Topic: Calibration of Station

[Downlinerz2]

   I am curious as to how many of you with Davis stations had to perform calibrations to temp, hum, ect?  Or did your perform perfectly out of the box?

[Wx4U]

Mine has worked just about perfect since right out of the box eleven months ago.  Sometimes the rain totals will disagree with my 4in by .01 or .02, but that is excellent in my book. In the summer I thought the temp was a little hi, but it wasn't the fault of the sensor. I believe there is a certain amount heat radiated off the black rain collector. Using a Blue Point laser thermometer I have checked the surface of the radiation shields adjacent to the rain collector and on the opposite sides and noted a substantial difference. I am thinking of painting or covering the outside surface of the rain collector.

[CookevilleWeatherGuy]

   I am curious as to how many of you with Davis stations had to perform calibrations to temp, hum, ect?  Or did your perform perfectly out of the box?

So far, mine is measuring incredibly well. Like Wx4U, the rain gauge is occasionally .01 or so off from the 4" manual gauge, but my LaCrosse 2317-el was consistently 20-25% off. 

[DJMWX86]

Mine which is 8 months old is working fine with exception of the barometer is a bit off as the QC MADIS states but the other readings are right on. 

[dasman]

Everything except the rain guage was perfect out of the box.  A couple adjustments to the rain guage aligned it with my 4in guage.  Now after a year I had to tweak the guage again.  with the new tweaks i've compared the totals over the past 5 rains.  The Davis had 1.38in 5rain total and the 4in had 1.39in 5rain total.  That is prety close.  And it was that close during the first year as well.

[d_l]

I did some calibration checking of my VP2 against a Kestrel 3500. As best as I could tell, they were in perfect agreement.  The Kestrel due to it's low mass, reacts to dynamic weather conditions much faster than the VP2 so that has to be considered when calibrating.

My Envoy DID need calibration adjustments.

[wxtech]

Mine was very close.  I correct the rain amounts on the console by comparing with CoCoRaHS and NWS manual rain gauges.
I put in -0.7º temperature offset to get the Davis to agree with the NWS Nimbus sensor.  
I painted the Davis black plastic parts white with Krylon Fusion white spray paint.  Fusion is for plastic surfaces.  I painted it white because the Davis is just a few feet from the NWS Nimbus temperature sensor and I didn't want the big black item affecting the NWS temperature sensor.
I use CWOP/MADIS QC to adjust the barometer.  Initially I set up the barometric sea level pressure by interpolating between Atlanta, Augusta, & Greenville NWS stations.

About the difference between rain gauges.  The 8 inch National Weather Service standard rain gauge isn't always in agreement with the 4 inch CoCoRaHS manual rain gauge.  And they are only a few feet separation.   
Point is - - two manual rain gauges won't always agree either.

[Mark / Ohio]

Mines always seemed OK when compared to my other cheap manual rain gauge and thermometers.  My trouble is the Davis is the most accurate and highest quality weather instrument I own.  So everything I compare it to is lower accuracy.  It does run inline with the local airport 6 miles away most of the time during calm weather and prolonged wide coverage rains.  So I have never found a need to worry about making further adjustments outside of the barometer.

[Downlinerz2]

Thanks for your replies.  I have been comparing my readings to another VP2 that is about one half mile down the road.  My temp/hum readings are off at times.  I have just started a log so I can compare them to find any trends.  I am thinking the differences are caused by my microclimate.  I have farm fields across the street and behind my house.  The other VP2 is in a subdivision.  But, I wanted to get an idea of how many of the Davis stations needed calibrating out of the box. It looks like they are pretty accurate from the start just as I expected.  Again, thanks all . If you have any other info you think would aid me in this send it on, it is much appreciated and needed.

[SlowModem]

 
Point is - - two manual rain gauges won't always agree either.

Just like two wxforum members.   

