Calibrate the Rain Gauge

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Items Needed:

Rain collector, the display unit, plastic cup, pin, screwdriver.

  1. First, make sure the rain collector is on a level surface.
  2. Place the display unit close by so you can monitor it during the calibration process.
  3. Make a pinhole in the bottom of a plastic cup. Hold the cup over the rain gauge and fill it with exactly 1 cup (8 oz.) of water, allowing the water to slowly drip into the rain gauge. You should hear the internal buckets tip and see the water drain through the rain gauge.
  4. A few seconds after each bucket tip, the display console will display rainfall in approximately 0.01" or more increments.
  5. The cup of water should take more than 20 minutes to empty; a quicker period will result in an inaccurate calibration. (We’re trying to simulate a normal steady rainfall.) When the cup is completely empty of water, the display console should register 1.68"

If the rain gauge doesn't register close to 1.68" after the cup is empty of water, then you should make an equal adjustment to the two calibration screws beneath the tipping lever. Be sure to adjust both screws the same amount. Turning screws clockwise will decrease rainfall amount. Turning screw counter clockwise will increase it.

Adjustment:

  1. To adjust the rainfall reading by 2.5% turn both screws 1/4 of a turn.
  2. To adjust the rainfall reading by 5% turn both screws 1/2 of a turn.
  3. To adjust the rainfall reading by 7.5% turn both screws 3/4 of a turn. 
  4. To adjust the rainfall reading by 10% turn both screws 1 full turn.
  5. There should be nearly an equal number of water drops between bucket tips. If not, then adjust the calibration screws beneath the tipping lever until an equal number of water drops are tipping the buckets. Then, restart the calibration procedure.

If you don't hear the buckets tipping and see water dripping alternately out of each drain, there may be an issue with the rain gauge or its adjustment.

 

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