Phase measurement using IR

Hello!

I'm new to the forum. I'm working on a project where I would like to measure liquid level (water to start with) in a glass container without contacting water. The container can have any kind of cap (including white IR reflecting material). I am looking to detect the liquid level from the bottom with accuracy of level measurement of up to 5mm, and range of liquid level from 5mm to 200mm. The minimum distance between the sensor and lowest water level would be 6-7mm. I read on this forum that IR with phase measurement could be used but I am looking for some additional information on how to practically implement it. I would be building and driving this from Raspberry Pi.

Thanks for all the help!

experimenter said:

Hello!

I'm new to the forum. I'm working on a project where I would like to measure liquid level (water to start with) in a glass container without contacting water. The container can have any kind of cap (including white IR reflecting material). I am looking to detect the liquid level from the bottom with accuracy of level measurement of up to 5mm, and range of liquid level from 5mm to 200mm. The minimum distance between the sensor and lowest water level would be 6-7mm. I read on this forum that IR with phase measurement could be used but I am looking for some additional information on how to practically implement it. I would be building and driving this from Raspberry Pi.

Thanks for all the help!

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I have used an IR sensor to detect water level in a capillary tube. By locating an IR emitter on one side of the tube and a photodiode on the other I found an abrupt change in light loss. This I used to indicate the water level passing a mark. To my surprise, the light loss through the air/water meniscus diminished. The change was used to indicate water level passing a mark with 0.1 mm accuracy.

If not possible to use the capillary tube but directly to detect air/water boundary through a bottle wall, you will have to experiment with IR sensor arrangement to obtain a reliable sensor response.

Other level sensors used in large tanks utilize microwave beam or ultrasound but have to be located above liquid level and operate as a radar system.
For smaller volumes like bottles you can use a weighing sensor to define liquid volume in a known bottle volume.

There is not a lot to go on in the question and some ambiguity. For example, does, "The container can have any kind of cap (including white IR reflecting material)," mean that the container(s) with which you will be confronted may have different kinds of caps over which you have no control, or do you mean you can specify the type of cap used? Also, I am presuming that what is not water in the vessel is air. Do you have to use IR? Why? What wavelength? Are the container and water both transparent to that wavelength?

Reflected light from the cap can be used to estimate water level, because the refractive index of water is so much greater than air. Thus, the light is slowed in passing through the water. As a reference, I have measured the water level in a bucket using reflected light (not IR) and a time of flight device. However, I am skeptical you can meet the specifications you give without some quite expensive equipment and/or other operating restrictions.

John