Current flow velocity meter

Hi masters i will built curent flow velocity to measure the velocity of river.. But i dont know how.. So i need yours help. I use arduino uno board n magnetic sensor

Well, since the "current" in a river varies from fast in the deep part to almost not at all on the very outer edges, where you like to measure? If you can fasten a rope or cable across the river, you could position a small motor and propeller, properly water proofed, so it was mid-stream. The motor would turn, generating a voltage that is proportional to the current velocity.

Research anemometers. They measure the velocity of the fluid called air. Same programs can be used to measure river velocity.

Paul

Stand on a bridge above the middle of a river. Drop in a twig. Go near to a bank. Drop in another twig. What do you observe ?

Your one instrument will not measure a useful quantity. The total flow rate is measured in cumecs which is a scaler. Velocity has a magnitude and a direction making it a vector quantity.

I'd move this post to project guidance where my comment is "not useful" as presently stated.

Paul_KD7HB: Well, since the "current" in a river varies from fast in the deep part to almost not at all on the very outer edges, where you like to measure? If you can fasten a rope or cable across the river, you could position a small motor and propeller, properly water proofed, so it was mid-stream. The motor would turn, generating a voltage that is proportional to the current velocity.

Research anemometers. They measure the velocity of the fluid called air. Same programs can be used to measure river velocity.

Paul

You don't want to mechnically load the turbine, typically a hall-sensor and a magnet would be used to sense the rotation rate. The rotation rate to water velocity mapping would be done from the calibration graph/equation for the sensor. A rotor driven by flow is technically a turbine, not a propeller, since it is not propelling anything.

Hall effect pipe flow sensors are fairly cheap, and I'm sure you could modify them with a funnel to measure low flow rates. eg: http://www.electrodragon.com/product/liquid-flow-sensor-turbine-meter/

We've been using the drag-tilt principle to measure flow velocities:

https://edwardmallon.wordpress.com/category/developing-a-flow-sensor/

mostly because precipitation & organics munged up our rotational sensors if the units were left in place very long. Any cheap accelerometer can give you tilt angle pretty easily.

Another interesting alternative to the traditional methods - if you have top down access while you take the readings (say from boat while your friends pull you across the surface of the river with ropes? or a boardwalk? etc) would be to use flex sensors on poles perpendicular to the flow. the salamander project was using this to measure stream flows a few years back.

With both methods you need some pretty serious smoothing/averaging. And calibration would take some work as both turbulence & drag are pretty complicated. But they are both cheap and easy to do with Arduinos.

google “open channel flow meter”