Emerson Rosemount 3308A, Reference Manual

Page: 116 / 226

Table 6-6: Incorrect level readings
(continued)
Symptom Possible cause and recommended actions
Level stuck in measuring range. • May be caused by a disturbing object in the tank. Read
the Echo Curve and adjust Thresholds, see
Adjust
thresholds .
• Check if the probe is bent and in contact with the tank
wall. This contact causes a false echo reading.
• Heavy coating or contamination on the probe. Clean
the probe.
Level stuck in empty. • Thresholds may be too high, see Adjust thresholds .
Level fluctuations (a couple of inches). • There is too much disturbing noise in the tank (from
foam, splashing etc.). Set the Performance Mode to
High to get a stable measurement signal, refer to
Resolve noise or weak surface echoes .
• There are rapid level changes in the tank. Select a faster
Update Rate, refer to
Configure update rate .
• Thin oil layer on top of water that is sometimes
detected, sometimes not. Set the Peak Detection
Method to Threshold Intersection to improve the
stability of level measurements in such applications.
Refer to
Resolve thin oil layers .
Table 6-7: Incorrect or missing interface level reading
Symptom Possible cause and recommended actions
Incorrect Interface Level reading. • The Upper Product Dielectric Constant is not correct,
see
Upper product dielectric constant .
• Air gap is too big when the Measurement Mode is set to
Interface Level with Submerged Probe. Reduce air gap
or switch the Measurement Mode to Product Level and
Interface Level.
Missing Interface Level reading (reported as NaN). • The Measurement Mode is set to Product Level. Set
Measurement Mode to Product Level and Interface
Level, refer to
Measurement mode .
• The Interface Peak is difficult to detect, because the
bottom product has a low dielectric constant, or the
signal is attenuated in the upper product. Check
Thresholds. For more information, see
Example 2:
Interface peak not found .
There are two products in the tank, but only the product
surface or interface is detected. • The upper product is too thin to be detected. No action
is needed. See
Interface measurements for minimum
interface thickness for different probe types.
• Check Thresholds, see Adjust thresholds .
There are two products in the tank, but no readings are
reported. • Check Thresholds, see Adjust thresholds .
Service and troubleshooting Reference Manual
February 2020 00809-0100-4308
116 Rosemount 3308 Series