Background Art Generally, a mass flow controller is designed to measure flux of a fluid flowing in various channels and control flowing of a fluid according to the measured value, and is widely used in many industrial fields including semiconductor industry, etc.

The method for measuring flux of a. fluid flowing through the channel can be largely classified into 1) a method for measuring volume flux and 2) a method for measuring mass flux.

Generally, in the case where a fluid is a gas whose specific gravity is small and whose condensation is large, it is known that flowing of a fluid could be more accurately controlled by the method using mass flux rather than the method using volume flux. Particularly, in case of flux control in chemical reaction apparatus, it is more convenient to measure and control mass flux, since chemical reaction is a reaction based on mass.

In case of measurement of such mass flux, a thermal method of heating a fluid and measuring a change. in temperature is widely used as a method of measuring very small mass flux.

FIG. 1 is a schematic, cross-sectional view of a mass

flow controller using the conventional thermal measuring method. Referring to FIG. 1, the conventional mass flow controller 100 includes: a mass flux measuring sensor 120 for measuring mass flux flowing through a channel 110; a valve operator 160 and a valve 130 for changing the opening of the channel 110 to control mass flux flowing through the channel 110; a controlling unit 140 for detecting mass flux measured by the mass flux measuring sensor 120, and transmitting an electrical signal to the valve operator 160 so that the opening of the channel 110 may be controlled.

Here, the mass flux measuring sensor 120 includes: a sample flowing tube 121 connected to the channel 110 for passing a predetermined portion of a fluid flowing through the channel 110 therethrough; a heating coil 122 wound around the outer periphery of the sample flowing tube 121, for converting electric energy provided from a power source 170 into heat energy to act as a heat source which heats a sample fluid flowing through the sample flowing tube 121; a first temperature sensing coil 123 wound around the outer periphery of the sample flowing tube 121 in the upstream of the heating coil 122, for functioning as a temperature measuring device for measuring a temperature of the upstream of the sample fluid; and a second temperature sensing coil 124 wound around the outer periphery of the sample flowing tube 121 in the downstream of the heating coil 122, for functioning as a temperature measuring device for measuring a temperature of the downstream of the sample fluid. Namely, the electrical signal that corresponds to the temperature of the sample fluid at the upstream is obtained at the first temperature sensing coil 123 and the electrical signal that corresponds to the temperature of the sample fluid at the downstream is obtained at the second temperature sensing coil 124.

Also, generally, the sample flowing tube 121 of the

mass flux measuring sensor 120 is connected to the channel 110 in such a way that its upper end is connected to the lateral wall of the channel 110 in a passing through manner and its lower end is connected to the lateral wall of the channel 110 in a passing through manner at the downstream compared to the upper end. With such arrangement, after flowing into the sample flowing tube 121 through the upper end, the sample fluid flows out of the lower end. At this time, to obtain more accurate measurement value, it should be guaranteed that the sample fluid is always collected at a constant rate from the fluid flowing through the channel 110. To this end, a flow guider such as a laminar device 150 is provided to the inner side of the channel 110 so that flowing line of the fluid passing by without passing through the sample flowing tube 121 may be changed.

Hereinafter, the principle for measuring mass flux using a temperature difference of the sample fluid measured at the upstream and the downstream of the sample flowing tube 121, respectively, as shown in FIG. 1, will be described in detail with reference to FIG. 2.

FIG. 2 schematically shows the principle for measuring mass flux using a temperature difference at the mass flux measuring sensor 120 shown in FIG. 1.

Referring to FIG. 2, if the sample fluid is not flowing at the state of being heated by the heating coil 122, the electrical signals that correspond to the identical temperature are obtained at the first and the second temperature sensing coils 123,124. On the contrary, if the sample fluid is flowing, the electrical signals that correspond to a temperature difference AT are obtained respectively at the first and the second temperature sensing coils 123,124.

Such temperature difference AT is generated because the sample fluid introducing from the upstream is heated by

absorbing a part of heat from the heating coil 122 while passing by the neighborhood of the heating coil 122 and the heated sample fluid moves to the downstream. Namely, the temperature difference AT is caused by convection phenomenon due to movement of the sample fluid in the inside of the sample flowing tube.

The temperature difference AT of the sample fluid is in functional relation with a heat flux Q provided from the heat source and the mass flux of the sample fluid passing through the sample flowing tube 121 heated by the heat flux Q. Therefore, as shown in the following [formula 1], the mass flux m of the sample fluid flowing through the sample flowing tube 121 can be calculated from a specific heat Cp of the sample fluid, the heat flux Q applied by the heat source, and the temperature difference AT of the sample fluid obtained from the electrical signals provided from the first and the second temperature sensing coils 123, 124.

