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Stephan Rudbäck
THE MATEMATICA APPROACH

This manual will show how to measure flow in tubes with throat devices. The environment can be everything from industrial plants to laboratories.
The performance of the flow measurement can be as good as 0.7 % uncertainty of actual flow from 10 to 100% flow if
- Design
- Manufacturing
- Installation in tube
- Instrumentation
- Calculation of the flow
is done according to the Matematica approach.
The Matematica approach gives You full control over every parameter that have an impact on Your flow measurement. Over 20 parameters, like physical properties of the fluid, pipe roughness, installation in tube, differential pressure transmitter performance has to be under Your control, or the flow measurement will malfunction. It cannot perform better then the weakest part.
The Matematica approach is described here , step by step, and every step is calculated and described by the computer software Processline from Matematica. The calculations are based on scientific documentation, like the standard ISO 5167-1 from 1991, amendment 1 from 1998 and german VDI/VDE journals 2040 and 2041, it means very good credibility.
The flow must be a one phase flow, it means the fluid can be a gas (-mixture) or a liquid (-mixture), but not a gas-liquid mixture. I will also show how to improve old installations of throat-devices. This is done by identification and reduction of the biggest error-sources and, if needed, improvement of the square root flow calculation by a new algorithm called the Matematica algorithm. This algorithm is a correction of the square root function, and can reduce the flow-calculation error for gases from sometimes 10% to 0%. This algorithm can be keyed into any modern computer as a function-block.

G. E. Mattingly
TWENTY -FIVE YEARS OF FLOW LAB COMPARISONS USING TANDEMS METER TRANSFER STANDARDS: LESSONS LEARNED AND LESSONS NOT LEARNED

At the first FLOMEKO in 1978, in Groningen, the Netherlands, the author with his NBS co-authors and his UK counterparts presented results from the first known international flow standards comparison using a tandem flow meter transfer standard. This comparison included a testing procedure designed to produce two, statistically independent flow meter calibration results that are “typical” of the lab’s normal calibration capability. As such, these results comply with the requirements for the Youden graphical analysis of variance to make conclusions regarding the comparability of the flow standards in the participating labs conducting these tests.
National flow lab metrologists in these years compared their standards on ad-hoc bases to assess values of different techniques a nd to evaluate improvements to existing methods. Results were generally kept among participants. In the ensuing 25 years, flow lab comparison testing techniques have evolved, appropriately in some sectors with significant lessons learned, but in other sectors, there are still lessons to be learned.
Through these years, local, national commerce and trade was satisfactorily conducted when the pertinent measurements -vendors specs and buyers requirements- were validated and made credible through some sort of traceability to the domestic National Metrology Institute (NMI). More recently, local, national commerce and trade have expanded to global and international and satisfactory exchanges now need measurement acceptability across national boundaries. To achieve this, the International Committee on Weights and Measures (CIPM) has, in 1999, signed into existence a Mutual Recognition Arrangement (MRA), see www.bipm.org . The central objective of this MRA is to eliminate measurement based barriers to international trade. To do this, Key Comparison (KC) tests are being planned to quantify how the flow standards in the NMIs are equivalent to each other. This equivalence is intended to be the key link enabling industries to trade satisfactorily across national borders. Where this equivalence clearly (i.e., with small uncertainties) quantifies respective NMI-to-NMI differences, vendor specs and buyer requirements will be clearly understood and useful for international commerce. Where this equivalence is quantified with unfortunately excessive uncertainty levels, trading industries in respective countries will have to suffer through such limitations. Therefore, the KCs designed to quantify NMI equivalencies will need to have highest reasonable levels of metrological quality and therefore they will need to use all of the lessons learned in the past 25 years of conducting flow lab comparisons.
This paper will describe the evolution of flow lab testing over the years since FLOMEKO 1978. Hopefully, over the next 25 years and more, satisfactory flow comparisons are done among the world’s NMIs and so that the results enable efficient, effective, and satisfactory international commerce and trade in fluid quantity and flow measurement products.

Wojciech Studzinski
PERFORMANCE OF ORIFICE METERS IN INSTALLATIONS WITH HEADERS

Headers commonly used in multirun meter stations can generate a variety of flow profile distortions influencing the measurement error of orifice meters. The experiments conducted at the low pressure air test facility at NOVA Research & Technology Centre covered a range of header configurations used in various meter station designs. The upstream piping configuration included a straight inflow pipe, a single elbow and two elbows in perpendicular planes in two orientations. It was found that some changes in flow configuration through the header and meter runs, as well as modifications to the geometrical dimensions of the header, can result in significant flow measurement errors up to 4.3%. There are some header configurations which provide error free operation of orifice meters. The finding validates concerns that the header effect depends on a particular geometry being used and is difficult for an up front assessment at the design stage.

