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Author Topic: U-Tube Manometer Level Sensor  (Read 1246 times)
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Good Evening All,
        I need to sense the level of water in the clear U-Tube manometer. The water will move 2.5" and i need to sense it down to an 1/8". I know there are many tools out there but the manometer tube is only 1/4" OD plastic tubing. Anyone have an idea on how to measure a change in the water level?
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Newcastle, NSW, Australia
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Can you replace the tube manometer entirely with an electronic differential pressure meter? That would open up your interfacing options.
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Peoples Republic of Cantabrigia
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Good Evening All,
        I need to sense the level of water in the clear U-Tube manometer. The water will move 2.5" and i need to sense it down to an 1/8". I know there are many tools out there but the manometer tube is only 1/4" OD plastic tubing. Anyone have an idea on how to measure a change in the water level?

If you can't use a pressure sensor directly, how about an array of LEDs and receivers? Presumably the liquid will diffuse the light differently than air in the tube.
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This is a tough one.  I agree with nitrolx, although 1/8" of water may be hard to measure, as it is only 0.0045 psi.

The array of LEDs might work, but seems way more complex.  Besides, a 5mm LED is already almost twice as wide as the 1/8" you want to sense.  You could stagger the LEDs, or double the resolution by slanting the tubing at 30 degrees from horizontal.  Food coloring added to the water may make it easier to sense. 
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Inclined tubes were a method used in the past for measuring low pressures but is of course sensitive to keeping the device level. 
Turning things on its head, so to speak, you could use the air space above the liquid column as the tuning tube of a "penny whistle"  If you then blew into the whistle mouth-piece the frequency of the note generated would be directly proportional to the length of the free space air column.  Measure this frequency and you have an indication of liquid height.
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Inclined tubes are the way to go for low pressures. With small sensors and emitters (think 0805-package SMDs) you can get pretty good part density though. I'd breadboard the concept, be sure it works, only then design the PCB arrays. I'd design the PCB to be mirror-compatible, so you can use one board for the emitters, one for the receivers and sandwich the tube in between.
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