The outer surface of the sensor pipe 1 is thinly coated with an insulating material made of polyimide resin diluted with toluene, and the above-mentioned sensor/sensor coil 7.8 is placed over the insulating material 100 mm in the length direction of the sensor pipe 1.
The coils are wound approximately 200 times, and the above insulating material is applied to form an insulating film to provide insulation between the coils and between the coil and the sensor pipe. The coil 7.8 is heated 50°C to 100°C higher than the fluid temperature, but the insulation of the upper seam is heat resistant and the coil insulation will not be destroyed.2 Figure 3 shows the upstream side of the sensor vibe 1 and 7.8 shows a means for detecting the temperature difference with the downstream side, and a heater/sensor coil 7.8
Assuming that the electrical resistance values of are R7 and Rs, this resistor constitutes a bridge circuit with another pair of fixed resistors R1 and R2. A constant current ib from the constant current source 10 flows through the bridge circuit, and the Joule heat of the coil 7.8 causes the sensor vibe 1 to be in a state where the temperature is 50 to 100° C. higher than the room temperature or the temperature of the fluid. Sensor flow rate Q, is Q, = O
In this case, the bridge is balanced and the unbalanced voltage ΔE of the bridge circuit is ΔE=O. When a flow rate Q flows through the sensor pipe 1, heat is transferred from the coil 7 to the coil 8 I! !
II, the temperature of the coil 7 decreases and the temperature of the coil 8 increases, causing the resistance values R7 and RA of the coil 7.8 to change, causing an unbalanced voltage E in the bridge circuit.
ΔE is taken out as the output of the differential amplifier 11, and this output is the sensor flow rate Q.

Since it is proportional to No convection occurs, and therefore zero drift and span drift due to changes in the attitude of the flow meter sensor S are eliminated.

FIG. 4 shows the measurement result (A
>, and for comparison, the results were also shown for the case of a stainless steel single-layer tube (B) and the case of a case where the outer surface of the stainless steel tube was plated with copper (C) under the same conditions. As can be seen from this figure, in the stainless steel single-layer pipe, the range in which the flow rate Q and the unbalanced voltage E change linearly is Qs = 7cc/
min, then ΔE- = 70 mV, and in a two-layer pipe with copper plating on the outer surface of the stainless steel pipe, the range of linear change is up to Qs = 8 cc/min, then ΔE = 45 mV In contrast, in this example, the range of linear change is Q, = 15 cc
/min, at that time ΔE=50 mV6, that is, in this example, although the detection sensitivity decreased somewhat, the upper limit flow rate in the linearly changing range increased approximately twice.

Next, the results of measuring the response characteristics to transient changes in the flow violet are shown in Figure 5.6 In Figure 5, as shown in (a), the flow rate Q is changed stepwise from O to 5 cc/min. The response of the unbalanced voltage ΔE when In the present example (c), the response time was τ-2 sec, and the response characteristics were improved.

Furthermore, if the fluid flowing inside the sensor vibrator is, for example, CIF, which is used in the semiconductor manufacturing field, the corrosion rate increases as the temperature increases, and stainless steel can withstand use only at temperatures below 120 degrees Celsius, and at higher temperatures. Although corrosion occurs in a short period of time, the sensor vibe 1 of this embodiment is made of nickel, which has higher corrosion resistance than stainless steel, so it can withstand use up to high temperatures of 600°C. For this reason, even when a large amount of fluid such as the above-mentioned halogen gas, which is particularly corrosive, is flowed in a high temperature range, it is now possible to ensure long-term life.In addition, in the above embodiment, the sensor vibe 1 is made of platinum. A similar effect occurs.

