JP4095362B2 - Flowmeter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a flow meter for measuring a fluid flow rate based on the principle of heat exchange.
[0002]
[Prior art]
As means for measuring the fluid flow rate of the micro, there is a flow meter for measuring fluid flow rate based on the principle of heat exchange, known those described in such as a flow meter for example Kokoku 8-14 5 05 No. It is.
[0003]
FIG. 5 schematically shows the configuration of the sensor unit 50 of the flow meter. In this figure, 51 is a pipe through which the fluid F to be measured flows, and a part 51 a thereof is cooled by the electronic cooling device 52. It is configured as follows. A first temperature detecting element 53 is provided in a portion (uncooled portion) 51b of the tube 51 that is not cooled by the electronic cooling device 52 upstream of the portion (cooled portion) 51a that is cooled by the electronic cooling device 52. A second temperature detection element 54 is provided in a portion 52a away from the tube 51 of the apparatus 52, and a third temperature detection element 55 is provided in the cooled portion 51a. In addition, although illustration is abbreviate | omitted, the sensor part 50 of the said structure is provided in the sealed case.
[0004]
Then, while controlling the temperature of the electronic cooling device 52 to be controlled so that the difference between the detected temperature of the first temperature detecting element 53 and the detected temperature of the second temperature detecting element 54 is always a predetermined value, The flow rate of the fluid F flowing through the pipe 51 is measured based on the difference between the detected temperature of the third temperature detecting element 55 and the detected temperature of the second temperature detecting element 54.
[0005]
According to the flowmeter having the above configuration, the flow rate of the fluid F flowing through the pipe can be measured in a non-contact manner, and the fluid F having a minute flow rate can be measured. For example, in the case of measuring a liquid with a minute flow rate, bubbles are not generated in the liquid. Therefore, it is possible to measure a liquid flow rate that easily generates a gas such as a low boiling point liquid. . Even if gas is dissolved in the liquid, it is not affected, and the temperature of the electronic cooling device 52 is changed according to the temperature change of the liquid, and the temperature of the tube that is not cooled by the electronic cooling device 52 and the electron Since the difference between the temperature of the cooling device 52 and the temperature of the cooling device 52 is always set to a predetermined value, measurement with high accuracy can be performed in combination with being not affected by the mounting posture.
[0006]
[Problems to be solved by the invention]
By the way, when the flow rate of the fluid F is measured by the flowmeter based on the principle of the heat exchange, the temperature of the fluid F flowing into the sensor unit 50 greatly affects the sensor sensitivity. That is, the sensor sensitivity increases as the difference between the temperature of the electronic cooling device 52 that is the heat exchange portion and the temperature of the fluid F increases. In the conventional flow meter, the temperature of the fluid F flowing into the pipe 51 is the same as the ambient temperature in the case where the first temperature detection element 53 provided in the non-cooling portion 51b of the pipe 51 is disposed. It is assumed that there is a temperature setting in the electronic cooling device 52.
[0007]
However, the temperature of the fluid F that actually flows into the pipe 51 does not necessarily match the ambient temperature. Therefore, even if the temperature of the fluid F actually changes in the usage environment, the temperature setting value of the electronic cooling device 52 does not change. As a result, the temperature change of the fluid F becomes a sensitivity change, and the stability of the flow rate measurement is greatly impaired.
[0008]
By the way, since the flow meter is provided in a fluid flow path that does not allow even a slight external leak, it is extremely difficult to directly contact the fluid and measure the temperature thereof. And as mentioned above, in the said flow meter, the temperature of the outer wall of a flow path (pipe) is measured. Therefore, actually, an intermediate temperature between the ambient temperature and the fluid temperature in the case where the first temperature detection element 53 is provided is measured. For this reason, the set temperature of the electronic cooling device 52 of the sensor unit 50 cannot be completely linked to the fluid temperature, and if the fluid temperature changes greatly, an error may occur in the measured value of the flow rate.
[0009]
Therefore, when using a conventional flow meter, the temperature change range of the fluid has been made as small as possible, but the desire to use it even when the temperature change range of the fluid becomes large comes out from the user side. In this regard, conventional flowmeters have not always been compatible.
