Manual EDM 180
Revision 1.0 29.03.2010 Page 11/61
2.5 Extreme ambient conditions
Altitude correction
The pressure altitude formula describes the vertical distribution of the (gaseous) particles in the Earth´s
atmosphere, means the change of the barometric pressure related to height. This is also called the vertical
pressure gradient. However, within the lower atmosphere because of the high weather dynamics it can
mathematically only be described with approximations. A noticeable change of the air density is
proportional to increasing height. The air pressure decreases because the air column is „shorter“ and thus
lighter. The rule of thumb here is: The air pressure decreases with increasing height by 12mBar per 100
meters.
Because of the low barometric pressure the volume flow accelerates with increasing altitude. That means
that the signal amplitude of the detected particles changes – it decreases and thus bigger particles will be
wrongly assigned to low channels which results in a wrong mass.
Thus the display of the flow meter, which is dependent on the barometric pressure, has to be corrected.
Displayed values =
valueScale
p
p
referenz
vorOrt
P
Reference
= 1013mbar
Scale value is the value which equals to 1.2 l/Min Mass - Flow at 1013mbar – here 60mm (Flow meter
ANALYT)
Pressure
[mbar]
Altitude[m]
740
2500
790
2000
840
1500
860
1300
870
1200
890
1075
905
900
910
850
920
775
930
675
940
600
950
500
960
425
970
350
980
250
990
175
1000
100
1013
0
Display 51,3 53 54,6 55,3 55,6 56,2 56,7 56,9 57,2 57,5 57,8 58,1 58,4 58,7 59 59,3 59,6 60
Hint: The float of the flow meter has to be flexible, i.e. an exact vertical and horizontal adjustment of the
flow meter is very important.
For adjusting the flow see 8.7 (Flow adjust with ^F in HYPER TERMINAL – The
adjustment then happens via + / - ).
To Next Page
Loading...
Need help?
General