JPH0325724B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method suitable for controlling the flow rate of various gases used in the manufacturing process of semiconductors, ICs, etc.
This invention relates to an improvement of a mass flow control device using a thermal sensor.

[Conventional technology]

Conventionally, as shown in FIG. 3, a mass flow rate control device using resistance heating elements (thermal sensors) 101A and 101B is known. Here, 102 is a sensor tube that divides the gas (usually several cc/min to several tens of cc/min)
This is used to determine the mass flow rate. In the resistance heating elements 101A and 101B, when gas flows as shown by the arrow in the figure, the resistance heating element 101 on the upstream side
A is more likely to lose heat. Therefore, the balance of the bridge circuit (not shown) to which the resistance heating elements 101A and 101B are connected is lost, and a change in resistance of the resistance heating elements 101A and 101B can be detected. Based on this, the mass flow rate of the gas is determined.

Therefore, it is desirable that the resistance heating elements 101A and 101B have a structure that allows accurate detection of the heat taken away by the gas in the sensor tube 102. Conventionally, the sensor tube 102 is surrounded by a filler 104 made of a material with high thermal conductivity such as an aluminum alloy at intervals, and the heat is released into the air between the sensor tube 102 and the filler 104. Thermal energy was made to be absorbed by the filler 104. According to this, since there is no increase or decrease in thermal energy in the air, no air movement (convection) occurs, and unnecessary heat transfer between the resistance heating elements 101A and 101B can be prevented, and accurate mass flow rate data can be obtained. is detected.

[Problem that the invention seeks to solve]

However, in the above method, it is necessary to place the filler 104 as close to the sensor tube 102 as possible, but in this case, not only the thermal energy in the air but also the resistance heating elements 101A, 101
Even the thermal energy of B itself is absorbed. As a result, the temperature of the resistance heating elements 101A and 101B decreases, resulting in a decrease in measurement sensitivity. Furthermore, the mass flow controller does not necessarily include the sensor tube 10.
2 is not necessarily used in the posture shown in FIG. For example, when the device in Fig. 3 is used in a 90° tilted position, thermal energy moves in the direction of the resistance heating element located above, resulting in a measurement error (posture error).

The present invention was devised in view of the shortcomings of the conventional mass flow control device, and its purpose is to accurately prevent unnecessary heat transfer between thermal sensors, and also to prevent the occurrence of the above-mentioned attitude error. It is an object of the present invention to provide a mass flow control device having a configuration that can prevent the above.

[Means for solving problems]

Therefore, in the present invention, in the portion of the pipe constituting the gas flow path where the thermal sensor is provided, the pipe is configured to be wrapped by a heat conductive member having a protruding piece whose tip is close to the pipe. Thus, the above objectives have been achieved.

[Effect]

According to the above configuration, by forming the protruding piece, in the space between the tube and the heat conducting member,
The surface area of the heat conduction member is large, and heat absorption is good even if there is a distance from the base of the heat conduction member to the tube.Moreover, just by bringing the tip of the protruding piece close to the thermal sensor, the temperature of the sensor itself can be reduced. There aren't many. Furthermore, the protruding piece prevents the movement of air, and no matter what attitude the mass flow control device is used in, it is possible to prevent the occurrence of so-called attitude errors.

〔Example〕

FIG. 2 is a block diagram of one embodiment of the present invention. In the figure, 2 indicates the gas inlet, and 3
indicates the gas outlet. When the gas enters the inlet section 2, it is branched into a bypass section 4 and a sensor tube 5.
A pair of resistance heating elements (thermal sensors) 6A and 6B are wound around the sensor tube 5 on the upstream and downstream sides of the gas flow. The resistance heating elements 6A and 6B are connected to a bridge circuit 7. When the gas passes through the sensor tube 5, heat is removed from the resistance heating elements 6A and 6B. At this time, the temperature of the resistance heating element 6A becomes lower than that of the resistance heating element 6B, and the resulting temperature difference is extracted in the bridge circuit 7 as a resistance value change. Based on this change in resistance value, the mass flow rate of gas flowing through the sensor tube 5 can be detected. On the other hand, since the division ratio between the sensor pipe 5 and the bypass section 4 is predetermined, the mass flow rate of the gas flowing through the sensor pipe 5 is
This value reflects the mass flow rate of the entire flowing gas.
Reference numeral 8 indicates a metal mesh interposed in the bypass section 4, and this mesh 8 maintains a predetermined division ratio of gas flowing through the bypass section 4 and the sensor tube 5. In addition, 9 is a casing of the sensor part,
The casing 9 prevents the resistance heating elements 6A and 6B from being influenced by the outside, thereby making it possible to detect the mass flow rate with high accuracy.

