Multipath ultrasonic flowmeters, by virtue of measuring more than one sound wave path through
the fluid, also have the ability to detect irregular flow profiles. Each sonic path between sensor pairs
in a transit-time ultrasonic flowmeter, called a chord, measures flow velocity. The velocities reported
for each chord may be compared to the flowmeter’s calculated average flow velocity, and expressed
as velocity ratios. A particular chord measuring a velocity greater than the flowmeter’s average will
report a velocity ratio greater than one (> 1), whereas a chord measuring a velocity less than the
meter’s average will report a velocity ratio less than one (< 1). In the Daniel four-chord ultrasonic
flowmeter, two chords (B and C) measure velocity near the center of the pipe while the others (A
and D) measure velocity closer to the pipe walls. In normal operation, the center chord velocity