Emerson Rosemount 5408, Reference Manual

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7.4.2 Managing disturbance echoes
There are two general methods for managing disturbance echoes:
• Set amplitude thresholds to filter out weak disturbance echoes and noise.
• Use the suppress false echoes function to manage strong disturbance echoes.
Amplitude thresholds
The amplitude thresholds are used to filter out noise and disturbing echoes from the
product surface echo. The transmitter uses certain criteria to decide which type of echo
peak that is detected. Only echoes above the amplitude threshold might be considered
the product surface. The amplitude threshold can either be set to a constant value, or split
into sections as defined by up to 10 anchor points.
If necessary, a customized amplitude threshold section can for instance be used to remove
the influence from the tank nozzle, or disturbances close to the tank bottom. Additionally,
it might be needed in areas where there are occasionally strong echoes present, for
instance due to wide mixer blades. Suppressing false echoes may not be sufficient in those
areas.
Note
Do not create a customized amplitude threshold section around echoes which are already
registered as false echoes.
General recommendations
Use the following best practices to apply custom threshold adjustments:
• Generally, set amplitude threshold to about 10 percent of surface echo amplitude.
• Do not set the amplitude threshold to less than 150 mV (50 mV for solids
measurements)
(3)
.
Adjust the threshold value
Prerequisites
It is recommended to adjust thresholds using Rosemount Radar Master Plus.
Procedure
1. In Rosemount Radar Master Plus, under Service Tools , select Echo Curve .
2. In the echo curve, drag the amplitude threshold point left or right, or type the
desired value ( Figure 7-4 ).
3. Select Save .
(3) If required in solids applications with weak surface echoes, the amplitude threshold can be set down to 50 mV, as long as it
is greater than the disturbance echoes.
Service and troubleshooting Reference Manual
February 2020 00809-0100-4408
118 Reference Manual