JP3864165B2 - Thermal flow meter - Google Patents

Description

  The present invention relates to a thermal flow meter of a type in which a thermal flow rate measuring unit is provided in a shunt pipe provided in a main pipeline to measure the flow rate of the main pipeline, and is suitable for measuring a mass flow rate of gas or liquid. It is a thing.

  Thermal flow meters have no moving parts, can measure minute flow rates with high sensitivity, and are used for gas and liquid flow measurement. In particular, gas has the feature that the mass flow rate can be measured without depending on the fluctuation of pressure, and therefore the application range is expanding. On the other hand, the thermal flow meter itself can also be applied to the measurement of the flow rate of a large-diameter pipe, and can be measured by inserting a flow rate measuring unit, that is, a sensor or the like in the pipe. As a method for measuring the flow rate in a large-diameter pipe, there is a method in which a flow dividing unit is provided and a flow rate measuring unit is attached thereto. In this method, a main flow line whose flow rate is to be measured is provided with a flow element or the like for generating a differential pressure depending on the flow rate, or an orifice or an aggregate of pores. A pipe line is provided. This method is advantageous in terms of cost because the same part of the branch pipe having the flow rate measuring unit can be used even if the diameter of the main pipe changes, and the versatility is excellent.

Japanese Patent Application Laid-Open No. 49-54060 discloses a heat type flow meter in which a flow rate measuring unit is provided in a shunt pipe as described above. In addition, a thermal flow meter is shown in which a temperature sensor is provided at a position slightly away from the heat generating portion on the upstream side and the downstream side. In this flow meter, the surface temperature of the heat generating part is kept higher than the fluid temperature, and the flow rate is measured by the difference in temperature detected by the upstream and downstream temperature sensors. That is, if the flow rate is zero, the measured temperature of the upstream and downstream temperature sensors is the same, but the measured temperature of the downstream temperature sensor increases as the flow rate increases.
JP-A-49-54060

  Although there is a thermal flow meter of a type in which a thin pipe is used as a shunting pipe and a heating part is provided with a heating wire wound around a part thereof, there is a thermal flow meter other than that disclosed in the above-mentioned JP-A-49-54060. It is difficult to improve accuracy due to errors such as the temperature of the temperature sensor increases the temperature measured by the temperature sensor by passing through a thin pipe that is a shunt pipe, and the influence on the temperature rise also varies depending on the flow rate. . Therefore, the present invention has a high accuracy with few factors of error in a thermal flow meter of a type in which a thermal flow rate measurement unit is provided in a shunt pipe provided in a main pipeline, and particularly a problem in a thermal flow meter. The purpose is to provide a low flow rate error and zero drift.

  The present invention solves the above-mentioned problem, and has a differential pressure generating mechanism provided in a main pipe and a diversion pipe communicating with the upstream side and the downstream side of the differential pressure generation mechanism, and a thermal flow rate measurement provided in the diversion pipe In the thermal type flow meter for obtaining the flow rate of the main pipe line by measuring the flow rate at the head part, the thermal flow rate measuring part is provided with a fluid temperature sensor and a heat generation type flow rate sensor at intervals in the shunt pipe, The flow rate is measured based on the heating power of the heat generation type flow rate sensor to maintain the difference between the temperature of the flow rate sensor and the measurement temperature of the fluid temperature sensor, and the location where the thermal flow rate measurement unit is provided The shunt pipe in Fig. 2 is vertical regardless of the direction of the main pipe, and the downstream side is up, and in the shunt pipe, the exothermic flow sensor is located at the same position in the vertical direction or above the fluid temperature sensor. Further provided The flow conduit is a thermal flow meter, wherein a flow rate adjusting throttle mechanism is provided. Here, the throttle mechanism for adjusting the flow rate is also characterized in that the opening degree of the throttle is variable. In addition, in the joint between the main pipe and the shunt pipe, a mechanism for changing the mounting direction is provided to position the shunt pipe at the position where the thermal flow rate measuring unit is provided so that the downstream side is in the vertical direction. It is also characterized by.

  According to the thermal flow meter of the present invention for measuring by providing a shunt pipe, the shunt pipe at the place where the thermal flow measuring unit is provided is in the vertical direction regardless of the direction of the main pipe, and the downstream side is Since the heat generation type flow rate sensor is provided at the same position in the vertical direction or above the fluid temperature sensor in the shunt pipe, the fluid temperature sensor is caused by the convection generated by the heat of the heat generation type flow rate sensor. There is no error in the measured value. Therefore, it is possible to provide a thermal type flow meter with small error at low flow rate and small zero point drift.

