Stream Flow Meter




Stream flow meters are expensive, so we made our own and calibrated them with the very expensive magnetic induction flow meters. Our stream flow meters were made using model boat propellers and bike odometers. When calibrated, these meters yielded results that were within 5% of the magnetic flow meters results.

Step 1: Materials

1 meter, 3/4" thick wall aluminum tubing 25 cm 1/2" thick wall aluminum tubing

model boat propeller 1" diameter

bike odometer ( inexpensive)

1/8 " rare earth magnet

1.5" plastic disk

1/8 stainless threaded shaft ( for model boats)

Step 2: Construction of the Handle

Drill a 1/2" hole through the center of the 3/4" rod at 6 cm from the end. This should be perpendicular to the 3/4 rod. Drill a 3/8 hole half way through the 3/4 rod at 3 cm above the 1/2" rod. Push and epoxy a 5 cm by 3/8 (OD) rod into this hole. This will be location of the signal pick-up.Push the 1/2 rod through the 1/2" hole so that about 19 cm sticks out the side of the 3/4 tube.

Step 3: Setting Up the Propeller Shaft

Drill a 9/64" hole through the 1/2" plastic plugs then push and glue the plugs into both ends of the 1/2" Al tubing. Slide the 1/8 stainless rod through the holes, (this should be freely moving).

Step 4: Installing the Propeller and Pick-up

Drill an 1/8 hole into the side of the plastic disk and glue a 1/8" x 1/4 rare earth magnetic cylinder into this hole. Slide and glue the plastic disk onto the non-threaded end of the stainless rod. Screw and secure the propeller onto the end of the shaft. Thread the computer pick-up through the 3/4 rod and 3/8 rods and epoxy in place.

Step 5: Installing the Bike Computer and Calibrating

Attach the bike computer on the top of the 3/4 rod and plug into the pickup. Spin the prop and check to see if the movement is recorded on the bike computer.

Calibration needs to involve another flow meter. This involves determining the flow rate with the standardizing meter the adjusting the bike computer to match the velocity of the stream. This will require a number of successive trials.



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    7 Discussions


    11 months ago

    Great instructable, many thanks.

    I have made this with some slight modifications

    The disc and pickup are shrouded, using a funnel and a piece of rain
    water downpipe to prevent turbulence around the disc.

    This seems to
    stabilize the readings and also protects the disc and pickup from damage.

    As the main tube is plastic the pickup is sealed within it and the magnet is fitted into the face of the disc rather than the edge. The propeller shaft is intended for a model boat and has bronze bearings at each end and as my original boat propeller was not working very well I replaced it with a fan from an old heating boiler which works great!

    Sugar KennA

    Question 1 year ago on Step 4

    I am new to this. Please be patient with me. What do you mean by thread the computer pick-up? There is no material indicated in the list as computer pick up

    1 answer
    notsosharpSugar KennA

    Answer 1 year ago

    Poor choice of words on my part. By thread the computer pick up I mean feed the pickup through the tubes.


    2 years ago

    Not unlike the one commercially sold by Global Water. Nice to know you can build a reasonably accurate pvm instead of spending big $ on a Hach or Marsh McBirney


    2 years ago

    I like this . I've got no use for one though. Were you also responsible for the anemometer that used a cheap bike oddometer in a similar manner?