The Tip Rate Compensator – Model 2400-50 minimizes further, the small amount of error inherent in the performance of any tipping bucket rain gauge. For a one-inch rainfall event a 1 sq mi (2.6 km2) area receives about 17.38 million gal (65.8 thousand m3) of water during a 1-inch rainfall event. This means that without the Tip Rate Compensator, the water estimate for a one-hour event with a 1.5% accuracy tipping bucket could be off by 261 thousand gal (987 m3). By using the Tip Rate Compensator, the error is reduced to 173.8 thousand gal (658 m3) or an improvement of 33% in the error.
The sensing mechanism of a tipping bucket rain gauge consists of a pair of “buckets” that pivot on a shaft and alternate positions beneath the rainfall collection funnel. When a calibrated amount of water has entered the bucket, the water weight causes the bucket mechanism to pivot and bring the opposite collection bucket into position to start collecting precipitation. Each tip of the mechanism causes a magnet to pass a reed switch that provides a contact closure to a counting circuit. While the tipping bucket is in the tipping process of tipping, some water will fall into the filled side before the center divide has passed the outlet of the funnel. The error will vary depending on the rate of rainfall and the rainfall rate the tipping bucket has been optimized for.
A tipping bucket can be optimized so the error is essentially zero at a given rate. High Sierra Electronics’ standard calibration optimization is 2 inches (50.8 mm) of rain per hour. A 12-inch (30.5 cm) diameter funnel will collect 2.5 fl oz (73 ml) of water with 0.04 inches (1 mm) of rainfall. The bucket is set to start tipping at 2.4 fl oz (72 ml) of water. At a 2 inches (50.8 mm) per hour rate, another 0.03 fl oz (1 ml) will fall into the bucket while it is tipping and has not yet passed the center divide, which bring the total collected to the desired 2.5 fl oz (73 ml). At rain rates less than 2 inches (50.8 mm) per hour, the bucket will slightly over report, and at rates greater than 2 inches (50.8 mm) per hour, it will slightly under report.
The Tip Rate Compensator mounts directly on the precipitation input connector on the top of the HSE Transmitter. A microprocessor in the Tip Rate Compensator tracks the time between tips and thus establishes the current rate of rainfall. With each tip, a proprietary algorithm calculates the water that falls into the full side of the bucket while it is tipping. When this amount totals the equivalent of a tip, the Tip Rate Compensator puts out a count just as a tip of the bucket would do which adds to the transmitter’s precipitation accumulator and initiates a transmission.
