Now that I have my rain gauge heater working, I thought I would tackle a modification to give me better accuracy to my rain gauge. And of course I am attempting to do it as cheaply as possible, and without too much destruction to the gauge itself.
I will keep you guys posted with my progress in the coming days. And I will try to keep a running total on cost. I am hoping to do the final working install on Jan 1, 2009 as this is when I am resetting my rain numbers for the new year, and I would rather not screw up my numbers for 2008 so late in the game.
EDIT: Here is the writeup, and my thoughts about installing it1. Start off with attaining the needed parts, tools and materials. You will need a funnel that has an opening to as close as you can get to 7 7/8 inches. I found one that was 7 3/8 inches wide. In fact I purchased two in case I screwed up the first or if I lose one to wind or something. Mine came in a group of 3 funnels from my local Advance Auto Parts store
(so now I have extras in the garage). You will need a sheet of cardboard, White Gloss spray paint for specifically plastic uses, a compass
(not the kind to find direction, but the kind you used in elementary school to make circles and such.), some white or clear silicone sealant, a hack saw, 10lb fishing line, sandpaper, a black Sharpie, a hobby knife, and an accurate ruler.
2. The original opening of the OS WMR-968 Rain Gauge Collection bucket is exactly 3 7/8 inches. I chose to use my compass and trace a circle of about 1 7/8 inches radius or roughly 3 3/4 inches diameter onto the cardboard.
<<<--- In retrospect I recommend that you bring this number down to about 3 1/2 inches. Then take your hobby knife and cut out that circle.
3. Take the cutout sheet of card board and place it down over your funnel and trace the circle with the sharpie onto your funnel.
(I found this to be the best method to "calculate" where to find my "cut point" on the funnel.)
4. You can now use the hack saw and cut across the funnel, using your line as guide. Then double check the above measurement using the ruler.
<<<--- Again I recommend that you bring this number down to about 3 1/2 inches. 
5. Clean off the "burrs" left after cutting the funnel. Clean the funnel of body oils and finger prints. Place the funnel in a safe location outside and spray paint it to match the OS rain gauge. As with any spray paint procedure, apply many thin coats between drying times rather than trying to cover it all at once. Once the paint on the outside of the funnel has dried well
(48 hours for me), flip it over and do it on the inside.
<<<--- I choose gloss paint that way when the rain drops hit the inside of the funnel they will be repelled better and force them down the funnel neck, rather than cling to the side.
...about the second or third coat
6. Again once the paint has had time to dry (48 hours), you can attach your funnel to your rain gauge. First, run a bead of the silicone sealant along the top edge of the rain gauge. And place the funnel on the bead and rain gauge, while the sealent is still wet, adjust your funnel to make sure it is as level as possible. Wait an hour or so for the sealent to set up a little bit. then run a bead of sealent along the outside of the funnel, where the rain gauge and funnel meet. Gently smooth this down with your finger, to fill in the gaps.
<<<<---- I choose the Silicone sealant because it will be easier to remove or replace in the future rather than a "more permanent" Crazy-Glue or adhesive option.
7. If you use the factory supplied metal screen that came with your rain gauge, you can still use it. All you have to do is sit it down inside the funnel. It won't be an exact fit as before, but it does fit well. While I was there I noticed that the string that was originally on the metal screen disingrated in my hands most likely from dry rot and the Sun's UV rays. So to secure my screen from getting lost to a brisk wind gust, I used some 10lb fishing line to tie it to my rain gauge shelf, but still with enough slack in it so i could place it in or remove it from the new funnel.
8. The Physical install is done, now time for the software changes. (Assuming you are using VWS or other software which allows you to make calibration settings.)
Now I will have the following Measurements, in regards to my
NEW rainfall collection funnel for the OS-WMR968 station.
d=3 7/8 Inches (Original collection funnel size on the unmodified rain gauge.)
D=7 3/8 inches (The size of the
NEW rain collection funnel)
So
Again using the formulas posted later on in this thread and a little logic we get...
New Gain = (d / D)
2 ...or me....
.2760 = (3.875 / 7.375)
2So I will enter into the VWS calibration window a gain of .2760
Be cautious that when you change this value it will alter any previous rain values you have recorded, so backup and write-down your rainfall data and prepare to edit those values. If you are fortunate enough like me to do this a few days before the new year, this will be a great help. In fact I am not going to change my gain value until 12:10 am on Jan 1st. In that way I will not corrupt my rainfall totals for December and more importantly for 2008.To get the new accuracy of resolution factor we do this math.
(Old Accuracy x New Gain) or again in my case...
(.04 x .2760) = .01104
Which translates to that after every internal bucket/lever trip that occurs in my rain gauge. I will record .011 inches of rain., instead of the original .04 inches of rain that occurred with the "Old" version of the rain gauge.
Enter your new gain here in VWS.
9. Congratulations, you are done. Now for the "Bean Counters", here is my total cost on items,
that I did not have around the house and had to purchase separately. Your costs may vary.
Silicone Caulk (Sealent) --- $2.87
Compass (My 11 year olds was broke) --- $2.49
Funnel Set (2 Qty-$2.49 Each) --- $4.98
+
Tax (5.0% rate in VA.) --- $0.51
----------------------------------------------------------------------
Grand Total --- $10.86
I hope everyone finds this helpfull, maybe the mods will make it a sticky.
