Users Manual Part 1

7.5.2 Handling disturbances at top of tank
Change the upper null zone
The Upper Null Zone defines a zone close to the transmitter where echoes are ignored.
This zone can be extended to block out disturbing echoes at the top of the tank.
Prerequisites
Note
Make sure the Upper Range Value (100%/20 mA) value is below the Upper Null Zone.
Measurements are not performed within the Upper Null Zone.
Procedure
1.
Identify desired Upper Null Zone using the echo curve plot.
a) In Rosemount Radar Master Plus, start the echo curve reading.
b) View the echo curve plot to find out if there are disturbing echoes close to
the transmitter.
2. Set the desired Upper Null Zone value.
a) Select Configure → Level Setup → Antenna.
b) Under Advanced, type desired Upper Null Zone, and then select Save.
Related information
Read the echo curve
Upper null zone
7.5.3 Tracking of weak surface echoes close to tank bottom
Use tank bottom projection
The Tank Bottom Projection function can be used to enhance measurement performance
in the tank bottom region.
If the product surface echo is weak in the tank bottom region and the bottom echo is
strong (typical for flat tank bottoms), the transmitter may lock on the bottom echo and
report a false level measurement (empty tank). If the application requires, the Tank
Bottom Projection settings can be user-defined. Figure 7-23 illustrates an example of the
Tank Bottom Projection when the tank is being emptied.
Reference Manual Service and troubleshooting
00809-0100-4418
September 2022
Rosemount 3408 Level Transmitter 99