TECHNICAL DESCRIPTION
MULTICAL
®
41
5512-313 GB/01.2010/Rev. C1
25
8.4
Signal path
8.5
Flow limits
In the meter’s working area from min. cut-off till far above Q4, there is a linear connection between the water
volume flowing through and the water flow measured.
In practice the highest possible water flow through the meter will be limited by the pressure of the installation or
by cavitation that has arisen as a consequence of a too low back pressure.
If the flow is lower than min. cut off or negative, MULTICAL
®
41 will not measure any flow.
The upper flow limit Q4 is according to OIML R 49 the highest flow, at which the flow sensor must operate for
short periods of time without exceeding the max. permissible error limit. During this period MULTICAL
®
41
has no
functional limitations when the meter operates over Q4. However, please note that high flow velocities >Q4 may
cause cavitation, especially at low static pressures.
8.6
Guidelines for dimensioning the MULTICAL
®
41
In connection with installations it is practical to work with pressures larger than the pressures state below:
Nominal flow Q3
Min. operating
pressure
[
bar
]
Max. flow Q4
[
m
3
/h
]
Min. operating
pressure
[
bar
]
1.6 1.5
2 2.5
Tabel 6
The purpose of recommended operating pressure is to avoid measuring errors as a result of cavitation or air in the
water.
It is not necessarily cavitation in the sensor itself, but also bubbles from cavitating pumps or adjusting valves
mounted before the sensor.
In addition, the water may contain air in the form of small bubles or air in the water.
The risk of these factors affecting the accuracy is reduced by maintaining a fair pressure in the installation.
Furthermore, it must be taken into consideration that the mentioned pressure is the pressure at the sensor, and
that the pressure is lower after a contraction than before (among other things due to cones). This means that the
pressure – when measured elsewhere in the installation – might be different from the pressure at the sensor.
This can be explained by combining the continuity equation and Bernoulli’s equation. The total energy from the
flow is the same at any cross section. For simplification, it can be written as : P + ½
ρ
v
2
= constant.
When dimensioning the flow sensor above must be taken into consideration, especially if the sensor is used
within the scope of OIML R 49 between Q3 and Q4 and in case of severe contractions in the pipe.
Q3: 1.6 m³/h
Parallel
The sound path is parallel to the
measuring pipe and is sent from
the transducers via reflectors.