Emerson Process Management ROSEMOUNT 5300 - Manual (Page 257)

Reference Manual
00809-0100-4530, Rev BA
July 2009
C-9
Rosemount 5300 Series
Reference Threshold
Amplitude threshold for detection of the Reference pulse.
Probe End Threshold
If the Probe End Projection function is used (see “Dielectric Constant
Settings” on page C-14), this threshold may need to be adjusted to make sure
that the probe end pulse is properly detected.
Full Tank Threshold Offset
The Full Tank threshold is related to the Reference Threshold, and can be
used for detecting that the tank is full. The given offset value determines the
gap between the Reference threshold and the Full Tank threshold. The
transmitter considers the tank full when the amplitude of the Reference Peak
has dropped to a value between the two threshold values.
If the amplitude of the Reference peak is below the Full Tank Threshold
(negative amplitude of the Reference peak), the tank is not considered full.
The Full Tank Threshold Offset should normally be set so that the Full Tank
Threshold coincides with an amplitude value equal to 90% of the Reference
Echo peak amplitude when the tank is not full.
Example
In the example below, the following assumptions are made (note the negative
sign):
Reference Echo peak amplitude = -2000 mV
Reference Threshold = -1000 mV
The target position for the Full Tank Threshold is at 10% below the Reference
Echo peak amplitude. In this example, it means that the Full Tank Threshold
should be located at 10% below the Reference peak at -2000 mV:
-2000 mV - (-200 mV)= -1800 mV
Since the Full Tank Threshold refers to the Reference Threshold, the resulting
offset value has to be expressed in terms of the distance to the Reference
Threshold:
Full Tank Threshold Offset = -1000 mV - (-1800 mV) = +800 mV.
Figure C-7. Example of how to
specify the Full Tank Threshold
By default, this value is 0 (function is not used). This is because highly
contaminated or condensed tank-seals, and turbulent or boiling surfaces,
which can cause splashing, may cause function to be triggered.
3.0 4.0 5.0
Ampl
itu
de (mV)
Reference Threshold
Full Tank Threshold
Offset = +800 mV
- 10%
Reference Peak=-2000 mV
Surface Threshold
Interface Threshold
Distance (m)