User's Manual

Appendix A: Technical reference
A.2 Echo processing
SITRANS LR250 (FOUNDATION FIELDBUS)
Operating Instructions, 01/2014, A5E32221411-AB
239
A.2.10
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 (2.5.9.1.)
describes the quality of an echo. Higher values represent higher quality.
Echo Threshold (2.5.7.3.)
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 (2.3.6.)
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:
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.
A.2.10.1
LOE Timer
Loss of Echo (LOE) Timer (2.3.6.)
determines the length of time a Loss of Echo (LOE) condition
will persist before the function block will show a status of BAD or UNCERTAIN. The default is
100 seconds.