Measuring and testing – Volume or rate of flow – System
Reexamination Certificate
2000-05-25
2002-09-10
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
System
Reexamination Certificate
active
06446503
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a flowmeter for measuring the quantity of flow of a fluid such as gas and, more particularly, to a flowmeter capable of accurately measuring a quantity of flow over a wide range of the quantity of flow.
1. Background Art
Some flowmeters for measuring the quantity of flow of a fluid, such as gas, calculate the quantity of flow by disposing a flow velocity sensor in a flow path and multiplying the flow velocity obtained by the flow velocity sensor by the cross-sectional area of the flow path.
FIG. 29
shows a specific configuration of such a conventional flowmeter. In the flowmeter, a flow velocity sensor
1
is disposed in the center of a fluid flow path in a pipe
2
. A flow quantity calculating unit
3
calculates the quantity of flow by multiplying the flow velocity in the center of the flow path obtained by the flow velocity sensor
1
by the cross-sectional area of the pipe
2
and the quantity of flow is displayed on a display unit
4
. In order to maintain the high accuracy in flow quantity measurement by the flow velocity sensor, the flow velocity sensor
1
has to be disposed in the most stable flow of the fluid.
The conventional flowmeter has, however, a problem such that a mounting position of the flow velocity sensor
1
is difficult to be determined since a drift occurs in the pipe
2
depending on the quantity of flow. It is necessary to set the flow velocity sensor
1
in a limited range of flow quantity where the drift is small. The measurable range of the flow quantity is accordingly narrowed and it is difficult to accurately measure the flow quantity of gas over a wide flow quantity range. The drift denotes here that the flow velocity varies according to places. The flow quantity range denotes the range of the quantity of flow. The definition will be the same in the following description.
As described above, in the conventional flowmeter, it is difficult to set a sufficiently wide flow quantity measurement range by using a single flow velocity sensor. In order to solve the problem, the following method is considered. The flow quantity measurement range is divided into, for example, two ranges of a larger flow quantity range and a smaller flow quantity range. A flow velocity sensor for the range of the larger quantity of flow is assigned to the range of the larger quantity of flow and a flow velocity sensor for the range of the smaller quantity of flow is assigned to the range of the smaller quantity of flow. The quantity of flow is calculated by switching output signals from the flow velocity sensors.
In the flowmeter constructed by using the plurality of flow velocity sensors as described above, however, the flow of the fluid is disturbed by the existence of one of the flow velocity sensors and there is the possibility that the disturbance exerts an adverse influence on the measurement accuracy of the other flow velocity sensor. As a result, it is difficult to measure the quantity of flow with high accuracy over a wide measurement range of the quantity of flow.
Meanwhile, a gas meter for home use having not only the function of measuring the quantity of flow of passing gas but also a safety function realized by mounting a microcomputer is practically used. According to the safety function, for example, when the quantity of flow of gas equal to or higher than a predetermined quantity is detected or when a predetermined gas flow quantity is detected for predetermined time or longer, a gas emergency trip valve is driven to shut off the gas flow path. By the functions, a leakage in the pipe, unnatural gas outflow, and the like are detected, so that an accident can be prevented and the safety can be assured. For the accurate operation of the functions, however, it is desired to accurately measure the gas flow quantity over a wide flow quantity range.
2. Disclosure of Invention
The invention has been achieved in consideration of the above problems and it is an object of the invention to provide a flowmeter capable of accurately measuring a quantity of flow of a fluid such as gas over a wide flow quantity range.
According to the invention, there is provided a flowmeter comprising: a pipe including a flow path through which a fluid passes and in which a measurement zone for smaller quantity of flow and a measurement zone for larger quantity of flow are provided along the longitudinal direction of the flow path; a flow path dividing member provided in the measurement zone for smaller quantity of flow in the flow path of the pipe to divide the flow path into a plurality of narrower flow paths each having a smaller cross-sectional area; a first flow velocity sensor provided in the measurement zone for larger quantity of flow in the flow path of the pipe, for outputting a signal according to the flow velocity of the fluid passing through the measurement zone for larger quantity of flow; a second flow velocity sensor provided in the narrower flow path formed by the flow path dividing member, for outputting a signal according to the flow velocity of the fluid passing through the narrower flow path; and flow quantity calculating means for calculating the quantity of flow on the basis of at least one of the output signal of the first flow velocity sensor and the output signal of the second flow velocity sensor, in accordance with the quantity of flow.
According to the flowmeter of the invention, a signal responsive to the flow velocity of the fluid passing through the zone is outputted from the first flow velocity sensor in the measurement zone for larger quantity of flow. On the other hand, a signal responsive to the flow velocity of the fluid passing through the narrower flow path formed by the flow path dividing member is outputted from the second flow velocity sensor in the measurement zone for smaller quantity of flow. The flow quantity calculating means calculates the quantity of flow on the basis of at least one of the output signal of the first flow velocity sensor and the output signal of the second flow velocity sensor in accordance with the quantity of flow. In the flowmeter, the scale of the flow velocity distribution in the cross section of each narrower flow path (variations in the flow velocity according to places), that is, the degree of a drift is smaller than that of the flow velocity distribution in the cross section of the whole flow path when the flow path dividing means is not disposed. The flow velocity in the narrower flow path near the flow path wall becomes higher as compared with the case where no flow path dividing means is provided.
According to the flowmeter of the invention, the first flow velocity sensor may be attachable to and detachable from the wall face of the pipe. The second flow velocity sensor may be also attachable to and detachable from the wall face of the pipe.
According to the flowmeter of the invention, the second flow velocity sensor may be disposed in the narrower flow path which is the closest to the wall face of the pipe among the plurality of narrower flow paths. The first flow velocity sensor may be disposed near the wall face of the pipe.
In the flowmeter of the invention, the plurality of first flow velocity sensors may further comprise mean flow velocity calculating means for the measurement zone for larger quantity of flow, which calculates a mean value of the flow velocities in the measurement zone for larger quantity of flow on the basis of the output signals of the plurality of first flow velocity sensors and outputs the mean value to the flow quantity calculating means.
In the flowmeter of the invention, the plurality of second flow velocity sensors may further comprise mean flow velocity calculating means for the measurement zone for smaller quantity of flow, which calculates a mean value of the flow velocities in the measurement zone for smaller quantity of flow on the basis of the output signals of the plurality of second flow velocity sensors and outputs the mean value to the flow quantity calculating means.
The flowmeter of the invention may still further compr
Kato Hideo
Komaki Mitunori
Matushita Masahiko
Nukui Kazumitsu
Tashiro Ken
Fuller Benjamin R.
Mack Corey D.
Oliff & Berridg,e PLC
Tokyo Gas Co. Ltd.
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