Also, the total mass flux passing through the channel 110 is calculated by multiplying the mass flux of the sample fluid passing through the sample flowing tube 121 by the ratio of mass flux of the sample fluid to the mass flux passing through the laminar device 150.

[Formula 1] m = Ql (Cp AT) Generally, the heat flux provided from the heat source is maintained constantly and the controlling unit 140 transmits a valve operating signal to the valve operator 160'in response to the temperature difference or the resistance difference between the upstream and the downstream of the sample fluid obtained by the electrical signals from the first and the second temperature sensing coils 123,124, and the valve operator 160 controls mass

flux flowing through the channel by operating the valve 130 and. adjusting the opening of the channel 110 according to the valve operating signal.

For the sample flowing tube of the mass flux measuring sensor, a general single tube type sample flowing tube is widely used as shown in FIG. 1 and FIG. 2, but there is also used the mass flux measuring sensor having a double tube type sample flowing tube, such that an inner tube 51 is provided in parallel lengthwise, with respect to the sample flowing tube 50, at the inside of the sample flowing tube 50 so that the channel of the sample flowing tube 50 forms a circular channel 58 and a linear flux range is extended remarkably compared to the case of the single tube type sample flowing tube, as shown in FIG. 3 and FIG.

4.

The mass flux measuring, sensor using such a double tube type is disclosed in detail in the Korean Patent Application Nos. 10-2001-81357,10-2002-14257, 10-2002- 26202,10-2002-79262, which have been filed by the applicant of the present invention.

As. described above, the mass flux measuring sensor of the conventional mass flux controller has such construction that the heating coil wound around the outside of the sample flowing tube, for heating the sample fluid, supplies a predetermined heat flux constantly and measures the mass flux value using the temperature difference (or resistance difference) between the upstream and the downstream of the sample flowing tube generated while the sample fluid is flowing in the inside of the sample flowing tube.

FIG. 5 is a graph showing a change in temperature difference between the first and the second temperature sensing coils with respect to a change in mass flux m in the conventional single tube type mass flux measuring sensor. As shown from the graph of FIG. 5, linear change

appears only at some region in the initial stage (within about 5-10scum), and non-linear change appears in the rest region beyond that initial stage.

Most important factor that causes non-linearity in the graph showing a change in temperature difference with respect to a change in mass flux m in such mass flux measuring sensor, is a positional movement of the maximum temperature and a change in the maximum temperature of the sample flowing tube, which is generated by convection phenomenon due to the movement of the sample fluid in the inside of the sample flowing tube.

The mass flux controller detects a mass flux value of the sample fluid passing through the sample flowing tube within the linear flux range of the mass flux measuring sensor, and calculates the whole flux using the ratio of mass flux of the sample fluid to the mass flux passing through the laminar device of the channel.

The fact that the linear flux range of the mass flux measuring sensor is narrow means that portion required for calculation of the whole flux gets large. This means that measurement error of the mass flux controller gets increased and reliability of the system may be deteriorated as well.

Disclosure of Invention Accordingly, the present invention has been made to solve the above-mentioned problems of the mass flux controller using the narrow linear flux range of the conventional mass flux measuring sensor, and it is an object of the present invention to provide a mass flux controller which can constantly maintain the position of the maximum temperature and the change in the maximum temperature due to movement of the sample fluid in the inside of the sample flowing tube, which is the most

principal factor causing non-linearity in the relation of a change in temperature difference according to a change in mass flux in the mass flux measuring'sensor, even in the case where the sample fluid is moved in the inside of the sample flowing tube, thereby remarkably increasing the linear flux range of the mass flux measuring sensor, improving measurement accuracy and measurement precision of the mass flux controller, and accomplishing stability of the system.

To achieve the foregoing object, the present invention controls the supply of the power source so that the temperature (or the resistance) of the heating coil wound around the outer peripheral surface of the sample flowing tube, for heating the sample fluid, may be maintained constantly at a predetermined temperature (or resistance) by separately providing a heating coil controlling unit to a mass flux controller.

More specifically, the sample fluid at room temperature that has introduced from the upstream of the sample flowing tube is heated by absorbing a part of heat from the heating coil while passing through the vicinity of the heating coil, and the heated sample fluid moves to the downstream, emits heat to the outside, and is cooled down again. Due to such convection phenomenon by movement of the sample fluid, heat loss is generated at the heating coil, whereby the temperature of the heating coil is lowered. The heating coil controlling unit functions to control the power source in such a way that the temperature (or resistance) of the heating coil may be maintained constantly at a predetermined temperature (or resistance) in the case where the temperature (or resistance) of the heating coil is changed due to the convection phenomenon as descried above.

