Dwyer UFC User Manual download pdf (Page 6)

1: General Description

Note: In addition to the 'A' and 'B' type sensors, type 'D' sensors (option) are available for use on pipes up to 197

inches (5000 mm). These sensors have a different mounting method. See Paragraph 1.3 for further details.

1.2 Principles of Operation

Figure 1.1 Operating modes

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 UFC 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,

Fluid flow

Separation

Distance

Separation

Distance

Separation

Distance

Separation

Distance

Reflex mode

Reflex mode (double bounce)

Reflex mode (triple bounce)

Diagonal 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 reflected

by the opposite pipe wall.

The separation distance is calculated by

the instrument in response to entered data

concerning the pipe and fluid characteristics.

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.

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.

This mode might be selected by the

instrument where relatively large pipes are

concerned. In this mode the transducers are

located on opposite sides of the pipe but the

separation distance is still critical in order

for the signals to be received correctly.

This mode can be used with the standard

‘A’ & ‘B’ transducer sets but for really large

pipe installations the optional transducer set ‘D’

might be recommended.

Upstream

transducer

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Dwyer UFC User Manual Page 6

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