User's Manual

Appendix A: Technical reference
A.3 Analog Output
SITRANS LR250 (HART)
Operating Instructions, 01/2014, A5E32220602-AB
227
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.)
STANDARD DEVICE
Options
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
Options
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
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.