GF PORTAFLOW 330, Инструкция по эксплуатации

Страница: 13 / 56

Design and function Instruction manual
12
5.4 Principles of Operation
When ultrasound is transmitted through a liquid the speed at which the sound travels through
the liquid is accelerated slightly if it is transmitted in the same direction as the liquid flow and
decelerated slightly if transmitted against it. The difference in time taken by the sound to
travel the same distance but in opposite directions is therefore directly proportional to the
flow velocity of the liquid.
The Portaflow 330 system employs two ultrasonic transducers attached to the pipe carrying
the liquid and compares the time taken to transmit an ultrasound signal in each direction. If
the sound characteristics of the fluid are known, the Portaflow microprocessor can use the
results of the transit time calculations to compute the fluid flow velocity. Once the flow
velocity is known the volumetric flow can be easily calculated for a given pipe diameter.
The Portaflow system can be set up to operate in one of four modes determined mainly by the
pipe diameter and the type of transducer set in use. The diagram below illustrates the
importance of applying the correct separation distance between the transducers to obtain the
strongest signal.
Reflex mode
This is the mode most commonly used. The two
transducers (U & D) are attached to the pipe in
line with each other and the signals passing
between them are eflected by the opposite pipe
wall.
The separation distance is calculated by the
instrument in response to entered data
concerning the pipe and fluid characteristics.
Reflex mode (double bounce)
In this mode the separation distance is
calculated to give a double bounce. This is
most likely to occur if the pipe diameter is so
small that the calculated reflex mode
separation distance would be impractical for
the transducers in use.
Reflex mode (triple bounce)
This illustration goes one step further to show
a triple bounce situation. This would normally
apply when working with very small pipes
relative to the transducer range in use.