  FIG. 1 is a sectional view of a thermal flow meter of the present invention. In this figure, it is assumed that a fluid flows upward in the main pipe line 1 whose flow rate is to be measured. The main pipe 1 is provided with an orifice 2 as a differential pressure generating mechanism, and an inlet 4 and an outlet 5 of the branch pipe 3 are connected to the upstream side and the downstream side, respectively. Since the internal diameter of the shunt pipe 3 in the present invention is about 10 mm, the pressure loss generated in this portion is small. In the thermal flow meter disclosed in Japanese Patent Application Laid-Open No. 49-54060 described above, the pressure loss increases because the inner diameter of the branch pipe is usually about 0.5 mm, although there is no particular description in the publication.

  The shunt pipe 3 is provided with a thermal flow rate measuring unit 6, which includes a fluid temperature sensor 7 and a heat generation type flow rate sensor 8, which are connected to a measurement circuit (not shown). The fluid temperature sensor 7 is generally a metal resistance thermometer, but a thermistor resistance thermometer or thermocouple thermometer can also be used. These temperature measuring elements are usually encapsulated in a stainless steel sheath (metal sheath), but are not limited thereto. The exothermic flow sensor 8 itself is composed of a resistance thermometer, a thermocouple thermometer, etc., like the fluid temperature sensor, but is used in a heated state. Usually, like the fluid temperature sensor 7, it is enclosed in a sheath. In the resistance thermometer, the resistance itself may be heated by energizing the resistor itself, but a method of energizing and heating the sheath can also be adopted, and this method can also be applied to a thermocouple thermometer.

  The fluid temperature sensor 7 and the exothermic flow rate sensor 8 are provided in the shunt pipe 3 with a space therebetween. The heat generation type flow rate sensor 8 is maintained at a temperature that is higher than the measurement temperature of the fluid temperature sensor 7 by a certain temperature, for example, 10 to 100 ° C. higher than the temperature measured by the fluid temperature sensor 7. At this time, when the fluid flow hits the exothermic flow sensor 8, heat is taken away. Therefore, in order to maintain the same temperature, it is necessary to increase the heating power in accordance with the flow velocity. Therefore, the flow rate can be measured without being affected by the temperature of the fluid based on the heating power of the heat generation type flow sensor for maintaining the difference between the temperature of the heat generation type flow sensor and the measured temperature of the fluid temperature sensor constant. it can. It is possible to heat the exothermic flow sensor with constant power and measure the flow rate based on the difference between the measured temperature of the exothermic flow sensor and the measured temperature of the fluid temperature sensor. The measurement based on this method has less temperature rise of the fluid and can accurately measure a wide range of flow rates.

  Here, in the present invention, as shown in FIG. 1, the shunt pipe 3 at the place where the thermal flow rate measuring unit 6 is provided is in the vertical direction, that is, the direction parallel to the direction of gravity, and the downstream side is up. To. Since the shunt line 3 branches off from the main line 1 and returns to the main line, it cannot be straight and is always bent halfway, but the vertical flow direction is provided by the thermal flow rate measuring unit 6 as described above. Usually, it is near the midpoint of the length of the shunt line. In the example of FIG. 1, the main pipeline 1 is also vertical, but generally the direction of the main pipeline is various and cannot be specified from the flowmeter. Regardless of the direction of the main pipe and the direction of the fluid flow in the main pipe, the location where the thermal flow rate measurement unit of the shunt pipe is provided in the vertical direction and the downstream side is on the upper side. is there.

  Further, in the present invention, the heat generation type flow rate sensor 8 constituting the thermal type flow rate measuring unit 6 in the shunt pipe 3 is provided at the same position in the vertical direction or above the fluid temperature sensor 7. For example, in FIG. 1, the heat generation type flow rate sensor 8 is provided at an upper position with respect to the fluid temperature sensor 7. With this arrangement, the fluid whose temperature has risen by touching the heat-generating flow rate sensor 8, especially when the flow rate is low or zero, does not ride on the upward flow and flow to the fluid temperature sensor 7. Therefore, measurement error at low flow rate and zero point drift at zero flow rate can be reduced.

