Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
2001-08-01
2003-09-16
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
Reexamination Certificate
active
06622096
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of setting a flow coefficient used in a flow meter for measuring a flow rate of a fluid.
BACKGROUND ART
A conventional flow meter will be described with reference to
FIG. 21. A
flow velocity measurement device
2
for measuring a flow velocity of a fluid, such as a thermal type flow sensor, is provided at a point in a fluid pipe
1
where a fluid passes therethrough. The flow velocity (Vm) obtained by the flow velocity measurement device
2
is multiplied by a cross-sectional area (S) of the fluid pipe
1
and a flow coefficient (K), so as to calculate a flow rate (Qm). The flow velocity measurement device
2
obtains the flow velocity (Vm) of the fluid by measuring the flow velocity of only a portion of the fluid in the vicinity of the flow velocity measurement device
2
. Therefore, an average flow velocity for the entire area of the fluid pipe
1
needs to be calculated as follows. A reference flow rate setting section capable of setting a reference flow rate is connected to the fluid pipe
1
so as to pass a fluid at an appropriate reference flow rate through the fluid pipe
1
and obtain an average flow rate (Qa). Then, the relationship (K=Va/Vm; “flow coefficient”) between an average flow velocity (Va), which is calculated from the average flow rate value and the flow velocity (Vm) measured by the flow velocity measurement device is obtained. This relationship is measured for various reference flow rates so as to obtain a number of data Bets each including the flow velocity (Vm) and the flow coefficient (K) of the fluid.
Next, the flow velocity (Vm) of the fluid measured by the flow velocity measurement device
2
is multiplied by the flow coefficient (K) and the cross-sectional area (S) of the fluid pipe
1
, thereby obtaining a measured flow rate (Qm). In other words, the measured flow rate (Qm) is obtained by calculating Qm=K·S·Vm. In
FIG. 21
, an arrow
3
denotes the direction of the fluid flow.
FIG. 22
illustrates a relationship between the flow velocity (Vm) and the flow coefficient (K) which are obtained as described above. In
FIG. 22
, the horizontal axis represents the flow velocity (Vm) measured by the flow velocity measurement device, and the vertical axis represents the flow coefficient (K). For example, if the flow velocity (Vm) of the fluid measured by the flow velocity measurement device
2
is about 2 m/s, the flow coefficient (K) can be read from
FIG. 22
to be about 0.89. Therefore, if the cross-sectional area (S) of the fluid pipe
1
is about 0.3×10
−3
m
2
, the measured flow rate (Qm) is:
Qm
=
2
×
0.89
×
0.3
×
10
-
3
m
3
/
s
=
0.534
×
10
-
3
m
3
/
s
=
1.9
m
3
/
h
.
The conventional flow meter has the following problems. That is, using a number of sets of data (see
FIG. 22
) each including the flow velocity (Vm) and the flow coefficient (K) measured by the flow velocity measurement device, the flow velocity range is appropriately divided into regions by visual observation so as to set an optimal approximate line for each region which optimally approximates a group of data sets (flow coefficients) within the region, thereby obtaining a kinked line which optimally approximates the group of data sets (flow coefficients) across all regions.
It is time consuming and labor intensive to set such an optimal approximate straight line by repeatedly performing complicated calculations. Moreover, because the setting operation is based on a visual observation, it has a poor reproducibility, and the obtained optimal approximate straight line may vary each time it is set. Although the optimal flow coefficient may be approximated by a high-degree curve, a low-degree approximation such as a linear or quadric approximation is preferred when the calculation is done by a microcomputer, or the like, because of the limitations associated with the use of a microcomputer such as the calculation time and the number of significant digits.
When the type of a fluid is changed from that used when measuring the reference flow rate and setting the flow coefficient, it is necessary to re-measure the average flow rate (Qa) and the flow velocity (Vm) of the new fluid so as to re-set a new flow coefficient (K).
When the temperature of the fluid changes, the characteristics of the fluid may also change, thereby changing the flow coefficient and deteriorating the flow rate measurement precision.
DISCLOSURE OF THE INVENTION
The present invention has been made to solve the above-described problems and provides a method of setting a flow coefficient, including the steps of: obtaining an optimal approximate line using a number n of consecutive sets of data points (Xi, Yi) of all flow velocity data points measured by a flow velocity measurement section, and reference data stored in a reference data memory section; increasing or decreasing the number n so that the n sets of data points are all within a predetermined error Er with respect to the optimal approximate liner performing a calculation operation for setting a region by a flow coefficient calculation section; and storing an obtained flow coefficient in a flow coefficient memory section.
With such a structure, according to the flow coefficient setting method of the present invention having such a structure, it is possible to easily and automatically set a flow coefficient using a personal computer, or the like, with good reproducibility, while suppressing the flow rate value within a predetermined error.
Another method of setting a flow coefficient of the present invention includes the steps of: obtaining an optimal approximate curve using a plurality of sets of data points (Xi, Yi) of all flow velocity data points measured by a flow velocity measurement section, and reference data stored in a reference data memory section, dividing the optimal approximate curve into a number m of regions; performing a calculation operation for approximating each region with an optimal approximate straight line by a flow coefficient calculation section; and storing an obtained flow coefficient in a flow coefficient memory section.
With such a structure, even if the number of data points available is limited, it is possible to select an optimal curve so that a flow coefficient can be set with a reduced error over a wider range, in a more efficient manner and within a shorter period of time.
A flow meter of the present invention includes: a flow velocity measurement section for measuring a flow velocity of a fluid; a flow coefficient memory section for storing a flow coefficient which is set by the above-described method of setting a flow coefficient; and a flow rate calculation section for calculating a flow rate of the fluid from the measured flow velocity using the flow coefficient stored in the flow coefficient memory section.
With such a structure, it is possible to provide a flow meter with a reduced error over a wide flow rate range.
Various embodiments of the present invention will be described below.
A method of setting a flow coefficient according to one embodiment of the present invention includes the steps of: obtaining an optimal approximate line using a number n of consecutive sets of data points (Xi, Yi) of all flow velocity data points measured by a flow velocity measurement section, and reference data stored in a reference data memory section; increasing or decreasing the number n so that the n sets of data points are all within a predetermined error Er with respect to the optimal approximate line; performing a calculation operation for setting a region by a flow coefficient calculation section; and storing an obtained flow coefficient in a flow coefficient memory section.
With such a structure, according to the flow coefficient setting method of the present invention having such a structure, it is possible to easily and automatically set a flow coefficient using a personal computer, or the like, with good
Barlow John
Lau Tung
Snell & Wilmer LLP
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