Instruction manual

Commissioning
58 Installation and Operations Manual
Dip table
The dip table is used to correct the level readings of the 7500 series RTG using
independently taken hand dips. The dip table is used in particular to adapt the level
gauge to the specific application conditions as mechanical offset and tank/stilling well
design. Depending on national regulations, national inspectors will dip the tank at one
to three levels during a calibration run and check the level readings. Only one value pair
must be entered into the dip table to correct the measurement offset. If a second value
pair is entered into the dip table, the 7500 series RTG accepts the corrected measured
values identically for both value pairs. All other measured values are determined by
linear extrapolation. If you enter more than two value pairs, the system carries out a
linear interpolation between adjacent value pairs. Outside these value pairs,
extrapolation is also linear.
Figure 7-7: Dip Table
To collect and enter data into the dip table, two alternative procedures may be carried
out. In order not to mix up measurement values corrected by the offset or linearization
of the dip table with uncorrected measurement values, it is recommended to use the
semi-automatic mode of the dip table to enter new data pairs. In this case, the first dip
value should be entered immediately after the basic calibration. Further linearization
points should be entered only after a level change of at least 2 m (see Figure 7-7, the
preferred choice) and a deviation between the “uncorrected measurement value” and the
hand dip value of at least > 4 mm. If this procedure can not be followed, then no value
pair should be entered into the dip table after basic calibration. Measurement data and
hand dip values should be collected over the full measurement range and be evaluated
with regard to a good linear fit. Only then should characteristic value pairs be entered
into the dip table using the “manual mode” (see Figure 7-7, right side). If further
linearization is needed, further hand dip values should be entered using only the
“semi-automatic mode”.
basic setup
history reset
dip table
alternatives
preferred choice:
and
immediate
correction in
mode
or adjust empty calibration
hand dip
offset
semi-automatic
collect hand dip and
measurement data over
full measurement range
collect further hand dip data;
if deviation from measurements
> 4 mm and level change > 2 m:
enter a new dip value
into dip table using the
modesemi-automatic
evaluate collected data;
enter characteristic value
pairs into the dip table
using the manual mode