JP6234743B2 - Thermal flow sensor - Google Patents

Description

  The present invention relates to a thermal flow sensor.

  As a conventional thermal flow sensor, as shown in Patent Document 1, there are wound coils that are heater and temperature sensors at two locations on the sensor flow path that branches off from the main flow path through which the fluid flows and returns to the main flow path. The fluid flow rate is calculated from the temperature difference when a constant current is passed through each winding coil or the power consumption difference of each coil when the temperature difference at each coil is kept constant. It has been known.

More specifically, the main flow path is penetrated through a block-shaped body, and a pair of ports communicating with the main flow path is provided at two locations of the body.
On the other hand, the sensor flow path is formed by a metal thin tube, and this metal thin tube is accommodated in a dedicated rectangular casing. The metal thin tube is accommodated by being bent into a U-shape inside so that each end is opened at an inlet and an outlet provided on the bottom surface of the casing, and the winding coil is placed in an intermediate portion of the U-shape. Is wound.
Then, by attaching a casing to the body, each end of the metal thin tube is connected to each port, and a part of the sample fluid passes through the metal thin tube which is a sensor flow channel from the main flow channel. is there.

  In such a thermal flow sensor, in order to improve sensitivity and output linearity, it is necessary to improve the heat exchange rate. To that end, it is an effective technique to increase the winding width of the winding coil. . This is because it takes a long time for the fluid in the metal thin tube to pass through the winding region of the winding coil, and as a result, the heat exchange rate is improved.

  However, it is not preferable to simply enlarge the casing in order to increase the winding width of the coil. For example, if the middle part of the metal thin tube around which the coil is wound is lengthened by increasing the pitch between the inlet and outlet of the casing, the mounting mode with the main body changes, and the existing main body is used. become unable.

JP 2009-300403 A

  The present invention has been made to solve the above-mentioned problems, and while increasing the winding width and thereby improving the sensitivity and output linearity, etc., while suppressing the increase in size, the existing parts The main problem is to provide a thermal flow sensor that can be used as it is.

That is, the thermal flow sensor according to the present invention branches from the main flow path, and the sensor flow path is configured to flow a predetermined ratio of the fluid flowing through the main flow path, and is wound around the sensor flow path. A temperature measuring coil, and measuring the flow rate of the fluid flowing through the main flow path based on the temperature indicated by the resistance value of the winding coil;
An inlet and an outlet of the sensor flow path are provided, and a casing in which the sensor flow path is formed is provided, and the winding coil is provided in an intermediate portion of the sensor flow path in the casing. And at least a part of the front part of the sensor flow path is located outside the inlet in the casing, and / or at least a part of the rear part of the sensor flow path in the casing, It is positioned outward from the outlet.

  In such a case, in the casing, the front part and / or the rear part of the sensor flow path extend outward from the inlet and / or outlet of the casing, so that the winding coil is provided between them. The part can be enlarged. As a result, since the winding width of the winding coil can be increased, the heat exchange rate can be improved and the sensitivity and output linearity can be improved as described above.

  Moreover, since the sensor flow path spreads outward in the casing to secure the length of the intermediate portion, it can be made the same as the conventional casing without increasing the distance between the inlet and the outlet. . As a result, the casing according to the present invention can be directly attached to the existing main body, and design changes and component changes can be minimized.

  The sensitivity can be improved by increasing the resistance value of the winding coil. Conventionally, since the winding width was limited to be small, in order to increase the resistance value of the winding coil and improve the sensitivity, a device such as double winding or triple winding has been devised, but according to the present invention, Since the winding width can be increased, an appropriate resistance value can be obtained even if the winding coil has a single winding, and a sensitivity equal to or higher than that of a conventional double winding can be obtained.

  In addition, in order to make the winding coil double winding, it is necessary to manually set the winding start position of the second stage. For this reason, the throughput is limited or the winding state varies. Although a difference may occur, if it is a single winding, it is possible to fully automate the manufacture of the wound coil, and it is possible to improve throughput and reduce instrumental differences in sensor characteristics.

  If the entire winding coil is coated with a resin such as polyimide whose viscosity is below a predetermined value and is fixed to the outer periphery of the sensor flow path, the winding coil will be unscrewed compared to fixing by spotting adhesive. The situation can be prevented as much as possible. Further, since the viscosity of the resin is low, it is possible to easily apply a uniform amount as compared with the case of using a highly viscous adhesive, and it is possible to suppress the variation in the heat capacity and to reduce the instrumental difference in the sensor characteristics.

