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[wxsig] Rain Gauge Calibration

William Beals will at beals5.com
Wed Feb 23 04:03:05 UTC 2005


Gary and Clay:

Russ and I remember this being a VERY hot topic earlier, even before the
T238 got involved with the rain sensor.  The question got answered, but
we're having trouble finding the archives that "proved it".

Russ remembers that it is not the inside diameter (5 7/8"), but rather the
diameter to the centerline of the lip (6.00") that matters, but that only
gets you to 15.67oz, not quite 16oz.  Several experts have been questioned,
hopefully an answer soon (if Gary doesn't beat me to it).

will

-----Original Message-----
From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
Behalf Of Gary R. Schenaman
Sent: Monday, February 21, 2005 10:57 AM
To: TAPR Weather Station SIG Mailing List
Subject: Re: [wxsig] Rain Gauge Calibration

I WILL TRY TO FIND THE METHOD THAT I USED TO CALIBRATE USING AN HPLC PUMP
THAT IS TRACIABLE TO NS.  ONCE I FIND IT I WILL EMAIL EVERYONE WITH THE
METHOD.  HPLC IS A LAB PUMP THAT STANDS FOR HIGH PRESSUSE LIQUID
CHROMOTOGRAPHY.  BIG G.
----- Original Message -----
From: "Clay Cottingham" <Clay at Cottingham.net>
To: "TAPR Weather Station SIG Mailing List" <wxsig at lists.tapr.org>
Sent: Sunday, February 20, 2005 9:25 PM
Subject: [wxsig] Rain Gauge Calibration


> Trying to understand the theory behind the operation of the rain gauge.
>
> I have the original Dallas Semiconductor rain gauge. The instructions that
> come with it state to "Adjust the calibration screws so that 16 Oz at the
1
> inch per hour rate produces 100 counts." This appears to correspond to
1.00"
> indicated on the T238 display.
>
> Where I am confused is this: Taking the measurement of the radius of the
> rain gauge and caculating the area exposed and converting to ounces gives
me
> about 15 ounces per inch of rain:
>
> 5.875 inches diameter
> 2.9375 inches radius
>
> = 27.109 square inches
>
> At 1" of rain, this would be 27.109 cubic inches
>
> Converting cubic inches to ounces;
>
> 1.80468751 cubic inches per ounce
>
> = 15.021 ounces.
>
> Why then do you calibrate with 16 ounces?
>
> Want to make sure I get this right before I go mount it on the pole!
>
> Thanks!
>
> Clay
>
>
>
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