  In FIG. 1, the fluid temperature sensor 7 and the heat generation type flow rate sensor 8 are provided on the same stream line, that is, provided at positions that overlap each other, but may be provided side by side at right angles to the stream line. FIG. 2 is a view showing the arrangement of such a fluid temperature sensor and a heat generation type flow rate sensor. In FIG. 2, reference numeral 10 denotes a part of the inner wall of the shunt pipe, but the fluid temperature sensor 7 and the heat generation type flow rate sensor 8 are provided at right angles to the stream line, that is, at the same vertical position. Further, in FIG. 2, the fluid temperature sensor 7 may be moved downward along the stream line (indicated by 7a), and the fluid temperature sensor and the heat generation type flow rate sensor may be positioned obliquely with respect to the stream line. Thus, in any case, in the present invention, the exothermic flow sensor is in a positional relationship such that it is in the same position in the vertical direction or above the fluid temperature sensor.

  In addition, as described above, in the present invention, the portion where the thermal flow rate measuring unit of the shunt pipe is provided is arranged in the vertical direction so that the downstream side is on the upper side. It is possible to more reliably prevent the upward flow generated from the sensor from flowing to the fluid temperature sensor. That is, if the shunt pipe is horizontal, the upward flow generated from the exothermic flow sensor hits the upper pipe wall and flows sideways or reverses, which may reach the fluid temperature sensor. This can be prevented. In the conventional thermal flow meter in which the fluid temperature sensor and the exothermic flow sensor are provided in the shunt pipe with a space, the shunt pipe is in the horizontal direction at the mounting position of these sensors. In the present invention, the downstream side is thus directed upward in the vertical direction.

  Also, the insertion depth of the exothermic flow sensor into the shunt pipe is such that the tip is between the center position of the shunt pipe and the vicinity of the back pipe wall (it is not preferable that the tip touches the pipe wall). It is preferable to insert it in the case, and if it is shallower than this, the measurement accuracy is lowered. Sensors are usually sensitive only to the tip, but the accuracy decreases if the insertion depth is shallow.The reason is that if the insertion depth is shallow and the tip is in front of the center of the shunt line, heat is generated. This is considered to be because the portion of the flow rate sensor that hits the flow decreases and the influence of the heat that escapes through the sensor itself becomes relatively large.

  Further, in the present invention, as shown in FIG. 1, a flow rate adjusting throttle mechanism 9 is provided in the diversion pipe. As a result, a differential pressure corresponding to the flow rate is generated, and the flow rate ratio between the main pipe and the shunt pipe is made constant over the entire flow measurement range by the relationship with the differential pressure generation mechanism such as an orifice provided in the main pipe. can do. This flow regulating throttle mechanism may be provided on either the upstream side or downstream side of the thermal flow rate measuring unit, but it is necessary to prevent the flow in the thermal type flow rate measuring unit from being disturbed. It is preferable to provide it at a position charged and separated from the flow rate measuring unit. In the example of FIG. 1, the flow rate adjusting throttle mechanism 9 is provided not in the straight pipe part provided with the thermal flow rate measuring part of the shunt pipe, but in another straight pipe part downstream thereof.

  Further, it is preferable to make the flow rate adjusting throttle mechanism variable in the throttle opening so that the distribution ratio of the fluid to the branch flow path can be finely adjusted. FIG. 3 is a cross-sectional view showing an example of such a flow rate adjusting throttle mechanism having a variable throttle opening. In FIG. 3, reference numeral 21 denotes a flow path in which fluid flows in the direction of the arrow. Therefore, this throttle mechanism for adjusting the flow rate is used by being incorporated in the bent portion of the shunt pipe. Reference numeral 22 denotes an orifice, and the throttle opening varies depending on the degree of insertion of the tapered valve stem 23 therein. FIG. 3 shows a position where the throttle opening is at an intermediate level, and the throttle opening can be adjusted by turning the leftmost part of the drawing with a screwdriver. In FIG. 3, reference numeral 24 denotes a lock nut for adjusting at the position after adjusting the throttle opening when the flow meter is calibrated.

  As described above, the directions of the main pipes are various and cannot be specified from the flowmeter, but it is troublesome to make the flowmeters according to the directions of the main pipes. In order to cope with this, in the joint between the main pipe and the shunt pipe, the mounting direction is changed so that the shunt pipe at the position where the thermal flow rate measuring unit is provided is positioned so that the downstream side is in the vertical direction. It is preferable to provide a mechanism.

  4A and 4B are diagrams showing an example of the attachment direction changing mechanism for the part of the branch pipe. FIG. 4A shows the joint 12 on the main pipe side, and FIG. 4B shows the joint 13 on the branch pipe side. . In FIG. 4 (a), there is a main pipeline (not shown) on the front side of the page, and in FIG. 4 (b), there is a portion on the shunt pipeline side of a flow meter (not shown) on the back side of the page. Accordingly, the joint is connected in such a manner that FIG. 4A is overlapped on FIG. 4B, and the bolts 14 are tightened and fixed to a plurality of bolt holes 14 provided around these joints. The bolt hole 14 is located at the apex position of the square, and can be fixed even at a position where the joint 12 on the main pipeline side and the joint 13 on the shunt pipeline side are turned 90 degrees each other.

