Rosemount 5401, Reference Manual

Page: 95 / 180

Reference Manual
00809-0100-4026, Rev FA
July 2009
7-5
Rosemount 5400 Series
The surface thresholds should be set to approximately 20% of the measured
signal amplitude of the product surface.
False Echo Area
. False Echo Areas are set during the
Measure and Learn
function (see “Guided Setup” on page 5-15), when the disturbing object is
larger than the surface echo. The False Echo Area can be adjusted manually.
Hold Off Distance - Upper Null Zone
. Measurements are not performed
within the Hold Off Distance. By setting the Hold Off Distance to zero,
measurements can be performed close to the flange. Consider near zone
accuracy. See “Near Zone Accuracy” on page A-1.
Tank Bottom
. Measurements are not performed after the Tank Bottom limit.
SURFACE PULSE NOT
FOUND
The amplitude thresholds are adjusted manually or during the
Measure and
Learn
function to appropriate values to filter out noise and other non-valid
measurements from the measurement signal.
The amplitude of the measurement signal, i.e. the amplitude of the signal
reflected by the product surface, is related to the actual dielectric constant of
the product.
Rosemount Radar Master (RRM) has a plot function that allows viewing of the
reflections in the tank.
If the amplitude threshold is too high, the product level will not be detected, as
illustrated in Figure 7-2. In a situation like this, the amplitude threshold is
lowered so that the Surface peak is not filtered out.
Figure 7-2. Example 1: surface
threshold is too high.
If there are disturbing objects in the tank, the threshold must be set carefully
to avoid locking on the wrong amplitude peak. In Figure 7-3, the transmitter
has locked on a peak above the actual product surface, i.e. a disturbance was
interpreted as the product surface.
A
m
p
litu
d
e, m
V
The Surface Threshold is
above the Surface peak
Surface Threshold=
Amplitude Threshold
Curve (ATC)
Distance, m
Reference