Why does the 80G short-range radar produce messy echoes and false readings in a small closed metal tank?

Answer: In a small closed metal tank the 80 GHz wave reflects repeatedly between the liquid surface, the metal walls and the lid. The real surface echo gets buried among multipath ghost peaks — in this case a strong interference peak appeared at about 17 cm — so the sensor cannot lock onto the correct echo. Upgrading the sensor to the latest ranging algorithm restores a correct and stable reading.

Symptom

The 80 GHz compact radar distance sensor (model JJY-YGD38M-18L) was installed on a stainless steel tank with a diameter of only 30 cm, and the tank was closed with a lid. The returned echo was very messy with multiple reflections, and a strong interference wave appeared at about 17 cm. The sensor could not read the correct level echo.

Field installation — the radar mounted on the closed 30 cm stainless steel tank:

Echo spectrum returned by the sensor before the fix — several overlapping peaks instead of one clean surface echo:

Root cause

A small, closed, all-metal vessel is a highly reflective environment: the 80 GHz signal bounces between the liquid surface, the cylindrical wall and the lid, producing strong multipath echoes. The true level echo is no longer the strongest peak in the spectrum, and the ranging algorithm locks onto a ghost peak (here at about 17 cm) instead of the real surface.

Solution

Upgrade the sensor to the latest firmware (ranging algorithm). The updated algorithm identifies the true surface echo among the multiple reflections and suppresses the ghost peaks caused by the metal walls and the lid. After the upgrade the sensor returned the correct level reading.

Recommendations for small closed metal tanks

• Mount the antenna centered on the tank roof and perpendicular to the liquid surface; keep the mounting nozzle as short as possible.
• Keep the beam away from the inlet stream, heating jackets and internal fittings.
• If the reading is still unstable, capture the echo spectrum with the upper-computer software and send it to our support team for analysis.

If you meet a similar application, contact our support team with your installation photo and the echo spectrum from the upper-computer software — we will help you select and tune the right radar level transmitter.

Related reading

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