Blocking Distance High And Blocking Distance Low Guidance; Blocking Distance High (Bdh) Guidance; Blocking Distance Low (Bdl) Guidance - Honeywell SLG 700 User Manual

2.7 Blocking distance high and blocking distance low guidance

The minimum blocking distances and accuracy in the transition zones may be compromised in
certain applications. In these cases and in order to meet the required specifications, it is
necessary to follow the guidance provided below. If the sensor performances in the transition
and blocking zones are compromised due to the presence of an obstruction and if the
performances cannot be improved, it is advisable to increase the configured blocking distances
accordingly. The latter will prevent the sensor from finding erroneous reflections in these
regions.

2.7.1 Blocking distance high (BDH) guidance

Meeting the blocking distance high specification may require recording a field background.
A field background is captured when the tank is empty or when the tank level is below the
minimum required distance (See Section 2.4.2). The field background records the reflected
signal near the process connector. The background data is subsequently removed from the
echo curve that is used for analysis.
The length of the field background depends on the type of sensor, the length of the probe and
the length of the nozzle (if used).

2.7.2 Blocking distance low (BDL) guidance

In order to meet the blocking distance low specifications, the following three conditions
apply:

The probe type needs to be configured properly. For example, it is necessary to indicate
if a coax, a rod or a wire is used and what is the termination (end weight, centering disk,
etc.).

The probe length needs to be configured accurately. The probe length is set at factory
time however if the probe has been cut or a centering disk was added it may be necessary
to reconfigure the probe length. See section
configured probe length.

In some cases, it might be necessary to adjust the end of probe model. For example, if the
end of probe is close to the bottom of the tank or to an obstacle, the default end of probe
model parameters might not be suitable. Refer to the SLG 700 HART Option manual,
#34-SL-25-06 or the SLG 700 FOUNDATION Fieldbus manual, #34-SL-25-07, for
details on adjusting model parameters.
Revision 7
SLG 700 SmartLine Level Transmitter User's Manual
3.2.5 for details on centering disks and
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