Emerson Rosemount 3308 Series Reference Manual page 212

Configuration parameters
February 2020
Upper null zone
Defines how close to the device's Upper Reference Point a level value is accepted. You can
extend Upper Null Zone to block out disturbing echoes close to the tank top. View the
Echo Curve to find out if there are disturbing echoes close to the tank top.
This parameter should only be changed if there are measurement problems in the upper
part of the tank. Such problems may occur if there are disturbing objects close to the
probe. By setting the Upper Null Zone, the measuring range is reduced.
Note
Measurements are not performed within the Upper Null Zone and level alerts located in
the Upper Null Zone will not be triggered. Always configure your level alerts below the
Upper Null Zone.
For narrow nozzles it may be necessary to increase the Upper Null Zone (UNZ) in order to
reduce the measuring range in the upper part of the tank.
Figure D-4: Upper Null Zone
A. UNZ
B. Nozzle height
By setting the UNZ equal to the nozzle height, the impact on the measurement due to
interfering echoes from the nozzle will be reduced. Amplitude Threshold adjustments may
also be needed in this case.
Related information
Change the upper null zone
Probe angle (only applicable to rigid probes)
Defines the angle compared to the plumb line at which the device with probe is mounted
(0 means that probe is mounted vertically).
Enter the angle between the probe and the vertical line. Do not change this value if the
transmitter is mounted with the probe along the vertical line (which is normally the case).
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Reference Manual
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Rosemount 3308 Series