Emerson Rosemount 3308, Reference Manual

Page: 88 / 128

Reference Manual
00809-XXXX-4811, Rev AA
February 2012
Rosemount 3308
7-8
PRELIMINARY
Interface Measurements
with Fully Immersed
Probes
The Rosemount 3308 transmitter has a measurement option which makes it
possible to handle interface measurements when the product level is not
visible, for example in a full bridle pipe as illustrated in Figure 7-6. In this case
the probe is fully immersed into the upper product, and only the interface level
is detected by the transmitter. Even if the upper product level drops, it is
ignored by the transmitter which continues to measure only the interface level,
but the measurement accuracy is reduced since the transmitter does not take
into account the influence of the air gap above the product surface.
The Measurement Mode parameter is available via the
HART command [1, 3, 3, 4]. Choose the
Interface when Immersed Probe
option.
Measurement mode Interface when Immersed Probe can also be activated in
the RCT software:
1. Open the Setup window.
2. Select the Tank Config tab.
3. Choose Measurement Mode
Interface when Immersed Probe .
4. Click the Send Page button.
NOTE!
Do not use Measurement Mode Interface when Immersed Probe in “standard”
applications when both Interface Level and Product Level are measured.
If the product level drops, the air filled region in the upper part of the pipe will
slightly reduce the measurement accuracy of the interface level. To achieve
high accuracy in this measurement mode the probe must be fully immersed.
Figure 7-6. Interface Level
measurements in a full bridle
pipe.
NOTE!
Adjust Threshold T2 if the level pulse is not detected.
Interface Distance
Interface Level
Product Level
is ignored
Interface Level is
measured