Narrow Pipe & Silo Radar Level Guide

Some installations defeat a default radar config: dusty grain silos, narrow threaded pipes, small closed metal tanks, and very short ranges. This guide collects the field-proven fixes for these difficult tanks and special applications on our 80GHz FMCW radar level transmitters (wired and 4G models, accuracy down to ±1 mm on wired units, IP68 housing).

For general echo/ signal faults start with the echo & signal diagnosis guide; for wiring, 4–20 mA and RS485 setup see the installation & wiring guide.

Grain & bulk solidsNarrow pipe / M38Small closed metal tanksShort-range error codes

Grain / bulk-solid silo tuning

Bulk solids such as soybeans scatter the radar signal, so with default parameters the surface echo is misidentified and the height reads inaccurate. On a grain silo with the JJY-YLD128HS-1.5, proven tuning is to raise the threshold/ sensitivity for dusty surfaces and, where needed, enable surface-tracking that tolerates the angle of repose. Case study: inaccurate grain-silo level and the parameters that fix it.

Narrow pipe / M38 threaded mounting

In a narrow pipe the beam must stay centred on the surface. If the M38 radar is mounted off-centre or tilted, part of the beam hits the pipe wall and the sensor locks onto the wall echo (about 1105–1106 mm) instead of the true level (~510 mm). Centre and plumb the antenna, and use the smallest feasible antenna/ window for the pipe bore. Worked example: M38 false reading inside a narrow pipe.

Small closed metal tank — multipath

In a small closed metal tank the 80GHz wave reflects repeatedly between the liquid surface, the metal walls and the lid, burying the real surface echo among multipath ghost peaks. Mitigate with a shorter blind zone where possible, narrow the window so the beam cannot see the side wall, and enable spurious-echo learning for the fixed internal reflections. Diagnosis: messy echoes in a small closed metal tank.

Short-range measurement errors & error codes

Very short ranges (tens of centimetres) stress the near-field behaviour. A short-range 80G unit that reads the wrong distance and throws error codes usually needs the correct near-field setup and a clear window in front of the antenna; lifting the sensor away from the target changes the geometry and hides the real fault. Model-specific case: short-range wrong distance and error codes.

Frequently asked questions

My grain reading wanders — is the sensor bad?

Usually no. Bulk solids scatter the signal; tune the surface-tracking and sensitivity for dusty solids first.

Why does my narrow-pipe reading lock onto a fixed value?

The beam is hitting the pipe wall because the antenna is off-centre or tilted. Centre and plumb it.

Small metal tank gives ghost peaks — can software fix it?

Partly. Enable spurious-echo learning for the fixed reflections and narrow the window so the side wall is out of view; physical geometry still matters.

Why does the short-range 80G radar read the wrong distance and throw error codes?

Model: JJY-YGD38M-18L — 80 GHz short-range radar level transmitter

Symptom

The customer needed the radar to measure correctly at an actual distance of about 0.12 m. With the radar lifted away from the target the reading was about 0.25 m, and in some cases an abnormal error code was output. During testing, even after lifting the sensor the reported distance was still around 0.11 m — far from the real value.

Root cause

In this very short measuring range the true surface echo competes with antenna and tank-wall spurious echoes. Without proper false-echo learning the unit locked onto a wrong echo.

Fix

Upgrade the firmware to the 0901 build and perform false-echo learning. After that the unit met the customer’s requirement; the remaining units are being upgraded and re-tested.

False-echo learning commands:

AT+FALSEECHO=2,0.12,0.18 — learn false echoes in the range 0.12–0.18 m (effective suppression).
AT+FALSEECHO=1 — enable false-echo learning.
AT+FALSEECHO=0 — disable false-echo learning.
AT+FALSEECHO=3 — clear the learned false echoes.
AT+FALSEECHO=2,a,b — learn false echoes in the distance range [a, b].

Also check and adjust the installation position.

Why does the M38 threaded radar read 1105 mm when the actual level is 510 mm inside a narrow pipe?

Answer: The radar was mounted off-center (or tilted) in the 108 mm pipe, so part of the beam hit the pipe wall and the sensor locked onto the wall echo — about 1105–1106 mm — instead of the true 500–510 mm level. Adjusting the installation position so the antenna sits centered in the pipe and perpendicular to the liquid surface fixes the reading.

Symptom

The M38 thread radar level transmitter (38 mm body, model JJY-YLD128D-W-32) was mounted on a pipe with a diameter of 108 mm. When the actual level was around 500 mm, the output jumped around and read about 1106 mm. With the true distance at about 510 mm, the sensor reported 1105 mm. Aimed at open ground the same unit read normally, which confirmed that the beam was hitting the pipe wall.

Field installation photos — the M38 transmitter mounted on the pipe:

M38 thread radar level transmitter installed on a 108 mm pipe

M38 radar transmitter mounted on top of a stainless steel pipe above the liquid

Echo spectrum at the moment of the fault — the sensor reported a false distance of 1.1056 m:

Echo spectrum showing the false 1.1056 m reading of the M38 radar inside the 108 mm pipe

Root cause

In a narrow 108 mm pipe, an off-center or tilted antenna lets part of the beam cone reach the pipe wall. The wall returns a strong echo from a longer path, so the radar locks onto the wall instead of the liquid surface. The output therefore shows a much longer and unstable distance, and it jumps whenever the beam footprint touches the wall.

Solution

Install the antenna in the center of the pipe so the whole beam stays inside the pipe diameter.
Keep the antenna axis perpendicular (90°) to the liquid surface — do not tilt the transmitter.
Avoid positions where the beam grazes the pipe wall, weld seams or internal fittings; shorten the mounting nozzle if one is used.

After the installation position was corrected, the readings became stable and matched the actual level.

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.

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.