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Reference Manual
IP2048/RM, Rev AA
Section 5: Service and Troubleshooting
February 2015
5.5 False echoes under certain ambient operating
conditions
In applications where elevated ambient temperatures of around 122 to 140 °F (50 to 60 °C) are
experienced, together with poor liquid surface conditions (excessive surface agitation, foam,
etc.), the transmitter may see a false echo and report a false high level measurement.
To overcome this issue, the near zone threshold (Threshold 1 Size P048) was changed from
software version V4.02 onwards to provide the following duty:
Threshold 1 Size P048
The factory default value of this parameter is 6% (prior to V4.02 software this had a
default value of 4%).
If Threshold 1 Size
P048 is equal to 6.0 (default), the transmitter automatically adjusts
the value of the initial threshold in use at elevated temperatures to eliminate false high
level readings.
If Threshold 1 Size
P048 is set to 6.0 and Threshold 1 Time P043 is equal to 2.9 (default),
the transmitter simultaneously adjusts the value of the initial threshold time in use at
higher temperatures.
If Threshold 1 Size
P048 is not equal to 6.0, the unit uses that value and Threshold 1
Time
P043 will be as programmed.
Note that operating at elevated ambient temperatures over 140 °F (50 °C) may have an
impact on the accuracy of the liquid level reading when the liquid level is within
approximately 0.5 m of the transducer face. The accuracy may be reduced from
±2.5 mm to +2.5/-5.5 mm or, in extreme conditions, +2.5/-8.5 mm.
Note
Parameters P048 and P043 are accessible only when using a Field Communicator or a
Mobrey MCU900 Series Control Unit. The main descriptions for these parameters are
on pages 137 to 138 in Appendix F: Configuring Using HART.