User's Manual

7ML19985FH01 SITRANS LR 400 – INSTRUCTION MANUAL DRAFT Page 35
mmmmm
Parameters (HART)
4.2.2.3: Dead band (F = 0.26 m)
Area below the flange in which measured values are ignored.
Specification of a *dead band in the units system selected according to Parameter 4.1.5
defines a minimum distance from the flange which the measuring medium must have for
the device to accept the measured values as valid. This suppresses reflective
interference generated by e. g. the nozzle, close obstacles, or the antenna.
4.2.2.4: Correction Factor (F = 1.0)
Correction factor for physical measuring influences
The propagation time of the microwaves between the antenna and the measuring
medium changes slightly depending on the pressure inside the vessel. If this pressure is
constant, however, it can be included in the evaluation according to the
equation:
K = correction factor, p = pressure inside the vessel in bar, Tgas = gas temperature in °C,
ε
r, G as
= dielectric of the overlying gas, e.g. ερ
, air
= 1.00059
Enter the correction factor K as a dimensionless value.
4.2.2.5: Filling Speed (F = 200 mm/min)
Typical speed of change of the level. Not displayed if user vessel is selected in Parameter
4.2.2.1.
This Parameter is not displayed when a user vessel is selected in Parameter 4.2.2.1. When
you determine that the displayed measured value does not follow the change in the
height of the level in the vessel, you can enter a value for the speed with which it
generally changes. This assigns a greater probability to measuring targets which move at
this speed.
Value
numerical value, Minimum value = Length of the antenna
Value
numerical value
Value
numerical value
Note: The dead band should exceed the antenna’s length.
K
1
1 ε
rGas,
1–()+
273 p⋅
T
Gas
273+
--------------------------
⋅
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chap6.fm Page 35 Tuesday, October 9, 2001 2:26 PM