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How to Build a Hot-Wire Anemometer

A hot wire anemometer is a device that measures wind speed. Two temperature-sensitive elements, one that is exposed to the wind and one that is sheltered, are compared to each other. The wind changes the electrical properties of one of the elements and a circuit compares the electrical characteristics of the two elements to determine the wind speed. In original hot-wire anemometers, two loops of wire were compared. Modern versions tend to use two temperature sensitive diodes.

Things You'll Need

9-volt DC power supply
LM7005 micro-power regulator
1NA122 micro amplifier
Panel meter Jameco 315301
2 1N4148 diodes and a 11N4007 diode
100-K, 1.2-K and 2 20-K resistors
10-K potentiometer
2 10-microfarad capacitors
16-ohm power resistor Jameco 660421
Red, green and white wire
Soldering equipment
3-inch length of ½ inch PVC and a ½ inch PVC cap (optional)

Instructions

- 1
  Make the sensor by connecting the two 1N4148 diodes in the same direction. The anode of one is connected to the cathode of the other. You need to connect three wires to this series of diodes. Connect a red wire to the anode end of the series, a green wire to the cathode end and a white wire between the two diodes. The diode connected to the green wire will be exposed to the wind.
- 2
  Connect the power supply through the 11N407 diode to Pin 1 of the LM7005. Connect Pin 2 of the LM7005 to ground, and connect Pin 3 to one end of the power resistor. Run capacitors from Pin 1 to ground and Pin 3 to ground. Run a wire from this same side of the power resistor to the Vs pin of the amplifier. Run a wire from the other side of the power resistor to the zero-adjust assembly.
- 3
  Wire the two 20-K resistors and the outer pins of the potentiometer in series, with the potentiometer in the middle, to make the zero-adjust assembly. One end of the assembly is connected to the power resistor, and the other end goes to ground. The wiper of the potentiometer goes to the V-in pin of the amplifier.
- 4
  Run the red wire to the same side of the power resistor that goes to the zero-adjust assembly. Run the white wire to the V+in pin of the amplifier. Run the green wire to ground. Connect the two Rg pins of the amplifier with the 1.2-K resistor. Connect the output of the amplifier through the 100-K resistor to the meter, and connect the other side of the meter to ground.

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