Emerson Rosemount 3308 Series Reference Manual page 131

Reference Manual
00809-0100-4308
Guidelines for setting the near zone threshold
• The Near Zone Threshold must be higher than the Surface Threshold to have an effect.
The threshold in the near zone is set to the highest value of the configured Near Zone
Threshold and Surface Threshold.
• The margin to waveform disturbances and noise must be at least 3 Cnts.
Set the near zone threshold
To manually set the Near Zone Threshold function:
Procedure
1. Read the Echo Curve.
2. Set the Near Zone Threshold.
Related information
Read the echo curve
Trim Near Zone function
The Trim Near Zone function is used to fine tune performance in the area close to the tank
top (Near Zone). The Near Zone stretches about 3.3 ft (1 m) into the tank from the lower
side of the device flange. Normally it is not necessary to use the function, but if you
experience problems related to the nozzle, pipe, or chamber installation, you may need to
use this function.
Figure 6-13
effect is only visible if measurement conditions so require.
Reference Manual
a) Start the Echo Curve reading.
b) View the Echo Curve plot to find out if there are disturbing echoes close to
the tank top.
a) Select Service Tools → Echo Tuning → Near Zone → Near Zone Threshold.
b) Under Threshold Control, select User Defined.
c) If using handheld communicator, select Send.
The Threshold and End Distance values can now be changed.
d) Under Threshold, type the desired value into the box.
e) Under End Distance, type the desired value into the box.
This value is the distance from Upper Reference Point to point where the
Near Zone Threshold ends.
describes the Trim Near Zone function and its effect on the echo curve. This
Service and troubleshooting
February 2020
131