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U408_flowthermNT_B_e_160420
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www.hoentzsch.com
5.3.2.4
Damping
The damping rate set here affects the measured value display, if FA is selected as sensor in the display
settings (5.3.20.1). Damping also affects the analog output if FA is selected as the source (5.3.18).
Damping/s:
enter the damping time of 01 to 99 seconds
Example 10 seconds: after every second the arithmetical average of the last 10 seconds is displayed.
5.3.3
FA - Density correction
Menu -> Settings -> Sensor -> FA Input -> Density correction
Liquids:
Liquids are virtually density resistant. No density correction needed.
Gases and vapours:
The density of gases and vapours can be strongly modified against pressure and temperature. Such severe
modifications have a minor impact on the measured value of a vane wheel sensor. This impact manifests it-
self in a determinable correction value, which is added to or subtracted from the measured value. The per-
centaged impact of this correction value is however negligible with average to high velocity flow. With low and
very low values, consideration of the density correction becomes more expediant.
To determine this correction value the measuring range initial value (starting value) of a vane wheel is
examined. The specified starting value in the vane wheel sensor documents arises from a medium density of
1.204 kg/m³ (calibration conditions). The only slightly deviating actual starting value, even with considerably
different working density of the medium (in the actual application) ensues in good approximation of the
following:
actual starting value = specified starting value x root of (density during calibration / working density of the
medium).
The correction value is now the difference between real and specified starting value. The characteristic of the
sensor is displaced by this value.
If the operating density of the medium is greater than the calibration density of 1.204 kg/m³, then the deter-
mined correction value must be deducted from the measured value. If it is less than the calibration density of
1.204 kg/m³, then the determined correction value must be added to the measured value.
The working medium density is needed to calculate the correction value.
Example:
A ZS25GE-mn40/100/p10 sensor with a specified starting value of 0.5 m/s is used in air at 1.013 bar and
100 °C, that is, with a working medium density of 0.946 kg/m³.
Entered in formula:
actual starting value = 0.5 m/s x root of (1.204 kg/m³ / 0.946 kg/m³) = 0.5 m/s x 1.128
= 0.564 m/s
correction value
= 0.564 m/s
– 0.5 m/s
= 0.064 m/s
With a displayed value of 15.00 m/s (without correction) and with density correction on, the correction value of
0.064 m/s would be allowed for and a corrected value of 15.06 m/s would be displayed.
Setting:
Selection:
N
= density correction
no
Y
= density correction
yes
then enter the density of the sample gas:
W-density/kg/m3:
enter the working medium density in kg/m³
