Electronics > Projects, Designs, and Technical Stuff
How to measure the amount of liquid water in a thin tube (like a syringe)
ogden:
Introduce some small intermediate reservoir with level sensor, then use miniature (peristaltic?) pump to fill it.
jogri:
Use a low power laser to shine through the pipette with a photodiode on the other side. Water and air will let the light pass, but the meniscus will mess with the reflection->drop in intensity right when the laser is at the same level as the meniscus. Take a peristaltic pump with a servo motor (you can scavenge an old HPLC instruments, they have accurate peristaltic pumps) and then just measure how many rotations of the servo motor/pump it takes to fill the pipette up after each hummingbird. Then just calculate the amount of liquid from the degrees of rotation it took.
Edit: I tested the laser/meniscus approach with 8mm test tubes, works like a treat (so it should also work with your 4mm ones, even with a crappy laser diode).
TheMG:
Another alternative would be a TDR (time domain reflectometer) level sensor. I don't know if any of the commercially made units would be small or accurate enough for your use case but with some effort it would be possible to roll your own.
drcubes:
--- Quote from: jogri on June 18, 2020, 04:55:09 pm ---Use a low power laser to shine through the pipette with a photodiode on the other side. Water and air will let the light pass, but the meniscus will mess with the reflection->drop in intensity right when the laser is at the same level as the meniscus. Take a peristaltic pump with a servo motor (you can scavenge an old HPLC instruments, they have accurate peristaltic pumps) and then just measure how many rotations of the servo motor/pump it takes to fill the pipette up after each hummingbird. Then just calculate the amount of liquid from the degrees of rotation it took.
Edit: I tested the laser/meniscus approach with 8mm test tubes, works like a treat (so it should also work with your 4mm ones, even with a crappy laser diode).
--- End quote ---
That's good to hear that it worked for you! Can I ask, what kind of photodiode did you use? And what power and wavelength of laser did you use?
jogri:
--- Quote from: drcubes on June 18, 2020, 06:11:27 pm ---That's good to hear that it worked for you! Can I ask, what kind of photodiode did you use? And what power and wavelength of laser did you use?
--- End quote ---
Sorry to disappoint you, but it was just a quick-and-dirty proof of concept. I moved a test tube filled with water in front of a laser pointer... The laser is right at the meniscus in the picture, as you can see the intensity drops quite a bit at this point.
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