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5.4.3.
Typical signal trends
The following diagrams show typical signals that have been recorded with the oscilloscope function.
Emitted pulse
Flange
Level signal
Emitted pulse
Flange
Level signal
Emitted pulse
Level signal
Emitted pulse
Level signal
Rod or cable probe with gain 1
Rod or cable probe with gain 2
Coaxial probe with gain 1
Coaxial probe with gain 2
The signal from coaxial probes does not include the flange reflection, due to the mechanical setup which does not produce any changes in impedance at the flange.
The amplitude of reflection from the medium surface increases as the level rises and decreases as the level falls.
5.4.4.
Automatic adjustment
To maintain a sufficiently strong reflection signal, the gain is adjusted automatically.
When the amplitude of the level reflection decreases, gain will increase to compensate for the loss in signal amplitude. Thus, the proportionality of gain and threshold
levels remain unchanged. At gain 3, the level signal for both figures.
The reflected useful signal level has dropped (weakens, smaller
amplitude) as the distance between the level and the flange increases.
The interference signals are now below the level threshold, of which lower limit
is 50 mV.
In both cases, the automatically adjusted gain of the threshold is at the half of the level signal value. In the event of operational or installation faults, you can frequently
identify the cause of the fault by means of this function and normally eliminate it yourself. Should the fault persist, please send an evidence (screen shots with F10) to
your NIVELCO Service Centre.
Procedure (example where the level measured is too low compared to true level):
Read off displayed peak amplitude using the oscilloscope function – see 5.1.2.4 function.
Modify level threshold value.