Correlation Algorithm - Honeywell SLG 700 User Manual

7.8.6

Correlation Algorithm

The method by which the distance to product surface and distance to interface is found is based
on correlation between the measured echo curve and reflection models. The algorithm slides the
models across the echo curve, and at each step calculates the difference between the model and
the echo curve, referred to as the Objective Function. Typically the smallest value of the Objective
Function corresponds to the level selected by the sensor algorithms but the values must be below
a user defined threshold. In case of multiple local minima, there is additional logic to select the
best candidate. The final best candidate is used to calculate the distance to the product surface
and/or the distance to interface.
Figure 22 shows the DTM display used for configuration and troubleshooting of the algorithm.
Figure 22: Advanced configuration: Correlation algorithm screen
Different captured echo curves can be selected for analysis from the list in the upper right corner.
The upper graph displays the echo curve with the found reflections as well as the reflection models of
interest, i.e. surface reflection model. The bottom graph shows the objective function and its
threshold. Algorithm parameters are entered in the configuration section to the right of the graphs just
below the list of available echo curves. This section consists of 4 panels accessed through the
combo-box pull-down control located at the top of this section, as shown below in Table
Revision 5
SLG 700 Series HART Option User's Manual
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