Patent ID: 12188807

ELEMENTS AND NUMBERING USED IN THE DRAWINGS

10Flow meter system having two or more dissimilar chordal integration methods20Signal processing means (computational electronics)21Acoustic processing unit (“APU”)25Central processing control and display unit27Microprocessor29Input/output with software (non-transitory computer readable medium)30Chordal path40Flow meter body

DETAILED DESCRIPTION

A system and method for detecting and estimating integration error associated with the use of an ultrasonic flowrate meter includes two or more dissimilar chordal multipath integration methods employed in a single meter body. The system differs from prior art systems and methods in that it compares two or more sets of overlapping chordal input data to detect and quantify the error. Because dissimilar integration methods are used, the comparison is less prone to production of false alarms. Additionally, the system does not require that the total number of chordal measurement planes be equal to the sum of the number of chordal planes used in each integration. Because the total number of planes can be less than the total number of chordal velocity inputs to the plurality of integration schemes, overall hardware requirements are reduced.

One example of how this is accomplished is to employ one even-numbered and one odd-numbered integration method or scheme of different type where at least one chordal path (and therefore at least one chordal plane) is shared between the two integration schemes. This method reduces the likelihood of a false alarm and reduces hardware requirements by constructing and operating the meter in such a way that two separate integrations are performed using overlapping subsets of chordal measurement data. For example, where a conventional approach would require seven chordal measurement planes in total to compare 3- and 4-chord integration schemes, only five chordal measurement planes in total are required here, with three of five chords being used for a first integration routine and four of five chords being used for a second integration routine. In a similar way, a combination of a 4-chord integration scheme with a 5-chord integration scheme can be achieved using only five chords when all chords are used in the 5-chord scheme and all but one in a dissimilar 4-chord scheme.

Referring toFIG.2, the system10can be used as part of the signal processing means20of an ultrasonic flow meter having two or more chordal measurement planes30within the meter body40. This type of meter typically includes transducers arranged upstream and downstream of one another in pitch-and-catch relationship to send acoustic energy along an acoustic path through the fluid flowing in a conduit (see e.g.FIGS.3and4). The signal processing means20determines the transit times for upstream and downstream signal transmission and uses those measured upstream and downstream transit times in combination with other inputs to calculate the velocity in each measurement plane and to infer the flow rate of the fluid.

The signal processing means or computational electronics20includes a transmitter or acoustic processing unit (“APU”)21and a central processing, control and display unit25(seeFIG.2). Commonly, the flow meter could have the electronics mounted directly to the meter body, and the functions of the APU21and central processing, control and display unit25could be separate or combined. The APU21controls the transmission and reception of the ultrasonic signals to and from the transducers. The central processing, control and display unit25, which includes a microprocessor27and I/O with software29(and memory), typically employs Gaussian integration schemes to process the transit time measurements along the various chordal paths30from the APU21and calculate flow rate. The central processing, control and display unit25can also function as the user interface.

Note there can be two sets of computational electronics attached to the transducers with one or more of the paths and the transducers shared between these electronics with one performing the first integration scheme and another performing the second integration scheme. In this embodiment, communication is required between the two sets of computational electronics so that each set does not use the same transducers at the same time.

A non-limiting example of this type of meter is a CALDON™ ultrasonic flow meter (s). The CALDON™ meter uses a compact transmitter enclosure that can be integrally mounted to the meter body or remote pipe mounted (seeFIG.10). Within the meter body are multiple pairs of fully integrated piezoelectric ultrasonic transducers forming acoustic measurement paths in multiple chordal planes. These paths typically cross the flow stream at an angle of between 45 and 65 degrees so that there is a difference in the transit time of the ultrasonic signals, depending on whether the sound pulse is traveling with or against the direction of flow. The difference in transit times is measured along each path. The meter's electronics infer velocity on each chord and perform an integration of axial velocity to compute an output of volumetric flow rate. In one preferred design, paths are arranged in crossed pairs in each chordal measurement plane. This arrangement of acoustic paths make the axial velocity calculation substantially immune to the effects of non-axial flow and eliminates the need for an upstream flow conditioner. By eliminating the interfering effect of non-axial flow the crossed-pair design enables the integration method to function properly and reducing the requirement for long upstream lengths of straight pipe.

Referring now toFIG.5, integration of the Reichardt profile by well-known methods shows that a 3-chord Anti-Gauss-Jacobian (“Anti-Gauss”) integration gives a comparable linearity to that of a 4-chord Jacobian integration. This result shows that the 3-chord Anti-Gauss integration is useful for accurate flow rate measurements. Additionally, the outer chords of the 3-chord Anti-Gauss integration are positioned at almost the same location as the outer chords of a 4-chord Gauss-Legendre integration (seeFIG.6).

