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Compare types of liquid level sensors by the boundary the process needs to measure. The top of a liquid, a foam layer, an interface between liquids and a high-level presence signal are different targets. A device that measures one cannot be assumed to report the others.
Write the target on the vessel section
Mark the expected layers, the inlet and the lowest and highest required positions. Include whether the contents mix, settle or change composition. A product described only as tank level leaves the supplier to guess which boundary the controller should track.
| Target | Required evidence | Avoid assuming |
|---|---|---|
| Upper surface | A usable response from the intended surface throughout operation. | Assuming every visible or reflective layer is the desired liquid boundary. |
| Liquid interface | Explicit model capability and suitability for the actual layer properties. | Assuming that every guided probe measures two liquids separately. |
| Point presence | Repeatable covered and clear states at the selected location. | Treating a switch output as a continuous height or tank volume. |
Types of liquid level sensors within the METRAVON range
MV-RD12 uses free-space radar for liquid measurement. MV-RD701 uses a rod or cable in contact with the contents. Neither description alone establishes interface measurement for an oil-water mixture or guaranteed performance through a foam layer.
For a presence check, MV-SP601 is an RF admittance point-switch option. Specify which material should activate it and what residue remains afterward. Its probe length places the sensing region; it does not produce a continuous level profile.
Separate direct measurement from calculated quantities
Level can be converted to volume using an appropriate vessel relationship. Mass also depends on density, which may vary with composition or temperature. Do not describe a level reading as measured mass merely because the controller can display kilograms.
When the real requirement is usable inventory, define whether foam, sediment or an unusable heel is included. The same geometric level can correspond to different usable contents. Record the assumptions in the conversion and test them against the process rather than adding an unexplained correction factor.
Q1. Should a contact probe be chosen whenever foam exists?
No. Examine the material properties, probe coating and required target. Contact installation introduces its own mechanical and maintenance constraints. A representative application assessment is needed before choosing between probe and free-space arrangements.
Q2. Can one instrument provide continuous level and an alarm?
A controller may derive an alarm from a continuous value if the system supports that function. That does not make the alarm independent of the same instrument's failures. Specify any separate protective requirement explicitly.
Summary
Send a vessel sketch showing the target surface or layer for a liquid-level technology review. A clear definition of what must be measured is more useful than a long list of sensor principles.
