7ML19985JF02 SITRANS LR250 (PROFIBUS PA) – INSTRUCTION MANUAL Page 117
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D: Technical Reference
Damping
.Filter Time Constant (2.3.1.4.) 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.
Echo Confidence (2.2.3.6.1.) describes the quality of an echo. HIgher values represent
higher quality.
Echo Threshold (2.2.3.1.2.)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 (2.4.1.) 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.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
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Series1 Series2
Level (m)
Time (s)
smoothed output
input (level)
Damping example
time constant = 2 seconds
input (level) change = 2 m
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