CN1116587C - Method for increasing measuring range and precision of orifice plate flowmeter - Google Patents

Abstract

The present invention relates to a method for enhancing the measurement range and precision of a hole plate flow meter. The method comprises the steps: a, setting the number n (n is an integral number greater than 1) of sections in the whole flow quantity measurement range; b, determining a common ratio q according to the flow quantity measurement range and the number n of the sections; c, determining the section points values of the sections on a liquid flow quantity curve according to the flow quantity measurement range, the common ratio q and the geometric progression relation; d, calculating the flow quantity of each section on the liquid flow quantity curve. Compared with known methods, the range of the present invention is enlarged in the same precision; or the precision of the present invention is enhanced in the same range.

Description

Improve the method for orifice flowmeter measurement range and precision

The present invention relates to the measuring method of orifice flowmeter.

Orifice flowmeter is the device that is used for measuring the flow of pipeline fluid, and it determines flow according to following calculating formula: $W=0.01252\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="C0013360500072.png"\; state="\{\{state\}\}">D</figure-callout>}}^2\&CenterDot;\mathrm{\&alpha;}\&CenterDot;{\mathrm{\&beta;}}^2\&CenterDot;\mathrm{\&epsiv;}\&CenterDot;\sqrt{\mathrm{\&gamma;}\&CenterDot;\mathrm{\&Delta;P}}$ In the formula: W: fluid flow (kg/h)

D: flowmeter internal diameter (mm)

^*α: coefficient of flow

β: the aperture is than (d/D), and d is the throttle orifice or the throat diameter of throttling element under the condition of work, and D is the flowmeter internal diameter

^*ε: inflatable coefficient

γ: specific gravity (kg/m ³) ^*Δ P: pressure reduction (Pa)

The calculating of relevant flow measurement can be referring to GB GB/T2624-93.

In the past in orifice flowmeter is measured, in whole measurement flow range (pressure differential range), only with a calculating formula.Because α and ε are the functions about Δ P, corresponding Δ P just uses corresponding α and ε substitution in whole pressure differential range, therefore, and only because the error of calculation just has influence on whole measurement range.Measure by this kind method, flow 65% near error near zero, leave herein after error increase gradually, as Fig. 1.Its measurement range degree (being maximum detection amount and minimum measurable ratio) only is 1: 4, precision only can reach ± and 4%, improve measuring accuracy again to ± 3% o'clock, near rangeability was reduced into 1: 2, when surpassing this boundary measurement, can splash by the interior mercury of build-up of pressure table, produce big measuring error.

By 1984, because the application of IC technology and computer technology, people's orifice plate graph of errors that begins one's study, the technician is partitioned into a flow region near precision on the curve ± 0% place (flow 65%), form the mathematical model of error of calculation minimum in this zone, calculating formula is in the past still used in other zone.This method error in determined zone diminishes, and the zone is outer then to produce very big error, and flow range increases, and error is also along with big more, thus can not obtain big measurement range degree, as Fig. 2.

This shows that only the whole flow range with a formula containing flowmeter is inappropriate, against in measuring principle.So, what is the method that reduces measuring error in whole measurement range? answer is very simple, promptly increases the quantity of calculating formula.

Phase one be at first the limits of error is fixed on ± 1% o'clock, analyzing has what with a calculating formula error of calculation, after the discovery flow range was divided equally with 30% ratio, its error was average, as Fig. 3.And error once is reduced into by ± 1% ± 0.5%, cutting apart flow range is 20%, as Fig. 4, and visible its error equalization.

This theory is further developed, can will segment between cut section, make error unlimited near zero.Yet problem is so not simple, the interval calculation of complexization that must make orifice plate of segmentation, because contain three variablees that have * in the aforementioned calculation formula, in the calculating of each sectional area, pressure differential deltap P that not only should the zone is different from other zone, but also the necessary variation of considering other two variable α and ε, calculate these two variablees and need carry out tight loaded down with trivial details mathematical formulae computing repeatedly, even use household PC, also will surpass 1 second its operation time, do not catch up with the variation of fluid in the pipeline at all.Therefore, the interval method of segmentation does not have practicality.And suitably segmentation just can be shortened operation time and compression memory storage amount.

