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A high-level setpoint below the radar dead zone can still leave too little room if liquid continues entering after the stop command. Valve travel, pump rundown and liquid already in the inlet line can consume the remaining space. Review the final level, not only the level at which the alarm changes state.
Separate three distances on the drawing
Mark the radar reference plane, the highest permitted liquid surface and the closest surface that the selected instrument can measure under the installation conditions. The top of a nozzle is not automatically the measurement datum. A mounting change alters these distances even when the tank's nominal capacity stays unchanged.
The METRAVON MV-RD12 lists a 0.1-30 m liquid measuring interval. That catalogue interval is a selection input, not approval to place a protective setpoint at its lower endpoint. Confirm the actual connection, near-range behaviour and required operating reserve for the installed arrangement.
A radar dead zone calculation does not establish stopping performance
Consider a hypothetical vertical tank with a constant horizontal area of 5 m2. An assumed inlet rate of 0.02 m3/s continuing for 15 seconds adds 0.30 m3, raising the surface by 0.06 m. These are example inputs, not METRAVON specifications. The 15-second interval in this example begins at the stop command; it is not an MV-RD12 update or response-time specification. Earlier measurement and controller-decision delays, flow outside that interval and uncertainty need separate assessment. Do not count the same inflow or valve-travel period twice.
If the tank's area changes with height, calculate the rise from its geometry instead of dividing by one constant area. Test or otherwise substantiate the actual stopping sequence. A software command time alone does not tell you when material stops arriving.
| Contribution | Evidence to obtain |
|---|---|
| Detection | Measurement update, configured filtering and the controller's processing behaviour. |
| Shutdown | Actual valve or pump response under the intended operating conditions. |
| Residual inflow | Material that continues to enter after the final element changes state. |
| Remaining space | Surveyed geometry and the permissible maximum level, with the project's uncertainty allowance. |
What to change when the reserve is insufficient
The responsible design team may need an earlier operating stop, a lower filling rate, a different mounting arrangement or a different protection design. Increasing a display span does not create more measurable free space. Nor does suppressing a near-range echo prove that a rising surface will remain detectable.
Keep normal level control separate from any required independent overfill protection. Neither the listed distance range nor this inflow calculation demonstrates the performance of a complete shutdown function. Have the responsible project team define and verify any required independent protection.
Q1. Can a longer nozzle solve a near-range problem?
It changes the reference distance but may introduce nozzle echoes or obstruct the antenna. Submit the revised bore, length and antenna position for review rather than assuming the added height is usable range.
Q2. Should the high-level limit simply equal the maximum calibrated level?
No. Calibration endpoints define signal scaling. An operating limit must also account for measurement capability, process response and the permitted final level.
Summary
Check where the surface ends up after filling is stopped. Provide the tank section, inlet rate and stopping sequence with the MV-RD12 enquiry so the near-range requirement is explicit.
