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How to measure the amount of liquid water in a thin tube (like a syringe)

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Harm314:
Given that you currently use video monitoring, I would suggest using automated analysis of the footage with computer vision, e.g. using OpenCV. This has the advantage that you already have a testset of data, and that verification of the automated measurement results is straightforward. The suggestion to add food colorant will likely help to make measuring the level easier.

Going forward, you could set up a camera in time lapse or event triggered (bird detected) mode, taking a snapshot before and after a bird visits the setup. I have used a raspberry pi with a camera for a vaguely similar goal (automated readout of a non-electronic counter). For your purpose, compression or averaging of the image along the width of the tube allows to minimize data without losing resolution.

With a camera solution the size of the setup will need to be large enough to minimize parallax effects, depending on the length of the tube, the camera, and the lens used. If you can use an enclosure around the whole measurement part, then optimizing the light source, optics, and camera together to give good contrast of the meniscus should be straightforward.

phil from seattle:
The feeders I am familiar with are closed end, inverted tubes.  The opening at the bottom sits in a shallow pan with the rim maybe 1/4" higher then the bottom of the tube.  The tube is filled with nectar and inverted.  As the hummers lick the nectar, it lowers the level in the pan. As this happens the pressure in the tube decreases. At some point the level of the pan gets low enough, a bubble of air enters and a small amount of nectar escapes into the pan and the the cycle repeats.

So the idea is that the pressure of the air in the top of the tube drops as the birds feed and then rapidly increases when a "bubble" event happens.  I don't know if the differential is significant enough to measure easily but if possible it you would be able to track pressure drops as a function of feeding.  You would need to correlate the pressure drop to amount of nectar removed.  It is also probably a function of how much head space you have in the tube so calibration is tricky.

nfmax:
If you can make the tube out of metal, mounted with its axis vertical, then it should be possible to use the cylindrical air space above the meniscus as the frequency-determining element of a microwave oscillator. Even tiny changes in frequency, caused by lowering of the meniscus as sugar solution is withdrawn from the feeder, should be measurable with a decent microwave frequency counter. You can use a coax cable to feed the signal back from the feeder to the counter, inside your lab.

If you take this approach it may be worthwhile making the tube larger, which will reduce the resonant frequency somewhat so as to lower the cable losses and/or cost.

SilverSolder:

--- Quote from: drcubes on June 18, 2020, 02:47:35 am ---[...]

- Digital scale: I have done very little on this front so far but I have a beam-shaped load cell with strain gauges on it and a strain gauge amplifier. No tests with this but my primary concerns are that the gauge will not have high enough resolution to detect the amount of liquid change from a single feeding. ( < 1 gram change per feeding event)

[...]
 

--- End quote ---

I would say this might be one of the more promising ideas.  I have a cheap Chinese scale in the lab that measures to 0.01g that I would definitely trust to 0.1g accuracy.  It is definitely a viable method of measuring sub - 1g quantities of H2O.

You could buy one of those and hack it, or re-use its parts to build your own...  it will likely be cheaper than trying to buy the parts separately!

E.g. https://www.amazon.com/MVZAWINO-Precision-Portable-Electronic-Stainless/dp/B07CL1HD8K/

Mechatrommer:
cheap jeweller's scale can measure 0.01g, you can reuse the hardware into your ADC/digital FW to tune to your specific need or you can even further reduce the resolution to like 1mg using lever mechanism, how much resolution do you need? i have one of this jeweller's scale and the reading changes significantly with just slight of air blow or breath, so you have to put it inside a chamber or still air to get stable/repeatable reading.

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