In the calculating process of segmentation, how segmentation is a major issue.Average discrete method, approximate mark point-score etc. are arranged in the present segmentation method.

The average discrete method that adopts as the U.S. is exactly flow curve to be adopted that impartial principle is divided into wait line segment, and its advantage is to utilize to divide calculating, and the relative discharge curve is the same between every section point, as Fig. 5.But because the absolute value difference of flow, every section ratio is different, and all the section point of segmentation can not guarantee to equate on the whole waypoint with the section point of relative variation, promptly is that the ratio from actual change is identical.

Though it is the same this shows above-mentioned waypoint, and be the same, then change different for each section point to total flow curve zone.As:

100％/80％＝1.25

80％/60％＝1.333

60％/40％＝1.5

40％/20％＝2

20％/7.7％＝2.59

The measurement range degree that is every section can be thought 2.59 variations in the region of variation difference at 20%～7.7%.Like this big rangeability is included in the interval characteristics that just can not fine embodiment segmentation computing.

Japan has adopted the method that is divided into different paragraph points according to the slope variation of the characteristics of flow curve or flow curve, as Fig. 6.Its segmentation method and principle adopt equal point-score substantially, but it is comparatively mild to consider that on indivedual paragraphs flow curve changes slope, so suitably relax herein, promptly 25%～60% intersegmental, thereby make flow instrument can reach high requirement under lower cost.Its waypoint changes as follows for each section point:

100％/80％＝1.25

80％/60％＝1.333

60％/25％＝2.4

25％/7.7％＝3.24

This shows that what it was followed still is a kind of equal point-score,, and fail to accomplish the same everywhere though the ratio of its every section branch has had some improvement than the directly all point-score of front.

In view of above-mentioned, the objective of the invention is to propose a kind of method that improves orifice flowmeter measurement range degree and precision.

The object of the present invention is achieved like this:

A kind of method that improves orifice flowmeter measurement range and precision the steps include:

A. be set in the segments n in the whole measurement flow range, n is the integer greater than 1;

B. according to measuring flow range and segments n, determine common ratio q;

C. according to measuring flow range and common ratio q, determine the section point value of each segmentation on the fluid flow curve by the geometric progression relation;

D. flow rate calculation is carried out in each interval on the fluid flow discharge curve.

The interval m of on the fluid flow discharge curve each, can carry out following flow rate calculation: $W_m=0.01252\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="C0013360500072.png"\; state="\{\{state\}\}">D</figure-callout>}}^2\&CenterDot;{\mathrm{\&alpha;}}_m\&CenterDot;{\mathrm{\&beta;}}^2\&CenterDot;{\mathrm{\&epsiv;}}_m\&CenterDot;\sqrt{\mathrm{\&gamma;}\&CenterDot;\mathrm{\&Delta;P}}$ In the formula: W _m: fluid flow (kg/h)

D: flowmeter internal diameter (mm)

α _m: coefficient of flow

β: the aperture is than (d/D), and d is the throttle orifice or the throat diameter of throttling element under the condition of work, and D is the flowmeter internal diameter

ε _m: inflatable coefficient

γ: specific gravity (kg/m ³)

Δ P: pressure reduction (Pa)

M: interval numbering is respectively and gets 1,2 ..., n

For different interval m, adopt the coefficient of flow α of corresponding pressure differential deltap P in this interval _mWith inflatable coefficient ε _m

The present invention has following advantage:

1. because the present invention adopts the geometric progression discrete method that whole measurement flow range is carried out segmentation, so its ratio obtains minimum relative ratio when guaranteeing same segments.

2. because the present invention adopts the geometric progression discrete method that whole measurement flow range is carried out segmentation, so can also be measurement range degree and precision that the present invention has improved orifice flowmeter greatly spending on a large scale and during high-acruracy survey, reaching higher level.

Describe in detail below in conjunction with drawings and Examples:

Fig. 1-Fig. 6 is the flow curve block plan of known method;

Fig. 7 is the relative error curve comparison diagram of the present invention and known method.

The present invention adopts the geometric progression discrete method that whole measurement flow range is carried out segmentation, it divides paragraph according to a fixed proportion given in advance, it is the same promptly requiring relative scale, be as the criterion with equivalent error 0.65%, the relative error that is every place is a constant, could guarantee that its relative error of every is the same.

