User's Manual

7ML19985JM01 SITRANS LR 460 – INSTRUCTION MANUAL Page 84
mmmmm
F: Technical Reference
LOE Timer
The LOE timer determines the time (in minutes) to elapse after the last valid reading
before Failsafe mode is activated. When the LOE timer expires, the material level to be
reported is determined by Failsafe Mode.
Failsafe Mode
Failsafe mode may be triggered by a loss of echo, a bad configuration, or certain device
faults. You can select can select one of three possible values to be reported when a
Failsafe mode occurs:
• Default value (Failsafe value) used as output value.
• Store last valid output value.
• Calculated output value is incorrect.
Failsafe value
Failsafe value is a user-defined value. This allows you to enter the safest output value for
your application.
For example, you may want to select a user-defined high value, to prevent an overfill
(Failsafe Hi). Or you may want to select a low value, to protect a pump from operating dry
(Failsafe Lo).
False Echoes
False echoes can appear during the receive cycle. They are often created by internal
impediments like a ladder rung, and are usually indicated by an incorrect high level
reading.
Near Range (Blanking)
Near Range allows you to set a distance in front of the antenna, within which any echoes
will be ignored. But Auto False-Echo Suppression is generally recommended in
preference to using Near Range.
Auto False-Echo Suppression
The TVT adjustment parameters allow you to set a TVT (Time Varying Threshold) curve, so
that SITRANS LR 460 will ignore false echoes.
The default TVT curve hovers above the echo profile, and effectively screens out small
false echoes. But if an obstruction is causing a large echo before the material level echo,
that echo will rise above the default TVT curve. You can use Auto False-Echo Suppression
to filter it out. If possible, rotate the instrument before using Auto False-Echo
Suppression, to lower the amplitude of false echoes.