[VaJim]

The subject of calibration and comparison can be very confusing.  I prefer to leave things alone and if I need to adjust, do so in accordance with the owners manual.  The comparison of 2 stations can be very tricky.  I'm currently running 3 (Rainwise, Davis Vue, Lacrosse 2810) and each data point can vary from time to time.  For me as long as each are within a 'reasonable' range, that works for me.  Not only do you have to consider manufacturer, but you also need to factor in mounting location.

One item I've noted in physical observation (not to be consfused with reading the display), the Rainwise station, by far, is more sensitive to wind/air movement.  Not to say that the Davis Vue doesn't pick up the winds it should, but I've seen cases where the Rainwise props are spinning like crazy and the Davis (only 20-25' away) is hardly moving.  I attribute most of this to wind funneling in my backyard.  I think I understand and can accept this.  But the Rainwise wins the overall sensitively award.  Even my hand held weather sensor agrees.  Heck...even the Lacrosse 2810 cups can read winds under 1 mph.  

[W3DRM]

I compare my CoCoRAHS rain readings with my VP2 and for the most part, they compare within 0.01 to 0.02 of each other unless we have high winds. Then, the numbers can be quite different even though they are within 5 feet of each other and at the same level above ground.

One other note, have you ever moved your cursor over the green thumbs on the CWOP quality page (MADIS rating)? If you do, you will see the percentage of accuracy of your readings. Just discovered that yesterday when I was checking my numbers. I would imagine you would see the same percentage numbers when it showed a red down thumb too.

[wxtech]

One item I've noted in physical observation (not to be consfused with reading the display), the Rainwise station, by far, is more sensitive to wind/air movement.  Not to say that the Davis Vue doesn't pick up the winds it should, but I've seen cases where the Rainwise props are spinning like crazy and the Davis (only 20-25' away) is hardly moving.  I attribute most of this to wind funneling in my backyard.  I think I understand and can accept this.  But the Rainwise wins the overall sensitively award.  Even my hand held weather sensor agrees.  Heck...even the Lacrosse 2810 cups can read winds under 1 mph.  

I have several wind sensors also.  I too have noticed the mechanical parts responding differently to the winds and they are just feet in separation.  The Davis VP anemometer has a high wind threshold.  During light winds, the R M Young impeller is spinning and the Davis VP anemometer cups are motionless.  Also the Vaisala anemometer has a much lower wind threshold than the Davis anemometer.
I'm putting the final touches on the RM Young Wind Monitor converter.  This device allows a RMY to connect to a Davis VP2.

[Downlinerz2]

   I have been checking my rain gauge with the CoCoRaSH gauge as well with same results with those mentioned.  
    I also agree with you VaJim that comparing 2 stations can be very tricky.  I never assume that another station is right and mine wrong, or the other way around.  That is why I am checking every angle. Day by day I am believing that my readings are good but final verdict is a few weeks away.

[DanS]

 
Point is - - two manual rain gauges won't always agree either.

Just like two wxforum members.   

[SlowModem]

What a great gif!    I've got to copy that!  

[LFWX]

 
Point is - - two manual rain gauges won't always agree either.

Just like two wxforum members.   

I disagree!

[Downlinerz2]

 
Point is - - two manual rain gauges won't always agree either.

Just like two wxforum members.   

I disagree!

                 

[jay_hoehn]

It is difficult to know how to compare my readings with others, when the closest station is 43 miles away.  I can only say that my Davis VP2 rain is always very close to my CoCoRahs gauge.

Jay

[tomcj2]

I calibrated my VP2 rain gauge last spring and got it almost dead on with my CoCoRaHS readings.  In the past couple of weeks I noticed that the VP2 is starting to read higher;  the difference has slowly been getting greater.  Today I looked at the tipping buckets and found a little dirt building up.  I cleaned the buckets with a soft damp rag, and hopefully it will return to a more accurate calibration

[Downlinerz2]

   `Thanks all!!!  My situation has pretty much been like yours.   

[DaculaWeather]

I calibrated my Vue baro with the NWS reporting station  5 miles away. The temp I adjusted maybe .7-.8 degrees to get the average temp where it needed to be. But it was all just fine tuning, nothing was way off.