There are various types of anemometer, but the one which we have used here is called Cup Anemometer.
In Cup Anemometer 3 hemispherical cups are mounted on one end of 3 arms (4 cup and 4 arms are also used), these arms from other hand are also mounted at equal angle to each other on a vertical pole with rotating mechanism. Mainly smooth bearings are used for rotating mechanism.
When air start passing across the cups horizontally, these cups collects the air which makes cups and arms attached to vertical pole (we call it rotating assembly) starts rotating. And these rotations are proportionate to wind speed.
For finding the average wind speed, rotations are observed for over a period of time.
So how to monitor each rotation?
Well, there are two ways, Optical method and other is Magnetic method.
Optical Method.
At the top end of vertical rotating pole we have cups attached through arms, in the same manner there is a small cap consist of one or more tooth is connected to bottom end which cuts the optical path of IR led and receiver and for each it gives out a pulse.
In this image you can see at bottom end we have a cap with few tooth.
In this image there is an IR sensor with groove through which tooths are passes.
Magnetic Method
In this method instead of IR groove sensor and tooth cap, either reed switch or hall sensor and magnet is used, magnet is attached with the rotating assembly and whenever it passes through reed switch or hall sensor it gives a pulse.
Hall Sensor
We can even place more than one sensor.
So both method gives us a pulse or few pulses for each rotation and are counted by a microcontroller (here we are using Arduino Board) over a period of time.
While designing and implementing, there are various interesting questions comes into action.
- From top view what shape will rotating assembly form?
- At what angle each cup via arm will be mounted on vertical pole?
- Once the angle is calculated, how actually cup via arm will get mounted on vertical pole?
- What is one rotation and how much distance will it cover in one rotation?
- What is the impact of placing more than one tooth or hall sensor?
- *How to calculate the wind speed? *
- How to define a period of time for monitoring rotations?
- How to calibrate the device?
- What is best method to monitor each pulse without missing any in microcontroller?
- How to code a mathematical calculation and calibration factor for wind speed?
Just start hands on with your own Anemometer and lets explore and discuss answers for each questions.
Happy Exploration and Making!