MadSci Network: Earth Sciences
Query:

Re: How can you measure the max speed each day using a home made anemometer

Date: Sun Feb 6 16:04:57 2000
Posted By: John Christie, MadSci Admin
Area of science: Earth Sciences
ID: 948221591.Es
Message:

Although this question is about an anemometer, it really could apply just as 
easily to almost any instrument.

How you would measure the maximum speed really depends on the practicalities of 
the output from your instrument -- what sort of gauge are you using?

There are two main practical approaches to obtaining maximum/minimum readings.

The first is to use a recording gauge. The wind speed measurement shows by moving 
a needle from right to left. So instead of the needle, let's have a pen that sits 
lightly on a chart mounted on a slowly rotating drum. That way we can get a chart 
that gives a map of just what the wind speed was at different times of the day, 
and it is easy to read a maximum off that.

The second approach is to fit a little slider on a wire across the face of the 
gauge, where it will be pushed from time to time by the gauge needle. It is a bit 
tricky to get it exactly right. There must be enough friction that the slider 
will not move accidentally, nor overshoot when the needle pushes it. But the 
friction must be small enough that the needle can move it without being hindered 
in its own movement when it is trying to show the instrument reading. The idea is 
that you push the slider to the left at the start of the day, and every time a 
wind gust comes along that is a little bit bigger than anything else that has 
happened so far, the slider gets pushed a little further to the right. At the end 
of the day, the slider will be left in a position that corresponds to the speed 
of the fastest wind gust that day.

The description of these two systems has been based on the idea that you have a 
mechanical read-out gauge -- a moving needle, or some similar device. If your 
read-out gauge is optical (rotating mirrors or similar) or electronic (output 
converted to an electrical voltage), you can use the equivalent ideas very much 
more easily.



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