Varec 7532, Installation And Operation Manual

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57
7532 Commissioning
6.5 Mounting calibration with VU 331
6.5.1 Function group "mounting calibr." (03)
Function "tank gauging" (030)
Using this function, you can either enter a dip table or carry out an auto-correction.
Function "auto-correction" (031)
When measuring levels with radar systems, so-called "multipath reflections" can affect
the level signal giving rise to serious measuring errors. "Multipath reflections" also
include radar beams which are received by the radar system, which have not been
reflected directly by the medium surface. They may reach the antenna via the basin wall
and the medium surface. This phenomenon is particularly noticeable with devices
mounted near to walls, as soon as the conical radar beam strikes the basin wall.
The 7500 RTG can automatically discover and correct measuring errors due to this
"multiple path" propagation. This is because it uses two independent sets of information
when evaluating reflection signals:
• Firstly, it evaluates the
amplitude
of the reflected energy using the so-called envelope
curve system.
• Secondly, it evaluates the
phase
of the reflected energy.
The decisive factor for a constant output signal is to assign the phase values to the
associated level values. This assignment is ensured using a correspondence table (index
correction table). The 7500 RTG learns this for the specific application after installation
(learning period).
Therefore, after mounting the device, and
after
completing the basic calibration, a
history reset
must be performed (enter "
yes
" in the "
history reset
"
(009)
function in the
"
basic setup
"
(00)
function group).
Do not switch off the radar system during filling and emptying operations during the
teach-in phase. Switching off when there are only negligible level changes produces no
error.
"
Caution!
During the learning period, fast filling/emptying or turbulent surfaces can result in
switching off and on the phase evaluation. Subsequently observed measurement errors
will disappear as soon as tank levels come back to areas measured by 7500 RTG
previously with activated phase evaluation. If the observed measurement errors are
curetted by dip table entries, the 7500 RTG will take care of these corrections and
automatically adjust the index correction table. Do NOT correct any settings in the basic
calibration or the extended calibration.
Note!
Immediately after installation, the 7500 RTG measures with the specified mm-accuracy.
Until the level range has been completely covered by the medium (setting up the
⇒
E
+ –
⇒
E
+ –
⇒
E +
–