Operating Manual

Accu-Wave Chapter 5 Radar Fine Tuning
TN Technologies 5-17
Clutter Data Management
Imperfections in the transition from the microwave head to the tank can cause microwave
energy to be reflected. These imperfections can be due to poor alignment of the nozzle pipe
during welding, pipe size mismatch, joints, valves, pipe liner, or material buildup.
Although the physical source of these reflections is normally outside the range of interest
(at or above the top of the tank), multiple bounces can cause these “phantom” echoes to
appear to be in the range of interest. These echoes will persist even when the actual
material level rises above the apparent distance to the phantom targets. These phantom
targets are referred to as clutter.
Erase Clutter
Even if these phantom echoes are not strong enough to confuse the system in the selection
of the proper echo, this clutter can cause errors when the distance to the material surface is
close to the distance associated with a phantom target. The effects of phantom targets can
be reduced by the use of clutter erase.
The gauge “learns” the phantom signals and mathematically removes them from
consideration. During the learn clutter (“Get clutter data”) operation, the system stores all
of the apparent target information over the maximum possible clutter zone, ~ 7.4 ft (2.25
m) or 25% of the maximum measurement distance, whichever is greater.
User Considerations
The gauge always measures the clutter data out to a fixed, maximum clutter distance. You
then specify the distance from the reference line for which the actual clutter removal is
performed. The clutter data will include any real (physical) targets located between the
reference line and the maximum clutter distance. It is essential that the specified clutter
removal distance not include any actual physical targets which might be covered by the
material surface during normal operation. (See the “Tank map setup” or “Regional
weighting setup” section in the chapter for information on how to mitigate the effect of
these reflections.)
The user-entered clutter distance must be at least 30 cm (~12 in) above the level of the
process material when the clutter data is taken. Otherwise, part of the real target’s echo
data will be considered to be clutter.
The measurement range can be essentially anything up to the maximum system capability.
However, the internal range is normally from about 8 m (27 ft) to the maximum system
capability. For user-entered ranges below the internal minimum, the system ignores targets
between the top of the range of interest and the internal minimum. The range of interest is
established by the “zero level point” entry, if the primary measurement is level. The ROI
can be overridden by the “maximum distance to be measured” entry.
If anything in the setup entries causes the internal range or the initial amplification to
change after clutter data has been taken, clutter erase will be disabled and the “bad entry”
message will be displayed. Initial amplification is normally a function of the dielectric
constant and the range of interest-related entries. The bad data message can be suppressed