User's Manual

Page 134 SITRANS LR250 (HART) – INSTRUCTION MANUAL 7ML19985JE03
mmmmm
D: Technical Reference
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 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.
S: 0 LOE S: 52 Fail-safe
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.
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 Timer (2.5.2.)
expires, depending on the device type (standard or NAMUR NE 43-compliant.)
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.
STANDARD DEVICE
Options
HI 20.5 mA (max. mA Limit)
LO 3.8 mA (min. mA Limit)
*HOLDLast valid reading
VALUE User-selected value defined in Level (2.5.3.)
NAMUR NE 43-COMPLIANT DEVICE
Options
HI 20.5 mA (max. mA Limit)
LO 3.8 mA (min. mA Limit)
HOLD Last valid reading
* VALUE User-selected value Level (2.5.3.), default 3.58 mA