The maximum allowable error of rainfall sensors for automatic weather stations is 10 ±04 mm and the common error is the over tolerance rainfall records, namely the abnormal rainfall records from rainfall collectors or generated by computers. Through the years use and maintenance practice, some experiences are accumulated; for example, by adjusting the base, namely changing sensor measurement tipping bucket deflection angle, the error usually can be controlled within the allowable range. Two cases of the SL3 1 rainfall sensor faults are described, in which regular/irregular multi count over tolerance records are processed properly.