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APPLICATION & PERFORMANCE
WARNING - Users should or note that:
a) The PORTAFLOW is not certified for use in Hazardous areas.
b) The local site safety regulations must be complied with.
c) Work is carried out in accordance with The Health & Safety at Work Act 1974.
The operational temperature of the fluid to be measured is -20°C to +125°C
The velocity of the liquid marginally accelerates the speed at which the ultrasound is
transmitted from transducer ‘A’ to ‘B’. However, when the direction of the transmission is
reversed, i.e. from transducer ‘B’ to ‘A’, a deceleration will occur because the sound is being
transmitted against the liquid flow. Therefore the difference in time taken over the same
distance is directly proportional to the flow velocity - see fig. 4.
Fig. 4
As it is not possible to determine from the outside what flow conditions prevail inside the pipe,
it must be assumed that the liquid is flowing uniformly in either a turbulent or laminar flow
condition, and that the flow velocity profile is also uniform for 360 degrees around the pipe
axis. Distortion of the flow velocity profile caused by bends, tees or any other type of
obstruction may create measurement errors.
LIQUID CONDITIONS
Transit time ultrasonic meters perform best on liquids that are totally free from entrained air
and solids. With sufficient air in the system, the ultrasound beam can be attenuated totally
and therefore prevent the instrument from working. Often it is impossible to tell whether there
is air in the system or not.
If a flow signal cannot be obtained, a simple test to determine whether the flow is aerated
involves cutting off the flow for a period of 10-15 minutes.
During this time, the air bubbles will rise to the top of the pipe and the flow signal should
return.
When the flow signal has returned, “switch on” the flow and if entrained air is still present then
signal loss
PORTAFLOW 204 Plus! OPERATING RANGE
A B
FLOW
Pipe NB
mm
100
75
50
25
13
0
0.07 0.10 0.13 0.22 0.29 0.32 0.42 5.9 8.2 11 14.76 23.94
0.02 0.03 0.04 0.07 0.09 0.10 0.13 1.8 2.5 4.5 7.3
.40
3.5
12