JPH0520978Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a thermal mass flowmeter, and particularly to a thermal mass flowmeter that can measure the mass flow rate of a fluid to be measured with high sensitivity.

BACKGROUND TECHNOLOGY In general, a thermal mass meter is equipped with a pair of temperature detection sensors made of self-heating resistors on the outer periphery of a sensor pipe that forms a sensor flow path branching from a bypass flow path, and heats the fluid to be measured. 2 of the sensor pipe due to the inflow of the fluid to be measured by the temperature detection sensor.
The mass flow rate of the measured fluid is determined by measuring the temperature difference between points. Therefore, if the heat of the pair of temperature detection sensors is taken away by the surrounding air, the sensitivity will decrease and the mass flow rate cannot be accurately measured. For this reason, in conventional thermal mass flowmeters, in order to prevent the pair of temperature detection sensors from being cooled by the surrounding air, the sensor pipe and temperature detection sensor are covered with a metal case such as aluminum. Ta. Further, when the air in the metal case is convective due to heating of the pair of temperature detection sensors, a temperature difference occurs between the pair of temperature detection sensors, and the flow rate is detected even when the flow rate is zero. Therefore, in order to prevent convection of heated air, a chamber surrounding the outer periphery of the sensor pipe through which the sensor pipe is inserted has been provided in the metal case.

Problems to be solved by the invention However, in the conventional thermal mass flowmeter with the above configuration, the inner wall of the chamber in the metal case is close to the sensor pipe, and the thermal conductivity of the metal case is relatively low. Because of the high temperature, the heat from the temperature detection sensor is transferred to the metal case and radiated from the metal case to the outside air. Therefore, the temperature of the temperature detection sensor is absorbed by the metal case and a heating loss occurs, resulting in a lower temperature and lower sensitivity when measuring the flow rate. Furthermore, if the sensor pipe comes into contact with the inner wall of the chamber of the metal case, the sensitivity and response of the temperature detection sensor will vary, so there is a drawback that it is necessary to hold the sensor pipe so that it does not come into contact with the inner wall.

Therefore, an object of the present invention is to provide a thermal mass flowmeter that eliminates the above-mentioned drawbacks.

Means for Solving the Problems The present invention provides a thermal mass flowmeter that measures the flow rate of a fluid to be measured flowing through a sensor pipe using a pair of self-heating resistors wound around the outer periphery of the sensor pipe. A heat-resistant material having a high heat resistance and heat resistance that can withstand high temperatures, and is formed in a hollow shape so as to cover the periphery of the pair of self-heating resistors, and a space between the pair of self-heating resistors is blocked. A partition wall provided around the outer periphery of the sensor pipe, and a case having heat insulating properties with lower thermal conductivity than metal and formed to surround the heat resistant material.

Function The present invention uses a hollow heat-resistant material with high thermal conductivity and heat resistance that can withstand high temperatures to surround a pair of self-heating resistors wound around the outer circumference of the sensor pipe inside the case. At the same time, a partition wall is provided between the pair of self-heating resistors, which prevents the self-heating resistors from being cooled by air convection that occurs within the case, and prevents the heat of the self-heating resistors from reaching the case. Prevent escape to the outside via the

Moreover, so that the heat-resistant material is formed in a hollow shape,
Since it can be installed so as to cover the outer circumference of the sensor pipe, for example, when performing maintenance or inspection of the self-heating resistor, the heat-resistant material can be easily removed from the sensor pipe for maintenance work such as maintenance or inspection of the self-heating resistor. can be done. Furthermore, since the heat-resistant material with high thermal conductivity is provided to cover the self-heating resistor, there is less time delay in the output signal with respect to minute changes in flow rate, and responsiveness is improved.

Embodiment FIG. 1 shows a first embodiment of the thermal mass flowmeter according to the present invention. FIG. 2 shows a flow rate control device to which the thermal mass flowmeter shown in FIG. 1 is applied.

