How to Install Radar in a Stilling Well

Back to Blog

Size and Prepare the Pipe

The pipe is part of the antenna, so its bore and its inner surface matter. Use a diameter the transmitter is rated to work in, because too large a pipe lets unwanted wave modes propagate and too small a pipe attenuates the signal. Keep the inside smooth and continuous: weld beads, diameter steps at flange joints, and rough deposits all scatter the microwave and create false echoes that the transmitter can mistake for the surface. A drawn or honed pipe with ground internal welds gives the cleanest signal.

Provide the holes the pipe needs to function. Vent holes at the top let vapour escape so the level inside is not held up by trapped gas, and equalization holes or slots let liquid pass freely so the level in the pipe tracks the vessel. Orient any slots away from the beam path and keep them consistent, because a hole passing through the beam is itself a small reflector. The still pipe is a cousin of the guide pole or stilling well used in tank gauging, and the same signal-integrity thinking applies.

Mount the Antenna to the Pipe

Mount the transmitter so the antenna is centered on the pipe axis and flush with, or correctly recessed into, the pipe entrance per the transmitter's requirement, because an off-center or tilted antenna launches the wave crookedly and degrades the return. Alignment inside a pipe is more forgiving than in open air for beam spreading, but the coupling into the pipe still depends on a clean, square, concentric mount. Use the manufacturer's still-pipe flange or adapter rather than improvising, since it sets the antenna position the configuration assumes.

Confirm the pipe runs straight and vertical for the full measuring range, with no dents or ovality, because the wave reflects along the whole length. A radar in a pipe is fundamentally the same instrument as any radar level transmitter; the pipe just constrains where the energy goes. The still pipe also imposes a near-field limit at the top, the same idea as the open-air blocking distance, so keep the maximum level below where the pipe entry region confuses the echo.

Configure Still-Pipe Mode and the Pipe Correction

The setting that catches people is propagation speed. Inside a pipe the microwave travels slightly slower than in free space, and the slowdown depends on the pipe inner diameter and the wave mode, so the transmitter reads a distance that is too long unless it is corrected. Enable the still-pipe or waveguide mode in the transmitter and enter the pipe inner diameter accurately, and the firmware applies the correction so the measured distance matches reality. Skipping this makes the level read consistently off in a way no zero adjustment fixes cleanly.

Set the reference distance and the empty and full calibration points as you would for any radar, mapping the near echo to full and the far echo to empty. Because the pipe suppresses agitation and shields the beam, you generally need less false-echo mapping than in an open vessel, but still run a false-echo scan on the empty pipe to record fixed reflections from vent holes and joints. The dielectric handling matters too: a low-dielectric hydrocarbon returns a weaker echo, so confirm the medium setting matches the liquid.

Verify the Reading in the Pipe

Verify against an independent measurement, since the pipe correction is exactly the kind of setting that is easy to get wrong and hard to notice. Compare the radar level against a hand dip through a gauge hatch or against a separate level device at a stable level. A reading that is consistently long or short by a fixed fraction is the classic symptom of a missing or wrong pipe-diameter correction, so recheck the still-pipe mode entry before anything else.

Check the echo quality too, not just the number. A healthy still-pipe installation shows a strong, clean surface echo with the fixed reflections from holes and joints sitting well below it after mapping. If the surface echo is weak or the transmitter hunts between echoes, the pipe may be fouled, the antenna coupling poor, or the dielectric setting wrong. When the level feeds a monitoring history, a slowly weakening echo or a creeping bias against periodic dips flags a fouling pipe before the reading fails outright.

Avoid the Common Mistakes

The most common error is forgetting the pipe-diameter propagation correction, which leaves the level reading a fixed amount long and tempts a wrong re-zero. Next is a rough or stepped pipe interior, from ungrounded welds or a mismatched flange bore, that scatters the signal into false echoes. Missing or wrongly placed vent and equalization holes make the level in the pipe lag or trap gas, so the pipe and vessel disagree. And building deposits inside the pipe slowly narrow the bore and change the correction.

Because a still pipe hides its own fouling, the reading can degrade quietly. Trending the level and, where the transmitter reports it, the echo strength lets a monitoring platform reveal a slowly fouling pipe as a gradual bias or a weakening return, well before the radar loses lock. The trend flags the drift; a hand dip and a look inside the pipe confirm whether it is deposits, a gas-phase change, or a configuration that was wrong from commissioning.

Frequently Asked Questions