Next, the substrate 2 of the thermal mass flowmeter sensor S is generally made of stainless steel, and the sensor vibe 1 is generally made of stainless steel.
must be identified to the substrate 2 with sealing properties. When the sensor vibe 1 is made of stainless steel as in the past, it is difficult to seal the sensor vibe 1 to the substrate 2.
Fixation could be easily achieved by brazing6 Note that the substrate 2 is of sufficient thickness and that the substrate 2
Although the temperature of the fluid in contact with the substrate 2 is not heated,
There is no problem with it being made of stainless steel. However, from the viewpoint of corrosion resistance, it is necessary to use a brazing material mainly composed of, for example, 2.7 Kel.6 However, when the sensor vibe 1 is made of, for example, nickel, the substrate 2 is When brazing is attempted, impurities in the brazing filler metal melt into the sensor pipe 1 and lower its melting point, causing the sensor pipe 1 to melt. Furthermore, when beam welding is attempted between the sensor pipe 1 and the substrate 2, the heat capacity of the sensor pipe 1 is significantly smaller than that of the substrate 2, so that proper welding cannot be performed.

Therefore, in this embodiment, as shown in FIG. 6, a stainless steel vibrator 9 is fitted onto each of the ends 1a and 1b of the sensor pipe 1, and the stainless steel pipe 9 and the ends 1a and 1b of the sensor pipe are connected to each other. Beam welding Y is performed between the stainless steel pipe 9 and the substrate 2, and brazing Z is performed between the stainless steel pipe 9 and the substrate 2. Regarding beam welding Y, there is not much difference in heat capacity between sensor pipe 1 and stainless steel pipe 9, and regarding brazing Z, since both stainless steel pipe 9 and substrate 2 are made of stainless steel, both are properly performed. It can be carried out. Note that the beam welding Y between the stainless steel pipe 9 and the tube ends 1a and lb of the sensor pipe and the brazing Z between the stainless steel pipe 9 and the substrate 2 may be performed in any order.

[Effects of the Invention] As explained above, according to the thermal mass flowmeter sensor of the present invention, the measurable flow rate range can be approximately doubled compared to the conventional example, and the response performance and corrosion resistance against corrosive gas can be improved. It has become possible to obtain a flowmeter with extremely excellent overall performance.

[Brief explanation of drawings]

Fig. 1 is an external view of an embodiment of the present invention, Fig. 2 is a front view when one case is removed, Fig. 3 is a circuit diagram of the bridge circuit, and Fig. 4 is an imbalance with respect to the sensor flow rate Q. Voltage Δ
FIG. 5 is a characteristic diagram showing the response of the unbalanced voltage ΔE to a step change in the flow rate Q. FIG. 6 is an enlarged cross-sectional view of the section X in FIG. S...Thermal mass flow meter sensor...Sensor pipe 2...Board 3...Mating surface 4.4'...Case 5...Groove 6...
... Insulation material 7 ... Upstream coil 8 - Downstream coil 9 ... Stainless steel pipe Y ... Beam welding Z ... Brazing

Claims (5)

[Claims] (1) In a thermal mass flowmeter sensor having a sensor pipe through which a fluid to be measured flows, a means for heating the sensor pipe, and a means for detecting a temperature difference between an upstream side and a downstream side of the sensor pipe, the sensor A thermal mass flowmeter sensor characterized in that the pipe is formed from a single-layer pipe made of a metal material that has higher corrosion resistance than stainless steel and higher thermal conductivity than stainless steel. (2) An upstream coil and a downstream coil formed by a heat-sensitive resistance wire are wound around the outer peripheral surfaces of the upstream side and downstream side of the sensor pipe through which the fluid to be measured flows, respectively, and the upstream coil, the downstream coil, and the other coils are wound. A thermal mass flowmeter sensor that forms a bridge circuit with a resistance of This thermal mass flowmeter sensor is characterized by being formed from a single-layer tube made of a metal material that is highly corrosion resistant and has higher thermal conductivity than stainless steel. (3) The thermal mass flowmeter sensor according to claim 1 or 2, wherein the metal material is nickel. (4) The thermal mass flowmeter sensor according to claim 1 or 2, wherein the metal material is platinum. (5) Fitting a stainless steel pipe onto the end of the sensor pipe, beam welding the stainless steel pipe and the end of the sensor pipe, and bonding the stainless steel pipe to the substrate of the thermal mass flowmeter sensor. The thermal mass flowmeter sensor according to any one of claims 1 to 4, wherein the thermal mass flowmeter sensor is brazed to the thermal mass flowmeter sensor.