Radar Nozzle Geometry: Diameter, Length and Antenna Position

A radar nozzle is part of the microwave path. Its diameter, length, internal bore, welds and the position of the antenna face determine whether the signal leaves cleanly or interacts with metal before reaching the product. A transmitter that fits the flange can still perform poorly when the antenna is recessed in unsuitable geometry.

Measure the as-built nozzle

Record inside diameter, total length, flange facing, reducer shape, internal welds and any lining. Use the antenna reference plane and process-facing surface from the exact product drawing. Nominal pipe size is not enough because schedules, reducers and liners change the clear bore.

Photograph the opening before installation and note nearby roof steelwork. For replacements, compare the old and new antenna position. An adapter may move the antenna upward even when the bolt pattern remains compatible.

Understand beam clipping and near-field echoes

A long narrow metal passage can reflect energy, narrow the effective path or create a strong fixed echo near the antenna. Check the manufacturer's permitted nozzle combinations for the selected antenna. A smaller beam angle does not automatically make every long nozzle acceptable.

Where required, the antenna face may need to project beyond the nozzle. Confirm projection, process temperature, mechanical protection and maximum level margin. Do not improvise an extension that changes the pressure boundary or invalidates certification.

Check the complete beam path

After the nozzle, map the beam to minimum level and include walls, ladders, coils, agitators and filling streams. For solids, consider pile slope and the point observed during filling and discharge. For liquids, include turbulence, foam and direct inlet impact.

Relocating or enlarging the nozzle is often more reliable than aggressive false-echo suppression. Software should address confirmed fixed interference only; it must not remove the real product target near high level.

Account for temperature and maintenance

Insulation, thermal extensions and condensation can change the effective geometry. Keep cooling sections exposed as specified and prevent water from collecting inside a recess. Ensure maintenance can inspect and clean the antenna without unsafe access or dismantling unrelated pipework.

A smooth nozzle bore helps inspection, but deposits can still form at cold bridges or process splash points. Define an early inspection interval from the actual service rather than assuming the opening remains clean.

Commission with echo evidence

Before applying false-echo mapping, save the raw echo curve and identify peaks by measured distance. Capture curves at low, normal and high level and during filling or agitation. Confirm reference plane, empty distance, blocking distance and output mapping.

The handover record should include nozzle dimensions, antenna projection, photographs, approved drawing and baseline curves. Future replacements can then reproduce proven geometry instead of repeating diagnosis.

Worked replacement example

A new radar is mounted on an existing flange through a reducer. The local display is stable but tracks a point 0.8 m below the flange. Measurement shows the new antenna sits higher inside the reducer than the old unit. The team removes the unsuitable adapter and uses an approved assembly that places the antenna at the required projection.

After correction, the near-field peak falls and the product echo remains continuous through filling. The adapter drawing and reference distance are added to the equipment record so the next replacement does not repeat the fault.

Information required before quotation

Provide a dimensioned nozzle drawing, vessel height, maximum level, internal obstructions, medium, temperature, pressure and photographs. Ask the supplier to state the exact antenna, projection, blocking distance and any unsupported geometry rather than returning only a model family.

Receiving inspection should compare the delivered antenna and adapter with the approved drawing. A substitute connection can recreate the same near-field problem even when the transmitter model and electrical output are unchanged.

Engineering checklist

Measure actual bore, length, reducers, lining and welds.
Use drawings for the exact antenna and reference plane.
Verify permitted nozzle geometry and antenna projection.
Map the full beam path and maximum-level margin.
Keep thermal sections and cleaning access correct.
Save baseline echo curves and as-built photographs.

Frequently asked questions

Can a narrow beam solve any long-nozzle problem?

No. The antenna can still interact with the nozzle before the beam enters the vessel.

Is an adapter harmless if the flange fits?

No. It can change bore, antenna projection, reference plane, dead zone and pressure-boundary approval.

Should the nozzle echo always be suppressed?

Only after it is identified as fixed interference and the full operating range is verified.

Need a project-specific review? Send the vessel drawing, process conditions, installation photographs and acceptance criteria through our contact page. METRAVON can help review the measurement scope before quotation.