[0010]
The present invention has been made in consideration of the above-mentioned matters, and its object is to provide a flowmeter capable of accurately and stably measuring a fluid flow rate even under conditions where the temperature change range of the fluid is large. Is to provide.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a flow meter according to the present invention includes a pipe through which a fluid flows, an electronic cooling device that cools a part of the pipe, and an upstream side of the portion to be cooled that is cooled by the electronic cooling device in the pipe. A first temperature detecting element for detecting the temperature of the non-cooled part on the side, a second temperature detecting element for detecting the temperature of the electronic cooling device, a third temperature detecting element for detecting the temperature of the part to be cooled, and an atmosphere Controlling the temperature of the electronic cooling device so that the difference between the detected temperature of the fourth temperature detecting element for detecting the temperature and the detected temperature of the second temperature detecting element and the detected temperature of the first temperature detecting element becomes a predetermined value; The temperature of the electronic cooling device is controlled based on the difference between the detected temperature of the fourth temperature detecting element and the detected temperature of the first temperature detecting element, and the detected temperature of the second temperature detecting element and the third temperature are controlled. Difference from detection temperature of detection element Based on and a calculation control unit for calculating the flow rate of the fluid flowing through the tube (claim 1).
[0012]
More specifically, in the present invention, a pipe through which a fluid flows is provided so as to pass through the inside of the case. In the case, a part of the pipe is cooled by an electronic cooling device, and more than the portion to be cooled of the pipe. A sensor unit in which a first temperature detection element is provided at an upstream non-cooled part, a second temperature detection element is provided at a part away from the tube of the electronic cooling device, and a third temperature detection element is provided at the part to be cooled. The temperature detected by the third temperature detecting element is controlled while controlling the temperature of the electronic cooling device so that the difference between the detected temperature of the first temperature detecting element and the detected temperature of the second temperature detecting element is always a predetermined value. In the flowmeter that measures the flow rate of the fluid flowing in the pipe based on the difference between the temperature detected by the second temperature detection element and the second temperature detection element, a fourth temperature detection element is provided for measuring the ambient temperature in the case. The fourth temperature detection element Based on the difference between the detected temperature of the the detected temperature first temperature sensing element so as to control the temperature of the electronic cooling device (claim 2).
[0013]
In the flowmeter having the above configuration, the temperature change state of the fluid flowing into the pipe is always determined based on the temperature in the case where the sensor unit is provided and the temperature of the pipe through which the fluid flows before being cooled. Since the temperature of the electronic cooling device that cools the tube is controlled based on the information obtained by monitoring, the set temperature of the electronic cooling device can be completely linked to the fluid temperature. Even when the temperature changes greatly, the flow rate of the fluid flowing in the pipe can be measured accurately and stably.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the details of the present invention will be described with reference to the drawings. 1 to 4 show one embodiment of the present invention. 1 to 3, reference numeral 1 denotes a flow meter according to the present invention. Reference numeral 2 denotes a rectangular parallelepiped case 2 made of, for example, stainless steel, and a tube 3 is provided so as to pass through the inside thereof. The tube 3 is made of, for example, a stainless steel tube having an outer diameter of 0.8 mm and an inner diameter of 0.6 mm, and a fluid F such as a liquid or a gas flows therein. 4 and 5 are joint members.
[0015]
In the case 2, a sensor unit 6 configured as follows is provided. That is, 7 is an electronic cooling device that cools a part 3a of the tube 3 in the case, and is thermally tightly coupled to the thermomodule 8 and the plate 9 that is thermally tightly coupled to the upper surface thereof and the lower surface. Heat sink 10 to be made. And the thermo module 8 is provided so that it may be located in the opening 11a opened in the printed circuit board 11. FIG. The plate 9 is made of a material excellent in thermal conductivity (for example, a stainless steel plate or a copper plate), and a part 9 a thereof is tightly wound around the cooled portion 3 a of the tube 3. Furthermore, the heat sink 10 is provided so as to close the lower opening of the case 2 and includes a plurality of heat radiation fins 10a outside.
[0016]
The printed circuit board 11 has an electric circuit (not shown) formed on the upper surface thereof, a constant current circuit for supplying a predetermined amount of current to four temperature detection elements described later, and the electronic cooling device. A constant temperature control circuit for controlling 7 is provided. Further, on the printed board 11, a connection terminal portion (not shown) 11b for connecting to an external circuit, for example, a flow meter main body portion (not shown) protrudes outside the case 2 (FIG. 1). reference).
[0017]
Reference numeral 12 denotes a first temperature detecting element that detects the temperature of the non-cooled part 3b upstream of the cooled part 3a of the pipe 3, and is provided on the pipe surface via an appropriate element holder 13. Reference numeral 14 denotes a second temperature detection element that detects the temperature of the electronic cooling device 7 and is attached to the plate 9. Reference numeral 15 denotes a third temperature detecting element that detects the temperature of the cooled portion 3 a of the tube 3 cooled by the electronic cooling device 7, and is attached to the holder portion 9 a of the plate 9.
