Kamstrup MULTICAL 401, Technical Description

Page: 39 / 75

TECHNICAL DESCRIPTION MULTICAL
®
401
5512-091 GB/02.2008/Rev. J1
39
8.6 Guidelines for dimensioning MULTICAL
®
401
In connection with installations it has proved to be practical to work with pressures larger than the pressures
stated below:
Nominal flow q
p
Min. operating
pressure
Max. flow q
s
Min. operating
pressure
[m³/h] [bar] [m³/h] [bar]
0.6 1 1.2 2
1.5 1.5 3 2.5
3 1 6 2
3.5 1 7 2
6 1.5 12 2.5
10 1 20 2
15 1.5 30 2.5
Table 14
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 bubbles or air in the water.
The risk of these factors affecting accuracy is reduced by maintaining a fair pressure in the installation.
In relation to above table, the steam pressure at actual temperatures must also be considered. Furthermore, it
must be considered that the above-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 – 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 will be identical at any cross section. To simplify, 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 EN 1434 between qp and qs, and in case of severe contractions in the pipe.