Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
2000-04-13
2003-11-18
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06647777
ABSTRACT:
TECHNICAL FIELD
The present invention belongs to a fluid flow rate detection technology, and particularly relates to a flow rate sensor, particularly a thermal type flow rate sensor for detecting the flow rate of fluid flowing in a pipe line. The flow rate sensor of the present invention is suitably used to accurately measure the flow rate of fluid having relatively high viscosity and also suitably used for the measurement of flow rate of inflammable fluid for which abnormal temperature increase is required to be avoided.
Further, the present invention belongs to a fluid flow rate detection technology, and particularly relates to a flowmeter for measuring the instantaneous flow rate and the integrated flow rate of fluid flowing in a pipe line.
Still further, the present invention relates to a portable flowmeter which can be mounted on a pipe line through which kerosene is supplied to a kerosene burning device such as a stove, boiler or the like to measure the flow rate of kerosene, and also easily portably carried.
Still further, the present invention belongs to a liquid discharge amount control technology field, and particularly relates to a discharge amount control apparatus for liquid discharging equipment. The apparatus of the present invention is suitably used to control a sprayed (atomized) fuel oil discharging amount of an oil burner for burning fuel oil and produce desired heating power.
BACKGROUND TECHNIQUE
Various types of sensors have been hitherto used as a flow rate sensor (or flow velocity sensor) for measuring the flow rate (or flow velocity) of various fluid, particularly liquid, and a so-called thermal (particularly indirectly heated type) flow rate sensor is used because the cost can be easily reduced.
A sensor in which a thin-film heating element and a thin-film temperature sensing element are laminated through an insulating layer on a substrate and the substrate is secured to a pipe line is used as an indirectly heated type flow rate sensor. By passing current through the heating element, the temperature sensing element is heated to vary the electrical characteristic of the temperature sensing element such as the value of the electrical resistance of the temperature sensing element. The electrical resistance value (varied on the basis of the temperature increase of the temperature sensing element) is varied in accordance with the flow rate (flow velocity) of fluid flowing in the pipe line. This is because a part of the heating value of the heating element is transferred through the substrate into the fluid, the heating value diffusing into the fluid is varied in accordance with the flow rate (flow velocity) of the fluid, and the heating value to be supplied to the temperature sensing element is varied in accordance with the variation of the heating value diffusing into the fluid, so that the electrical resistance value of the temperature sensing element is varied. The variation of the electrical resistance value of the temperature sensing element is also varied in accordance with the temperature of the fluid. Therefore, a temperature sensing device for temperature compensation is installed in an electrical circuit for measuring the variation of the electrical resistance value of the temperature sensing element to suppress the variation of the flow-rate measurement value due to the temperature of the fluid at maximum.
An indirectly heated type flow rate sensor using thin film elements as described above is disclosed in JP-08-146026(A), for example.
The conventional indirectly heated type flow rate sensor is secured to a linear pipe line portion, and also the substrate of a flow rate detector or a casing which is thermally connected to the substrate is exposed from the wall surface of the pipe line to the fluid.
When the fluid is viscous fluid, particularly viscous fluid having relatively high viscosity, the flow-velocity distribution on the section perpendicular to the flow of the fluid in the pipe line is more remarkable (there is a great difference in flow velocity between the center portion and the outer peripheral portion on the section). In the case of the conventional sensor in which the substrate or the casing portion connected to the substrate is merely exposed to the fluid at the wall of the pipe line, the flow-velocity distribution has a great effect on the precision of the flow-rate measurement. This is because the flow velocity of the fluid flowing at the center portion on the section of the pipe line is not taken into consideration, but only the flow velocity of the fluid in the neighborhood of the wall of the pipe line is taken into consideration. As described above, the conventional flow rate sensor has such a problem that it is difficult to measure the flow rate of fluid accurately when the fluid is viscous fluid having relatively high viscosity.
Even when fluid has low viscosity at room temperature, it induces a problem connected to the above viscosity problem because the viscosity of the fluid increases as the temperature is lowered.
Further, the above problem is more remarkable when the flow rate per unit time is relatively low than when the flow rate per unit time is high.
The flow rate sensor is required to be used under an extremely broad temperature environment in accordance with a geographical condition, an indoor or outdoor condition, etc. Further, these conditions are added with a season condition, a day or night condition, etc., and the temperature environment is greatly varied. Therefore, there has been required a flow rate sensor which can detect the flow rate accurately under such a broad environmental temperature condition as described above.
Therefore, an object of the present invention is to provide a flow rate sensor which can accurately measure the flow rate of fluid flowing in a pipe line even when the fluid is viscous fluid having relatively high viscosity.
Further, an object of the present invention is to provide a flow rate sensor which can accurately measure the flow rate of fluid flowing in a pipe line even when the flow rate is relatively small.
Still further, an object of the present invention is to provide a flow rate sensor which can accurately measure the flow rate of fluid flowing in a pipe line under a broad environmental temperature condition.
In the conventional indirectly heated type flow rate sensor, a constant voltage is applied to the heating element to obtain a desired heating value. A part of the heating value is endothermically transferred to the fluid and the remaining part of the heating value is transferred to the temperature sensing element. Therefore, the surrounding temperature of the heating element is varied in accordance with the flow rate of the fluid. When the flow rate of the fluid is high, the temperature increase is small. On the other hand, when the flow rate of the fluid is low, the temperature increase is large.
The problem occurs when fluid, particularly liquid is extinguished for some cause. In this case, the endothermic action of the fluid is lost, so that the temperature of the temperature sensing element is sharply increased, resulting in deterioration of the flow rate sensor with time lapse.
In the case where the fluid is kerosene or other inflammable and volatile fluid, the fluid is vaporized if the fluid is supplied when the sharp temperature increase as described above arises or after the sharp temperature increase, and then if air is mixed with the fluid, ignition and explosion may occur.
Therefore, an object of the present invention is to prevent excessive increase of the surrounding (environmental) temperature of the heating element of the thermal flow rate sensor, thereby preventing the deterioration of the flow rate sensor with time elapse and the ignition and explosion of inflammable fluid to be detected.
Further, when fuel fluid such as kerosene or fuel gas is supplied to demanders, the flow rate (instantaneous flow rate) of fuel fluid to be supplied to each demander is measured and integrated to determine an integrated flow rate, and then the rate corresponding to the
Inoue Shin'ichi
Kawanishi Toshiaki
Koike Atsushi
Kotaka Hirofumi
Miyajima Hiromitsu
Baker & Daniels
Dickens C.
Lefkowitz Edward
Mitsui Mining & Smelting Co. Ltd.
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