Honeywell SLG 700 User Manual page 112

Table 22, and include:
Reference
Process Connector
Surface
Interface
End Of Probe
The Reference reflection is a reflection caused by an impedance change where the transmission
line connects to the sensor board that generates the radar pulses. This reflection is always present
and its characteristic shape is not altered by any environmental or process conditions. In cases
where the sensor housing is directly connected to the process connector, the Reference reflection
serves as an internal datum point for locating the position of the transmitter's Reference Plane in
the echo curve.
The Process Connector model is only used in cases where the sensor housing is separated from
the process connector by the optional 3m Remote Mount Cable. Since the remote cable may be
subject to a high temperature gradient, a reflection within the process connector is used as the
datum point for locating the transmitter's Reference Plane, eliminating temperature dependences
of the level measurement. This reflection is located at the start of the process connector.
The Surface model is used to describe the characteristics of the reflection caused as the radar
pulse encounters the boundary between a vapor and a liquid product. The Interface model is used
to describe the reflection caused as the radar pulse encounters the boundary between two liquid
products. Refer to section 7.7.4 for a description of when each of these types of reflections may be
present.
The End of Probe model is used to describe the characteristics of the reflection caused as the
radar pulse encounters the physical end of the probe or a centering disk attached to the probe.
The shape of these reflections vary depending on the probe type and end treatment as well as the
transmitter model and other mounting considerations. While the physical end of the probe is
always present, depending on the transmission characteristics and amount of product(s) above the
end of the probe, this reflection may not be noticeable in an echo curve.
Linear Attenuation Model
The gain (amplitude) of the radar reflection is exponentially decayed based on the linear
attenuation coefficient. This accounts for radar pulse energy dissipation to the vapor and media
surrounding the probe and is a function of the distance travelled. This is modeled as:
Where:
x = the distance from the reference plane
α = the linear attenuation coefficient
The linear attenuation of the gain is plotted in red in the upper graph in Figure 23. There is one
linear attenuation coefficient for each possible medium in the tank:

Vapor

Upper product

Lower product
These are available on the Attenuation Model panel shown in
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SLG 700 Series HART Option User's Manual
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