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Tank level units can stay unchanged on a display while a range revision changes the physical meaning of every percentage. Before editing a span, identify what 0% and 100% represent, where the conversion occurs and which alarms or records depend on it. Changing a label is not the same as preserving a measurement definition.
A percentage needs two endpoints
For a linear level percentage, level = level at 0% + (percentage / 100) x (level at 100% - level at 0%). Both endpoints use the same physical datum and unit. An instruction saying only "scale to tank height" omits the lower endpoint and may also confuse the instrument reference with the tank zero.
| Defined level interval | 50% represents | Interpretation |
|---|---|---|
| 0 to 8 m | 4 m | Halfway through this zero-based level span. |
| 0 to 10 m | 5 m | The same percentage now represents a different physical level. |
| 2 to 10 m | 6 m | The nonzero lower endpoint is included: 2 + 0.5 x (10 - 2). |
These are arithmetic examples, not METRAVON range or accuracy tests. Confirm whether the received variable is level or sensor-to-surface distance, and whether the configured direction is increasing or decreasing with liquid level. Correct arithmetic applied to the wrong variable still gives the wrong result.
Tank level units must identify the quantity
Fifty percent of a selected height interval is not automatically half the vessel's usable volume. A horizontal cylinder or a tank with shaped ends has a nonlinear level-to-volume relationship. A percentage may instead refer to a defined volume range; that is a different variable and needs its own stated calculation.
Keep distance, level, volume and mass distinct in tag names and exports. Converting metres to millimetres changes the unit but not the physical quantity. Converting level to volume requires the vessel geometry or tank table. Converting volume to a mass estimate also requires a defensible density basis. None of these meanings can be established from the word "percent" alone.
Record the MV-RD12 signal before editing the receiver
The METRAVON MV-RD12 uses radar distance measurement for liquid-level applications. Ask which variable the selected electronics will actually provide and how the receiving system should interpret it. Do not assume every ordered version supplies a volume result or a particular set of digital variables.
Write down the chain from instrument output to PLC, display, historian and exported report. Assign each conversion to one identified system. If the transmitter and PLC both apply an offset or a unit multiplier, an apparently familiar label can conceal a double conversion. A correction on the local HMI does not automatically update the archived or exported value.
| Record item | Information to keep | Check during a revision |
|---|---|---|
| Measured variable | Distance, level, percentage or an explicitly calculated quantity | Confirm that the receiver still reads the intended variable. |
| Range | Both endpoints, direction, units and configuration revision | Compare the transmitter and each receiving conversion. |
| Physical reference | Datum, reference plane and any approved offset | Identify whether mounting or geometry changed as well as scaling. |
| Effective period | The time the revised definition entered service | Apply the appropriate definition to historical and current observations. |
Keep old percentages tied to the old range
Save the accepted settings and the original records before making a revision. A historical 50% sample belongs to the range in effect when it was acquired, not whatever range the dashboard uses today. Retain a physical level or distance where the system provides it, together with the metadata needed to interpret that value.
If only percentage was archived, reconstructing level requires the applicable endpoints, variable and datum. Where that information is missing, mark the limitation. A new range is not evidence of what the old one was, and smoothing a discontinuity does not recover the missing definition.
When a range change accompanies new hardware, the sensor-changeover and historical-data guide covers the separate before-and-after reference and handover tests. Keep the reason for a scaling revision distinct from a correction to an earlier measurement error.
Check the dependent functions before release
List the alarm thresholds, trends, totals and exports that consume the revised value. Compare several safely available known conditions with the expected engineering values and verify their units downstream. Include points relevant to the operating alarms, rather than checking only that a midpoint looks plausible.
An electrical or software simulation can test the receiving conversion from its injection point onward. It does not establish the radar's actual measurement of the liquid. Label simulated observations, remove temporary overrides through the site's release process, and retain the as-left configuration with its effective time.
Questions when a range changes
Q1. Should old percentages be recalculated automatically?
Only under a documented correction with a valid physical basis and the original definitions available. Preserve the original series and identify the corrected series, method and applicable period. If the old range is unknown, do not invent a precise level history from the percentage alone.
Q2. Can departments display different units?
Yes, if each display uses an explicit conversion from the same defined quantity and revision. Check exported files as well as screens. A level percentage, observed volume and temperature-corrected volume should not share an ambiguous label that hides their different meanings.
Q3. Can the old alarm numbers remain after the span changes?
Only after tracing what those numbers represent in the receiving logic. An alarm expressed in physical level may remain the intended requirement while its raw input conversion needs updating. A threshold stored as percentage may now correspond to a different height. Verify the physical alarm condition and the control interpretation before approving the revision.
Summary
Specify the quantity, endpoints, conversion owner and effective revision together. Send those details with the receiving-system requirements in an MV-RD12 integration enquiry. Controlled range definitions make the current display useful without silently changing the meaning of earlier tank records.