[0018]
The configuration so far is the same as the conventional flow meter shown in FIG. In the present invention, the fourth temperature detection element 16 for measuring the ambient temperature in the case 2 is provided, and based on the difference between the detection temperature of the fourth temperature detection element 16 and the detection temperature of the first temperature detection element 12. The temperature of the electronic cooling device 7 is controlled. In other words, in the present embodiment, the fourth temperature detection element 16 is provided on the surface of the printed board 11 and relatively close to the first temperature detection element 12. In addition, the installation position of the 4th temperature detection element 16 may be anywhere as long as it can measure the atmospheric temperature in the case 2. In addition, the case 2 has an airtight state in which the inside is shut off from the outside, the upper opening of the case 2 is closed by a suitable lid member (not shown), and the insertion portion of the tube 3 The protruding portion of the printed circuit board 11 is configured such that no gap is generated by an appropriate compound. The sensor unit 6 having the above configuration is configured to be controlled by an arithmetic control unit on the main body side (not shown).
[0019]
Next, the operation of the flow meter will be described. In the flow meter having the above-described configuration, a current of a predetermined magnitude (for example, 1.0 mA) is supplied to each of the temperature detection elements 12, 14, and 15 by a constant current circuit, and the detected temperature T _{1 of} the first temperature detection element 12. In the constant temperature control circuit, for example, PID is used in the electronic cooling device 7 so that the difference (T ₁ −T ₂ ) between the first temperature detecting element 14 and the detected temperature T _{2 of} the second temperature detecting element 14 becomes a predetermined value (for example, 10 ° C.). To control.
[0020]
When the fluid F does not flow in the tube 3 under the above conditions, the temperature on the plate 9 of the electronic cooling device 7 is all the same temperature, so that the detected temperature T _{3 of} the third temperature detecting element 15 and the second temperature detection The detection temperature T ₂ of the element 14 is equal, that is, the difference (T ₃ −T ₂ ) is zero. When the fluid F flows in the tube 3, the detected temperature T ₃ of the third temperature detecting element 15, since increases in proportion to the flow rate of the fluid F, the temperature detected by the third temperature detecting element 15 A difference (T ₃ −T ₂ ) is generated between T ₃ and the detected temperature T _{2 of} the second temperature detecting element 14. Therefore, the flow rate of the fluid F flowing in the pipe 3 can be obtained by obtaining the difference (T ₃ -T ₂ ) so that the difference (T ₁ -T ₂ ) becomes a predetermined value. .
[0021]
Meanwhile, the flow rate signal corresponding to the flow rate of the fluid F flowing through the tube 3 is proportional to the difference between the temperature T ₂ of the temperature T ₁ of the electronic cooling device 7 of the fluid F, the flow rate signal is greater if the temperature difference is greater Become. Therefore, it is necessary to accurately measure the temperature T ₁ .
[0022]
Therefore, in order to always maintain a constant temperature difference between the set temperature of the electronic cooling device 7 and the temperature of the fluid F, the ambient temperature in the case 2 in which the temperature detecting elements 12, 14, and 15 are provided is changed. 4 detected by the temperature detecting element 16, a difference between the detected temperature T ₁ of the detected temperature T ₄ and the first temperature detecting element 12 of the temperature detecting element 16 (T ₄ -T _1), the temperature of the electronic cooling device 7 In addition to the control value, the temperature of the electronic cooling device 7 is controlled so as to follow the temperature change of the fluid F.
[0023]
For example, now, as the difference between the detected temperature T ₂ detected temperatures T ₁ and the second temperature detecting element 14 of the first temperature detecting element 12 (T ₁ -T ₂₎ is 10 ° C.), the constant temperature control circuit For example, when the electronic cooling device 7 is controlled using PID, the temperature T ₇ of the electronic cooling device 7 is controlled as shown in the following equation (1). That is,
T ₇ = 10 ° C. + α (T ₄ −T ₁ ) (1)
Where α is an arbitrary correction factor.
Therefore, for example, when the temperature of the fluid F shifts to the minus side (becomes low), the temperature difference (T ₄ −T ₁ ) shifts to a plus and the flow rate signal shifts to a minus. The correction in this case adds a temperature difference (T ₄ −T ₁ ) to the temperature control value (T ₁ −T ₂ ) of the electronic cooling device 7. By doing so, the difference between the set temperature of the electronic cooling device 7 and the temperature of the fluid F is increased, the flow rate signal is shifted to plus, and the flow rate signal is corrected. On the contrary, even when the temperature of the fluid F shifts (becomes higher) to the plus side, the flow rate signal can be corrected in the same manner as described above.
