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I have a weird technical issue I’m trying to solve. I need to measure the amount of water which flows through a hose. But I cannot use a flow meter due to compliance costs and budget restrictions mean I cannot use an ultrasonic sensor for a flow meter due to unit cost.

I was wondering if there is another way I could measure the volume without touching the water or going inside the tube.

The water stations vary between sensor for water dispense and push button.

Flow ranges are very low between 1-5L per min.

For more context I need to display the volume of water which has been passed through the fountain. It adds together everytime the fountain is used. Accuracy doesn’t need to be perfect just reasonable enough to not be very noticeable. Thanks everyone

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    \$\begingroup\$ Ultrasonic sensing seems by far seem to be the cheapest choice. Can you please put numbers to your problem, namely what speeds you need to monitor with what kind of precision (metering with 20% tolerance will be much cheaper than with 0.02%!) and what your cost constraints actually means. \$\endgroup\$
    – sina bala
    Mar 8 at 9:31
  • \$\begingroup\$ Please edit the question to indicate the range of flows you anticipate. \$\endgroup\$
    – Theodore
    Mar 8 at 16:07
  • \$\begingroup\$ Hi, of course thanks for your help. So the range is very low between 1-5L per min. The accuracy does not need to be very high. \$\endgroup\$
    – Joeblogs
    Mar 9 at 23:27
  • \$\begingroup\$ Other sensor technologies: thermal (many flavors, none a good fit for a hose tbh), spinny-disk-with-magnetic-pulse-counter (cheap! but makes contact), differential pressure sense vs orifice, coriolis (true mass flow, non contact, but costly). \$\endgroup\$
    – Pete W
    Mar 10 at 2:20
  • \$\begingroup\$ Another approach is to use a mechanical device to cause constant flowrate, then just count time. Obviously there would be contact. A "pressure compensated orifice" would be the thing to look for. Basically a spring based differential P regulator with an orifice in the middle. Simple mechanical device with housing, one moving part and one spring. Probably want an adjustable one, which adds a screw and a seal. \$\endgroup\$
    – Pete W
    Mar 10 at 2:22

2 Answers 2

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You could shop around for better prices on ultrasonic flow meters. They are relatively inexpensive as process instruments go.

Another approach, perhaps somewhat cheaper all things considered, would be to use a peristaltic metering pump so you get a known amount per revolution of the shaft. The hose is threaded through the peristaltic pump so you don't go inside of it.

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    \$\begingroup\$ Thanks for your answer, certainly interesting thing to think about. But even at $300 it’s way out of price range. Looking a producing over 200 units. Do you have any suggestions on ultra sonics that aren’t super accurate but are very cheap? Thanks again \$\endgroup\$
    – Joeblogs
    Mar 9 at 23:29
  • \$\begingroup\$ The general principle would be the same. Shopping around for sensors or metering pumps or whatever is actually your job. \$\endgroup\$ Mar 10 at 16:13
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Flow is proportional to a pressure difference divided by a hydraulic resistance. The pressure at the business end of the hose is atmospheric. The resistance of the hose is near constant in many situations. If your situation is of that type, you can measure pressure at the tap, and figure out the resistance by timing how long it takes to fill a known volume.

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  • \$\begingroup\$ Since it’s for a water fountain. When someone’s used the fountain I need to determine what volume of water they have used. Would that be possible with that calculation? I guess if I had a way to start the timer then it would be. Thanks again \$\endgroup\$
    – Joeblogs
    Mar 9 at 23:30

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