Because of this, an arrangement of five chordal measurement planes in total can be used to closely approximate mathematically prescribed integration schemes for both 3- and 4-chord integrations. For example, the 3-chord Anti-Gauss and the 4-chord Legendre can both be realized by adding a single diametric chordal measurement plane to the 4-chord Legendre arrangement.

In this case the chord locations normalized to the pipe diameter for the 4-chord Legendre scheme are −0.861136, −0.339981, 0.339981 and 0.861136. For the 3-chord Anti-Gauss scheme the chord locations are −0.866025, 0 and 0.866025. The five-chord scheme can therefore be realized by placing the two outermost chords at between −0.861136 and −0.866025 and between +0.861136 and +0.866025, e.g. −0.863581 and +0.863581. The corresponding weighting factors for the velocities measured on each plane would then be applied as given in Table 1 below.

TABLE 1Weighting Factors.Integration method 1Integration method 2weighting factorsweighting factorsChordChord(three chord(four chordnumberlocationintegration)integration)1−0.8635810.1666670.1125802−0.3399810.390438300.66666740.3399810.39043850.8635810.1666670.112580

FIG.7provides an example of how this system can be implemented on the software of the central processing, control and display unit and used as part of the signal processing means of an ultrasonic flow meter. For the two distorted flow profiles shown, the 4-chord integration error (y-axis) is plotted versus the difference between the 3- and 4-chord integrations for various orientations of the profile with rotation of the flow profile in 5 degree steps from 0 to 180 degrees. The integration error in the 4-chord integration is approximately equal to ⅕th of the difference between the 3- and 4-chord integrations, thus allowing the detection and estimation of the integration error as a function of the difference between calculated flowrates.

FIG.8shows a similar plot comparing a single diameter path against the 4-chord configuration for the same two distorted profiles ofFIG.7. There is a much poorer correlation between the difference value and the integration error in the 4-path meter. Therefore, the approach illustrated byFIG.7using the three- and four-chord schemes is more effective at detecting and quantifying integration errors than is the approach using a 4-chord and single-path scheme as illustrated byFIG.8. The example above uses locations for the chordal planes and weighing factors that correspond with the abscissa and weights of an appropriate integration rule. Any two of a variety of integration methods may be used for the first and second integration methods. Gauss-Legendre and Gauss-Jacobi are two well-known integration rules, the Anti-Gauss-Jacobi rule is a less well-known rule. Other integration schemes may be used, such as the Optimal Weighted Integration for Circular Sections (“OWICS”) scheme optimized especially for flow measurement purposes.

As an alternative to these rules that have pre-defined abscissa, similar methodologies can be applied where the chord locations (of at least one of the two alternative subsets) are selected arbitrarily or based on other considerations and then the weighing factors are calculated accordingly. In one such possible scheme, four chordal locations could be selected according to the rules of a first integration method with an even number of abscissas, and a fifth chordal plane could be added in the central diametric plane. For the first integration the standard 4-chord weighting factors would be applied and the diametric chord would be ignored, and for the second integration a new set of non-zero weighting factors would be applied to all five chordal velocity inputs.

A preferred embodiment of a method of detecting integration errors—the method being performed by a non-transitory computer readable medium with computer instructions stored thereon executed by a processor—includes the step of: executing a first chordal integration scheme and a second different chordal integration scheme, the chordal integration schemes sharing at least one chordal path in a discrete chordal measurement plane across a conduit section of the meter body. The total number of chordal paths (and planes) is less than a sum of the chordal paths (and planes) used in the first and second different chordal integration schemes. Path locations and weighting factors of one of the first and second different chordal integration schemes can correspond with an abscissa and weights of a numerical integration scheme with pre-determined abscissae. Alternatively, path locations can be selected independent of an abscissa and weights of a numerical integration scheme with pre-determined abscissae, with appropriate weighting factors being calculated for those paths.

One of the chordal integration schemes can be implemented in the form

v¯a=∑i=1Nwa,i⁢v⁡(ha,i)Qa=v¯a⁢A=A⁢∑i=1Nwa,i⁢v⁡(ha,i)
with the other chordal integration schemes implemented in the form

v¯b=∑j=1Mwb,j⁢v⁡(hb,j)Qb=v¯b⁢A=A⁢∑j=1Mwb,j⁢v⁡(hb,j)
wherein the total number of chordal measurement planes P is less than the sum of N plus M such that at least one of the chordal measurement planes at location ha,iis the same as one of the chordal measurement planes at locations hbj.

The preferred embodiments described here are for illustrative purposes. The scope of the invention is defined by the following claims and includes the full range of equivalents to the elements recited.