User's Manual
Table Of Contents
- 8 Parameter reference
- 9 Service and maintenance
- 10 Diagnosing and troubleshooting
- 11 Technical data
- 12 Dimension drawings
- 12.1 Threaded horn antenna
- 12.2 Threaded horn antenna with extension
- 12.3 Flanged horn antenna
- 12.4 Flanged horn antenna with extension
- 12.5 Flanged encapsulated antenna (2"/DN50/50A sizes only)
- 12.6 Flanged encapsulated antenna (3"/DN80/80A sizes and larger)
- 12.7 Threaded PVDF antenna
- 12.8 Threaded connection markings
- 12.9 Raised-Face flange per EN 1092-1 for flanged horn antenna
- 12.10 Raised-Face flange per EN 1092-1 for flanged encapsulated antenna
- 12.11 Flat-Face flange
- 12.12 Process connection tag (pressure rated versions)
- A Appendix A: Technical reference
- B Appendix B: Communications via Foundation Fieldbus
- C Appendix C: Certificates and support
- 13 List of abbreviations
- 14 LCD menu structure
- Glossary
- Index
Appendix A: Technical reference
A.2 Echo processing
SITRANS LR250 (FOUNDATION FIELDBUS)
Operating Instructions, 01/2014, A5E32221411-AB
231
A.2.2
Echo Selection
Time Varying Threshold (TVT)
A Time Varying Threshold (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
(Page 236) for more details.
①
default TVT
②
echo profile
③
material level
④
echo marker
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.
Algorithm (2.5.7.1.)
The true echo is selected based on the setting for the Echo selection algorithm. Options are
t
rue
F
irst Echo,
L
argest Echo, or
b
est of
F
irst and
L
argest.