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Background

I am on a project where they want a non invasive sensor for usage. There are many sensor available but they need to cut down the pipe to place within.

Specifications

  • Pipe is PVC 1-1/4" OD, meaning 1.38" inside diameter, near 0.14 inch wall thickness.
  • The water inside is not pure. It contains less than 20% impurities (chemical waste like salts, potash, ammonia).
  • To cut down pipe mean to insert a water valve type sensor but it is a fixed solution. Our project needs a portable device
  • I am not interested in actual amount in cubic meters, I just want how much it is filled.
  • As for as temperature sensor is concerned the temperature change is a big factor because otherwise we would need to calibrate it according to ambient temperature.
  • The pipes are placed horizontal and water is pumped by 5 horsepower motor.

The Ask

Can any one can tell me how can I make a sensor that can check level of water inside pipe like 75% filled. We need to detect if water approach a specified threshold . I tried magnetic coils but they are not working under varying temperature and dust. My circuit take 12 volt dc.

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    \$\begingroup\$ water's non-magnetic, so any magnetic solution would be doooooomed before you start. It is electrically conductive however, capacitor plates on the outside of a PVC pipe should work, making assumptions about what you've not told us. \$\endgroup\$ – Neil_UK Oct 26 '16 at 10:22
  • \$\begingroup\$ You need to give more details and explanations here to get relevant answers. " 1/4' " = 3 inches? Or, is this a typo? "... cut down the pipe to place within..." - meaning what? The sensor takes up room inside the pipe? Or, you literally need to cut open the pipe to place the sensor within it, and that's not practical? Is this pure water flowing in the pipes, or dirty drain water? What was the operating principle of the "magnetic coils" you refer to? E.g. did they sense the water directly, or the level of a float within the pipe? Photos or diagrams would help too. \$\endgroup\$ – FiddyOhm Oct 26 '16 at 12:05
  • \$\begingroup\$ Variable pipe fill eliminates the possibility of using a ultrasonic flow sensor. Are you only looking for FILL %? or actual flow? Depending on the thermal conductivity of the pipe, you might use a small temperature based flow sensor. \$\endgroup\$ – R Drast Oct 26 '16 at 12:22
  • \$\begingroup\$ Sorry, it was 1-1/4" meaning 1.38 inch inside diameter, near 0.14 inch wall thickness, material pvc. The water inside is not pure. It contains less than 20% impurities (chemical waste like salts, potash, ammonia). To cut down pipe mean to insert a water valve type sensor but it is a fixed solution. Our project needs a portable device though \$\endgroup\$ – abdul qayyum Oct 26 '16 at 12:35
  • \$\begingroup\$ @RDrast I am not interested in actual amount in cubic meters. I just want how much it is filled. As for as temperature sensor is concerned the temperature change is a big factor because otherwise we would need to calibrate it according to ambient temperature. \$\endgroup\$ – abdul qayyum Oct 26 '16 at 12:38
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a capacitive sensor (like a stud finder) will detect water in a plastic pipe by its dielectric constant but getting precision in a portable device could be tricky.

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  • \$\begingroup\$ Good suggestion. I think he can slide it up and down the pipe to find the edge of the water, actually. \$\endgroup\$ – Vince Patron Dec 27 '16 at 6:50
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If you need a switch, then try a capacitive sensor. I have no idea what dimensions of your pipe is and what do you mean by check qualitatively amount level.

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  • \$\begingroup\$ 1/4 '' pipe . by level i mean threshold like if horizontal pipe is 75 % filled, we need to switch to a specified output that is fed to a fpga for further processing. \$\endgroup\$ – abdul qayyum Oct 26 '16 at 11:46
  • \$\begingroup\$ I have edited my question so it may make things clear \$\endgroup\$ – abdul qayyum Oct 26 '16 at 11:50
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You can borrow this idea from dishwashers' salt tanks:

A magnet, encapsulated in plastic to protect it from corrosion, adjusted such that it floats (styrofoam?), floats on the water inside your pipe. Outside of the pipe, you attach a reed contact just high enough for your needs.

In dishwashers, the magnet/plastic isn't floating on the surface, but inside the salty water. Once the salt solution becomes too thin, the magnet, I believe, starts to sink deeper into the tank, and activates the reed contact.

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  • \$\begingroup\$ Your idea is good but it still needs to open the installation. \$\endgroup\$ – abdul qayyum Oct 27 '16 at 5:48

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