This British Standard provides guidance on the selection, installation, operation and calibration of diagonal path transit time gas ultrasonic flowmeters (USMs) for industrial gas applications
It is applicable only to those devices in which the entire gas stream flows through the body of the USM and the transducers are in contact with the fluid (wetted or invasive type). This includes both full-bore and insertion type meters employing direct or reflective paths. It is also applicable to "dirty gases" i.e. where the gas is contaminated with solids and/or liquids in small quantities.
It is not applicable to clamp-on/externally mounted meters.
NOTE As an aid to selection, this standard incorporates an uncertainty classification for USMs. This takes into account the components of uncertainty relating to the meter plus those additional uncertainties associated with installation and operation effects. There are four classifications offered. These range from high accuracy "fiscal" applications (class 1) to general-purpose process flow indication and control applications (class 4).