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

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 (
Calibration Point
), below the TVT curve (
disregarded. The remaining portions of the Echo Profile are evaluated using the echo
select algorithm (
3.2.9.2. Confidence
confidence (
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 it's 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 (
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.

Echo Selection

Time Varying Threshold (TVT)

A TVT curve describes a threshold below which any echoes will be ignored. The default
TVT curve is used, until
Suppression Range
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
Auto False Echo Suppression
more details.
The device characterizes all echoes that rise above the TVT as potential good echoes.
Each peak is assigned a rating based on its strength, area, height above the TVT, and
reliability, amongst other characteristics.
Page 258 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS
2. 1 2.2.1. Algorithm
), and the Echo Profile portion providing the best echo
) is selected.
3.2.9.1. Figure of Merit
2.12.3. 1 . Auto False Echo Suppression
are used to create a new 'learned TVT curve' .
Shaper Mode and
below for
2.12.4. TVT Shaper
) are automatically
).
and
default TVT
echo profile
2.2.1. Low
2. 1 2.3.2. Auto False Echo
material
level
echo marker
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