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 Author Topic: Accuracy of Davis Vantage Pro outside RH% sensor?  (Read 916 times) 0 Members and 1 Guest are viewing this topic.
Old Tele man
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 « on: December 18, 2011, 03:04:44 PM »

Q: has anybody calibrated or analyzed the accuracy of the Davis Vantage Pro outside RH% sensor(s)?

1) Are they linear over their 0-90% RH operating range? If not, how much of a deviation (or curve) is there?
2) Are they linear over their 90-100% RH operating range? If not, how much kink, deviation, curve or flattening is there?
3) What is their typical temperature coefficient (spec: 0.03% RH per ºF, referenced @ 68ºF) and which direction, up or down with temperature?
4) What is their typical drift (spec: ±0.5% RH per year) and which direction, up or down?

Why do I ask? Because I am trying to "back-door" calibrate the THGN801 RH-sensor with my WMR200A against a near-by CWOP CW5619 station which has a Davis Vantage Pro.

Below are the X-on-Y linear regression equations & coefficients that I got when I compared 6-days of my TEMP/DP/RH% data with same 6-days of CW5619's data (Y = CW5619, X = DW6988 (my station)):

• TEMP:  Y = 0.9457(X) + 2.9256; R^2 = 0.9857 (excellent!)
• DEWP: Y = 0.7011(X) + 14.9852; R^2 = 0.7722 (lousey)
• RH%:  Y = -0.0000017(X^3) - 0.0051(X^2) + 1.7070(X^1) - 6.8781(X^0); R^2 = 0.9903 (excellent, but CURVED, not straight!)
 « Last Edit: December 18, 2011, 09:12:37 PM by Old Tele man » Logged

• SYS: Davis VP2/WL-IP & Envoy8X/WL-USB
• CWOP: DW6988 - Cortaro, AZ
• WU: KAZTUCSO202 - Countryside Homes
DanS
Chiang Mai weather
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 « Reply #1 on: December 18, 2011, 05:31:09 PM »

I believe this is what is used if not close  http://www.sensirion.com/en/01_humidity_sensors/03_humidity_sensor_sht15.htm
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Dan ThaiWx website
DeKay
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 « Reply #2 on: December 18, 2011, 05:39:47 PM »

Close, I think.  The console uses a SHT-11.  I would think the outdoor sensor is the same.  I wrote about this here, and linked to the appropriate datasheet.

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DanS
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 « Reply #3 on: December 18, 2011, 06:03:55 PM »

ooops, you're right. After looking closer at the spec's and what member SloWeather posted earlier on this subject I now see. http://www.sensirion.com/en/01_humidity_sensors/02_humidity_sensor_sht11.htm  The humidity graph here matches Davis' spec sheet. Thanks for the correction.
 « Last Edit: December 18, 2011, 06:28:00 PM by DanS » Logged

Dan ThaiWx website
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 « Reply #4 on: December 18, 2011, 11:26:06 PM »

Although the current Davis products use the SHT-11, the CW number suggests it was obtained about 2007, so the instrument may have the earlier analog sensors.
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johnd
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 « Reply #5 on: December 19, 2011, 03:05:24 AM »

..the CW number suggests it was obtained about 2007, so the instrument may have the earlier analog sensors.

Only if the Mfg Code starts A4 or A5 (ie manufactured in 2004 or 2005). There is always stock proceeding slowly/steadily through the supply chain including an often-large buffer stock at Davis themselves but I would have expected virtually all 2005 manufacture stations to have been sold by late 2006.
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