In Fig. 2, the flow rate control device 1 generally consists of a flow rate measurement unit (thermal mass flowmeter) 2, a stepping motor 3, a rotating linear exchange mechanism 4, a valve stem 5, a bellows 6, a valve body 7, and a valve seat 8. It is configured.

Further, a throttle 10 is provided in the bypass flow path 9, and the fluid to be measured is passed through the bypass flow path 9 at a predetermined division ratio by the throttle 10, and the sensor is formed by a sensor pipe 11 branched from the bypass flow path 9. The flow is divided into two channels. The sensor pipe 11 is bent into an inverted U-shape, and is made of, for example, a stainless steel pipe that has good thermal conductivity and takes into account corrosion caused by the fluid to be measured. In addition, the sensor pipe 11
A pair of self-heating resistors 12 and 13 are wound around each of the resistors 12 and 13 as temperature detection sensors that serve both for heating and temperature detection, respectively.

As shown in FIG. 1, the pair of self-heating resistors 12 and 13 of the flow rate measuring section 2 are heated by being energized via a bridge circuit 14. The fluid to be measured flows into the sensor pipe 11 and the pair of self-heating resistors 1
It is heated when it passes between 2 and 13. As a result, the pair of self-heating resistors 12 and 13 detect a temperature difference depending on the flow rate of the fluid to be measured. Further, the resistance value of the pair of self-heating resistors 12 and 13 changes in response to a change in temperature, and the flow rate of the fluid to be measured is measured as a change in the current value of the bridge circuit 14.

The bridge circuit 14 is composed of the resistance values of a pair of self-heating resistors 12 and 13 and a pair of resistors 15 and 16, and is maintained in equilibrium when the flow rate of the fluid to be measured is zero. Therefore, when the resistance values of the self-heating resistors 12 and 13 change due to the flow rate of the fluid to be measured, the bridge circuit 14 becomes unbalanced and a detection signal is output.

The flow rate control device 1 drives and controls the stepping motor 3 based on the detection signal from the bridge circuit 14 to displace the valve body 7 and adjust the valve opening degree.

Reference numerals 17 and 18 are heat-resistant materials with high thermal conductivity, which are wound around the outer peripheries of the self-heating resistors 12 and 13 and the sensor pipe 3, respectively. Note that the heat-resistant materials 17 and 18 are made of cellulose cotton gauze, which has good thermal conductivity and has a heat resistance temperature of 280°C. Moreover, the square cloth-like heat-resistant materials 17 and 18 are placed so as to cover the outside of the sensor pipe 11, and the sensor pipe 11 is shaped so that it has a hollow shape with a hollow portion through which the sensor pipe 11 is inserted.
The lower part of the sensor pipe 11 is sewn to wrap around the outer periphery of the sensor pipe 11. For this reason, the self-heating resistors 12, 13
When the sensor pipe 11 is heated, the surrounding air is also heated as the temperature rises, but since the outer periphery of the sensor pipe 11 is wrapped with heat-resistant materials 17 and 18, the influence of convection of the heated air can be suppressed. Furthermore, since the heat-resistant materials 17 and 18 have high thermal conductivity, the pair of self-heating resistors 12 and 13 have good responsiveness with little time delay in output signals to minute changes in flow rate.

Moreover, since the heat-resistant materials 17 and 18 are hollow and made of cellulose cotton gauze, they can be easily attached to the outer periphery of the sensor pipe.
For example, when performing maintenance or inspection of the self-heating resistors 12, 13, the heat-resistant materials 17, 18 can be easily removed from the sensor pipe 11 and the self-heating resistors 12, 13 can be easily removed.
Can perform maintenance work such as maintenance and inspection. Moreover, after the maintenance work is completed, heat-resistant materials 17 and 1 are placed to cover the self-heating resistors 12 and 13.
8 is simply attached to the sensor pipe 1, maintenance work can be carried out efficiently.

