[wxqc] Non-linear Humidity Sensor

[Tim Crummel]

Peet bros seem to have a new sensor for their U2100 which I have found to be
quite accurate been testing for a year and it seems to follow me reference
model A heath kit with a Honeywell sensor And this sensor is about 50
dollars so I would try the new peet bros and see.

TIM

-----Original Message-----
From: wxqc-bounces at lists.gladstonefamily.net
[mailto:wxqc-bounces at lists.gladstonefamily.net] On Behalf Of Gerry Creager
N5JXS
Sent: Saturday, April 15, 2006 11:37 PM
To: Discussion of weather data quality issues
Subject: Re: [wxqc] Non-linear Humidity Sensor

How old is the sensor?  It might want to be replaced.  I'm not sure if 
the Peet sensor is a gold-leaf type, but if so and if it's been 
distorted, it could well have decided it's not gonna work right.

gerry

jwilson wrote:
> Hi,
>  
> I have a question on how to handle a non-linear humidity sensor.  I have 
> occasionally been getting error reports indicating my dew point is in 
> error.  In order to see if I could determine a better calibration for my 
> system (Peat U2000) I purchased a sling psychrometer and have been 
> running tests periodically for the past two months.  What I have 
> discovered is that the humidity sensor is non-linear.  Particularly at 
> low humidity readings, although it is also off at high humidity levels 
> also.  This information seems to correspond to the days I get the big 
> red X on my QC data.
>  
> I determined the non-linearity by plotting the data from the 
> psychrometer and from my weather station in an X-Y scatter plot and then 
> applying a trend line to the data (using Excel).  The "best fit" 
> provides me an equation of y = -0.0041x2 + 1.6786x - 25.872, where x is 
> the psychrometer data and y is the weather station data.
>  
> http://pond1.gladstonefamily.net:8080/cgi-bin/wxqchart.pl?site=AP677
>  
> Does anyone have any ideas as to how to correct this problem?  Is this a 
> common problem with humidity sensors?
>  
> Thanks
>  
> *Monty Wilson, AP677*
> jwilson at ncfcomm.com <mailto:jwilson at ncfcomm.com>
>  
> 
> 
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-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University	
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843
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