KROHNE CARGOMASTER - Manual (Page 70)

CARGOMASTER®5
Operators Manual - 70
Remember that you also have to include the actual density of the fluid in the
aritmethics.
Gain adjustment
Gain adjustments may be applied where you have deviations that are not
constants, but where the deviation is a certain percentage of the reading, e.g.
where the deviation is 5% at both 50% level and 98% level. Applying a gain
of 1.05 will add 5% to the reading whereas gain 0.95 will subtract 5% from the
reading.
Note: It is necessary to use a pressure calibrator in order to precisely determine the deviation
in reading from the sensors. The use of experience data alone may not be sufficient to achieve
the highest possible accuracy.
In the following example, the tank shown is displaying a 130mm H2O too low
value for 98% level. When the level drops to nearly empty tank, the reading
displays very close to correct, with only a few mm deviation.
Linear deviation - offset increases
with filling level
0
1000
2000
3000
4000
5000
6000
Tank level, mm
Actual level
Sensor reading
Our example tank is 18000 mm high. Consider the numbers:
Level % 70 98
Actual Level mm 12600 17640
Sensor reading, mm 12510 17510
Necessary gain adjustment 12600/12510=1.0072 17640/17510=1.0074
Note that the deviation at 70% level is 90 mm and at 98% it is 130mm.
However, the deviation factor is the same, and both readings can be tuned in
buy applying the same gain correction: 1.007.
Do not forget to include actual density in the arithmetic when you calculate
what the correct reading should be. Actual Density = Density compensated for
the actual temperature. (See also Density Variables on page 58 )