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A radar blind zone is not the only reason a level display stops rising. The transmitter may have reached its usable near limit, its output may have reached the configured upper endpoint, or the PLC may be limiting the displayed percentage. These conditions can look identical on an operator screen but require different corrections.
Locate the plateau in the measurement chain
At a safely established process condition, compare raw distance, local level, transmitted value and PLC indication. Record their units and status. Do not deliberately fill towards the antenna to reproduce a suspected blind-zone problem; use existing trends or an approved low-risk test arrangement.
| Pattern | Where to investigate |
|---|---|
| Distance stops | Check target validity, near-distance restrictions and fixed echoes before changing output scaling. |
| Current stops | If distance remains valid, check the assigned variable, upper endpoint and documented output limit. |
| PLC stops | If the incoming value changes, examine display clamping, conversion and alarm logic in the controller. |
| Status changes | Determine whether the shown number is a current measurement, a substitute or a retained previous value. |
A radar blind zone cannot be removed by relabelling the range
The METRAVON MV-RD12 lists a liquid distance interval of 0.1-30 m. Use the near limit for the exact assembly and installation when checking the highest surface. A software endpoint labelled 100% does not authorise measurement closer to the antenna.
Conversely, a valid distance measurement may continue beyond the level assigned to 20 mA while an analogue receiver displays only its configured span. That does not establish a blind-zone fault. Compare the selected output behaviour with the documented electronics configuration rather than assuming all transmitters extend their current above the upper endpoint in the same way.
Correct the layer that caused the limit
If the mechanical arrangement places the surface too close, review antenna position and usable tank capacity. If only the analogue endpoints are wrong, revise both transmitter and receiver coherently. If the PLC clamps the display, determine why that limit exists before removing it; downstream alarms or volume calculations may rely on the same scale.
After an authorised correction, confirm several known positions below the operating limit. Check that invalid measurement is still visible and that high-level actions use the intended quantity. Record the former and revised settings so a later replacement does not restore the original error.
Questions about a 100% reading
Q1. Does 20 mA mean the vessel is full?
It means the configured output is at that endpoint under the selected operating behaviour. The endpoint may represent a usable process level below the physical roof. Check the assigned variable and scale before interpreting it as remaining capacity.
Q2. Can a negative distance offset recover the upper measuring region?
An offset changes the reported reference; it does not create missing measurement capability. Applying one to hide a near-zone failure can corrupt otherwise valid levels and must not be used as a substitute for an installation correction.
Summary
Find where the value stops changing before altering the range. Send raw distance, local level, output and PLC readings with the MV-RD12 installation dimensions to distinguish a physical limit from a configured display limit.
