ANSI AWWA C750-19 pdf download.Transit-Time Flowmeters in Full Closed Conduits
4.3.1 Measurement section. The measurement section shall either be a part of the user’s process piping or be a part of the flowmeter provided by the transit-time flowmeter manufacturer.
4.3.2 Transducers. Transducers shall either be factory-mounted on a measurement section or they shall be field-mounted. Field-mounting shall be by (1) clamping to the outside surface of the measurement section, (2) threading through a tap installed on the measurement section, or (3) mechanically fixing or bonding to the interior surface of a large-diameter measurement section. Transducers may be wetted or nonwetted. Wetted transducers are in direct contact with the liquid and inject ultrasonic pulses directly into the flowstream. The nonwetted transducers are separated from the flowstream by the wall of the measurement section or by a shield (Figure 2).
4.3.3 Electronic component. The electronic component of the transit-time flowmeter commonly includes a microprocessor that operates the transducers, makes the measurements, processes the measured data, and displays or records the results in engineering units specified by the purchaser.
Transit-time flowmeters may be single-path or multipath, arranged in either direct or reflective mode. In a direct mode, the transducers are installed on the opposite sides of the pipe. In a reflective mode, the acoustic energy is reflected off the inside of the pipe wall to another transducer. Single-path flowmeters have a pair of transducers in the measurement section, and multipath flowmeters have a pair of transducers for each path in the measurement section (Figure 3). Single- path flowmeters make a single-line velocity measurement that uses a meter factor determined by calibration or by prediction of the low velocity profile. Multipath flowmeters place several paths across the measurement section, thus measuring the velocity profile across the entire conduit cross section. Each of these path arrangements is used in a particular flow condition. Single-path meters shall be used in applications where flow conditions are conducive to a relatively uniform velocity across the measurement section. Multipath flowmeters shall be used in applications subject to nonuniform velocity, such as disturbed flow conditions or instances where a very high accuracy level is required.ANSI AWWA C750-19 pdf download.