  According to the present invention configured as described above, the front portion and / or the rear portion of the sensor flow path extend outward from the inlet and / or outlet of the casing, and therefore the intermediate portion provided with the winding coil therebetween. Can be long. As a result, since the winding width of the winding coil can be increased, as described above, the heat exchange rate is improved, and the sensitivity and output linearity can be improved.

  Moreover, since the length of the intermediate portion is secured by spreading the sensor flow path outward in the casing, for example, it is possible to make it the same as the conventional casing without increasing the distance between the inlet and the outlet. It becomes. As a result, the casing according to the present invention can be directly attached to the existing main body, and design changes and component changes can be minimized.

1 is a schematic external view of a thermal flow sensor according to an embodiment of the present invention. The typical block diagram of the thermal type flow sensor in the embodiment. The front view which shows the casing main body in the same embodiment, and the thin tube accommodated in the inside. Sectional drawing which shows the internal structure in the upper body which attached the casing to the base and the main body in the same embodiment.

  An embodiment of a thermal flow sensor according to the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the thermal flow sensor 100 according to the present embodiment is a thermal mass flow sensor to be precise, and is a sample gas G that is a fluid used in a semiconductor manufacturing process, for example. This is for measuring the flow rate of a semiconductor processing gas (for example, SF ₆ or the like).

Specifically, as shown in FIG. 2, the thermal flow sensor 100 is branched from the main flow path 2 through which the sample gas G flows, and downstream of the branch point. The sensor flow path 3 set as a part of the branch flow path 3A returning to the main flow path 2 at the merge point, the flow rate detection mechanism 4 for detecting the flow rate of the sample gas G, and the branch point in the main flow path 2 merge. And a laminar flow element 5 as a resistor provided between the points. The laminar flow element 5 is such that the diversion ratio between the main flow path 2 and the sensor flow path 3 becomes a predetermined design value, and is composed of a resistance member such as a bypass element having constant flow characteristics. As the laminar flow element 5, one formed by inserting a plurality of thin tubes into the outer tube, or one formed by laminating a plurality of thin discs having a large number of through holes is used. Can do.
As shown in FIG. 2, the main flow path 2 is formed by penetrating through a main body 200 made of metal (for example, stainless steel).

  As shown in FIGS. 2 to 4, the sensor flow path 3 is formed by a thin tube 300 made of metal (for example, stainless steel), and is made of metal (for example, stainless steel) attached to the main body 200 via a base 600. The product is accommodated so as to pass through the inside of the casing 500.

  As shown in FIG. 2, the flow rate detection mechanism 4 includes a sensor unit 41 for detecting a flow rate divided into the sensor flow channel 3, and a sample that flows through the main flow channel 2 by acquiring an output signal from the sensor unit 41. A flow rate calculating unit 42 for calculating at least a mass flow rate of the gas G.

  The sensor unit 41 includes an upstream winding coil 411 and a downstream winding coil 412 in which a heating resistance wire whose electrical resistance value increases or decreases with changes in temperature is wound around the outer peripheral surface of the thin tube 300. . The upstream winding coil 411 and the downstream winding coil 412 serve both as a heater and a temperature sensor.

  The flow rate calculation unit 42 is an electric circuit having the upstream winding coil 411 and the downstream winding coil 412 as a part of its configuration, and includes a bridge circuit, an amplification circuit, a correction circuit, and the like. In terms of function, the flow rate calculation unit 42 detects the instantaneous flow rate of the sample gas G as an electrical signal (voltage value) from the upstream side winding coil 411 and the downstream side winding coil 412, and detects in the sensor flow path 3. The flow rate of the sample gas G in the main flow path 2 is calculated based on the diversion ratio between the main flow path 2 and the sensor flow path 3, and a sensor output signal (flow rate) corresponding to the calculated flow rate is calculated. Measurement signal). The specific circuit configuration of the flow rate calculation unit 42 differs between the constant temperature control method and the constant current control method, but since this is known, detailed description thereof is omitted.

  However, the thermal flow sensor 100 according to this embodiment is characterized by the casing 500. Therefore, the casing 500 and related members will be described in detail below.

As shown in FIGS. 1, 3, and 4, the casing 500 is a flat rectangular plate formed by bonding a hollow casing body 51 whose front is open and a lid 52 that seals the opening. It is mounted on the pedestal 600 upright.
FIG. 3 shows the casing body 51 as viewed from the opening side.

  An inlet 5a and an outlet 5b are formed at a predetermined interval on the bottom surface of the casing body 51, and the narrow tube 300 is disposed so as to pass through the inside of the casing 500 through the inlet 5a and the outlet 5b. Yes.

