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Diagnosing and Troubleshooting
11.5 Noise Problems
Symptom
Echo profile request results in an
error icon that displays for 5
seconds before returning to the
echo profile request menu.
Data log files are empty or log-
ging has stopped.
11.5
Noise Problems
Incorrect readings can be the result of noise problems, either acoustic or electrical, in the
application.
The noise present at the input to the ultrasonic receiver can be determined by viewing the
echo profile locally via the LUI, or alternatively, using remote software such as SIMATIC PDM,
AMS Device Manager, FC375/475, or DTM. View also parameters Noise Average 3.2.9.4.)
(Page 250) and Noise Peak (3.2.9.5.) (Page 250). In general, the most useful value is the
average noise.
With no transducer attached the noise is under 5 dB. This is often called the noise floor. If the
value with a transducer attached is greater than 5 dB, signal processing problems can occur.
High noise decreases the maximum distance that can be measured. The exact relationship
between noise and maximum distance is dependent on the transducer type and the material
being measured. An average noise level greater than 30 dB may be cause for concern if the
installed transducers maximum operation range matches the range of the application (e.g. 8
m application using an 8 m XRS-5). Using a larger transducer with greater transmitted energy
should help to improve performance in a noise condition.
11.5.1
Determine the Noise Source
Disconnect the transducer from the SITRANS LUT400. If the measured noise is below 5 dB,
then continue here. If the measured noise is above 5 dB go to Non-Transducer Noise Sources
below.
1. Connect only the shield wire of the transducer to the SITRANS LUT400. If the measured
noise is below 5 dB, continue with the next step. If the noise is above 5 dB, go to Common
Wiring Problems below.
2. Connect the white and black transducer wires to the SITRANS LUT400. Record the average
noise.
280
Possible Cause
Another external communica-
tion is trying to access an echo
profile at the same time.
•
Data Logging is not enabled.
•
USB extension cable has
been used (although may
not currently be connected).
Operating Instructions, 04/2021, A5E33329501-AG
Action
Wait for several seconds and
then retry the echo profile re-
quest, or disconnect / disable
any external communications
that may be requesting an echo
profile.
•
Verify that Data Logging is
enabled. See Data Logging
(2.10.) (Page 214).
•
If a USB extension cable has
been used (remove if cur-
rently connected), a power
reset of the device is re-
quired to restart Data Log-
ging.
SITRANS LUT400
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Table of Contents
Troubleshooting