  Further, the joint 12 on the main pipeline side in FIG. 4A is provided with a branch flow inlet 15 and a branch discharge outlet 16, one of which is at the center of a square formed by four bolt holes 14 (here In the following description, it is assumed that the diversion inlet is at the center position). In addition, the surface (back side of the paper surface) of the joint 12 on the main pipeline side facing the joint 13 on the flow dividing pipeline side is a mere plane. On the other hand, the joint 13 on the branch pipe side in FIG. 4B is also provided with a branch inlet 17 and a branch outlet 18 at positions facing the branch inlet 15 and the branch outlet 16 of the joint 12 on the main pipe side, respectively. However, an annular groove 19 is further provided in communication with the shunt discharge port 18 on the surface facing the joint 12 on the main pipeline side. By providing the groove in this way, the fluid can be sent between the joints regardless of the position of the joint 12 on the main pipe side and the joint 13 on the shunt pipe side that are turned 90 degrees each other by the bolt hole 14. it can. Therefore, regardless of whether the main pipe line is vertical or horizontal, and in which direction the flow is, the shunt pipe line at the location where the thermal flow rate measuring unit is provided is vertical and the downstream side is up. Can be installed as.

  The attachment direction changing mechanism for the part of the diversion pipe is not limited to that shown in FIG. For example, the surface of the joint 12 on the main pipe side facing the joint 13 on the shunt line side is described above as a mere plane. However, in the joint on the main pipe side, the annular groove is located at a position facing the groove of the joint on the shunt pipe side. It may be provided. Further, the position of the diversion outlet (the diversion inlet when the diversion outlet is the center of the joint) may be at any circumferential position of the annular groove. Further, it is preferable to provide a gasket (not shown) between the joint on the main pipe side and the joint on the branch pipe side to prevent fluid leakage. The direction of the main pipe line is not so inclined, but if the joint is made circular instead of the square as shown in FIG. Can also deal with. In this case, the joints may be fixed by separately providing a clamp such as a clamp instead of the bolt.

Sectional view of the thermal flow meter of the present invention Diagram showing arrangement of fluid temperature sensor and exothermic flow sensor Sectional view showing the flow rate adjusting throttle mechanism with variable throttle opening It is a figure which shows the attachment direction change mechanism of the part of a shunt line, Comprising: (a) is a joint by the side of a main pipe line, (b) is a joint by the side of a shunt line

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main pipe line 2 Orifice 3 Divided pipe line 4 Inlet 5 Outlet 6 Thermal type flow measurement part 7 Fluid temperature sensor 8 Heat generation type flow sensor 9 Flow control throttle mechanism 10 Shunt pipe inner wall 12 Joint on main pipe side 13 Divided pipe side Joint 14 Bolt hole 15, 17 Split flow inlet 16, 18 Split flow outlet 19 Groove 21 Flow path 22 Orifice 23 Valve rod 24 Lock nut

Claims (3)

It has a differential pressure generating mechanism provided in the main pipe and a diversion pipe that connects the upstream side and the downstream side of the mechanism, and the flow rate of the main pipe is determined by measuring the flow rate with a thermal flow rate measuring unit provided in the diversion pipe. In the thermal type flow meter to be obtained, the thermal type flow rate measuring unit is provided with a fluid temperature sensor and a heat generation type flow rate sensor at intervals in the shunt pipe, and the temperature of the heat generation type flow rate sensor and the measurement temperature of the fluid temperature sensor are The flow rate is measured based on the heating power of the exothermic flow sensor to keep the difference constant, and the shunt pipe at the location where the thermal flow meter is installed is vertical regardless of the direction of the main pipe The heat generation type flow rate sensor is provided at the same position in the vertical direction or above the fluid temperature sensor in the flow dividing line, and the flow rate is further in the flow dividing line. An adjustment throttle mechanism is provided. Thermal flow meter, characterized in that there. 2. The thermal flow meter according to claim 1, wherein the throttle mechanism for flow rate adjustment has a variable opening degree. At the joint between the main pipe and the shunt pipe, there is provided a mechanism for changing the mounting direction for positioning the shunt pipe at the location where the thermal flow rate measuring unit is provided so that the downstream side is in the vertical direction. The thermal type flow meter according to claim 1 or 2, wherein

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