  As shown in FIG. 4, the pedestal 600 is provided with a pair of through holes 61 penetrating in the thickness direction, and the narrow tube 300 extending outward from the inlet 5 a and the outlet 5 b passes through the through hole 61. In the vicinity of the back surface of the pedestal 600, it spreads in a trumpet shape and is welded to the inner peripheral surface of the through hole 61. The pedestal 600 is bolted to the main body 200. At this time, the end opening of the branch flow path 3A provided in the main body 200 matches the back surface opening of the through hole 61, so that the branch flow The path 3A is connected to the sensor flow path 3, that is, the narrow tube 300. A packing S such as an O-ring for preventing leakage is provided between the end opening of the branch channel 3A and the end opening of the narrow tube 300 (the back surface opening of the through hole 61).

  Returning to this discussion, when the narrow tube 300 in the casing 500 is divided into the front part 31 corresponding to the upstream side, the rear part 32 corresponding to the downstream side, and the intermediate part 33 therebetween, for convenience, the front part 31 is divided. The rear portion 32 extends from the inlet 5a and the outlet 5b obliquely outward, then extends vertically, and then curves inward to reach the intermediate portion 33. The shapes of the front portion 31 and the rear portion 32 are bilaterally symmetric.

  Here, the outer side than the inlet 5a means the side opposite to the outlet 5b when viewed from the inlet 5a, and the outer side than the outlet 5b is the side opposite to the inlet 5a when viewed from the outlet 5b. Say that. Specifically, the region corresponding to the outer side is a region outside the region sandwiched by imaginary lines L1 and L2 passing through the outer ends of the inlet 5a and the outlet 5b in FIG. When the narrow tube 300 passes through the region, it is defined as passing through the outside.

  The intermediate portion 33 is a straight pipe parallel to a virtual line connecting the inlet 5a and the outlet 5b, and the upstream side winding coil 411 and the downstream side winding coil 412 are disposed at symmetrical positions in the intermediate portion 33. Each is wrapped.

Each winding coil 411, 412 is a single winding. In this embodiment, the entire winding coils 411 and 412 are coated with polyimide resin and fixed to the outer periphery of the thin tube 300. As the coating material, a material having excellent heat insulating properties and insulating properties is preferable, and it is also important to evaluate mechanical strength, viscosity, elasticity, chemical resistance and the like. In addition to that, polyimide resin is adopted here because it has many excellent points such as heat resistance, mechanical properties at high temperature, chemical resistance, low expansion coefficient, and incombustibility. . In addition, inorganic ceramic coating materials, silicone sealing materials, glass coating materials, fluororesins, and the like can also be used.
A cable extending from each of the winding coils 411 and 412 is electrically connected to a terminal 72 (shown in FIG. 1) extending to the outside through a terminal plate 71 held in the casing 500. Electrical signals of the winding coils 411 and 412 are taken out from the terminal 72. 3 and 4 indicate the insulating plate 8 that holds the terminal plate 71.

As shown in FIGS. 3 and 4, each end portion of the intermediate portion 33 is thermally connected to a heat radiating member 9 having a rib shape integrally extended from the inner wall of the casing 500. The heat dissipating member 9 is for securing a path through which heat from the winding coils 411 and 412 escapes to shorten the time until the temperature distribution of the sample gas is stabilized. In this embodiment, the distance from the outer ends of the winding coils 411 and 412 to the heat radiating member 9 is set to be larger (1 mm → 1.5 mm) than before. In addition, the code | symbol 9a in a figure is a putty member rich in thermal conductivity.
Next, the effect of the thermal flow sensor 100 having the above configuration will be described.

  First, in the casing 500, since the thin tube 300 spreads outward from the inlet 5a and outlet 5b of the casing 500, the intermediate portion 33 provided with the winding coils 411 and 412 can be lengthened. As a result, since the winding width t1 of the winding coils 411 and 412 can be increased, the heat exchange rate is improved, and the sensitivity and output linearity can be improved.

  Moreover, since the narrow tube 300 spreads outward in the casing 500 to ensure the length of the intermediate portion 33, the distance p1 between the inlet 5a and the outlet 5b can be made the same as that of the conventional casing. . As a result, the casing 500 can be directly attached to the existing main body, and design changes and component changes can be minimized.

