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Zone 3: Actual measuring zone
By default, the device searches for the largest reflected signal along the length of
the probe. If the pulse is lost, the display freezes at the last value measured in
this zone and the transmitted values freeze. The display will say
“Echo lost”.
Zone 4: Maximum measuring distance (Far-end blocking): P06
If the signal is lost (or within this range), the device returns the maximum
measuring distance or the values calculated from it. The display shows “E” for
empty, “Echo in far blocking.” “Echo in far blocking” can also be detected
during
HyView polling.
5.3.1.1.
Gain and Voltage Amplitude
Based on the principle of measurement, the TDR guided radar emits a radar pulse
and then “waits” for its reflections in time: it registers them as a time
-varying
voltage. The it calculates the distance from the time and the propagation speed
of the radar signal. The eternal question is which reflection comes from the target
we are looking for.
This is decided by a complex algorithm running on the transmitter microcontroller.
It is important to configure it well.
Ideally, such a reflection with the largest voltage amplitude comes from the level
of the material in the container. However, reflections from many other objects and
the background noise of the electronics also interfere with the measurement. It is
easy for the extent and amplitude of the reflections from the disturbances to rival
its level.
−
For strong, high-
amplitude signals, the “Threshold” line is used to help
differentiate between level echo and interference.
−
In case of a weak signal, the amplification also helps, it highlights the signal
from the noise, which is easier to measure.
−
The automatic gain switching has its own limits
Signal gain example (automatic by default):
Gain factor
The gain is automatically set by default to make the measured signal as ideal as
possible.
In addition, a custom value or gain range can be set with parameter
P24
.
The amplitude of the signal is proportional to the dielectric factor (
r
) of the
measured substance.
For small amplitudes, gain must be used.
The applicable gain depends on the dielectric constant (
r
) and the type of
probe.
Stage
Gain factor
1
1.00
2
2.111
3
4.4
4
8.927
Threshold line
The threshold line is used to filter out interference. The principle of operation is
as follows:
•
Reflections in the area below the line: noise and disturbance signals must
not be selected as the echo peak of the measured level.
•
However, as soon as the level reaches the interference, the amplitude of
the signal from the disturbance and the signal from the level add up. It
crosses the threshold and is selected as the level indicator.
The factory default threshold can be used for most average measurement tasks,
but may need to be modified depending on the particular installation and
application:
•
Measuring mediums with very low dielectric constant (
r
), like oil.
•
In case of multiple interference reflections or due to unfavorable installation
conditions.
•
To avoid measuring for deposits on the probe.
For tank connection with impedance coupling other than factory setting
The figure below shows a radar echo diagram and a threshold line with threshold
extension:
