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A separator may need two different measurements: the height of the upper liquid surface and the position of the boundary between liquids. A transmitter reporting the first does not necessarily report the second. Radar liquid interface measurement must be specified as its own duty before selecting the instrument or assigning a control signal.
Write down the quantity the valve needs
| Required quantity | What the measurement must distinguish |
|---|---|
| Total level | The upper surface relative to the vessel reference. |
| Interface level | The boundary between the upper and lower liquid phases. |
| Layer thickness | The separation between two identified boundaries, not simply one surface reading. |
For example, a drain controlling the lower phase cannot rely on total level alone. The vessel may retain a similar overall liquid height while the proportions change. Assigning the wrong quantity to that controller creates an application error that a more precise surface measurement will not correct.
Radar liquid interface measurement requires suitable instrument functions
Some guided-wave instruments evaluate returns from both a liquid surface and an underlying interface. That capability depends on the instrument design and the phases being measured; it is not a property of every rod or cable probe. Ask how the proposed unit distinguishes the required boundary and which operating conditions invalidate the result.
Provide the identity and expected composition of both phases, temperature range, contamination and mixing behaviour. If an emulsion layer forms, define what the process considers the interface and how the reference measurement will represent it. Do not specify a sharp-boundary acceptance test for a process that has no repeatable sharp boundary.
Confirm the model and measured boundary
METRAVON MV-RD703 uses a dual-cable guided-wave probe and is listed for separately assessed interface duties. Suitability for a particular oil-water mixture still needs confirmation. Provide both phases, dielectric information where available, upper-layer thickness, emulsion behaviour and required output variables before requesting the ordered configuration.
The MV-RD12 product information supports a non-contact liquid-level assessment. It does not establish an oil-water interface function.
The MV-RD701 is a guided-wave model with rod and cable arrangements. Those construction details also do not, by themselves, confirm interface detection, multiple simultaneous outputs or an emulsion-handling function. Obtain explicit documentation before naming it in an interface purchase specification.
Agree how separate measurements reach the control system
If total level and interface level are both required, identify each variable and its receiving channel. A single analogue output should not be assumed to carry two independent quantities. For a digital arrangement, confirm the documented variable map and invalid-reading behaviour rather than inferring it from an RS485 connection.
Q1. Does changing the scale convert a surface sensor into an interface sensor?
No. Scaling changes the interpretation of a measured variable; it does not create detection of a second boundary. First establish that the instrument measures the required interface.
Q2. What should an interface trial prove?
Compare the required variable with an agreed independent reference while the phase proportions change. Include the compositions and mixing states expected in service, and document any condition in which the boundary cannot be resolved.
Summary
Specify the phase boundary, output and acceptance reference before choosing a model. Submit the separator duty and phase information for an MV-RD703 interface-duty review. The proposal must identify the ordered probe and electronics, required variables and unresolved trial conditions; a general level specification is not interface approval.