A cross-sectional view of the main parts of the casing 9 is shown in FIG.
91 indicates a heat conductive member. A large number of protruding pieces 92 are formed on the inner wall of the heat conducting member 91 at predetermined intervals. The protruding piece 92 extends from its base 93 to its tip 94.
The structure gradually becomes thinner toward the end, and its tip 9
4 is close to the sensor tube 5 and goes around the circumference of the sensor tube 5. In this embodiment, the protruding piece 92 configured in this manner is assumed to be formed at a portion where the sensor tube 5 extends in the horizontal direction in FIG. 2. Therefore, the adjacent protruding pieces 9
A chamber 95 is formed between 2, and this chamber 95 is communicated with the adjacent chamber 95 by a slight gap 96 formed by the tip 94 of the protruding piece 92 and the sensor tube 5. ing.

Therefore, the surface area of the inner wall of the heat conductive member 91 (the part that wraps around the sensor tube 5) is extremely large, and even when the distance from the base 97 of the heat conductive member 91 to the outer wall of the sensor tube 5 is relatively long. However, the thermal energy within the room 95 can be well absorbed.
Moreover, the tip 94 of the protruding piece 92 does not come into contact with the sensor tube 5, and therefore does not absorb heat from the resistance heating elements 6A, 6B, so that there is no reduction in measurement sensitivity. Furthermore, since the protruding piece 92 communicates between the chambers 95 only through the gap 96 and basically blocks the chambers 95,
Air (heat) movement is less likely to occur, making extremely accurate flow rate detection possible. This protruding piece 92 prevents the occurrence of so-called posture error for the same reason as described above, no matter what posture the mass flow rate control device is placed in.

The explanation will be given by returning to FIG. 2 again. bridge circuit 7
The output signal is amplified by the amplifier circuit 10 and output from the sensor output terminal 11 to an external display device (not shown), etc., and is also output to the comparison circuit 12.
A setting signal corresponding to a predetermined value of a desired mass flow rate is input to the comparison circuit 12 from the outside at a setting signal input terminal 13.
given through. The comparison circuit 12 compares the output signal of the amplifier circuit 10 and the setting signal, and outputs a signal according to the difference. This signal is applied to the valve drive circuit 14, and the valve drive circuit 14 applies a drive voltage to the valve heater 15 based on the above signal. 16 indicates a valve. This valve 16 is of a normally open type (the valve is in the (open) state when no voltage is applied, and the valve is in the (closed) state when voltage is applied). A valve heater 15 is inserted into a metal pin 17, and as the metal pin 17 expands due to the heat generated by the valve heater 15, a spherical valve body 18 fixed to the tip of the metal pin moves up and down, and the valve body 18 is moved up and down against the gas passage. Adjust the orifice.

According to the mass flow rate controller 1 configured in this way, the signal corresponding to the mass flow rate detected in the sensor tube 5 reflects the mass flow rate of the entire gas, so this signal and the setting signal can be By controlling the valve 16 so that there is no difference between the two, it is possible to control the mass flow rate appropriately and with high precision.

In addition, in the embodiment, the tip 94 of the protruding piece 92
Although it is made flat, it may also be sharp. Further, the protruding piece 92 does not need to become thinner from the base portion 93 toward the tip end 94. Furthermore, the tip 94 of the protruding piece
Although the protruding pieces are continuous so as to go around the circumference of the outer wall of the sensor tube, it is also possible to have a structure in which the protruding pieces stand in a forest like a mountain range and obstruct the movement of air. Similar effects can also be achieved by this.

〔Effect of the invention〕

As explained above, according to the present invention, unnecessary heat transfer between thermal sensors can be accurately prevented by the protruding piece, and the occurrence of so-called posture errors can also be prevented by this configuration alone. be.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional perspective view of a main part of an embodiment of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a diagram showing a conventional example. 5...Sensor tube, 6A, 6B...Resistance heating element, 91
...Thermal conduction member, 92...Protrusion piece, 94...Tip.

Claims (1)

[Claims] 1. A thermal sensor is provided on the outer wall surface of the pipe constituting the flow path in order to extract a temperature signal of the gas in the flow path, and the flow rate data obtained by this thermal sensor and the set flow rate data are set. In a mass flow control device that controls the mass flow rate of gas by adjusting the opening degree of the valve using a valve drive signal based on the comparison result, in the part of the pipe where the thermal sensor is provided, the tip thereof is A mass flow rate control device characterized in that the tube is spaced apart from and wrapped around the tube by a heat conductive member in which a protruding piece is formed close to the tube. 2. The mass flow rate control device according to claim 1, wherein the tip of the protruding piece extends around the circumference of the tube while being close to the tube.