Davis Pro2 Rain Gage fix

4/2017
 D Vautier

Tum cornix plena pluviam vocat improba voce
The crow with rude cackles cries for rain.

                           Publius Vergilius Maro

 


My Davis Pro2 collector bucket got blocked with debris so I cleaned it out instead of dumping it out.  The resulting volume of water flowing down destroyed the reed switch.  I determined that it was just the reed switch and not the instrument panel by shunting across the switch about 6 times in one minute.  This registered .25 inches so I felt that just the reed switch had to be replaced.  I ordered a new one from Davis for $3.

Removal

I removed the collector bucket and cut the wires to the seesaw unit.  This unit is held in place by two tabs.  Pry each tab back while lifting at the base.

 

 

Here I have freed the seesaw from both tabs.  Now I took it and got off the roof.  

Here is the seesaw.

Under the seesaw unit are four little tabs that have to be pried back

Here is the reed switch and its cover.  I will Install a new reed switch, reassemble and re-solder.  The reed switch closes in any magnetic field so it does not have to be oriented in any way but I put my new one in face up.

Calibration

Since I had the seesaw unit out I decided to measure calibration.  Each tip of the seesaw records .01 inch on the monitor and it is supposed to take 5.44 ml (109 drops) of water for one tip or 54.4 ml for 10 tips since the seesaw may not be symmetrical or have different adjustments for each side and 10 sounded like a big enough sample.  So I put 54.4 ml in a small container, (rather I put 54.4 grams of water in a small container) and then took my measurement using a syringe.  During this calibration I did not have the reed switch in place.  It can burn out.

After 10 tips I had almost one full tip left so I lowered both screws 360 degrees (clockwise) to get more water into each bucket.  The next several tests left me over about 5 drops which was pretty accurate, probably within .05 percent.  When I got to within 3 drops I decided it was close enough.  The adjustment required a 360 clockwise turn on each screw and then minus about 10 degrees.

I got the 5.44 ml value to tip by measuring the collector size (6.5 inches = 33.183 sqin = 543.77 ml /100 = 5.44 ml).  I think Davis has the same figure.

  Here is the installed unit.  I solderd leads and then capped.