Emerson Rosemount 1408A Reference Manual page 60

Service and troubleshooting
May 2021
7.4.1 Adjust the general threshold
If necessary, the general threshold value can be increased if a disturbance echo is
interpreted as the product surface. Alternatively, a lower threshold may be required to
handle weak surface echoes (e.g. due to excessive foaming or turbulence).
Prerequisites
The general threshold is set at factory for optimum performance and should not normally
need an adjustment.
Before changing the factory default value, study the position and amplitude of the
different echo peaks.
Procedure
1. Under Menu, select Parameter → Advanced Setup.
2. In the General Threshold box, enter the desired value.
3. Select Write to device.
Related information
Analyze the echo peaks
General threshold
7.4.2 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 by analyzing the echo peaks.
2. Set the desired Upper Null Zone value.
60
a) Under Menu, select Diagnosis → Echo Peaks.
b) View the echo peaks to find out if there are disturbing echoes close to tank
top.
a) Under Menu, select Parameter → Geometry → Advanced.
b) Enter the desired Upper Null Zone value.
c) Select Write to device.
Reference Manual
00809-0200-4480
Rosemount 1408A Level and Flow Transmitter