  In the casing 500, the fact that the narrow tube 300 spreads outward from the inlet 5a and the outlet 5b, conversely, reduces the distance between the inlet 5a and the outlet 5b while securing the winding width t1. In addition, the distance p2 from the outlet 5b to the outer end of the casing 500 can be increased. In this embodiment, the casing 500 containing the thin tube 300 is joined to the pedestal 600, and the pedestal 600 with casing is bolted to the main body 200, but from the inlet 5a and the outlet 5b to the outer end of the casing 500. When the distance p2 is short, distortion due to bolting acts on the inlet 5a and the outlet 5b, and unexpected leakage may occur. According to this sensor configuration, the distance from the inlet 5a and the outlet 5b to the outer end of the casing 500 Since p2 can be increased, the above-mentioned leakage problem can be suitably prevented.

  In addition, since the winding width t1 is larger than the conventional one, an appropriate resistance value can be obtained even if the winding coils 411 and 412 are a single winding, and a sensitivity equal to or higher than that of the conventional double winding can be obtained. .

  Furthermore, since it is a single winding, manufacturing of the winding coils 411 and 412 can be completely automated, and throughput can be improved and instrumental differences in sensor characteristics can be reduced.

  In addition, since the entire winding coils 411 and 412 are coated with polyimide resin and fixed to the outer periphery of the thin tube 300, the winding coils 411 and 412 are unscrewed as compared with fixing by spotting with an adhesive. Compared to the case of using a high-viscosity adhesive, a uniform amount can be applied easily and the variation in heat capacity can be suppressed to prevent instrumental error in sensor characteristics. It can also be reduced.

  On the other hand, as described above, the response speed can be increased by the heat radiating member 9, but if the heat radiating member 9 is too close to the winding coils 411, 412, the heat capacity becomes large and consumption by the winding coils 411, 412 is increased. The power increases, and the winding coils 411 and 412 always consume a large amount of power in addition to the power exchanged with the sample gas, so that the output linearity with respect to the flow rate is also deteriorated.

On the other hand, in the present embodiment, the response speed is slightly slowed by slightly increasing the distance t2 from the heat dissipation member 9 to the winding coils 411 and 412 as compared with the conventional case, but the output linearity can be improved and at the time of manufacture. The variation in the distance is easily absorbed, and the instrumental difference in response speed can be reduced.
The present invention is not limited to the above embodiment.

The shape of the front portion and the rear portion of the thin tube is not limited to that shown in FIGS. 3 and 4, and any shape may be used as long as a part thereof is outside the inlet and the outlet. For example, it may be a winding thing.
Only the front part is outside the entrance and the rear part is inside the exit, or only the back part is outside the exit and the front part is inside the entrance .
The intermediate part is a part where at least the winding coil is wound, and the upstream side or the downstream side from that part may be the front part or the rear part immediately after that part. As in the form, the intermediate portion may be from the portion where the winding coil is wound to the upstream side or the downstream side by a predetermined distance.

The intermediate portion of the thin tube to which the winding coil is attached is not limited to a straight tube, and may be curved. Moreover, the edge part of this intermediate part may exist in an outer side rather than an inlet_port | entrance and an exit.
The winding coil may be a multiple winding.
The flow rate control device may be configured by providing a flow rate adjustment valve for adjusting the flow rate of the main flow path on the upstream side or the downstream side of the thermal flow rate sensor.

  In addition, it is needless to say that the present invention may appropriately combine a part or all of the above-described embodiments and modified embodiments, and various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 ... Thermal flow sensor 2 ... Main flow path 200 ... Main body 3 ... Sensor flow path 300 ... Narrow tube 4 ... Flow rate detection mechanism 411 ... Upstream winding coil 412 ... Downstream winding coils

Claims (3)

A sensor flow path branched from the main flow path so that a predetermined ratio of the fluid flowing through the main flow path flows, and a winding coil as a temperature sensor wound around the sensor flow path, In what measures the flow rate of the fluid flowing through the main flow path based on the temperature indicated by the resistance value of the winding coil,
The main flow path is a separate body from the main body formed therein , and includes a casing in which an inlet and an outlet of the sensor flow path are provided so that the sensor flow path is formed inside. The winding coil is provided in an intermediate portion of the sensor flow path in the casing, and at least a part of a front portion of the sensor flow path is positioned outside the inlet in the casing, and / Or a thermal flow sensor, wherein at least a part of a rear portion of the sensor flow path is positioned outside the outlet in the casing.   The thermal flow sensor according to claim 1, wherein the winding coil has a single winding.   The thermal flow sensor according to claim 1 or 2, wherein a substantially entire winding coil is coated with a resin such as polyimide having a viscosity of a predetermined value or less and fixed to the outer periphery of the sensor flow path.