Rosemount 5401, Reference Manual

Page: 165 / 180

Reference Manual
00809-0100-4026, Rev FA
July 2009
C-5
Rosemount 5400 Series
Level Alarm is Not Set When Tank is Empty
If the echo from the product is lost in the area close to the tank bottom (Empty
Tank Detection Area), the device enters Empty Tank State and triggers an
alarm. Two types of alarms are triggered:
• Invalid Level (can be seen in the Diagnostics window)
• The Analog Output enters Alarm Mode
Full Tank Handling
Full Tank Detection Area
This parameter defines a range where the surface echo can be lost. If the
echo is lost in this range, the tank is considered full (the device enters Full
Tank State) and the device presents maximum level indication.
When the tank is full, the device searches double the Full Tank Detection Area
for the product surface. When a new echo is found in this range, it is identified
as the product surface.
It is important to filter out any disturbances in this area.
Level above Hold Off Distance Possible
This function should be enabled if the level can rise above the Hold Off
Distance/UNZ and it is necessary to display the tank as full in that case.
Normally, the device will be able to track the surface, and the product level will
never rise to that height. If the function is not enabled and the surface is lost at
the top of the tank, the device searches the whole tank for a surface echo.
Level Alarm is Not Set When Tank is Full
If the surface echo is lost, close to the top of the tank. The level value will
normally be displayed as “invalid.” This parameter should be set to suppress
the “invalid” display.
NOTE
Setting this parameter disables the analog output so it does not enter alarm
mode for invalid levels close to the antenna.
See “Full Tank Handling” on page C-10 for more information.
Double Bounce
Some radar waves are reflected at the surface and then reflected against the
tank roof and back to the surface before being detected by the transmitter.
Normally, these signals have a low amplitude and are ignored by the
transmitter. For spherical and horizontal cylinder tanks however, the
amplitude may be strong enough for the transmitter to interpret the double
bounce as the surface echo. Setting the
Double Bounce Possible
parameter
can solve this type of measurement situation. This function should only be
used if double bounces cannot be corrected by changing the mechanical
installation. See “Double Bounce” on page C-11 for more information.
Surface Echo Tracking
Slow Search
This variable controls how to search for the surface when a surface echo is
lost. With this parameter set, the transmitter starts searching for the surface at
the last known level, and gradually increases the search region until the
surface is found. If this variable is not set, the transmitter searches the whole
tank. This parameter is typically used for tanks with turbulent conditions.