Troubleshooting guide

84
Reference Manual
00809-0100-4308, Rev BA
Section 6: Service and Troubleshooting
December 2014
Service and Troubleshooting
6.4.2 Adjusting thresholds
Measurement with the Rosemount 3308 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.
By default, the amplitude thresholds are automatically adjusted to appropriate values in order
to filter out noise and other non-valid measurements from the measurement signal, as
illustrated in Figure 6-3. The configured Upper Product Dielectric Constant is used for setting
the automatically calculated amplitude thresholds. Normally no other threshold adjustment is
needed. But if the transmitter still does not track for example the product surface, it may be
necessary to manually adjust the thresholds.
Figure 6-3. Threshold Principle
The different amplitude thresholds used for the Rosemount 3308 Series Transmitter are
described in section “Thresholds” on page 176.
Note
Before changing the amplitude thresholds, check that the Upper Product Dielectric Constant
parameter is set as accurately as possible. The Upper Product Dielectric Constant is used for
setting the automatically calculated amplitude thresholds.
3.0
A
A
B
B
The echo peak is below the
threshold (dotted line) and is
suppressed by the device.
DISTANCE
AMPLITUDE
This echo peak is interpreted
as the product surface, since
it is the first peak closest to
device that is above the
surface threshold.
Threshold