Loss Of Echo (Loe); Fail-Safe Mode - Siemens 7ML5431 Operating Instructions Manual

A.3.3

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 (2.8.6.1.) describes the quality of an echo. Higher values represent higher
quality.
Echo Threshold (2.8.4.3.) 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 (2.5.2.) 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 Fail-safe.
A.3.4

Fail-safe Mode

The purpose of the Fail-safe setting is to put the process into a safe mode of operation in the
event of a fault or failure. The value to be reported in the event of a fault is selected so that a
loss of power or loss of signal triggers the same response as an unsafe level.
LOE Timer (2.5.2.) determines the length of time a Loss of Echo (LOE) condition will persist
before a Fail-safe state is activated. The default setting is 100 seconds.
Material Level (2.5.1.) determines the material level to be reported when LOE Timer (2.5.2.)
expires, depending on the device type (standard or NAMUR NE 43-compliant.)
Options
Options
Upon receiving a reliable echo, the loss of echo condition is aborted, the Service Required
icon and error message are cleared, and the reading and mA output return to the current
material level.
SITRANS LR250 with mA/HART
Operating Instructions, 10/2019, A5E32220602-AG
STANDARD DEVICE
HI 20.5 mA (max. mA Limit)
LO 3.8 mA (min. mA Limit)
* HOLD Last valid reading
VALUE User-selected value defined in Fail-Safe mA Value (2.5.3.)
NAMUR NE 43-COMPLIANT DEVICE
HI 20.5 mA (max. mA Limit)
LO 3.8 mA (min. mA Limit)
HOLD Last valid reading
* VALUE User-selected value Fail-Safe mA Value (2.5.3.), default 3.58 mA
Appendix A: Technical reference
A.3 Analog Output
243