Upstream Transit
Time Measurement Cycles
An electrical excitation causes the downstream
transducer to emit a wave of ultrasound. From
these signals, the flowmeter derives an accurate
measure of the "transit time" it took
for the wave of ultrasound to travel from one
transducer to the other.
Downstream Transit Time Measurement Cycles
The same transmit-receive sequence of the upstream
cycle is repeated, but with the transmitting
and receiving functions of the transducers reversed
so that the liquid flow under study is bisected
by an ultrasonic wave in the downstream direction.
Again, the flowmeter derives and records from
this transmit-receive sequence an accurate measure
of transit time.
Just as the speed of a plane is affected by
headwinds and tailwinds, the transit time of
ultrasound passing through a conduit is affected
by the motion of liquid flowing through that
conduit. During the upstream cycle, the sound
wave travels against flow and total transit
time is increased by a flow-dependent amount.
During the downstream cycle, the sound wave
travels with flow and total transit time is
decreased by the same flow-dependent amount.
The EESIFLO EASZ 10FP flowmeter subtracts the
downstream transit time from the upstream transit
times utilizing shear wave ultrasonic signals.
This difference of integrated transit times
is a measure of volume flow.
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