ABSTRACT
Ultrasonic flowmeters are suitable for both liquids and gases, and are increasingly being used in custody transfer applications and is probably the only meter capable of being used on large diameter pipes (above 3 m bore) at a reasonable cost and performance.
The term ‘ultrasonic’ applies to frequencies from as low as 5 kHz through to 10 MHz or even higher – but is generally applied to frequencies above the normal hearing range of human beings (20 kHz).
This chapter looks initially at basic ultrasonic technology centred on transducers employing piezoelectric ceramic crystals that transmit and receive the acoustic signal. It then goes on to examine acoustic propagation and the differences between longitudinal and shear waves.
A brief look is then taken at the Doppler effect meter and its shortcomings and how these are overcome in the transit time meter. The limitations of using a single path beam are then discussed and how these problems are addressed through the use of multiple path systems.
The discussion then centres on how gas measurement poses some unique problems not found with liquids – essentially fouling and condensate.
The chapter closes with a discussion on the working principle shortcomings and benefits of clamp-on instruments.
