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Anemometer sensor types

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TheMerovingian

Mon Mar 01 2010, 12:16AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

For my project I built a classic cup-type anemometer with an optical reflectance sensor. Despite it construction simplicity I found many problems in making it reliable and operational.

Pros:
1)Unlimited speed of detection
2)Resolution depends on integration time and number of pulses per single rotation, making the calibration simple
3)No interation with the rotor (cogging etc)
4)Ease of design and very high immunity to noise (using hysteresis)

Cons:
1)Alignment is not trivial, and can be a very big pain...
2)Water droplets refract the IR light, causing possible problems.
3)Spurious light can blind the sensor (actually depend on the sensor shielding)
4)Too high power consumption (most of which goes to the IR led)

I know another type of speed sensing based on induced EMF on a coin (like in windmaster II anemometers) but need very careful design of the preamplification to reject noise and have a low minimum detected speed.

Are there any other type of rotation speed sensors for an application like this?

Let's discuss togheter the cons and the pros.

Henry H

Mon Mar 01 2010, 01:11AM

Registered Member #2298 Joined: Sat Aug 15 2009, 08:16PM
Location: ex UK, now Santa Cruz, CA
Posts: 35

I think some use hall effect rotary encoders.

There are also several varieties of non-cup-type anemometers, e.g. hot-wire or ultrasound.

TheMerovingian

Mon Mar 01 2010, 12:52PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Hot wire consumes too much power and is difficult to calibrate. Maybe the hall effect can be a viable solutions, but will be difficult to achieve a reasonable resolution because it is difficult to house more than 10 small magnets on the rotor. The hall effect seems to match the low power and ease in aligning goal. Also it is simple to make it completely waterproof using resin.

Dave Marshall

Mon Mar 01 2010, 01:39PM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Some of the simplest and most reliable I've seen so far in the home-brew class use recalibrated bicycle speedometer to measure the rotational speed of the cups.

There is an ultrasonic anemometer project is in my not-too-distant future. Probably late this spring when the storm season quiets down.

-Dave

Bjørn

Mon Mar 01 2010, 02:29PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Too high power consumption (most of which goes to the IR led)

Optical detection can be done at very low power consumption by running the LED at extremely low duty cycle and the lowest power possible.

will be difficult to achieve a reasonable resolution because it is difficult to house more than 10 small magnets on the rotor.

For measuring wind speed you only need one magnet. If you need more resolution to measure turbulence you need to use a different method with no inertia anyway.

Proud Mary

Mon Mar 01 2010, 02:47PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Digital controlled rotation sensor
United States Patent 4195291

Ice free wind speed sensor
United States Patent D366841

ROTATIONAL SPEED SENSOR
United States Patent 3725668

worth a look perhaps

Electroholic

Mon Mar 01 2010, 04:33PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

How about this guy, 10bit per rotation, up to 10Hz or 600rpm.

Sulaiman

Mon Mar 01 2010, 05:24PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I agree with the comment that you don't need resolution.
The inertia of the rotating parts would swamp any resolution.
For really low power (zero) use a reed switch and rotating magnet.
De-bouncing will be required, e.g. R.C filtering.
The wire run length can be very long.

IntraWinding

Mon Mar 01 2010, 07:09PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

I used a HDD bearing, a reed switch, tiny magnet and spare cycle speedometer and calibrated it on a tall stick in a car on a still day. Probably easier just to buy one now.

TheMerovingian

Mon Mar 01 2010, 08:16PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

BjÃ¸rn wrote ...

Optical detection can be done at very low power consumption by running the LED at extremely low duty cycle and the lowest power possible.

It will be difficult to detect the reflected light and the alignment will be more difficult

BjÃ¸rn wrote ...

For measuring wind speed you only need one magnet. If you need more resolution to measure turbulence you need to use a different method with no inertia anyway.

Sulaiman wrote ...

I agree with the comment that you don't need resolution.
The inertia of the rotating parts would swamp any resolution.
For really low power (zero) use a reed switch and rotating magnet.
De-bouncing will be required, e.g. R.C filtering.
The wire run length can be very long.

I need gust measuring, that's why i need high resolution X integration_time. For gust I mean brief bursts of wind (2-4 seconds) which my mechanical part is able to handle without problems (low intertia moment, since the heaviest part is the bearing and is close to the axys of rotation)

I am more and more liking the hall effect sensor/switch type. It can be very low power,easy to aligh and small magnets (5mm 2.5mm 1.5mm N42) are easy and cheap to buy (

). It can work even with a small coil to detect the pulses but i have to becareful in designing the amplifier stage.

THe IC is quite good, it resembles the windmaster anemometer system. Figuring out if they send samples to students...

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