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A radar level transmitter measures a distance to an interpreted reflection. The displayed level and the value in a PLC are derived from that measurement using configured references and scaling. When two displays disagree, trace those transformations before adjusting the radar's sensing settings.
From the antenna reference to liquid level
METRAVON MV-RD12 uses free-space radar for liquid measurement. The antenna sends electromagnetic energy toward the contents, and the electronics evaluate returned signals to estimate the target distance. Nozzle reflections and other structures must be distinguished from the intended surface.
For a vertical installation with a reference height H above the chosen zero, level h is H minus measured distance d. All three values must use the same units and reference convention. A change to bracket or nozzle geometry can therefore alter the level calculation without any fault in the distance measurement.
A radar level transmitter example with explicit assumptions
Consider an illustrative tank configuration with H = 10 m and d = 6 m. The calculated level is 4 m. If the selected analogue output is configured as 4-20 mA for 0-8 m of level, that level corresponds to 12 mA. These are example settings and calculations, not a prescribed MV-RD12 range or a field test result.
| Stage | Example result | What to check |
|---|---|---|
| Distance | 6 m from the configured reference. | The selected echo and physical reference are correct. |
| Level | 10 m minus 6 m gives 4 m. | The empty-reference height and units match the installation. |
| Loop | 4 m is halfway across the example 0-8 m span, giving 12 mA. | The PLC uses the same lower and upper level values. |
If the PLC instead interprets 4-20 mA as 0-10 m, it displays 5 m at 12 mA. In that example the error is scaling, not a 1 m error in radar distance. Verify the actual configuration before applying this diagnostic reasoning.
Digital communication still needs an interpretation
An RS485/Modbus connection removes the analogue conversion at that interface, but units, scaling, data type and register meaning still matter. Request the map for the selected electronics. A register containing distance must not be treated as level simply because both are expressed in metres.
Q1. Can echo filtering fix an incorrect PLC span?
No. It changes the measurement behaviour rather than the downstream conversion. Compare local distance, local level, output and PLC result to find the first stage that disagrees.
Q2. Does a plausible number prove the measurement is current?
No. Check the documented measurement status and communication behaviour. Define how the system distinguishes an updated valid result from a retained, missing or unsuitable observation.
Summary
Send the reference dimensions and signal configuration for a radar loop review. Keep the physical distance, calculated level and receiving-system interpretation visible in the commissioning record.
