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Title: Proving Liquid Ultrasonic Flow Meters For Custody Transfer Measurement
Author: Raymond Kalivoda
Source: 2007 South East Asia Flow Measurement Conference
Year Published: 2007
Abstract: Liquid Ultrasonic Flow Meters (LUFMs) continue to gain popularity in petroleum measurement with the promise of high accuracy and low maintenance. These are favorable features, but because of the high volume and value of petroleum products buyers and sellers must have a high level of confidence in the measurement. This assurance in Custody Transfer measurement is gained by adherence to the standards, procedures and methods that define the measurement process. There are two fundamental ways that petroleum products are measured - statically or dynamically. The measured volume determined by either method must be validated at operating conditions and traced to a fundamental standard. In a static system the product is transferred to a tank or similar container. After the transaction is completed the volume can be measured and validated by a suitable method. In a dynamic system PD, turbine or ultrasonic meters provide instantaneous information on the rate and volume of the transfer. As with static methods the measurement results must be validated by a suitable method. A key difference between a static and dynamic measurement is time. A static measurement is similar to a bank transaction, where the cash draw can be pulled and verified at any time. When a static transaction is complete there is time to review the measured volume, and if an error is suspected the volume can be re-measured. With a dynamic system the measurement must be right the first time there is no means to re-measure the volume. The proving system and process are essential in either static or dynamic measurement systems to validate the accuracy of volume measured. There are various worldwide standards and regulations that define the measurement system requirements, but they are fundamentally the same. Each is traceable to a national standard which in turn is traceable to the international standard. In dynamic measurement systems this link is the prover volume. There are gravimetric and volumetric methods where the prover volume is traceable the International Bureau of Legal Metrology (BIML). The technical arm of the bureau is OIML (International Organization for Legal Metrology). This is an intergovernmental organization that deals with all aspects of legal metrology. It has 59 Member States and 50 Corresponding Members. In this way all the countries are tied to the same weights and measurement standards, which facilitates world trade. The various measurement standards either directly or indirectly define the accuracy requirements over a range of operating conditions which include: flow rate, viscosity, temperature, pressure, piping configurations, etc. It is therefore important in the proving process to define both the operating conditions and the accuracy requirements because they are interdependent. A change in operating conditions can affect the meters accuracy. As a general rule the meter must be proven at operating conditions to validate its accuracy with the highest degree of confidence. The greater the change in operating conditions, the more uncertainty is introduced into the measurement. The object of all Custody Transfer meters is the same, highly accurate measurement, but the procedures to achieve the results may vary with the different meter technologies. This paper will focus on the standards, procedures and methods used to prove ultrasonic meters.

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