Emerson Rosemount 5408 Reference Manual page 103

Table 7-6: Incorrect Level Readings
(1)
Symptom
Level value drops to a lower value when
product surface is close to antenna.
Measured value jumps to a lower value.
Measured level fluctuates.
Rosemount 5408 and 5408:SIS Level Transmitters
(continued)
Possible causes
Product surface is within the
Upper Null Zone and a dis-
turbance echo is interpreted
as the product surface.
Time
Multiple products in the tank,
e.g. thin oil layer on top of
water that is sometimes de-
tected, sometimes not.
Time
Excessive foaming or turbu-
lence.
Time
Service and Troubleshooting
Recommended actions
Check the setting of the Upper Null Zone,
see Upper null zone.
Set Double Surface Handling to Track Up-
per Surface or Track Lower Surface, see
Double surface handling.
• Under turbulent conditions with low
level rates, consider increasing the
Damping value, see Damping
• Enable the Foam parameter or Turbu-
lent Surface parameter, or both. See
Process conditions.
• If two surfaces are seen in foamy appli-
cations, set Double Surface Handling to
Track Lower Surface. See
Double surface handling.
value.
93