Xue Chunling, Lv Deyue, Sun Yanzuo
CORRECTION FOR K FACTOR OF GAS TURBINE FLOW METER

According to the International Standard ISO 9951 all gas turbine flow meters should have a maximum permissible relative error of ± 1% over the higher flow range (from 0.2 Qmax to Qmax), in the lower flow range (Qmin to 0.2 Qmin) the maximum permissible relative error is ± 2%. Usually the linearity of k factors, in percent, is used to express the basic relative error of a gas turbine meter. That means in the higher flow range the gas turbine meters shall have maximum permissible linearity of ± 1%, and in the lower flow range the gas turbine meters shall have maximum permissible linearity of ± 2%. The method commonly used to determine the mean k factor, K0, is: At first, the values of K<sub>max and K<sub>min are found out in the higher flow range, and then the mean K factor, K0, is calculated. Finally, the maximum deviation of K factors from K0 in the higher and lower flow ranges are evaluated to make an error judgment. In some cases this method might introduce a bias error into the K0, because the shapes of K factor signature curves ( the different modes of K factors distribution in different flow range) were not considered. Therefore, it is necessary to make different corrections for K0 in different cases. Our approaches are as follows: When K<sub>min appears in the lower flow range and the K<sub>max appears in the higher flow range, K0 = (A K<sub>max + K<sub>min) / 2, here A = 1.0099; When the K max appears in the lower flow range and the K<sub>min appears in the higher flow range, K0 = (B K<sub>max + K<sub>min) / 2, here B = 0.9902; When both the K<sub>max and the K<sub>min appear simultaneously in the same lower or higher flow range, K0 =(C K<sub>max + K<sub>min) / 2, here C = 1.0. During the individual calibration of each turbine meter this method has shown clear positive effects. While consideration was given to meter’s performance in the higher flow range, the performance of turbine meter in the lower flow range has been improved, therefore, more gas turbine meters are ensured to be up to standard. Based on the European Standard PrEN12261:1998 Turbine Gas Meter, the WME (Weighted Mean Errors) were calculated. The WME show that this is an easy method to obtain the proper value of mean K factor for gas turbine meter.

Tom Kuperij
WIB - WORKING-PARTY ON INSTRUMENT BEHAVIOUR

In 1962, five leading Dutch process industries (BPM now Shell, Algemene Kunstzijde Unie now AKZO, DSM, Hoogovens now Corus and Unilever) got together to explore combining tests and sharing the results on process instrumentation. Companies were at the time carrying out these activities individually at very high costs. The five concluded that sharing instrument evaluation reports, even with direct competitors, would be to the benefit of all.
A follow-up meeting held on the 16th December 1963 resulted in the formation of a co -operation panel under the Dutch name "Werkgroup voor Instrument Beoordeling", shortened to WIB. An independent laboratory, the Institute for Applied Physical Research -TNO, was approached and asked to carry out testing on behalf of WIB. TNO was also made responsible for the administration of the association, supervised by a Board of WIB members.
WIB activities attracted high interest from companies abroad wanting to join and a few years later the official language became English. WIB was translated into "Working-party on Instrument Behaviour". It was officially registered as a non- profit association in 1968.

Koen H. Commissaris, Geeuwke de Boer
REALISATION OF COMPACT METERING RUNS WITH ULTRASONIC GAS FLOW METERS AND REDUCING MEASUREMENT UNCERTAINTY

This paper presents the results of the application of an ultrasonic gas flow meter in combination with a flow conditioner. This development aims at both reducing measurement uncertainty and the possibility of realising compact (short) metering runs, requiring less investment in piping and installation while maintaining good accuracy.
For this purpose a package of a four-path ultrasonic gas flow meter with inlet pipe section and a modified Spearman (NEL) design flow conditioner placed at 3D upstream of the meter was found to be a good combination for reducing variability in the flow profile. This set-up was extensively tested at the Ruhrgas test facility in Lintorf.
The test results demonstrate that combining an ultrasonic gas flow meter with a flow conditioner improves measurement uncertainty (due to installation e ffects) and reduces the required straight inlet of the ultrasonic meter by 50%, offering the potential of a compact installation.

