User's Manual

Commissioning
Page 26
Item Name Description
FC
Freeze RSP data The freeze Radar Signal Processing data is a command that
stores all relevant radar processing data in RAM memory.
Wait approximately 5 seconds before requesting the next
data.
5C
Number of peaks above threshold This item contains the number of peaks above the threshold
settings. The maximum number is 15; when more peaks are
detected, only the 15 strongest peaks are listed.
5D.0.1
Position of detected peaks Format according to item
LD
(indexed item; 15 elements).
Each element contains the distance from the radar
reference position to the detected peak.
5E.0.1
Amplitude of detected peaks Format according to standard power format (dB)
(indexed item; 15 elements).
Each element contains the amplitude of the corresponding
peak in item
5D
.
When obstructions are expected and there cannot be made a reflection diagram, these items are very
helpful to select the obstruction zones. However, the best results can be obtained from the information of a
reflection diagram.
Obstruction reflections
Objects that are in the microwave path will cause reflections. All reflections from objects other than the
product surface are called: ‘obstruction reflections’.
Note:
In the reflection diagram you will probably also see second order reflection peaks, found at double
distance.
Obstruction reflections can be caused by heating coils, welding seams from tank shell or stilling well, etc.
Special examples of obstruction reflections are the antenna reflection and the bottom reflection.
Obstruction reflections can influence the level measurement:
• When an obstruction reflection is detected above the zone threshold, it becomes a candidate for the
selection of the level peak. This is not a problem, as the peak detection software can handle this.
• When the product peak approaches an obstruction peak, the two peaks will influence the calculation
of their positions. The influence starts when the peaks are 0.4 m (16 ") apart. The obstruction reduces
the accuracy of the calculated level position. In many cases this is a one-side phenomenon, where
the obstruction reflection disappears as the product submerges the reflecting object.
• The AdvancedDSP level calculation is less sensitive for the presence of an obstruction reflection. But
the inaccuracy of the normally calculated level position may cause a jump of the AdvancedDSP level
of 15 mm ( / "). These jumps can be prevented by declaring an obstruction zone around the
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position of the obstruction peak.
The SmartRadar software provides for setting of obstruction zones and obstruction threshold for each zone.
This can be used to prevent obstruction reflections from appearing in the list of detected peaks. From the list
of detected peaks the product level peak is selected. As explained above, the peak detection software can
cope with the presence of obstruction reflections without the obstruction zone settings.
However, it is advised to define obstruction area’s around obstruction peaks when the AdvancedDSP level
calculation is used. It is then not required to set obstruction thresholds; only the zone definition is required.