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SPEED SENSORS

For discussion of DIY weather equipment - sensors, accessories, improvements to existing kit etc
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JIM
Posts: 5
Joined: Sun 12 Jun 2011 6:44 am
Weather Station: watson 8681
Operating System: vista
Location: croydon

SPEED SENSORS

Post by JIM » Wed 25 Dec 2013 1:47 pm

Are they all the same ...moving magnet and switch below it to pulse when wind blows

AllyCat
Posts: 1045
Joined: Sat 26 Feb 2011 1:58 pm
Weather Station: Fine Offset 1080/1 & 3080
Operating System: Windows XP SP3
Location: SE London

Re: SPEED SENSORS

Post by AllyCat » Thu 26 Dec 2013 9:59 am

Hi,

By "speed", I presume you mean Windspeed. "Cup" anemometers are by far the most common type because they are reasonably accurate and linear (rotational speed proportional to windspeed), and independent of the wind direction. Similarly, magnetic sensing (reed switch or Hall sensor, etc.) of the revolutions is by far the easiest, but other methods such as optical beam interruption are sometimes used.

A few systems have used a "propeller" which is turned to face into the wind and there are other methods such as measuring the cooling of a "hot wire". But probably the most common "other" (meteorological) type uses "Ultrasonic Time of Flight": Sound waves are transmitted in two (horizontal) directions, usually at right angles, and the time taken to reach a pair of receivers is measured. Variations of the time delay indicate whether the apparent speed has been helped or hindered by the movement of the air. An advantage is that there are "no moving parts", so it's particularly suitable for adverse conditions such as mountain tops.

Cheers, Alan.

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