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Belfort 5915 Precipitation Gage Rebuild

C. Bronson H. Crothers
01, May 2015

To measure the amount of precipitation that has fallen on the watershed, Belfort 5915 precipitation gages are used, as can be seen in the following photo:

ID plaque of Belfort 9515.
The serial No. 956 Belfort 5915 precipitation
gage electrical, exposed by removing the overall shroud.

The picture above is of the electrical interface of a Belfort 5915 precipitation gage.

This particular gage has an electronic output, as well as the legacy mechanical, two throw pen/ink drum system.

The rebuild of this gage was done in the spring of 2013. The gage itself was one of five similar Belfort 5915 gages, used by the BBWM research effort. After many years in service, the potentiometer in the unit developed a dead spot. This often happens when a potentiometer wiper is moved back and forth across a small area of the resistive surface. In an instrument such as the Belfort 5915, this often happens. As precipitation fills a catch bucket, the bucket depresses a spring. That spring may only move a small amount, which in turn moves the potentiometer wiper a small amount. The precipitation then stops. When it stops, despite efforts to prevent it, some of the precipitation, just deposited, then evaporates. This causes the wiper to move back across the same area again and again. Over time this one area will wear out more quickly.

Background

ClockDrive-DSCN4532
The serial No. 956 Belfort 5915 precipitation gage clock drive,
and battery holder.

The clock drive is used to spin a drum with graph paper on it. This was the default method of collecting, and storing precipitation data from the BBWM sites. Also mounted on the base plate is a dual "D" size battery holder. This was used as a power source for the clock drive. At one site AC power was available for a time, and an AC powered version of the clock drive was used.

At one site AC power was available for a time, and an AC powered version of the clock drive was used.

The Summit, Camp, and East Bear precipitation collectors all used battery powered clock drives. Most were powered by 12 volt solar systems, with standard 12 volt lead-acid (car battery) battery backup. The Camp installation used much higher capacity "golf cart" batteries, although of the same 12 volt rating, not the standard 6 volt golf cart voltage.

ID plaque of Belfort 9515.
The serial No. 956 Belfort 5915 precipitation gage placard,
exposed by removing the overall shroud.

The standard means of recording precipitation data was by using the standard Belfort Inc. dual traverse (up, then down) graph paper recording drum and paper.

ID plaque of Belfort 9515.
The serial No. 956 Belfort 5915 precipitation gage recording drum.
It sits upon the catch bucket platform of the gage itself.

A wand with an ink pot, or small felt tip marker would sweep upward to mark the collection of the first 6" of precipitation. Then the arm would sweep back downward to mark the next 6" of precipitation. All the while the drum would rotate such that one drum rotation occurred in about 8 days. In this way a full 12" of precipitation could be recorded over one week of time, without overwriting the previous week's line.

If there was an overwrite, as would happen from time to time due to site access issues, the graph would have to be interpreted by the examiner. Performing the interpretation was usually straight forward.