Brief Description of Drawings The above objects, features and advantages of the present, invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic view showing the construction of the conventional single tube type mass flux controller; FIG. 2 is a view schematically showing a change in temperature distribution according to a change in mass flux in the sample flowing tube of the conventional single type mass flux measuring sensor; FIG. 3 is a schematic view showing the construction of the conventional double tube type mass flux measuring sensor; FIG. 4 is a cross-sectional view of the conventional double tube type mass flux measuring sensor taken along line V-V'; FIG. 5 is a graph showing a change in temperature difference according to a change in mass flux in the conventional single tube type mass flux measuring sensor; FIG. 6 is a schematic view showing the construction of the single tube type mass flux controller according to the present invention; FIG. 7a and FIG. 7b are schematic views showing the construction of the single tube type mass measuring sensor according to the present invention; FIG. 8 is a schematic view showing the construction of the double tube type mass flux measuring sensor according to the present invention; FIG. 9a and FIG. 9b are schematic views showing the construction of the single tube type mass flux measuring sensor of the present invention that employs a thin film layer in the vicinity of the heating coil; FIG. 10 is a schematic view showing the construction

of the double tube type mass flux measuring sensor of the present invention that employs the thin film layer in the vicinity of the heating coil; FIG. 11 is a view schematically showing a change in temperature distribution according to a change in mass flux of the sample flowing tube in the single tube type mass flux measuring sensor that adopts the construction of the mass flux controller of the present invention; and FIG. 12 is a graph showing a change in temperature difference according to a change in mass flux in case of the mass flux measuring sensor that adopts the construction of the mass flux controller having the heating coil controlling unit of the present invention, compared with the case of the mass flux measuring sensor that adopts the construction of the conventional mass flux controller.

Best Mode for Carrying Out the Invention Construction and operation of the mass flux controller according to the preferred embodiment of the present invention will be described with reference to the accompanying drawings in the following.

FIG. 6 is a schematic, structural view of the mass flux controller according to the preferred embodiment of the present invention.

Referring to FIG. 6, the mass flux controller of the present invention includes: a sample flowing tube 221 installed so that a sample fluid can be always collected in a constant ratio from a fluid flowing through a channel 110; a heating coil 222 wound around a predetermined region in the central part on the outer peripheral surface of the sample flowing tube 221, for heating the sample fluid flowing in the inside of the sample flowing tube 221; a mass flux measuring sensor 200 consisting of a first temperature sensing coil 223 for sensing a temperature of

the upstream of the sample fluid and a second temperature sensing coil 224 for sensing a temperature of the downstream of the sample fluid ; a laminar device 150 for allowing a fluid not passing through the mass flux measuring sensor 200 but merely passing by, to pass through the channel while always maintaining a constant ratio with respect to the mass flux of the sample fluid passing through the sample flowing tube 221; a heating coil controlling unit 270 for controlling a power source in order to maintain a change in the temperature (or resistance) of the heating coil 222 due to movement of the sample fluid passing through the sample flowing tube 221 of the mass flux measuring sensor 200, at a predetermined temperature (or resistance); a bridge circuit 141 for generating an electrical signal in response to a temperature difference between the upstream and the downstream of the sample fluid on the basis of the signals from the mass flux measuring sensor 200; an amplifying circuit 142 for amplifying the electrical signal outputted from the bridge circuit 141; a comparison controlling circuit 143 for comparing a mass flux set value preset by a user, with a measured value from the mass flux measuring sensor 200 to output a comparison signal, operating a value operator 160 in response to the comparison signal, and transmitting a controlling signal in such a way that the measured value may converge to the set value; and a valve operator 160 for controlling the whole mass flux passing through the channel by operating a valve 130 for controlling the opening of the channel according to the controlling signal applied from the comparison controlling circuit 143. In addition, the mass flux controller may also separately include a display unit 145 for displaying a mass flux value converted from the difference in the temperature or the resistance measured from the mass flux measuring

sensor 200. Here, the constant temperature value (or resistance value) of the above-mentioned heating coil specifically means a relative constant temperature value with respect to the outside.

FIG. 7a and FIG. 7b are exemplary views showing the construction of a single tube type mass flux measuring sensor adopting the construction of the mass flux controller of the present invention.

Referring to FIG. 7a and FIG. 7b, the mass flux controller of the present invention includes: a sample flowing tube 70 installed in such a way that a sample fluid always collected in a constant ratio from the channel can flow; a heating coil 71 installed in the central region on the outer peripheral surface of the sample flowing tube 70, for heating the sample fluid while maintaining at a predetermined constant temperature; a first temperature sensing coil 72 for sensing a temperature of the upstream of the sample fluid; and a second temperature sensing coil 73 for sensing a temperature of the downstream of the sample fluid.

FIG. 8 is an exemplary view showing the construction of a double tube type mass flux measuring sensor adopting the construction of the mass flux controller of the present invention.