J. T. M. Bergervoet
SPIN-OFFS FROM THE DEVELOPMENT OF ROTARY GAS METERS

The basic principle of a rotary gas meter consists of two rotors in the form of a figure -8 that rotate inside each other with the precision of a gear wheel. The outer edges of these rotors turn in a very close fitting measurement chamber. The outer edges of the turning rotors transfer fixed quantities of gas from the inlet to the outlet like small buckets. Because the radii of the sealed streams in the middle between the two rotors always vary there is a discontinuous volume of gas passing per angle revolution of the rotors. The shape of variation is near a sinus and the frequency is four times the frequency of the rotor revolution and the amplitude is near 12% of the average flow. These variations give an irregular rotating of the rotor at low flows and pressure and flow pulsation’s at higher flows. These pulsation’s can lead to resonance’s in the installation where they are mounted in. This can give sound problems and mis-indication of the rotary gas meter itself or to other devices in the installation.
The by Instromet developed DUO rotary principle (Dutch patent number 1004751) has two pair of rotors which are synchronized in such a way that both sine waves of the transferred volumes per angular movement are in opposite phases to each other. This results in only a small variation with double frequency. To develop a rotary meter with a large measure range it is nece ssary to keep all leak gaps along the rotors as small as possible. The combination of DUO Principle and narrow leak gaps has demonstrated that this type of meter is suitable as high-grade reference meter. This type of meter shows a flat calibration curve o ver a large measuring range. It has a high-grade reproduction and a small pressure dependency over a large pressure range.
With rotary meters of the DUO principle as reference meters, Instromet has developed a series of low-pressure test benches (ITF) measure range 0.5 to 10000 m³/h at a very compact construction. For a measure range up to 1000 m³/h only two rotary meters are being used as a reference. For a measure range up to 4000 m³/h more rotary meters are being used parallel as a reference. Above 4000 m³/h also a large turbinemeter will be used as a reference. The total uncertainty in the determination of the measurement error of the meter under test is strongly dependent of the chosen trace to the primary standards. A total uncertainty less than 0.23 % is possible. For small flows, the extent of the enclosed volumes and temperature and pressure stability in the test room also determines highly the final total uncertainty.
For high pressure test facilities the “Instromet Rotary Piston Prover” IRPP is developed. The heart of the meter is a cartridge, type DUO rotor meter provided with extra narrowed leak gaps. The cartridge is placed into a cage, which is span with a flexible rubber sleeve. The measurement module, cage and sleeve on itself are put as a assembled unit into a pressure body designed for a design pressure of 100 bar. This assembled unit can be seen as the “real meter”. Now it’s easy and inexpensive to transport the “real meter” without its pressure body, for calibration at specialised high pressure laboratories that may be located far away.
These IRPP’s are already in use by the NMi in their new re-calibration system of high pressure test facilities “Trasys” and as a sleeping standard in facility of Trans Canada Calibration in Winnipeg, Canada.

John D. Wright
WHAT IS THE “BEST” TRANSFER STANDARD FOR GAS FLOW?

National metrology institutes around the world have embarked on an effort to compare their primary gas flow standards under the supervision of the Comité International des Poids et Mesures and its Working Group on Fluid Flow. As the pilot laboratory for the key comparison of low-pressure gas flows below 1500 L/min (CCM.FF-K6), NIST is designing the transfer standard package with the assistance and advice of the other participants.
A number of topics are studied as part of the transfer standard design process. An analysis of the flow ranges and types of primary standards used by the possible key comparison participants based on their Calibration and Measurement Capabilities is given. The goals of the key comparison and the desirable characteristics of the transfer standard are considered in a general way. Next, a survey of the gas flow comparison literature suggests that laminar flow elements a nd critical flow venturis are the most practical candidates as transfer standards. These two flowmeter types are compared analytically and experimentally regarding their sensitivity to the external influences of temperature and gas composition. Finally, the calibration stability for these two flowmeter types is considered.

Volker Hans, Christian Filips
IMPROVING VORTEX FLOW METERING USING ULTRASOUND

Commercial vortex flowmeters use the well-known effect of Karman vortex street. The frequency of vortices generated in the wake of a bluff body is proportional to the average flow velocity. Usually it is detected by pressure sensors which are not very sensitive. Therefore bluff bodies of big sizes are required. An alternative method to detect the vortices in the streaming fluid is to use a high sensitive ultrasonic wave which is complex modulated. The demodulation can be executed by digital signal processing. Small sizes of bluff bodies can be realized. The bluff body size and the carrier frequency must be harmonized.

Johan Bats
THE APPLICATION OF MEMS TECHNOLOGY TO ON-LINE ANALYZERS FOR NATURAL GAS

Process Gas Chromatographs have been in use in the natural gas industry since the early eighties. The core analytical elements are commonly manufactured with conventional fine-mechanical tools. Recently MEMS technology has opened the doors to a new level of performance for on-line natural gas analysis.

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