Install A Transducer With A Narrower Beam; Fixed Reading; Obstructions In The Sound Beam; Nozzle Mountings - Siemens SITRANS L 7ML5400 Operating Instructions Manual

Diagnosing and Troubleshooting

11.7 Fixed Reading

11.6.4

Install a Transducer with a Narrower Beam

A consistent, incorrect level reading may result due to interference echoes from the sides of a
vessel. If this occurs, try installing a longer range (narrower beam) transducer, enter the new
Transducer (2.1.6.) (Page 174) model, and (if necessary) optimize aiming and frequency
again.
Always contact Siemens service personnel before selecting a transducer to solve this type of
problem.
11.7 Fixed Reading
If the Reading is a fixed value, regardless of the transducer to material surface distance,
ensure the:
1. Transducer acoustic beam is free from obstruction.
2. Transducer is properly aimed
3. Transducer is not in contact with any metal object.
4. Material mixer (if used) is operating while the SITRANS LUT400 is operating. If it is stopped,
ensure that the mixer blade is not stopped under the transducer.
11.7.1

Obstructions in the Sound Beam

Check for (and remove if present) any acoustic beam obstruction, or relocate the transducer.
If an obstruction cannot be removed or avoided, adjust the Time Varying Threshold (TVT)
curve to reduce the Echo Confidence derived from the sound reflected by the obstruction.
Use SIMATIC PDM to adjust the TVT curve. (See TVT Shaper (2.12.4.) (Page 229) under Echo
Profile Utilities in LUT400 Communications manual
Communications for SITRANS LUT400 (HART) Manual (7ML19985NE01)
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11.7.2

Nozzle Mountings

If the transducer is mounted on or in a nozzle, grind smooth any burrs or welds on the inside
or open end (the end that opens into the vessel). If the problem persists, install a larger
diameter or shorter length nozzle, bevel the inside of the bottom end, or cut the open end of
the nozzle at a 45° angle.
See the transducer manual for complete mounting instructions.
If the mounting hardware is over tightened, loosen it. Over tightening changes the resonance
characteristics of the transducer and can cause problems.
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Operating Instructions, 04/2021, A5E33329501-AG
SITRANS LUT400