Low Dielectric Applications - Honeywell SmartLine SLG 700 User Manual

In general, absorption will tend to be higher in media with higher dielectric constant.
Therefore, the measurable thickness range of the upper product will be lower with higher
upper product dielectric constant applications (DCU >3 or 4).
When the upper product thickness drops below 15 cm approximately, the surface and
interface reflections start to overlap. The transmitter will continue to measure the upper
product thickness accurately down to 7 cm although the echo curve might only show one
reflection for both surface and interface. If the transmitter fails to measure upper product
thicknesses below 15cm or if the measurement of thin interfaces is inaccurate, it might be
necessary to adjust the reflection models using the Honeywell DTM. Refer to the SLG 700
HART Option manual, #34-SL-25-06 for details on adjusting model parameters.
Note: The level transmitter is designed to measure properly only when the upper product
thickness is greater or equal to 7 cm. For example, upon restart the transmitter will not
attempt to provide a surface and interface measurement if the upper product thickness is less
than 7 cm.
Note: If the surface level is never going to exceed the minimum blocking distance high (min
BDH) for the transmitter configuration, it is recommended to keep full tank detection option
off.
For two-liquid non-flooded applications, the transmitter can simultaneously calculate a
number of related parameters related surface and interface positions.

Low Dielectric Applications

R200 introduced a new measurement technique that can be helpful when the surface
reflection is either very small or otherwise unstable.
For any reasonably transparent medium, the sensor can detect the pulse reflected at the end of
the probe. Since the level of fluid influences the propagation time for the radar pulse, the end
of probe signal will appear to recede as the tank fills. This apparent shift of the end of probe
signal is used to calculate the level of the surface.
However, this technique requires precise knowledge of both the probe length and the
dielectric constant of the medium. It is not recommended for regular single liquid
applications with dielectrics over approximately 2.5.
A procedure is available on the display or DTM to initiate an automatic probe length
calibration. This can be helpful in setting up this measurement mode and should of course
only be performed on an empty tank. Level measurement through the end-of-probe reflection
algorithm is a pay-for-feature option.
In some cases, this mode can provide level measurements where the single liquid application
fails when excessive turbulence, foam or emulsions block the reflection from the surface but
still allow the end of probe to be detected by the transmitter. It should be noted that the
measurement accuracy when using this application type can be greater than the nominal ±3
mm possible with the other application types.
The end of the probe must be readily detectable for this method to work. In practice, this
means that rod and coax probe types are preferred as they produce bigger end reflections.
Wire probes with end weights are less preferred but still possible. Wire probes with other end
terminations are not recommended unless it is known that the end reflection is usable.
Additionally, surface reflections and material attenuation should be considered.
SLG 700 SmartLine Level Transmitter User's Manual
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