Concrete steps are:

A. be set in the segments n in the whole measurement flow range, n is the integer greater than 1, selects n=10 herein;

B. according to measuring flow range and segments n, determine common ratio q, corresponding n is 10 situation, common ratio q=1.29;

C. according to measuring flow range and common ratio q, determine the section point value of each segmentation on the fluid flow curve by the geometric progression relation, thereby flow curve is divided into 10 segmentations by geometric progression.

D. flow rate calculation is carried out in each interval on the fluid flow discharge curve.

Calculate and still adopt following traditional calculating formula (subscript m is represented interval numbering): $W_m=0.01252\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="C0013360500072.png"\; state="\{\{state\}\}">D</figure-callout>}}^2\&CenterDot;{\mathrm{\&alpha;}}_m\&CenterDot;{\mathrm{\&beta;}}^2\&CenterDot;{\mathrm{\&epsiv;}}_m\&CenterDot;\sqrt{\mathrm{\&gamma;}\&CenterDot;\mathrm{\&Delta;P}}$

For different interval m, adopt the coefficient of flow α of corresponding pressure differential deltap P in this interval _mWith inflatable coefficient ε _mSo each interval calculating formula that adopts is inequality.

The ratio q of tabulation comparative analysis the present invention and the U.S., Japanese three kinds of discrete methods below.

Can see when analyzing the ratio relation of different range degree, the method of average is pressed equipartition principle, the time can accomplish relation in beginning near 1, but at degree place on a large scale, then demonstrate the deficiency of its equal division methodology respectively, be followed successively by 3.33,4 (five equilibrium 10 segmentations of the U.S.) and 7.575,10 (four segmentations of Japan), can not well satisfy the constant principle of q value.And the present invention is divided into equally in the q of geometric progression value under 10 sections the situation, is respectively 1.29,1.35,1.40,1.446, and promptly to change be not very greatly to the ratio that changes relatively, but is well positioned to meet the constant requirement of q value.It with rangeability 1: 40 requirement, the ratio q of the U.S. is 4 when equalization method, Japan is 10, but be 1.446 in the method for geometric progression of the present invention, compare with the U.S. that to differ twice many, promptly under the prerequisite of same segments, the q value of geometric progression discrete method of the present invention obtains minimum relative ratio when guaranteeing same segments.Fig. 7 has shown that relative error of the present invention is minimum, and in whole measurement flow range, relative error equates everywhere.

The present invention has all reached state's levels such as U.S., day at rangeability 1: 13 and precision ± 1% o'clock, but exceeds a level than states such as U.S., days when spending on a large scale, so under equal accuracy, rangeability of the present invention has obtained expansion, or under same rangeability, precision of the present invention is improved.

Claims (2)

1. a method that improves orifice flowmeter measurement range and precision the steps include:

A. be set in the segments n in the whole measurement flow range, n is the integer greater than 1;

B. according to measuring flow range and segments n, determine common ratio q;

C. according to measuring flow range and common ratio q, determine the section point value of each segmentation on the fluid flow curve by the geometric progression relation;

D. flow rate calculation is carried out in each interval on the fluid flow discharge curve.

2. the method for raising orifice flowmeter measurement range degree as claimed in claim 1 and precision is characterized in that: the interval m of each on the fluid flow discharge curve, carry out following flow rate calculation: $W_m=0.01252\&CenterDot;D^2\&CenterDot;{\mathrm{\&alpha;}}_m\&CenterDot;{\mathrm{\&beta;}}^2\&CenterDot;{\mathrm{\&epsiv;}}_m\&CenterDot;\sqrt{\mathrm{\&gamma;}\&CenterDot;\mathrm{\&Delta;P}}$ In the formula: W _m: fluid flow (kg/h)

D: flowmeter internal diameter (mm)

α _m: coefficient of flow

β: the aperture is than (d/D), and d is the throttle orifice or the throat diameter of throttling element under the condition of work, and D is the flowmeter internal diameter

ε _m: inflatable coefficient

γ: specific gravity (kg/m ³)

Δ P: pressure reduction (Pa)

M: interval numbering is respectively and gets 1,2 ..., n

For different interval m, adopt the coefficient of flow α of corresponding pressure differential deltap P in this interval _mWith inflatable coefficient ε _m

Images