A02YYUW False Echo / Ghost Reading Inside 89mm PVC Stilling Well
Siva.Bala Vignesh 2026-06-17 20:42:13 216 Views1 Replies Hi everyone,
First time here.
I'm working on a water tank monitoring project using the A02YYUW waterproof ultrasonic sensor. The sensor is mounted at the top of a vertical PVC stilling well with outer diameter is around 89mm (3.5").
The system is working, but I'm observing a persistent false echo (ghost reading) at around 300mm (~1 foot). The value is stuck there. if I take the sensor out of the stilling pipe and tank, its working. Guess acoustics echo because of wide angle.
A few details:
- Stilling well inner diameter: approx. 87mm - Sensor mounted flush at the top of the pipe - Pipe length: 1.5meter - Ghost reading stuck at: approx. 300mm
What is the minimum(optimal) recommended pipe inner diameter?
Note: If I place the sensor without stilling pipe, the value is still stuck at around 1.5 or 1.8 feet.
I would appreciate any guidance from anyone who has used the A02YYUW in a similar water-level application.
Thank you.
Hello,
This issue is very likely caused by reflections inside the PVC stilling well.
A02YYUW has a relatively wide reference angle, so an 87mm inner diameter pipe is too narrow for a 1.5m measuring path. The ultrasonic wave can easily hit the pipe wall and create false echoes, which may explain the fixed reading around 300mm.
There is no recommended stilling well diameter specified for this sensor, but for this application we do not recommend using such a narrow pipe.
If a stilling well is required, a much larger diameter pipe or a narrower-beam / different type of level sensor would be more suitable.
Yx 
