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Davis anemometer pulse count function

Benjamin.vial Dec 9, 2020 09:45 AM

Hello,

I know a lot of people try this, with more or less success, but cant find the good topic about my problem.

I have a multiparametric station where I want to install a Davis Cup anemometer (retrieve from a dead stuff).

The Davis anemometer wind direction is ok, I can have the wind heading.

But I'm not understand how to get the pulse from the anemometer. I used the PulseCount function, as for the Young anemometer (for example), and I know the Davis anem. have a reed switch as the Young. So it's generating a pulse. I haven't oscilloscope for now but my voltmeter seen some peak, about 500mV on each rotation.

But it seem that there is a positive peak, followed by a negative one. Maybe that's the problem ?

How works the Young anometer for example ?

Benjamin.vial Dec 9, 2020 10:16 AM

Really, I worked during a day on this and just after create my topic I find something ... I used POption in the PulseCount function as Counts, not Frequency.

Now it seem I'm able to see the revolutions, so last question : is the WS_ms variable result the number of revolution / scan ?

And for posterity, for people who want to put some davis anemometer on a CR800, the is my wiring diagram :

Yellow - VX1

Red - ground

Black - P1

Green - 1L (in my case)

And use this PulseCount function : PulseCount(WS_ms,1,1,0,0,0,0.2)

I'm not sure about the multiplier but here is what I will use to calculate wind speed :

According to the Davis Anemometer technical document 1 mile per hour is equal to 1600 revolutions per hour.

Using the formula V = P(2.25/T) we can calculate the speed in miles per hour.

  • V is speed in miles per hour
  • P is number of pulses per sample period
  • T is the sample period in seconds

smile Dec 14, 2020 06:21 PM

Hi 

I see wrong parameters, I suggest to use:

- switch closure

- frequency output (so you don't have to worry about scanning)

- multiplier to 2.25

- offset 0 it depends on how you intend to use the lulls, as the cups could stay still in very low wind, I don't find this value quickly for this anemometer (as specification of this Davis sensor) but I think 0.5 m / s (1.11847 mph) could be fine.

like so:

PulseCount(WS_mph,1,1,2,1,2.25,1.118470)

then convert from mph to m/s

WS_ms=WS_ms/2.23694

Smile

Benjamin.vial Dec 15, 2020 08:24 AM

Hi,

thanks a lot for this informations, I will make the changes on my program.

bye

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