davis uv sensor

[jerryg]

When i first got my vp2 stations i did not see the need forthe solar or uv sensors, then i decided to get a solar to see how it worked and like messing with it so ordered one for the backup station. Well, when i bought a used station it had the uv sensor with it, it was several years old but still worked. I compared readings with other stations and found it was reading somewhat low but i could live with it then it started to add a whole 1 to the reading for up to a half hour at a time. Well nuts, lol. I really do not like having something not working  even if i do not see the need for it in the first place, so when Archer put his on sell i bought a replacement for the quirky one. I had no intention of getting the old one repaired but got some Xmas money and i sent it in to Davis for refurb. I got it back today and put it out on the backup station and was eager to compare the two. Well i was surprised to see the repaired sensor reading about 1 higher than the new one. I looked up the specs and it says +or - 8, well that means if your uv is 10 then the good specs could be as low as 9.2 and as high as 10.8 a 1.6 spread and still withing specs. The big difference i noticed is the new sensor quit reading at 4:30 pm and the one just back from Davis did not quit until 5:30 pm. It seems to me that is a large difference in sensitivity. It looks to me like there is quite a bit of leeway on these things. I guess my main point is it will be hard to compare one uv reading with another nearby because of the large spread in each sensor. Just a little info for anyone trying to compare readings. Davis says they should be recalibrated annually to give accurate readings, seems to me with this big a spread in specs they may be a bit much.

[Weather Display]

yes, they do tend to read higher than should over time (i.e drift in calibration)
adding a offset to the software can compensate for that

[JACK10562]

You would think the two would at least be fairly close.

There's a saying I read here, somewhere:

"A man with a watch knows what time it is. A man with two watches is never sure."

I think it was dale...

[archae86]

The big difference i noticed is the new sensor quit reading at 4:30 pm and the one just back from Davis did not quit until 5:30 pm.

The "quit reading" matter might well be a manifestation of the rather odd characteristic of the Davis UV sensor that it reports zero once the value it would report drops below 0.5.  With an unobstructed view of the sun on a cloudless day, this gives a rather clipped appearance to the beginning and the end.  As you have owned one for a long time, I doubt this is a surprise, but I add it to the thread in case others might be surprised by the "quit reading" phenomenon.

[johnd]

The "quit reading" matter might well be a manifestation of the rather odd characteristic of the Davis UV sensor that it reports zero once the value it would report drops below 0.5. 

This characteristic is determined by the console firmware, not by the UV sensor, so there shouldn't be any difference between old and new sensors if checked on the same console.

[jerryg]

Well i just got back from the post office, i called Davis about the differences i was seeing between the repaired sensor and the new one i got at the end of December and the tech said they should read pretty close to each other and that i should send it in for warranty recalibration. So in a few weeks i should get it back and will post how close the reading is with the repaired one, should be interesting.

[jerryg]

Ok got the recalibrated sensor back from Davis and the readings look real good. The first sensor i had repaired was showing 3.7 and the new one they recalibrated is showing 3.6, pretty darn close. That is what the tech told me the new sensor should be showing. I would never had known the new sensor was reading so low if i did not have the repaired one for reference. How do you know if yours is right are not? I have been doing alittle comparing of my max readings compared to the one wu is posting using their formula and today they forecast a high of 6.9 and i had a high of 7.0, so maybe that reading can be used carefully to get an idea of how close it is. I am lucky that i have 2 metars nw and se of me withing 8 to 12 miles from me, gives me a good idea of what i should show on my readings.