User's Manual

7ML19985LT01 SITRANS LR560 (PROFIBUS PA) – OPERATING INSTRUCTIONS Page 121
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D: Technical Reference
Damping
Filter Time Constant (2.5.8.1.) smooths out the response to a sudden change in level. This
is an exponential filter and the engineering unit is always in seconds.
In 5 time constants the output rises exponentially: from 63.2% of the change in the first
time constant, to almost 100% of the change by the end of the 5th time constant.
Loss of Echo (LOE)
A loss of echo (LOE) occurs when the calculated measurement is judged to be unreliable
because the echo confidence value has dropped below the echo confidence threshold.
Confidence (2.4.7.1.) describes the quality of an echo. HIgher values represent higher
quality.
Echo Threshold (2.4.5.3.)defines the minimum confidence value required for an echo to be
accepted as valid and evaluated.
If the LOE condition persists beyond the time limit set in LOE Timer (2.3.3.) the LCD
displays the Service Required icon, and the text region displays the fault code S: 0 and the
text LOE.
If two faults are present at the same time, the fault code, error text, and error icon for
each fault are displayed alternately. For example, Loss of Echo and faulty power supply:
S: 0 LOE S: 2 NO TECH POWER
Upon receiving a reliable echo, the loss of echo condition is aborted, the Service
Required icon and error message are cleared, and the reading returns to the current
level.
LOE Timer
LOE Timer (2.3.3.) determines the length of time a Loss of Echo (LOE) condition will persist
before a Fail-safe state is activated. The default is 100 seconds. Fail-safe Mode
determines the level to be reported when the Fail-safe timer expires.
Level (m)
Time (s)
smoothed output
input (level)
Damping example
time constant = 2 seconds
input (level) change = 2 m