Anemometer switch

[dodulation]

Hi there,

I am trying to find a piece of electronics which function as a switch operated by an anemometer. The anemometer measures a certain programable windspeed and at that particular windspeed it switches a relay. My anemometer is nothing more than a rotating magnet that passes a reed switch at every rotation. The purpose I want to use this piece of electronic for is to open vents operated by an electric linear actuator, but if the wind gets too strong the vents need to close. So, I need to count the rotations (pulses) of the anemometer and if it exceeds a certain (programmed) amount of pulses per second it needs to operate a relay. This relay will operate the closing circuit of my linear actuators. I would like to keep it as simple as possible.

Does any of you how I can easily build something like that?

 

[Harald Kapp]

There are several methods. Which one you chose depends on factors like expected accuracy, your knowledge and last not least how much fun you can get out of experimenting. Here are just 2 possibilities:

• A microcontroller can easily count the number of pulses per minute and control any subsequent action. This will require some programming on your side.
• The pulses from the switch can be filtered by a low pass filter to create an anlog voltage proportional to the angular speed of the anemometer. A comparator circuit would become active once the analog voltage passes a certain threshold. By varying the reference voltage of the comparator you can adjust the windspeed at which the actuator is activated.

 

[Minder]

If not familiar with micro's, another way would be a LM2907, freq to analogue IC and use a LM311 comparitor on the output to set what rpm value you want to trip.
Then there is the issue of short momentary gusts, which probably should/would be ignored,
This is where the micro has an edge, you can program all kinds of features in.
A simple 8pin 12F series microchip would ace it.
M.

 

[Harald Kapp]

Then there is the issue of short momentary gusts, which probably should/would be ignored,

This would be an inherent feature of the low pass filter solution - provided the corner frequency is chosen low enough, say at 0.1 Hz or so.

 

[Alec_t]

provided the corner frequency is chosen low enough, say at 0.1 Hz or so.

You might have to introduce a time delay of seconds/minutes/hours, depending on the speed at which the actuators move. You wouldn't want them opening/shutting too frequently.

 

[BobK]

The time of the switch closure is going to shorten as the anemometer runs faster, which tends the counteract the frequency to voltage relationship. You probably would want to use a one shot to make the pulses identical before going into the integrator (or what Harald called a low pass filter.)

Do you have any idea what is range of RPMs and the range of switch closure times at different RPM? These would affect the design.

Bob

 

[Harald Kapp]

You probably would want to use a one shot to make the pulses identical before going into the integrator

Good point, Bob.