Echo Processing; Echo Selection; Time Varying Threshold (Tvt) - Siemens SITRANS LUT400 Operating Instructions Manual

A.2

Echo Processing

SITRANS LUT400 uses next generation Sonic Intelligence
Next generation Sonic Intelligence provides adaptive digital filtering of the transducer signal.
For example, when noise levels are high, filters are adjusted to maximize the signal to noise
ratio. This advanced Sonic Intelligence not only allows for better filtering, but provides
improved tracking of echoes, and more sophisticated echo positioning algorithms.
Echo processing consists of echo enhancement, true echo selection, and selected echo
verification.
Echo enhancement is achieved by filtering (Narrow Echo Filter (2.12.2.4.) (Page 221)) and
reforming (Reform Echo (2.12.2.3.) (Page 221)) the echo profile.
True echo selection (selection of echo reflected by the intended target) occurs when that
portion of the echo profile meets the evaluation criteria of Sonic Intelligence.
Insignificant portions of the echo profile outside of the measurement range (Low Calibration
Point (2.2.1.) (Page 171)), below the TVT curve (TVT Shaper (2.12.4.) (Page 223)) are
automatically disregarded. The remaining portions of the Echo Profile are evaluated using
the echo select algorithm (Algorithm (2.12.2.1.) (Page 220)), and the Echo Profile portion
providing the best echo confidence (Confidence (3.2.9.2.) (Page 245)) is selected.
A confidence value is a static test of a single snapshot profile so to maintain a valid reading,
it imposes that each individual profile show its peak above the threshold. The window may
be locked on the profile for hours or days so if the profile drops below the TVT curve just
once, a loss of echo may occur
The SITRANS LUT400, with its advanced tracking ability, can find and track the real echo
amongst stationary clutter echoes. Therefore, even if the echo drops below the tvt curve, it
can be identified with near certainty for approximately 30 seconds. This capability is
measured by the FOM (Figure of Merit (3.2.9.1.) (Page 244)).
Selected echo verification is automatic. The position (relation in time after transmit) of the
new echo is compared to that of the previously accepted echo. When the new echo is within
the Echo Lock Window, it is accepted and displays, outputs, and relays are updated. If the
new echo is outside of the Window, it is not accepted until Echo Lock requirements are
satisfied.
A.2.1

Echo Selection

A.2.1.1

Time Varying Threshold (TVT)

A TVT curve describes a threshold below which any echoes will be ignored. The default TVT
curve is used, until Auto False Echo Suppression (2.12.3.1.) (Page 222) and Auto False
Echo Suppression Range (2.12.3.2.) (Page 223) are used to create a new 'learned TVT
curve'.
A TVT hovers above the echo profile to screen out unwanted reflections (false echoes).
In most cases the material echo is the only one which rises above the default TVT.
In a vessel with obstructions, a false echo may occur. See Shaper Mode and Auto False
Echo Suppression (Page 293) below for more details.
SITRANS LUT400
Operating Instructions, 07/2019, A5E33329501-AC
for echo processing.
®
291