Author Topic: Speed Constant / Slope / Pulse Factor for 3rd Party Anemometer  (Read 519 times)

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Offline kclifton

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Speed Constant / Slope / Pulse Factor for 3rd Party Anemometer
« on: December 05, 2019, 05:26:35 PM »
I sent this question to Davis Support two days ago, still waiting for a reply.  Does anyone know if there is a place in WeatherLink Live to enter a speed constant for a 3rd party anemometer?   I can find the setting for "3rd Party Anemometer" in the Advanced Settings for WeatherLink Live in the app and on the Web, but it does not look like there is a place to enter in any speed constant/slope/pulse factor.

The anemometer I want to use has a magnetic reed switch, I was going to add two 47 ohm resistors, one on each side of the reed switch so the resistance matches the Davis anemometer -- no problem with that.  But, the new 3rd party anemometer has a speed constant of 1.25 mph = 1 pps, whereas the original Davis anemometer has a speed constant of 1 mph = 2.25 pps as far as I can tell.

Thanks for any ideas.
Davis Vantage Pro-Plus 24Hr FARS
CWOP:KJ4HF WU: KNCSALIS64
Web: KenClifton.com

Offline johnd

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Re: Speed Constant / Slope / Pulse Factor for 3rd Party Anemometer
« Reply #1 on: December 06, 2019, 03:41:03 AM »
Does anyone know if there is a place in WeatherLink Live to enter a speed constant for a 3rd party anemometer?

Not that I know of. Pretty sure that there isn't such an option.

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...whereas the original Davis anemometer has a speed constant of 1 mph = 2.25 pps as far as I can tell.

Think you'll find that the Davis calibration is 1mph = 0.444 Hz (or pps if you like) - it's the gating window that's 2.25 secs long.
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline kclifton

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Re: Speed Constant / Slope / Pulse Factor for 3rd Party Anemometer
« Reply #2 on: December 06, 2019, 03:12:29 PM »
Think you'll find that the Davis calibration is 1mph = 0.444 Hz (or pps if you like) - it's the gating window that's 2.25 secs long.
Thanks for the reply with the information johnd !

Here is a link to the original Davis site & document with the 2.25 sec interval, I will keep the 0.444 Hz in mind: http://toolbox.davisnet.com/downloads/weather/Misc/7911_Anemometer/7911%20OEM%20Applications.pdf

In the Davis document they mention the formula is the same whether large cups or small cups are used.  I would have thought the size of the cups would change the calibration...
Davis Vantage Pro-Plus 24Hr FARS
CWOP:KJ4HF WU: KNCSALIS64
Web: KenClifton.com

Offline johnd

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Re: Speed Constant / Slope / Pulse Factor for 3rd Party Anemometer
« Reply #3 on: December 06, 2019, 03:33:41 PM »
In the Davis document they mention the formula is the same whether large cups or small cups are used.  I would have thought the size of the cups would change the calibration...

No, the aerodynamic design is such that they spin at the same speed. The small cups were the original design - probably 25-30 years old now. But the large cups provide easier startup at low wind speeds and hence have better sensitivity. However, the small cups (especially in the older 7911 arm shape) will need a slightly different secondary speed correction vs wind direction, as provided by the console firmware, which is why a distinction is still made in the console set-up.
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline kclifton

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Re: Speed Constant / Slope / Pulse Factor for 3rd Party Anemometer
« Reply #4 on: December 13, 2019, 03:40:34 PM »
I finally heard from Davis Technical support on this issue.  It took about 8 days from the initial email, I am just glad they answered at all... I am sure they are busy folks.  Here is the pertinent content regarding calibration of 3rd party anemometers with WeatherLink Live (6100) units:
Quote
Only the direction reading can be calibrated by degree values in the weatherlink live. The only receiver we have that has the ability to directly calibrate the raw pulse rate is the Vantage Vue console. Also, our enviromonitor system has internal drivers that correctly process the pulse rate variances form many 3rd party anemometers attached to the nodes, but that is a totally different system altogether.  Currently there are a few solutions for you in this situation. 
@johnd: I see on your ProData site and blog that you started testing the LCJ ultrasonic anemometer with your Davis Enviromonitor system back in April 2018.  Just curious if you have made any posts about how that is going?

Davis went on to say their 6410 anemometer was about the only option unless I wanted to use a Vue console as a go-between. 
Davis Vantage Pro-Plus 24Hr FARS
CWOP:KJ4HF WU: KNCSALIS64
Web: KenClifton.com