May 2016
Reference Manual
00809-0100-4530, Rev DD
304
C.4
Threshold settings
Measurement with the Rosemount
™
5300 is based on the fact that the radar signal pulses
are reflected by the product surface and the interface between two liquids. Signal
amplitude thresholds are used to separate the measurement signal from disturbing echoes
and noise. See
“Analyzing the measurement signal” on page 151
for more information
about threshold principle.
By default, the device automatically calculates threshold values depending on the
measurement mode, various dielectric constant values and process conditions that you
have configured. Normally, no manual threshold adjustment is needed. But if the
transmitter is having difficulties to track for example the product surface, it may be needed
to manually adjust the thresholds.
Note
Before manually changing the amplitude thresholds, check that the Upper Product
Dielectric Constant parameter is set as accurately as possible. It is used for setting the
automatically calculated amplitude thresholds.
Guidelines for setting the Surface Threshold (ATC)
Before changing the Surface Threshold, make sure the product level is at least 20 in. (0.5 m)
from the lower side of the device flange.
Set the Surface Threshold to about 1/3 of the weakest surface echo amplitude in
the measuring range.
Surface Thresholds should never be set to values less than:
700 mV at distance 0-20 ft (0-6 m) from the upper reference point.
500 mV at distance more than 20 ft (6 m) from the upper reference point.
Amplitude (mV)
Distance
Surface Threshold
Surface echo
About 1/3 of surface
echo amplitude
