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1% relative humidity outside - I don't think so!

Discussion specific to Davis weather stations
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martinu
Posts: 45
Joined: Wed 01 Jan 2014 7:54 pm
Weather Station: Davis Vantage Vue
Operating System: Windows 7
Location: Leyburn, North Yorkshire

1% relative humidity outside - I don't think so!

Post by martinu » Thu 31 Jul 2014 6:11 am

I noticed that my temperature graph in Cumulus showed the dew point doing silly things: since about midnight it started going downhill and has now settled on -40 deg C :o

The cause seems to be the humidity which has gone from around 30-50% to 1%. See these graph (over a 48 hour period):

Humidity

Image

Temp

Image


This is on a Davis Vantage Vue. Does it look like a fault? Could there be some dirt or moisture on the sensor head or is it likely to be a warranty claim (I got the weather station at the beginning of this year)? Cumulus is showing that all 8 TX batteries are OK, as is the console battery.

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steve
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Re: 1% relative humidity outside - I don't think so!

Post by steve » Thu 31 Jul 2014 6:25 am

martinu wrote:This is on a Davis Vantage Vue. Does it look like a fault?
Assuming that the console is also showing an invalid RH value, then yes, almost certainly a faulty sensor.
Steve

martinu
Posts: 45
Joined: Wed 01 Jan 2014 7:54 pm
Weather Station: Davis Vantage Vue
Operating System: Windows 7
Location: Leyburn, North Yorkshire

Re: 1% relative humidity outside - I don't think so!

Post by martinu » Thu 31 Jul 2014 8:14 am

steve wrote:
martinu wrote:This is on a Davis Vantage Vue. Does it look like a fault?
Assuming that the console is also showing an invalid RH value, then yes, almost certainly a faulty sensor.
Yes the console is showing the same value. Interesting that it's gradually given lower and lower readings rather than just suddenly switching to a silly value.

How does a humidity sensor work? Is it likely to be a foreign body in or around the housing that's causing the problem or is it likely to be the sensor itself which has gone loopy? When the rain has stopped I might get my ladder out and take the weather sensor off its pole to look for anything obvious.

martinu
Posts: 45
Joined: Wed 01 Jan 2014 7:54 pm
Weather Station: Davis Vantage Vue
Operating System: Windows 7
Location: Leyburn, North Yorkshire

Re: 1% relative humidity outside - I don't think so!

Post by martinu » Thu 31 Jul 2014 1:53 pm

martinu wrote:
steve wrote:
martinu wrote:This is on a Davis Vantage Vue. Does it look like a fault?
Assuming that the console is also showing an invalid RH value, then yes, almost certainly a faulty sensor.
Yes the console is showing the same value. Interesting that it's gradually given lower and lower readings rather than just suddenly switching to a silly value.

How does a humidity sensor work? Is it likely to be a foreign body in or around the housing that's causing the problem or is it likely to be the sensor itself which has gone loopy? When the rain has stopped I might get my ladder out and take the weather sensor off its pole to look for anything obvious.
Ants! That's what was causing the problem :o

I took the sensor unit down and dismantled the shield plates as described in the manual. And loads of ants fell out. When I took off the gauze shield around the sensor, it was absolute packed with the little buggers. Having cleaned it thoroughly and put it back together, it's now giving sensible values of about 50-60% humidity and hence sensible dew point values that are not around -40 deg C.

I'll need to keep an eye on that one if I see the humidity going lower than normal.

TwoTonTed
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Joined: Wed 26 Aug 2015 5:39 pm
Weather Station: Davis Vantage Vue
Operating System: Windows 7
Location: St Brides, Vale of Glamorgan

Re: 1% relative humidity outside - I don't think so!

Post by TwoTonTed » Sun 27 May 2018 11:44 am

had my Vue for 2 years without following the cleaning instructions so very pleased I found this thread. Outside humidity was reading 1%. Took the shield apart, and it was all gummed up with debris. Cleaned the shield and sensor and now working fine.

TwoTonTed
Posts: 8
Joined: Wed 26 Aug 2015 5:39 pm
Weather Station: Davis Vantage Vue
Operating System: Windows 7
Location: St Brides, Vale of Glamorgan

Re: 1% relative humidity outside - I don't think so!

Post by TwoTonTed » Mon 04 Jun 2018 2:01 pm

that said, it has failed again. I'm told by Prodata that I need to buy a new harness at £188. I had a new harness under warrantee 2 years ago for a separate problem but am no longer covered :(

I live a mile inland from the sea in S Wales and we do get violent weather and see spray in not uncommon. It seems this can be very damaging to the combined humidity/tem sensor in the Vantage Vue. 2 years life seems poor however.

Any advice I can follow? I can see that the much more expensive vp2 station is more flexible for changing this part, and I assume cheaper in that regard. Is the Vue perhaps too lightweight for my location; it does get a battering in the winter.

Thanks for any help.

ExperiMentor
Posts: 50
Joined: Tue 24 Nov 2015 11:30 pm
Weather Station: Fine Offset
Operating System: Windows 7; Linux
Location: Switzerland

Re: 1% relative humidity outside - I don't think so!

Post by ExperiMentor » Thu 07 Jun 2018 10:00 pm

The retail price of a temperature and humidity sensor is less than a fiver (see for example https://shop.pimoroni.com/products/digi ... ity-sensor). I'm not saying this will fit your station - just that if they're charging a pile more it's a rip-off

AllyCat
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Re: 1% relative humidity outside - I don't think so!

Post by AllyCat » Sat 09 Jun 2018 3:43 pm

Hi,

I thought that Davis use one of the "Legacy" (analogue) Sensirion SHT... Humidity sensors. They're more expensive, difficult to obtain and very small SMD devices, so difficult to fit. Take a look at this thread and perhaps look for posts from Belfyboy on the forum.

Cheers, Alan.

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