Honeywell SLG 700 User Manual page 100

Amplitude Tracking:
This feature enhances the sensor to track levels under dynamic conditions or when the radar pulse
attenuations in the media are not well known. Once the sensor has locked onto a correct level, it
will track the amplitude rather than use the initial (user specified) model amplitude. These values
are periodically permanently stored and are hence recovered after a power down. Stored values
are cleared and re-initialized to the user provided amplitudes by turning off Amplitude Tracking
(and applying this change) and then turning it back on it. Amplitude tracking is not a replacement
for setting correct correlation models and will not track pulses whose amplitudes differ more than
about 40% from the user specified pulse model amplitudes.
Background Type:
The physical components used to mount the transmitter to the tank will always cause some
reflection of the radar pulse as the pulse leaves the confines of the process connector and starts to
travel through the medium in the region near the reference plane. Depending on the configuration,
these reflections may appear very similar to the reflections from the products in the tank and
therefore should be ignored. In addition obstacles present close to the wave guide can cause
reflections that mimic levels. The SLG 700 transmitter utilizes a means of subtracting out these
static background reflections before processing the data for reflections from the product(s).
All transmitters have pre-configured backgrounds for standard probe configurations which can be
selected with the Factory option. In all but the simplest applications, these should be replaced if
possible in-situ with one of the other two options using the capture mechanism described below.
The Field option is meant to reduce the effect of the process connector reflection created
when the radar pulse traverses between two regions of different impedances. The preset
length varies from 1.32m (standard temperature and pressure gauge) to 2.38m (high
pressure high temperature model) from the measurement Reference Plane. The user needs
to ensure that the level in the tank is below these values when acquiring the
background. The field background is stored in permanent memory.
The Obstacle option is similar to the field background but is intended to both suppress
process connector reflections as well as any false echoes generated by obstacles in the tank
(ladders, pipes, valves) in the vicinity of the probe. There is no limit on the length that can be
specified by the user. As with the field background, the level in the tank needs to be about
30cm below the end of the requested echo. One difference between the obstacle
suppression echo and the field background echo is that the sensor algorithms analyze this
echo and store only those sections of the profile that are found to contain false echoes. For
example, if a ladder exists 2m down a tank and a pipe inlet 19m down the tank, the user
should obtain an obstacle echo up to approximately 20m. The sensor will automatically
detect the two objects and permanently store the relevant data, omitting quiet regions in
between.
The active Background Type selection is independent of the capture Background Type described
below. New backgrounds are applied immediately once captured. However, it is not possible to
stay in obstacle mode after collecting a field type background because it is likely that the obstacle
background is significantly longer than the field background just collected. Normal operation is to
choose a background mode, apply, then collect a background in that mode. Backgrounds can be
verified on the Echo Curve display on the Monitor menu.
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SLG 700 Series HART Option User's Manual
Revision 5