Proximity Sensor for Clear Liquid

[davidschlender]

I'm looking for a proximity sensor that needs to precisely measure fluid level in a tank (to the nearest millimeter or better), (within 0mm to 50mm), but the fluid may be clear in color. I don't believe IR sensors would work because the fluid would be transmissive. Ultrasonic wouldn't work because they aren't precise enough (to the nearest cm) and generally work at medium distances (1-2 meters). Am I wrong about the IR sensors? Would they work or is there something better to use?

[adafruit_support_bill]

Ultrasonic wouldn't work because they aren't precise enough (to the nearest cm) and generally work at medium distances (1-2 meters)

Ultrasonics are my usual go-to-sensors for liquid level sensing and the Maxbotix HR series ultrasonics have a 1mm resolution: https://www.adafruit.com/product/1343
The catch is the minimum distance - 30cm. Your vessel would need to have enough headroom to mount the sensor at least 30cm from the maximum fill level.

I don't believe IR sensors would work because the fluid would be transmissive.

But you might get enough specular reflection from the surface for the IR to work. Especially in an enclosed tank which would block out any ambient IR interference from other sources.

The VL6180X works in the 0-100mm range. It has resolution to 1mm, but you will need to carefully control the temperature and supply voltage to limit the drift and preserve accuracy.
https://www.adafruit.com/product/3316
https://cdn-learn.adafruit.com/assets/a ... asheet.pdf

[davidschlender]

Bill, I think the IR solution would be better than the ultrasonic solution. It's for a level sensor on a resin 3D printer, so the available distance from the top of the tank is very limited, and to avoid interference from the build plate, it would need to be able to measure the fluid level near the edge of the basin. I need to measure from a distance of ~10mm to ~50mm with preferably a resolution better than 1mm. Perhaps a capacitive sensor would work over the fluid, but I believe that would only work as a threshold reading (true/false) rather than a continuous value?

[adafruit_support_bill]

Analog Devices has a white-paper on capacitive level sensing here: https://www.analog.com/en/analog-dialog ... -cdcs.html
But it doesn't look like an off-the-shelf solution. Given your constraints, the IR solution is probably worth investigating.