BS 7965:2009 pdf download

BS 7965:2009 pdf download.Guide to the selection,installation, operation and calibration of diagonal path transit time ultrasonic flowmeters for industrial gas applications.
USM manufacturers recognize the potential for operating problems, and most USMs have diagnostic capabilities that indicate whether acoustic noise impairs meter performance while operating. Strategies have also been devised by users and manufacturers to estimate and/or limit a USMs susceptibility to noise interference, such as:
• evaluation of USMs response to acoustic noise prior to station installation;
• enhanced signal processing to improve ultrasonic pulse recognition and detection;
• signal filtering to narrow the bandwidth surveyed for better/faster pulse recognition;
• installation of fittings, such as blind tees or filters, to isolate the noise source from the USM;
• development of specialized silencers that are installed in the piping between the USM and the noise source to isolate the meter from the noise.
In general, noise sources upstream of USMs have a more adverse impact on meter performance than those installed downstream, although downstream installation of pressure reduction or other noise generating equipment does not guarantee interference will not occur. Also, greater separation between a noise source and the USM and the consequent increased number of fittings, provides more attenuation than would be the case if the meter and source were installed in close proximity to each other.
When considering installation of a USM, particularly in the vicinity of pressure or flow regulation (the most common noise generators), the factors that should be taken into account during the USM station design phase are:
• the installed position of valves (as potential noise sources) relative to the meter (upstream, downstream, distance between meter and source, number and type of fittings between meter and source);
• the operating frequency of the meter and the range of frequencies generated by the noise source (noise reduction trim valves are of particular concern since the design generates noise exceeding audible frequencies which is often in the ultrasonic range);
• whether additional attenuation between noise source and USM is required, which could include blind tees or other fittings or acoustic filters (see 5.2.4);
• whether enhanced filtering of digital signal processing has to be applied and, if so, whether it slows signal processing time beyond acceptable limits (limits are given for a linear measuring device in API MPMS Chapter 21.1 [2]);
• the cost/benefit of pursuing one or more strategies to limit USM exposure to offending acoustic noise.
When installation of a USM near a potential noise source is anticipated, it is recommended that users contact manufacturers for recommendations specific to their products and the proposed installation prior to finalizing USM station design. Cooperation between specifiers/users and manufacturers during the design of the facilities can avoid the need for potentially expensive remedial actions at a completed meter installation.
5.2.5 Gas composition restrictions
The presence of certain gases might impact on the performance of a meter (for example, high levels of carbon dioxide and hydrogen in a gas mixture can influence and even inhibit the operation of a USM owing to thier acoustic absorption properties); meter manufacturers should be supplied with the expected constituents of the gases to be measured and the associated pressure and temperature range.
5.3 Installation conditions
5.3.1 Flow direction
Where the flow is in one direction only, the user should ensure this is clearly marked on the body of the meter. For bi-directional applications, both ends of the USM should be considered upstream and the markings attached to the meter spool clearly indicating the primary flow direction.
NOTE For example, plates may be affixed to the meter as a means of marking.
5.3.2 Upstream and downstream fittings
COMMENTARY ON 5.3.2
Various combinations of upstream fittings (valves, bends, expanders, tees, reducers, etc.) might produce velocity profile distortions and swirl at the inlet to the USM that could result in measurement errors. The magnitude of error is dependent on the type and severity of the flow distortion and the ability of the USM to compensate for this distortion. To a much lesser extent, downstream fittings could also affect the accuracy of the meter.