Topic: Diameter of the radiation shield and its effects on humidity readings

[jgentry]

I think I figured out why Davis VP2s & Vue stations typically report higher RH values (which affects DP temp readings) compared to Campbell Scientific stations and Airport stations. I'm beginning to believe that humidity sensors that are housed in a smaller diameter radiation shield reads lower during the day and in some cases higher at nighttime compared to the bigger diameter shields like Davis.  What are your thoughts?

[WheatonRon]

I think I figured out why Davis VP2s & Vue stations typically report higher RH values (which affects DP temp readings) compared to Campbell Scientific stations and Airport stations. I'm beginning to believe that humidity sensors that are housed in a smaller diameter radiation shield reads lower during the day and in some cases higher at nighttime compared to the bigger diameter shields like Davis.  What are your thoughts?

Since upgrading to the SHT31, I don't have humidity reporting issues with either of my two VP2s. My thought? Not an issue.

[CW2274]

I think I figured out why Davis VP2s & Vue stations typically report higher RH values (which affects DP temp readings) compared to Campbell Scientific stations and Airport stations. I'm beginning to believe that humidity sensors that are housed in a smaller diameter radiation shield reads lower during the day and in some cases higher at nighttime compared to the bigger diameter shields like Davis.  What are your thoughts?

Since upgrading to the SHT31, I don't have humidity reporting issues with either of my two VP2s. My thought? Not an issue.

Same. Superior performer, high or low.

[jgentry]

My grandparents live next to me and they have an Acurite temperature/humidity sensor. It's housed in an Acurite radiation shield and under a tree. Even though Acurite sensors specs aren't like the SHT 31, their unit does report dew point readings that are the same as the ASOS located around 16 miles north of here; whereas my VP2 (passive) station typically reports DPs 2-3° higher (sometimes it's the same or 1° different). I've noticed the 24hr Davis FARS station that's located 3 miles south will typically record DPs around 1-2° lower than my station (both units have SHT 31 sensors).

When I did a comparison one time at the Extension office (with them having a Campbell Scientiftic CR-10 station with RM Young passive shield) and I having a SHT 15 housed in a Davis passive shield; I've noticed that the Campbell station DP readings were typically 2-3° lower during the day and basically the same to 1° variance at night. 

I've also noticed that whatever sensor is used for that Campbell Scientific station, the humidity readings typically goes up to 100% fairly easy whereas the new Davis VP2 station at the office only goes up to 98-99% (SHT 31 24hr FARS).

So my thinking has been now is that the diameter of the Davis shield and maybe the filter cap that Davis uses causes higher DP readings and a lack of 100% RH readings? Then again, it might be possible that the VP2 is more accurate than the Campbell, ASOS, and especially Acurite?

[CW2274]

Then again, it might be possible that the VP2 is more accurate than the Campbell, ASOS, and especially Acurite?

I think waaaay too many variables to make a truly accurate comparison, but get the effort.

[jgentry]

Then again, it might be possible that the VP2 is more accurate than the Campbell, ASOS, and especially Acurite?

I think waaaay too many variables to make a truly accurate comparison, but get the effort.

True. I see where Valentine Weather is dealing with a similar issue with comparing his Davis with ASOS

[dendrite]

I think I figured out why Davis VP2s & Vue stations typically report higher RH values (which affects DP temp readings) compared to Campbell Scientific stations and Airport stations. I'm beginning to believe that humidity sensors that are housed in a smaller diameter radiation shield reads lower during the day and in some cases higher at nighttime compared to the bigger diameter shields like Davis. What are your thoughts?

I'm trying to understand the scientific reasoning of the bolded.

[jgentry]

I think I figured out why Davis VP2s & Vue stations typically report higher RH values (which affects DP temp readings) compared to Campbell Scientific stations and Airport stations. I'm beginning to believe that humidity sensors that are housed in a smaller diameter radiation shield reads lower during the day and in some cases higher at nighttime compared to the bigger diameter shields like Davis. What are your thoughts?

I'm trying to understand the scientific reasoning of the bolded.

I know it really doesn't make sense. The only thing I can conclude is maybe the larger shield is doing a better job of reducing the effects of solar radiation than the smaller diameter shields would?  I really don't know.