Introduction: Pitot Tube Using Pressure Sensors
In this manual you can learn how to make your own Pitot tube to determine the velocity of the studied body of water using pressure sensors instead of conventional height measurements. The upward force the water exerts on Styrofoam cylinders inside the tubes is measured by the pressure sensors, which can be rewritten to find the velocity at a chosen height.
The curved tube measures the hydraulic head H; H = z + p/(ro*g) +u^2/(2*g)
Whereas the straight tube only measures the elevation height h; z+p/(ro*g)
The difference between these two is the velocity height, from which the velocity can be computed.
Step 1: Materials and Preperation
The materials you’ll need are:
-6x tie wraps
-tape that sticks on both sides
-sheet of metal (iron/tin)
-2x barbecue sticks
-2x sensor for pressure measurement
-3x 220 Ω and 6x 110000 Ω resistors
-2x garden hose connectors
The first main component consists of wood. This will be the supporting structure. Shape some wooden beams as displayed below:
The dots in segment 1 are representing holes. You should drill those holes with a hand-drill. For segment 2, you should be taking a thicker beam, or put several of those planks together, so it will be like 5 centimeters thick. You’ll need 2 times segment 2.
Saw off two plastic tubes (diameter +/- 1 cm), the one larger than the other. Bend the larger one using a heat generating device, like a blow-drier, under a 90 degree angle.
Make two long cylinders of Styrofoam that will fit into the tubes (+/- 15 cm long). Those will be the floats in the tubes. Make two smaller cylinders as well (+/- 2 cm long). Those will be the connectors between the floats and the sensors. You can do this by sawing of Styrofoam from a larger block. After that you can shape it using a file to make it fit into the tubes.
Step 2: Assembling
Step 1: Glue part 1 and parts 2 together. The parts should stick together on the marked places. After that, glue part 3 on parts two. You should now have 2 parallel beams (segment 1 and 3) with on both ends segments 2 between.
Step 2: Stick some tie wraps through the holes you made in segment 1. Put a strip of double-sided tape on the length of the area covered by the tie wraps. Attach the tubes to segment 1 using the tape and secure the tubes using the tie wraps. The tubes should be attached on the outer side of the structure. Use the picture on the cover of this manual to have an idea about how the tubes are attached.
Step 3: Stick the barbecue sticks in the topside of the large Styrofoam units (the floats). Place those into the tubes. Make sure the barbecue sticks are on the top side of the device.
Step 4: Place the garden hose connectors on the top side of both tubes with the barbecue sticks sticking out. After that, place the Styrofoam connectors on the other side of the barbecue sticks. In the first picture, the Styrofoam connectors should not be seen as they are hidden in the garden hose connectors (the orange things on top).
Step 5: Glue segment 4 on one of the sides of the structure. In the first picture, segment 4 is the horizontal plank on which the Arduino and the other electrical circuits are placed. Then use some double-sided tape to secure both the Arduino and the circuit board onto section 4.
Step 6: Bend the metal sheet in a U-form as seen in the first picture. Cut two openings in the lower part using a strong pair of scissors. Make sure those openings are big enough, so both garden hose connectors can fit in. Make sure it’s a tight fit, so that the metal is fixed to the connectors.
Step 7: Stick the sensors on the bent metal sheet using duct tape. Make sure that, when you attach the metal structure on the garden hose connectors, the sensors are exactly above the Styrofoam connectors or the sensor won’t pick up the applied pressure.
Step 8: Use duct tape to secure the LED’s on the top of the metal sheet (or anywhere you please).
Step 3: Arduino Code and Use
Build the circuitry as depicted in the picture on your circuit board.
Place the device in a stream. In the laboratory the device can be fixed on the sides using clamps. Make sure the water height is sufficient, the water must be able to exert upward force on the Styrofoam and the threshold value for the pressure sensors must be reached.
Calibrate using known water heights and velocity’s. Assign a chosen high and low value in the Arduino code to the LED’s so the device can provide you with the range the velocity is in without you having to look at a computer screen.