[0025]
FIG. 4 schematically shows the relationship between the temperature change of the fluid F and the sensor output of this type of flow meter. The horizontal axis represents the temperature change (° C.) of the fluid F, and the vertical axis represents the sensor output (V). Each is shown. In the conventional flow meter shown in FIG. 5, when the measurement is performed within the required accuracy width A, the temperature change width of the fluid F flowing in the pipe 3 is 0 as shown by the symbol B in the figure. ℃ did not take so large mainly, according to the flowmeter of the present invention, as indicated at C in the figure, rather large bets are by Uninari than the conventional, thus, large fluid F of temperature change The flow rate can be measured accurately and stably.
[0026]
As the temperature detection elements 12, 14, 15, and 16, a linear thermistor, a platinum thermometer, a resistance temperature element, a winding, a thermocouple, and the like can be suitably used. In addition to stainless steel, the tube 3 may be made of a metal material such as aluminum, copper, or nickel, or a fluoroethylene resin, a polymer, or the like when the thickness is reduced. Moreover, the flowmeter of this invention can be used not only for liquids but also for measuring the flow rate of gases such as air, argon or corrosive gases.
[0027]
【The invention's effect】
As described above, in the flowmeter of the present invention, the temperature change of the fluid flowing into the pipe based on the temperature in the case in which the sensor unit is provided and the temperature of the pipe through which the fluid before being cooled flows. The temperature of the electronic cooling device that controls the temperature of the tube is controlled based on the information obtained by this monitoring, so that the set temperature of the electronic cooling device is completely linked to the fluid temperature. Even when the fluid temperature changes greatly, the flow rate of the fluid flowing in the pipe can be measured accurately and stably.
[Brief description of the drawings]
FIG. 1 is a plan view schematically showing a configuration of a flow meter of the present invention.
FIG. 2 is a longitudinal sectional view of the flow meter.
FIG. 3 is a perspective view showing the flow meter as seen through.
FIG. 4 is a diagram schematically showing a relationship between a temperature change of a fluid and a sensor output in a flow meter that measures a fluid flow rate based on the principle of heat exchange.
FIG. 5 is a diagram schematically showing a configuration of a sensor unit of a conventional flow meter.
[Explanation of symbols]
2 ... Case, 3 ... Tube, 6 ... Sensor part, 7 ... Electronic cooling device, F ... Fluid.

Claims (2)

A pipe through which a fluid flows, an electronic cooling device that cools a part of the pipe, and a first temperature detection that detects the temperature of an uncooled part upstream of the cooled part that is cooled by the electronic cooling device in the pipe An element, a second temperature detecting element for detecting the temperature of the electronic cooling device, a third temperature detecting element for detecting the temperature of the cooled part, a fourth temperature detecting element for detecting an ambient temperature, and the second The temperature of the electronic cooling device is controlled so that the difference between the detected temperature of the temperature detecting element and the detected temperature of the first temperature detecting element becomes a predetermined value, and the detected temperature of the fourth temperature detecting element and the first temperature The temperature of the electronic cooling device is controlled based on the difference between the detection temperature of the detection element and the tube is controlled based on the difference between the detection temperature of the second temperature detection element and the detection temperature of the third temperature detection element. Calculate the flow rate of flowing fluid Flowmeter, characterized in that it comprises a calculation control unit. A pipe through which a fluid flows is provided so as to be inserted through the case. In the case, a part of the pipe is cooled by an electronic cooling device, and the pipe is placed in an uncooled part upstream of the part to be cooled of the pipe. A first temperature detection element is provided, a second temperature detection element is provided at a location away from the tube of the electronic cooling device, and a third temperature detection element is provided at the cooled location to form a first temperature detection while controlling the temperature of the electronic cooling device such that the difference between the detected temperature of the detected temperature and the second temperature sensing element of the device is always a predetermined value, the detection of the detected temperature and the second temperature detecting element of the third temperature detecting element In the flowmeter configured to measure the flow rate of the fluid flowing in the pipe based on the difference from the temperature, a fourth temperature detection element for measuring the ambient temperature in the case is provided, and the fourth temperature detection element Detection temperature and first temperature detection Flowmeter is characterized in that so as to control the temperature of the electronic cooling device based on the difference between the detected temperature of the child.

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