This paper has the dual intention of providing a brief historical insight into ultrasonic gas flow measurement as well as to give an understanding of the technology used therein. In addition, it also attempts to render some practical guidelines that would be of assistance to prospective users who are faced with applications of flow metering in dry and wet gas, either in a new line or an existing one, but who have a little or no prior knowledge of such instruments. One of the most challenging problems for designers of ultrasonic meters has been to overcome the ultrasonic noise problems in applications where the meters come to be located in the vicinity of large noise sources such as control valves, regulators and flow conditioners. While adoption of proper installation procedures have helped, many solutions have undesirable trade-offs. Mechanical silencing devices are effective noise suppressors but are expensive, bulky and heavy. Signal averaging techniques (stacking) may help in certain situations but are limited by instabilities in the flow and the associated delays inherent to the process itself. Instromet has developed a signal processing technique using a frequency domain algorithm combined with a broadband ultrasonic transducer to detect ultrasonic signals in environments previously too hostile. This technique, called Coded Multiple Burst (CMB), has an inherent advantage that meter update times do not increase; in fact using the Series-IV Electronics platform, the system operates with the highest burst rate available on the market today. This paper will present the results from real-world field installations comparing the above stated new technique in contrast to traditional techniques. In addition, the paper will also examine the design criteria that would lend support to the ability of ultrasonic meters to operate accurately in a noisy environment. The paper also addresses three other key areas of concern that have been expressed by operators over the years in connection with ultrasonic gas flow meters. These concerns are the practical aspects of flow meter installation, calibration and validation methodology and maintenance requirements. The paper attempts to raise the awareness and confidence levels of potential users of ultrasonic flow meters.
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