Reference numeral 19 denotes a partition wall, which has a through hole 19a through which the sensor pipe 11 is inserted, and a pair of heat-resistant materials 1
7 and 18 and the self-heating resistors 12 and 13. The partition wall 19 is made of, for example, cotton gauze, a foamed material, or a synthetic resin, and has a heat insulating effect that prevents heat transfer between the pair of heat-resistant materials 17 and 18. That is, while the self-heating resistors 12 and 13 are heated, the air between the sensor pipe 11 and the heat-resistant materials 17 and 18 is heated, but the partition wall 19 that defines the space between the heat-resistant materials 17 and 18 blocks air convection. There is no possibility that the pair of self-heating resistors 12 and 13 will be affected by heated air.

Reference numeral 20 denotes a case that houses the flow rate measuring section 2 having the above configuration. The case 20 is made of a material such as synthetic resin, which has lower thermal conductivity than metal. For this reason, the case 20 has a self-heating resistor 1
It has a heat insulating effect that prevents the heated heat from being removed to the outside. That is, since the case 20 prevents the heated heat from being radiated to the outside, the heating temperature of the pair of self-heating resistors 20 can be increased. Therefore, sensitivity is improved compared to the conventional structure in which the sensor pipe 11 is covered with a metal case.

In addition, in the above embodiment, a pair of heat-resistant materials 17 and 18
In the above description, the sensor pipe 11 is wrapped. However, for example, the outer periphery of the sensor pipe 11 may be wrapped with two or more heat-resistant materials 17 and 18. Alternatively, the heat-resistant materials 17 and 18 may be formed of large cotton gauze, and the heat-resistant materials 17 and 18 may be spirally wound around the sensor pipe 11 in two or three layers.

Effects of the Invention As described above, according to the thermal mass flowmeter of the present invention, the surroundings of the pair of self-heating resistors are surrounded by a hollow heat-resistant material having high thermal conductivity and heat resistance that can withstand high temperatures. Because a partition wall is provided between the pair of self-heating resistors, heat-resistant material can be easily attached to the outer circumference of the sensor pipe. It can be removed from the sensor pipe for maintenance work.

Furthermore, because the heat-resistant material is surrounded by a case with lower thermal conductivity than metal, the temperature of the self-heating resistor is radiated to the outside air through the case, for example in the case of conventional sensors where the sensor pipe is inserted into the metal case. Therefore, the heating temperature of the self-heating resistor can be maintained and the measurement sensitivity can be improved. Furthermore, since the heat-resistant material surrounding the sensor pipe has good thermal conductivity, there is less time delay in the output signal to minute changes in flow rate, improving responsiveness, making it possible to measure minute flow rates with high precision and reliability. It has features such as being able to improve performance.

[Brief explanation of the drawing]

Fig. 1 is an enlarged view of the main parts of an embodiment of the thermal chamber mass flowmeter according to the present invention, and Fig. 2 is a flow rate control to which the thermal mass flowmeter shown in Fig. 1 is applied. FIG. 3 is a longitudinal cross-sectional view of the device. 2...Flow rate measuring section, 11...Sensor pipe, 1
2, 13... Self-heating resistor, 14... Bridge circuit, 17, 18... Heat resistant material, 19... Partition wall, 2
0...Case.

Claims (1)

[Claim for Utility Model Registration] A thermal mass flowmeter that measures the flow rate of a fluid to be measured flowing through a sensor pipe using a pair of self-heating resistors wound around the outer periphery of the sensor pipe, which has high thermal conductivity; and a heat-resistant material having heat resistance capable of withstanding high temperatures and formed in a hollow shape so as to cover the pair of self-heating resistors, and the sensor pipe so as to block between the pair of self-heating resistors. A thermal mass flowmeter comprising: a partition wall provided on the outer periphery of the heat-resistant material; and a case having heat insulating properties with a lower thermal conductivity than metal and formed to surround the heat-resistant material.