Table 1 - Standard Calibration Quantities s
Cal: | 32.43 | milliliters | ||
Cal: | 16.215 milliliters | |||
@ .Ol” (std) | Cal: | 8.24 | milliliters | |
@ .05” | Cal: | 41.2 | milliliters | |
Flow rate for calibration: l/2 ml per second.
Accuracy desired is & 4% of volume at
After making changes to the bucket stop screws, retest the rain gauge operation using the calibration bottle and a large volume of water to produce 50 to 100 tips at a rate of 1 to 2 inches per hour. Remember to thoroughly wet the funnel and buckets first!
The total number of tips generated should correspond to the volume of water run through the gauge (expressed in milliliters; 1 quart = 946.3 milliliters) divided by the calibration quantity indicated in milliliters in Table 1. A tolerance of + 6% or better should be obtained through testing using this method. A more accurate test can be made in the lab using controlled conditions and more accurate test equipment.
Chapter 5: Maintenance
Rain gauges require regular maintenance. Gauges located in heavily forested areas or where airborne debris is a consideration should be serviced more often. The bucket assembly and drain screens should be inspected to ensure they are clean and free from debris such as leaves and insects. The tipping buckets should be carefully wiped clean to remove mud and dirt. Inspect the small tube of the main funnel and remove any obstructions inside it.
Test the gauge for correct operation and accuracy of the tipping buckets. Refer to Section 4.
Annually or after 6 months of heavy operation, put a drop of light machine oil onto each rotating part, specifically, the bucket assembly shaft at the bearings.
Should the tipping bucket fail to rotate freely about its axis, check the two small right angled brackets that hold the shaft and the bearings onto the main mounting bracket. These two
brackets can become loosened or misaligned causing the shaft to bind. The brackets ’ edges should be at the same level.
Severe friction will create excessive wear in the plastic bushings resulting in the magnet making contact with the switch and stopping the bucket assembly from tipping. Replace worn
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