Measuring and testing – Volume or rate of flow – Proportional
Reexamination Certificate
2003-01-29
2004-08-31
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
Proportional
Reexamination Certificate
active
06782743
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fluid flow metering technique, and particularly to a flow metering method and a flowmeter for metering an instantaneous flow rate or integrated flow rate of fluid flowing in a pipe.
BACKGROUND TECHNIQUE
A flowmeter is used to meter the flow rate of fluid such as kerosene, water, gas or the like consumed at home or business enterprise. A thermal type (particularly, indirectly heated type) flow sensor which is easily reduced in cost has been used as a flowmeter.
There is known such an indirectly heated type flow sensor that a sensor chip comprising a thin film heating element and a thin film temperature-sensing element which are laminated through an insulating layer on a substrate by using a thin film technique is disposed so that heat transfer is allowed between the sensor chip and fluid in a pipe (containing a fluid flow passage provided in a flowmeter so as to intercommunicate with an outer pipe). The temperature-sensing element is heated by making current flow into the heating element to vary the electrical characteristic, for example, the value of electrical resistance of the temperature-sensing element. The variation of the electrical resistance value (based on increase in temperature of the temperature-sensing element) is varied in accordance with the flow amount (flow rate) of fluid flowing in the pipe. This is because a part of the heating value of the heating element is transferred to the fluid, the heating value diffused into and absorbed by the fluid is varied in accordance with the flow amount (flow rate) to thereby vary the heating value to be supplied to the temperature-sensing element. Therefore, the electrical resistance value of the temperature-sensing element is varied. The variation of the electrical resistance value of the temperature-sensing element is made different in accordance with the temperature of the fluid. Therefore, there has been utilized such a manner that a temperature sensing element for temperature compensation is installed in an electrical circuit for measuring the variation of the electrical resistance value of the temperature-sensing element so that the variation of the metered flow-rate value due to the temperature of the fluid is suppressed to the minimum level.
Such an indirectly heated type flow sensor using a thin film element as described above is disclosed in JP-A-11-118566, for example. This flow sensor uses an electrical circuit containing a bridge circuit for achieving an electrical output corresponding to the flow rate of fluid.
In the flowmeter as described above, a fin plate for the heat exchange between the sensor chip and the fluid is projected into the fluid flow passage, and an electrical circuit portion containing a circuit board for calculating the flow rate, a display portion, a communication circuit connecting portion and other parts are disposed at the peripheral portion of the flow sensor, and all the function portions of the flowmeter containing the above parts are accommodated in the housing.
In a flowmeter using an indirectly heated type flow sensor, a part of the heating value occurring in the heating element (heater) is transmitted to the fluid, and on the basis of the fact that heat absorption is performed in accordance with the flow rate of the fluid, the output value of the electrical circuit which corresponds to the heat absorption amount is converted to the flow rate value by using a calibration curve. The calibration curve is achieved on the basis of an experiment or the like which was performed on fluid to be subjected to the flow-rate metering. Accordingly, when the fluid to be subjected to the flow rate metering has the same thermal property as the fluid used when the calibration curve was created, substantially no error occurs in the flow-rate metering when the conversion using the calibration curve is carried out.
However, when the target fluid which is to be subjected to the flow-rate metering is formed of a mixture containing plural kinds of molecules which are different in molecular weight such as kerosene, the fluid to be actually subjected to the flow-rate metering does not necessarily have the same thermal property as the fluid used when the calibration curve was created. That is, standards such as JIS or the like are provided to kerosene, however, such standards have some degree of permissible range for physical property values. As a matter of fact, as a result of investigation of kerosene which is actually sold in the market, it has been found that there is some dispersion in the thermal property thereof. This dispersion is caused by variation of compositions of kerosene due to the difference in oil factory in which kerosene is achieved from raw petroleum, etc.
As described above, some kinds of kerosene are different in thermal property because they are fluid belonging to the same category of kerosene, but have different compositions. Therefore, when fluid to be subjected to the flow-rate metering has a thermal property different from that of fluid used when the calibration curve is created, some error may occur in the metered flow-rate value when the conversion using the calibration curve is carried out in the flow-rate metering. Specifically, when a consumption amount of kerosene is metered by a flowmeter equipped to a kerosene consumer such as each home or the like, kerosene to be supplied does not necessarily have a fixed composition and a fixed thermal property. In some cases, an amount different from the actually-consumed kerosene amount is achieved as a metered flow-rate value.
Not only kerosene, but also gasoline, naphtha, diesel oil, liquefied petroleum gas (LPG), solution having concentration variation, slurry, sol or the like is cited as an example of fluid which is targeted for the flow-rate metering and has variation in composition causing variation in thermal property as described above.
Therefore, the present invention has an object to perform flow-rate metering having little metering error even when the thermal property of fluid is varied due to variation of the composition of fluid or the like. Particularly, the present invention has an object to provide a method and a flowmeter for the flow-rate metering as described above.
DISCLOSURE OF THE INVENTION
According to the present invention, in order to attain the above object, there is provided a method of metering a flow rate of fluid by making the fluid under metering flow into a metering flow path, achieving the electrical output corresponding to a metered flow rate of the fluid under metering in the metering flow path by an electrical circuit constructed so as to contain a thermal type flow sensor disposed in the metering flow path and converting the electrical output corresponding to the metered flow rate to a flow-rate value by using pre-created calibration curves, wherein:
the fluid under metering is filled in a reference flow path so as to freely flow, and the electrical output corresponding to a reference flow rate of the fluid under metering in the reference flow path is achieved by an electrical circuit constructed so as to contain a thermal type reference flow sensor disposed in the reference flow path;
the calibration curves contain reference flow-rate calibration curves and metered flow rate calibration curves that are achieved with reference to plural temperatures for reference fluid; and
on the basis of the electrical output corresponding to the reference flow rate achieved for the fluid under metering, a deviation amount of the temperature on the reference flow-rate calibration curve corresponding to the electrical output corresponding to the reference flow rate from a reference temperature is determined, a temperature correction amount to the metered flow rate calibration curve of the reference temperature is achieved on the basis of the deviation amount, and the conversion to the flow rate value of the fluid under metering is performed on the basis of the electrical output corresponding to the metered flow rate of the fluid under metering by using the metered
Furuki Shinya
Hiraizumi Kenichi
Koike Atsushi
Yamagishi Kiyoshi
Frommer & Lawrence & Haug LLP
Lefkowitz Edward
Mitsui Mining & Smelting Co. Ltd.
Santucci Ronald R.
Thompson Jewel V.
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