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I'm trying to figure out how to get an automated measurement of a trickle of water over time. (Application is measuring the water output by a dehumidifier; overall output would be a few pints of water per hour.)

Most automated tools for measuring water quantities are for full pipes and/or MUCH higher flow rates. For this type of super-low flow, it looks to my eyes like a tipping bucket sensor would be suited to the job. But the tipping bucket sensor isn't quite ideal for my needs. Specifically, the tipping bucket just dumps out the water after the measurement. I can't just allow the exiting water to dump anywhere because that would encourage mold, so that means I'd need to enclose the tipping bucket in a canister which routes the post-measurement water to a drain.

Currently this dehumidifier output is routed through a nice 1/2" PVC pipe to get the condensate to its proper drain. So, hook up a big canister, which has a tipping bucket inside of it, then routes the spilled water to an internal drain and back to the 1/2" PVC seems like a really clumsy solution. Is there a more elegant way to make this measurement in an automated fashion?

EDIT A few other requirements I should have thought to state up front:

  • Reasonable cost (willing to spend up to USD$100 or so on this)
  • Was hoping to find a prefabricated solution (for example something like a "picohydrometer"... but that's just a word I made up) rather than inventing something, if at all possible. But that's looking doubtful.
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With infinite budget, there are fantastic thermal micro-flow sensors, though they too have issues for drip-drip type situations.

One thought, still same overall concept as the tipping bucket, could be to send the flow in a clear tube oriented vertically, with a normally-closed solenoid valve at the bottom. Have your automation optically detect (conceptual example) when the water reaches a fixed pre-set level. Determine the resulting fill volume between the sensor and valve ahead of time. Have the automation record the time it takes to reach the fill level, which results in a measure of the average flow rate. Then activate the valve long enough to drain it, restarting the cycle. You would need a tube big enough that it drains consistently, and also big enough that drops don't get stuck in the tube and fool the detector -- the example I linked is on the too-small side but hopefully illustrates the concept.

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  • $\begingroup$ Electronics ftw $\endgroup$
    – Stilez
    Jan 16 at 0:17
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    $\begingroup$ Yeah I see that Sensirion has some nice solutions, if only my target budget had an extra digit in it ;-) I like your fill-then-empty idea; another way to do this might be level sensors like this eTape sensor or this single-point contacting sensor, both from Sparkfun. Unfortunately, finding a good low-cost solenoid well-suited to small volumes of water is looking to be a pretty difficult problem :-/ $\endgroup$
    – Mr. Snrub
    Jan 16 at 2:27
  • $\begingroup$ I've used Sensirions's flow products quite a bit, tho this application would run into all their weaknesses at once - near-zero pressure vs tight ID, intermittent flow, wet-dry. I like the liquid level sensor, though that one is optical too. The e-tape sensor looks very cool, I haven't seen that before! $\endgroup$
    – Pete W
    Jan 16 at 14:43
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Rain gauge tipping bucket data loggers are quite small. The whole thing is the size of a cookie tin. Bucket size (resolution) is about 1 cc.

Decent explanation in the video below.

https://www.youtube.com/watch?v=RruQhoXrVoE

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  • $\begingroup$ In other words "no, there isn't really any way that's much more elegant than a tipping bucket sensor". Yep, I'm starting to come to the same conclusion. $\endgroup$
    – Mr. Snrub
    Jan 16 at 2:31
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A variation of the tipping bucket - this is used for constructed wetlands to ensure an intermittent feeing of the wastewater.

The water enters a container. The outlet of the container is near the bottom, a flexible piece of tubing is connected to this outlet that serves as a hinge for a short piece of pipe. at the end of the pipe, theres a swimmer.

How it work:

  • water enters the container,
  • the swimmer keeps the pipe inlet above the water level.
  • at one point, the water level is so high that the length of the tubing and pipe don't allow the inlet to the pipe to rise higher
  • water flows int o the pipe
  • the additional weight of the water allows the pipe to sink with the water level, essentially draining the container

I havent seen one with my own eyes, but these are mentioned in the literature (that I don't have at hand so no pictures). I think a typical size in the constructed wetlands application is DN50 to DN100 (2" to 4"). At the small size we are talking about here, the buyoancy of the tubing and pipe could play a bigger role (because more of the volume is made up of wwalls and less of filling). Make an experiment, look for thin walled pipe and tubing and the smallest swimmer you can find.

How to measure with this: use a reed contact or similar (like you would with a tipping bucket) to count the emptyings.

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  • $\begingroup$ Thanks, I appreciate the idea, but do you have any ideas (or references) as to how this could be applied to actually measure the quantity of water? In the case of the tipping bucket, the assembly moves back-and-forth along a fixed path, so it's easy to trigger a mechanical switch, Hall effect sensor, opto-interruptor, or similar. With this flexible pipe + swimmer arrangement, what would be the mechanism that actually measures the water? $\endgroup$
    – Mr. Snrub
    Jan 15 at 8:35
  • $\begingroup$ Oops! @Mr.Snrub see question! $\endgroup$
    – mart
    Jan 15 at 8:44

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