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26 GHz radar level meters can behave differently near the bottom of a liquid tank than at mid-level. If the indication drops to empty while liquid remains, do not immediately reset the zero. The instrument may be following a bottom reflection, losing the liquid return, or reporting a correctly measured distance through an incorrect level calculation.
Compare the last part of draining with filling
Record the raw distance, displayed level and available echo information while the surface passes through the troublesome interval under an approved operating procedure. Mark whether the tank is filling or draining. A change that repeats at the same low height deserves a different investigation from a constant error across the entire span.
Weakly reflecting liquids can allow energy to reach a strongly reflecting tank bottom. Whether that causes an incorrect reading depends on the liquid, depth, geometry and instrument processing. It is a possible mechanism to investigate, not a statement that every 26 GHz instrument fails on oils or solvents.
26 GHz radar level meters need a defined low operating limit
The METRAVON MV-RD902 is a liquid radar with a listed distance interval of 0.3-30 m and several horn sizes. The far-distance value does not prove that the smallest remaining liquid layer can be distinguished from a tank floor. Identify the lowest level needed for the process and how that level will be checked.
| Finding | Next check |
|---|---|
| Early empty | Compare selected distance with the floor position and the independently known liquid surface. |
| Fixed offset | Review the antenna reference and level zero across several stable positions. |
| Host only | If local distance is correct, inspect PLC scaling, clamping and the assigned output variable. |
| Brief loss | Record validity status and the controller's handling of missing measurement during discharge. |
A low-level test should match the actual liquid
A water check may verify geometry and signal transfer without representing the reflectivity of the process liquid. Use a safe, approved reference appropriate to the actual service. Do not open a pressurised or hazardous vessel to obtain an informal dip measurement.
Retain the echo evidence before adjusting tank-shape parameters or suppression. An arbitrary offset may make one point agree while spoiling the rest of the range. Suppressing a bottom-region return without knowing the true surface can also remove useful measurement near empty. Obtain the procedure for the supplied firmware and antenna.
Where the required low point cannot be demonstrated, record the unresolved operating interval. Pump protection or residual-inventory decisions must not silently depend on an unverified value. The remedy may involve a different installation or measurement arrangement rather than another display adjustment.
Questions near empty
Q1. Does zero on the display prove the tank is physically empty?
No. Zero may be a configured process datum or a clamped output. Check the raw distance and the definition of zero before treating the indication as evidence of an empty vessel.
Q2. Will changing to a higher frequency necessarily fix the problem?
No. Compare the proposed antenna and demonstrated low-level behaviour in the actual liquid. Frequency is only one design characteristic; a replacement still needs an installation review and a relevant trial.
Summary
Investigate the low-level transition before modifying offsets or declaring the transmitter defective. Provide the liquid specification, bottom geometry and distance trend with an MV-RD902 enquiry or support request.