Referring to FIG. 8, the mass flux controller of the present invention includes: a sample flowing tube 70 installed in such a way that a sample fluid always collected in a constant ratio from the channel can flow; an inner tube 75 installed in parallel lengthwise in the inside of the sample flowing tube 70 so that the channel of the sample flowing tube 70 may be formed in a circular shape; a heating coil 71 installed in the central region on the outer peripheral surface of the sample flowing tube 70, for heating the sample fluid while maintaining at a

predetermined constant temperature; a first temperature sensing coil 72 for sensing a temperature of the upstream of the sample fluid; and a second temperature sensing coil 73 for sensing a temperature of the downstream of the sample fluid.

FIG. 9a and FIG. 9b are exemplary views showing the construction of an alternative single tube type mass flux measuring sensor adopting the construction of the mass flux controller of the present invention.

Referring to FIG. 9a and FIG. 9b, the mass flux controller of the present invention includes: a sample flowing tube 90 installed in such a way that a sample fluid always collected in a constant ratio from the channel can flow; a heating coil 91 installed in the central region on the outer peripheral surface of the sample flowing tube 90, for heating the sample fluid while maintaining at a predetermined constant temperature; a first temperature sensing coil 92 for sensing a temperature of the upstream of the sample fluid; a second temperature sensing coil 93 for sensing a temperature of the downstream of the sample fluid; and a thin film layer 94 formed on the outer peripheral surface of the sample flowing tube 90 corresponding to the heating coil 91.

FIG. 10 is an exemplary view showing the construction of alternative double tube type mass flux measuring sensor adopting the construction of the mass flux controller of the present invention.

Referring to FIG. 10, the mass flux controller of the present invention includes: a sample flowing tube 90 installed in such a way that a sample fluid always collected in a constant ratio from the channel can flow; an inner tube 95 installed in parallel lengthwise in the inside of the sample flowing tube 90 so that the channel of the sample flowing tube 90 can be formed in a circular

shape; a heating coil 91 installed in the central region on the outer peripheral surface of the sample flowing tube 90, for heating the sample fluid while maintaining at a predetermined constant temperature; a first temperature sensing coil 92 for sensing a temperature of the upstream of the sample fluid; a second temperature sensing coil 93 for sensing a temperature of the downstream of the sample fluid; and a thin film layer 94 formed on the outer peripheral surface of the sample flowing tube 90 corresponding to the heating coil 91..

Here, for the thin film layer employed by the present invention, there are used the materials such as Al, Cu, Au, Ag whose heat transfer performance is superior (i. e., thermal diffusivity is larger to) to stainless that is used for the sample flowing tube. With use of such material, the thermal equilibrium reaching time of the sample flowing tube in the vicinity of the heating coil is shortened and maintaining of a constant temperature of the heating coil by the heating coil controlling unit can be performed in a more rapid and accurate manner.

Installation of such a thin film layer may be realized by the winding of the thin film made of the above- mentioned material, on the outer peripheral surface of the sample flowing tube a predetermined number of times, or by coating or plating, application of the above-mentioned material, on the outer peripheral surface of the sample flowing tube, or by the chemical vapor deposition method, etc.

FIG. 11 is a view schematically showing temperature distribution characteristics of the sample flowing tube of the single tube type mass flux measuring sensor of the present invention and shows a change in temperature distribution according to a change in mass flux of the sample fluid with the heating. coil of the sample flowing

tube maintained at a constant temperature.

FIG. 12 is a graph showing a change in temperature difference according to a change in mass flux in case of the conventional mass flux measuring sensor compared with the case of the mass flux measuring sensor according to the present invention. As shown in FIG. 12, it is revealed that the linear flux range and a change in temperature difference according to a change in mass flux are much larger for the case where the temperature of the heating coil is maintained constantly, compared with the case of the conventional mass flux measuring sensor.

Industrial Applicability According to such a mass flux controller of the present invention, the heating coil controlling unit is provided separately so that the temperature of the heating coil is maintained constantly, thereby eliminating the most principal factor that causes non-linearity in the relation of a change in temperature difference with respect to a change in mass flux in the mass flux measuring sensor. Also, the linear flux range in the mass flux measuring sensor can be increased remarkably and a change in temperature difference with respect to a change in mass flux gets larger even more, thereby insignificantly improving measurement accuracy and measurement precision of the mass flux controller.

Furthermore, the thin film layer is formed on the outer peripheral surface of the sample flowing tube in corresponding position of the heating coil with use of the material whose thermal conductivity is excellent, so that controlling of the power source by the heating coil controlling unit for maintaining the heating coil at a constant temperature, is carried out easily and a response speed of the mass flux measuring sensor can be improved.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by, those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.