JPS61231415A - Apparatus for detecting mass flow - Google Patents

Abstract

PURPOSE:To make it possible to accurately detect a wide range of a flow amount with high sensitivity, by fixing not only a resistance heat generator to the single surface of an insulating substrate but also two temp.-sensitive resistors to the other surface thereof to constitute a detection part and arranging the surface of said detection part along the direction of a gas stream to be detected while supplying the resistance heat generator to heat the same. CONSTITUTION:The surfaces of the temp.-sensitive resistors 2, 3 of a detection part S are allowed to coincide with the direction of the stream of gas, for example, air of which the flow amount must be detected and the detection part S is earthed. The air stream being the gas stream changes not only the temp. distribution of a substrate 1 heated by a resistance heat generator 4 generating heat by the current applied from a power source 7 but also the resistance value ratio of the resistors 2, 3 fixed to the substrate 1. As a result, the signal voltage corresponding to the flow speed or flow amount of the air stream is generated between output terminals 10, 11. Because the flow amount of this gas is the function of the product of the cross-sectional area and flow speed of the flowing gas, if signal voltage is measured, the flow amount can be determined.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a mass flow detection device for measuring the flow rate of gas.

(Prior art) In general, mass flow detection devices are sensitive to the flow rate of gas, and utilize changes in electrical resistance, voltage, current, and other electrical quantities caused by the flow rate of gases such as air, helium, and argon. It is used in the detection parts of flowmeters, flow rate regulators, etc.

In recent years, there has been a trend in industry toward systemization, and for this reason, the development of various types of sensors is desired. For example, many gas flow rate sensors are used in semiconductor manufacturing factories, but since semiconductor production requires particularly precise control, there is a need for something that can accurately and sensitively detect a wide range of flow rates. There is. however,
There is no sensitive mass flow detection device that can reliably detect the flow rate of the gas to be detected over a wide range, and conventionally used sensors of this type include those using platinum wire, but they are difficult to use in control systems. It did not satisfy all the conditions for use, such as detection ability, linearity of detection output, and not being affected by the environment such as ambient temperature.

(Problems to be Solved by the Invention) The present invention provides mass flow detection using a simple configuration that eliminates the problems of the conventional flow rate sensor described above with respect to linearity of detection output, detection range, dependence on environmental temperature, etc. The purpose is to provide equipment.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention fixes a resistance heating element on one side of an insulating substrate and two temperature-sensitive resistors on the other side to serve as a detection section. By arranging the surface of the part along the direction of the gas flow to be detected and heating the resistance heating element by applying electricity,
By means of a configuration in which the gas flow rate is detected by an output representing a change in the resistance value of the temperature-sensitive resistor due to the gas flow to be detected, and in addition to this configuration, the sum of the resistance values of the two temperature-sensitive resistors is By providing a feedback control means to maintain a constant value and heating the resistance heating element by energizing it.

Furthermore, the flow rate sensor is more reliable.

(Function) With the above-described configuration, the present invention is not influenced by the environment, and enables accurate, highly sensitive, and wide-range flow rate detection.

(Example) Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the mass flow detection device of the present invention, in which (a) is a plan view and (b) is a sectional view thereof. 1
is a substrate, on one side of which temperature sensitive resistors 2 and 3 are provided, and on the other side a resistance heating element 4. 5 is a lead wire connection terminal (not shown) for applying current.

In addition, as its constituent material, the substrate 1 is made of an alumina plate.
SiC-based thermistors are used for the temperature-sensitive resistors 2 and 3, and a platinum wire resistor is used for the resistance heating element 4.

The above configuration is hereinafter referred to as a detection unit S. In this configuration, a current is passed from a power supply (not shown) to the resistance heating element 4 to generate heat, and the heat is transmitted to the temperature sensitive resistors 2 and 3 via the substrate 1. It will heat up.

FIG. 2 shows a specific circuit that uses the detection section S shown in FIG. A current is applied from 8 and 9 are resistors. With this circuit configuration, a current corresponding to the resistance value ratio of the temperature sensitive resistors 2 and 3 can be obtained as a gas flow rate signal from the signal terminal 10.11 in the operation described below.

Now, the sensing section S is grounded with the surfaces of the temperature sensitive resistors 2 and 3 of the sensing section S aligned with the flow direction of the gas whose flow rate is to be detected, for example air.

Furthermore, Figure 3 shows a structure that facilitates the above-mentioned grounding.
The detection part S is fixed in a cylindrical tube 12, and the lead wire 13 from the lead wire connection terminal 5 is appropriately reinforced and taken out laterally into the tube 12, and the gas is drawn out in the direction indicated by the arrow 14.
It flows in from the direction of. therefore.

Gas always flows approximately parallel to the surfaces of the temperature sensitive resistors 2 and 3. Now, returning to FIG. 2, the flowing gaseous air is generated by the resistance heating element 4 which is generating heat due to the current applied from the power source 7.
The temperature distribution of the heated substrate 1 is changed, and the resistance value ratio of the temperature sensitive resistors 2 and 3 fixed to the substrate 1 is changed. As a result, a signal voltage E corresponding to the flow velocity or flow rate of the air flow is generated between the output terminal 10.11. Since the flow rate of gas is a function of the product of the cross-sectional area of the flowing gas and the flow velocity, the flow rate can be determined by measuring the signal voltage E described above.

