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Gauging the truth

Three MU Students reshape the way rain is measured
Friday, March 5, 2004 | 12:00 a.m. CST; updated 7:32 a.m. CDT, Wednesday, July 9, 2008

In the scientific community, it’s been known for sometime that the tipping-bucket rain gauge, the most popular type of automated rain gauge, was in need of a design revision.

The present design, which uses two chambers in a tipping device to catch water from a suspended funnel, has remained virtually unchanged for more than 300 years. Unchanged, and essentially inaccurate during heavy rains, that is.

But the rain gauge recently received its long overdue redesign when three MU seniors slightly remodeled it and, in the process, improved the instrument’s accuracy. The students — Christian Volz, Donnie Golden and Seth Studer — redesigned the instrument for their semester project in a capstone course for senior biological engineering and agricultural systems management students.

An idea is born

The idea for the project originated after Volz heard a presentation at Sanborn Field that mentioned the rain gauge’s weakness of not accurately recording precipitation during heavy rainfalls.

In the original design, .01 inches of rainfall shifts the center of gravity of one chamber, which is then dumped, triggering an electronic pulse to a data-logger. The gauge automatically logs each tip, providing a record of the amount of rain that has fallen.

Inaccuracies occur when water accumulates, and then goes unmeasured, in the tipped side. During heavy rains, while the chambers are switching frequently, some water is unaccounted for because excess builds up in the chamber that has just tipped. This creates a larger margin for error and a less accurate weather assessment.

The tipping-bucket mechanism is less expensive to operate than the cylinder-shaped rain gauges used at weather stations, which require manual maintenance and recording. Meteorological scientists use the tipping bucket because it can be placed at remote locations and is self-monitoring, despite its inaccuracy.

The capstone course instructor, Allen Thompson, associate professor of biological engineering, said that after leaving Sanborn Field, Volz approached him and asked if the group could redesign the rain gauge as a capstone project.

“In the capstone course, students take an existing problem and try to design a solution,” Thompson said.

Making better gauges

Volz said the team first tried new system designs, focusing on factors such as the conductivity and weight of the water. But they eventually realized that altering the existing design would be more efficient.

Because students are encouraged to work within the existing constraints of the problems they choose to tackle, Thompson said he was happy that Volz, Golden and Studer’s new design does not change the original data-logger, funnel or base of the gauge.

The key to the group’s revision was raising the tipping point on the portion of the instrument that collects the water. This modification reduced the axis of rotation and shortened the tipping time, thus reducing the amount of water left unmeasured.

Using simulations inside the biological engineering department’s 50-foot rain tower, tests showed the improvements made the instrument more accurate when monitoring rainfall of three to four inches per hour.

“While our testing procedure does not make it possible to establish that we have achieved our goal of plus or minus 1.1 percent (margin of error), it did tell us that the new design’s error does not increase with precipitation rate,” Volz said. “Our tests indicate that the error will decrease with increasing precipitation on the prototype.”

Thompson added that the new design is as reliable in light rain conditions.

On the road

On March 26, Golden and Volz will head to St. Joseph for the Mid-Central Conference of the American Society for Agricultural Engineers, the society for engineering in agricultural, food and biological systems.

The group will represent MU in a competition against design teams from Iowa State, Kansas State and the University of Nebraska.

Armed with the new and improved gauge, a shortened version of the capstone paper and a presentation for the judges, Volz said he is excited about meeting people who share his interests and exchanging new designs and ideas.


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