AFLOWT BUF, Руководство по эксплуатации

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1.4. Design and operation
1.4.1. Operation principle
1.4.1.1. The flow meter is designed on the base of a pulse-phase method of ul-
trasonic flow measurement. Its operation principle is based on
measuring the time difference between the time it takes for an
ultrasonic signal (USS) to travel through the liquid with the direction of
flow and against it.
Regarding the sounding principle, the flow meter utilizes the meth-
od of one-time simultaneous sounding. Flow meters of this type have
two simultaneously operating signal paths. Each signal path is formed
by a transmitting/receiving path of the flow meter consisting of electron-
ic circuitry [Secondary Converter (CS) and communications cables with
Electroacoustic Converters (PEAs)] and an acoustic path (PEA
– fluid –
PEA).
1.4.1.2. PEAs are diametrically (see Fig.2) installed into the measuring section
(Pipeline Section, PS) making up together the Primary Converter (CP).
Fig.2. Diagram showing Pipeline Section (PS) with PEAs installed
1.4.1.3. The CS generates electric sounding pulses which simultaneously come
to PEA1 and PEA2.
USS generated by one PEA is projected through the liquid flowing
in the pipe and is received by the other PEA. Because of liquid flow, a
sound wave is shifted, which in turn leads to the difference in upstream
and downstream times of USS travel: it takes less time for an ultrasonic
signal to travel in the flow direction (from PEA1 to PEA2) than that in
the opposite direction (from PEA2 to PEA1). The difference in upstream
and downstream time of USS travel through an acoustic path
dT is
proportional to flow velocity of fluid v and, correspondingly, to volumetric
flow rate
Q .