Measuring Principle - Siemens OpenAir G..B181.1E/KN Series Technical Basics

Differential pressure
sensor
Note
V %
Setting the
n
characteristic value
V %
Effect of
n
V %
Calculation of
n
(Χp = nominal pressure)
n
Calculation example
Siemens
Building Technologies
2.6

Measuring principle

A measuring device for acquiring the differential pressure – usually a measuring
cross, measuring orifice or Venturi tube in the airflow – represents the basis for air
volume flow measurement.
The air volume flow is measured with a differential pressure sensor. The actual
value of the air volume flow (absolute and/or relative value) can be transmitted
over the bus together with the actual value of the damper position (relative, in %) to
be used by a supervisory controller or for management purposes. The differential
pressure sensor operates long-term stable and without recalibration.
In critical cases material compatibility tests should be made while giving
consideration to harmful substances and concentrations.
The VAV box manufacturer (OEM) uses the parameter V
range of the differential pressure sensor (0...300 Pa) to the actual VAV box
nominal pressure Χp
at the factory. The effect of V
n
below.
0
1 0
90
80
70
60
50
40
30
20
10
0
0 50 100
300 Pa
%
V
<
n
Δp Pa
n
Assume that a VAV box is designed for a nominal pressure of Δp
V has to be set to 1.58:
n
300 Pa
V % 2.5
< <
n
120 Pa
VAV compact controller KNX/PL-Link G..B181.1E/KN
150 200 250
1.58
<
to adjust the operating
n
is illustrated in the diagram
n
300
= 120 Pa. Then,
n
CE1P3547en
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2017-03-23