[Weather] 1-wire humidity sensor for outdoor use?

[Karl Uppiano]

----- Original Message ----- 
From: "Dave McGuire" <mcguire at neurotica.com>
To: "List for 1 Wire Weather Stations and devices" <weather at buoy.com>
Sent: Wednesday, November 29, 2006 11:09 AM
Subject: Re: [Weather] 1-wire humidity sensor for outdoor use?


> On Nov 29, 2006, at 1:59 PM, Karl Uppiano wrote:
>>>> I have had good results with mine once I shielded it from the   light. 
>>>> I
>>>> found
>>>> that even indirect sunlight on a bright sunny day -- even inside a
>>>> radiation
>>>> shield -- would cause the sensor to get all flaky. I put a small 
>>>> piece
>>>> of
>>>> black heat shrink tubing over it, leaving openings at each end  for 
>>>> the
>>>> air
>>>> to circulate (i.e., I did not shrink the tubing, I just allowed  it  to
>>>> remain
>>>> loose). This sensor has been in place for about 18 months, and the
>>>> original
>>>> one might have been OK too, if I had shielded it from the light.
>>>
>>>   The datasheets even state that the component is light sensitive.
>>
>> Yes, however, I was surprised how light sensitive. IIRC, the data  sheet 
>> said
>> avoid direct sunlight, but mine was affected by indirect sunlight.  I'm 
>> just
>> saying, if your sensor is flaky, make it *really* dark.
>
>   Ahh ok, I see what you mean.  Yes, the degree of photosensitivity  is 
> surprising.  Making it really dark while still ensuring adequate 
> environmental exposure can be difficult.  I wonder if it'd be useful  to 
> mount it in the middle of a small serpentine tube, open at both  ends, 
> with a small fan to push air through it lightly.
>
>               -Dave

I noticed that my AAG humidity sensor would start indicating erratically 
every afternoon at about 2:00PM, but only on sunny days. Direct sunlight 
could never reach my sensor, but it must have been bright enough ambient 
light to trigger problems. So, I just cut a 3/4" piece of 1/4" heat shrink 
tubing and slipped it over the HIH-4000 and snapped the cover back on. 
Problem solved. Up here in Northwest Washington State, we get lots of rain, 
and the sensor frequently indicates 100% RH. But I do not think it gets 
soaked with condensation on a regular basis.

I wonder how the sensitivity/accuracy would be affected by placing a small 
amount of gauze over the sensor in very wet environments...