Figure 4 is a characteristic diagram of the relationship between the flow rate and the output obtained as described above, which shows that the voltage between the output terminals 10 and 11 (vertical axis) is almost linear with respect to the flow rate (horizontal axis). It can be confirmed that Note that the detection unit S at this time is 3. OXo, 5X6. It was Omm. Also, the temperature sensitive resistors 2 and 3 are 1Ω to Ω, and the resistors 8° and 9 are both 10Ω to Ω.
The voltages of power supplies 6 and 7 are both 5V, and the voltage of tube 12 is
The one with an inner diameter of 5 mm was used.

In the embodiment described above, when the flow rate increases, the way the heat is removed from the detection part S is different between the front part and the rear part in the gas flow direction, so that the heating temperature for the temperature-sensitive resistor 2.3 is The result is a narrow dynamic range characteristic as shown in Figure 4.

FIG. 5 is for explaining another embodiment in which this problem is solved by maintaining the partial temperature change of the sensing part S and keeping the heating temperature constant on average. Current power supply 15, signal adder 16 and signal amplifier 1
7 constitutes a feedback control circuit, and the other configurations are the same as in FIG. 2. This feedback control circuit keeps the sum of the resistance values of the heat-sensitive resistors 2 and 3 constant at a certain value. The resistors 8 and 9 are selected to have a resistance value sufficiently higher than that of the temperature-sensitive resistors 2 and 3, for example, 10Ω shown in FIG. The constant current power supply 15 is for supplying a constant current to the resistors 8 and 9 and the temperature sensitive resistors 2 and 3, based on their resistance value ratio.

Current mainly flows through the temperature sensitive resistors 2 and 3. Adder 1
6 adds the combined resistance of the resistors 8 and 9 and the temperature-sensitive resistors 2 and 3, the signal obtained from the constant current power supply 15, and a certain set value (ref), and calculates the value of the temperature-sensitive resistors 2 and 3. Obtain an output signal corresponding to the value of the sum of the resistance values. This output signal is applied to the amplifier 17 and amplified, and then heats the resistance heating element 4. Therefore, if the flow rate increases and the temperature of the detection part S decreases, the sum of the resistance values with the temperature sensitive resistors 2 and 3 increases, the output signal of the adder 16 increases, and is further amplified by the amplifier 17. As a result, the amount of heating charge applied to the resistance heating element 4 of the detection section S increases. That is, the average heating temperature of the detection section S can be controlled to be constant, and the above-mentioned disadvantages are eliminated.

Fig. 6 is a flow rate detection output characteristic diagram similar to Fig. 4 when the above-described feedback sensing section S is held in the holding structure shown in Fig. 3; It was observed that the amount of change in the detected output voltage (vertical axis) did not decrease even when the flow rate (horizontal axis) was large compared to FIG.

(Effects of the Invention) As is clear from the detailed explanation above, the present invention has an extremely simple configuration, a gas flow rate with good linearity, a wide detection range, and a high sensitivity that can be influenced by five surrounding areas. Since it is a mass flow detection device that can be obtained without any problems and can be manufactured at low cost due to its structure, it is extremely effective when used in the manufacturing industry, particularly in semiconductor manufacturing factories that use a large amount of gas and require precise control of its flow rate.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are a plan view and a sectional view showing the structure of an embodiment of the present invention, FIG. 2 is a circuit diagram of FIG. 1, and FIG. 3 is an installation structure for the device of the present invention. 4 is a characteristic diagram of one embodiment of the present invention, FIG. 5 is a circuit diagram of another embodiment, and FIG. 6 is a characteristic diagram of the device according to the embodiment of FIG. 1... Board, 2, 3... Temperature sensitive resistor, 4...
・Resistance heating element, 5... Lead wire connection terminal, 10° 11... Signal terminal, 12... Tube, 15...
Constant current power supply, 16... Adder, 17... Signal amplifier, E... Signal voltage. Patent Applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 2. 3...6 IC 15 Aiku, Arashi 4) and N4...Isacrifice Release λ Sales) Hi + 〃 7 7 Day 3 Figure 4 Figure 5 15. □1゜16..., % rental road Figure 6 ash! (Lyrics? Spoon Zubu-1 and 2

Claims (2)

[Claims] (1) A resistance heating element is fixed to one side of an insulating substrate and two temperature-sensitive resistors are fixed to the other side to form a detection section, and the surface of this detection section is placed in the gas flow to be detected along the direction of the flow. The mass flow detection device is characterized in that the flow rate of the gas is detected by an output that detects a change in the resistance value of the temperature-sensitive resistor due to the gas flow to be detected by heating the resistive heating element with electricity. (2) Claim (1) characterized in that a feedback control means is provided to make the sum of the resistance values of the two temperature-sensitive resistors to a certain constant value, and the resistance heating element is heated by electricity.
The mass flow detection device described in section.