Instruction manual

Varec, Inc. 55

7532 Radar Tank Gauge

7.5 Mounting Calibration with VU331

Function group “mounting calibr.” (03)

Function “tank gauging” (030)

Using this function, 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, and 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

walls, as soon as the conical radar beam strikes the basin wall. The 7500 series RTGs

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 series 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 the radar system when there are only negligible level changes produces no

error.

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