Electronically Operated Tipping-Bucket Rain Gauge

1. Field of the Invention

This invention relates to rain gauges and more particularly to a gauge for measuring low-to-moderate rainfall rates wherein incremental volumes of rain water are removed from the bottom of a column of the collected rain water, whereby the rainfall rate is calculated by determining the number of increments of rain water removed from the column during a period of time.

2. Description of the Prior Art

Various techniques have been employed for measuring rainfall rates, such as, measuring the flow of water between capacitor plates; measuring the momentum of drops formed from the collected rain and allowed to fall a fixed distance; or measuring the water accumulation with a commercially available tipping-bucket rain gauge. While these gauges have been satisfactory for their intended purposes, they have not been found satisfactory for the measurement of low-to-moderate rainfall rates; for instance, in the order of 0.3 to 30 mm/h. In the case of the commercially available tipping-bucket rain gauge, a two-compartment tipping-bucket arrangement is utilized which tips when a certain quantity of water, usually 8.1 ml, has accumulated in one compartment, thereby emptying that compartment and exposing the other compartment for filling. Because of the relatively large quantity of water required to tip such a bucket arrangement, the best resolution obtainable is in increments of 0.25 mm of rainfall.

To overcome the disadvantages of hitherto employed rain gauges for the measurement of low-to-moderate rainfall rates, the rain gauge of the present invention has been advised which comprises, essentially, a rotary bucket wheel positioned beneath and communicating with a water column of collected rain. When the water column exceeds a certain height, as determined by an electronic probe circuit, the bucket wheel is actuated whereby a predetermined volume of water, for instance 0.1 ml, is removed from the bottom of the water column. By the construction and arrangement of the rain gauge, rainfall can be measured in increments of 0.005 mm.

FIG. 1 is an end elevational view of the rain gauge of the present invention;

FIG. 2 is an enlarged, side elevational view, partly in section, of the rain gauge of the present invention; and

FIG. 3 is a block diagram of the electronic probe circuit employed in the rain gauge of the present invention.

Referring to the drawings and more particularly to FIG. 1 thereof, the rain gauge of the present invention comprises a rotary stepping motor 1 connected to a wheel 2 having buckets 3 provided in the peripheral surface thereof, the wheel being positioned beneath a water-channeling block 4 through which collected rain water is conducted from a funnel 5 to the buckets. The collected water is sequentially discharged from each bucket to a trough 6 positioned beneath the wheel during rotation of the bucket wheel, to be described more fully hereinafter.

A fixed cam shaft 7 is connected to a suitable support block 8 which, together with the trough 6 and stepping motor 1, are mounted on a suitable base 9.

The details of the construction of the bucket wheel 2 and water-channeling block 4 are shown in FIG. 2 wherein it will be seen that the buckets 3 consist of a plurality of radially extending cylinders, each having a piston 10 slidably mounted therein and biased radially inwardly by a spring 11 mounted between the inner peripheral surface 2a of the ring and a collar 12 secured to the piston rod 13. The springs 11 bias the inner end of each piston rod against the peripheral edge of a cam 14 fixedly secured to the shaft 7. The development of the cam 14 is such that as the bucket wheel is rotated counter-clockwise each piston is progressively urged radially outwardly to the outer end of its respective cylinder until the spring is fully compressed. After one revolution of the wheel, the respective piston rod arrives at the stepped portion 14a of the cam whereupon the biasing force of the spring moves the piston rod radially inwardly until the piston once again is positioned at the bottom or inner end of the cylinder. The volume of each cylinder is only 0.1 ml; thus, by the construction and arrangement of the cam-actuated, spring-biased pistons, surface tension, which causes a problem when filling a small volume with water, is eliminated.

The pistons are provided with O-rings 15 to prevent leakage of water along the piston rods and a thin layer of oil is applied to the peripheral surface of the bucket wheel, as at 16, for lubrication and to prevent water leakage between the wheel and the water-channeling block 4. The side wall at the lower end of each cylinder is provided with a vent opening 17 to facilitate the sliding movement of the piston within its respective cylinder.

The water-channeling block 4 is provided with a main bore 18 communicating at the upper end thereof with the discharge end 5a of the funnel, the lower end of the main bore communicating with the upper end of each cylinder or bucket in the wheel 2. A laterally extending bore 19 is formed in the block 4 and communicates between the main bore and a recess or pocket 20 formed in the block providing a well for the receiving of an electrical probe 21.

The water-channeling block 4 and funnel 5 are stabilized on the base support 9 by a hold-down spring 22, and a hold-down bracket 23 secured to a rigid arm 24 fixedly secured to the base support 9.

The electronic probe circuit for actuating the rotary stepping motor 1 is illustrated in FIG. 3, and includes a probe amplifier and trigger 22, a monostable multivibrator 23, and a power amplifier 24 connected in the circuit between the probe 21 and the rotary stepping motor 1.

In the operation of the rain gauge of the present invention, when the water column in the well 20 reaches the level of the electric probe 21, the probe amplifier and trigger circuits 22 detect a current flow between the probe elements to thereby generate a trigger signal which switches the monostable multivibrator 23 into its active mode to thereby produce an output for 40 ms. This output is then amplified and applied to the rotary stepping motor 1 which causes the bucket wheel 2 to advance its position whereby 0.1 ml of water is removed from the bottom of the water column in main bore 18. Simultaneously, the next succeeding bucket is moved to the filling position. Before a bucket reaches the filling position, it is emptied completely into the trough 6 by the outward movement of the piston during one revolution of the wheel as described hereinabove. By employing a 40 ms output signal from the multivibrator, the probe circuit is disabled to prevent false triggering of the gauge while the bucket wheel is advancing. Each 0.1 ml of water removed from the bottom of the water column represents a 0.005 mm increment of rainfall; thus, the output of the multivibrator can be recorded as a hack-mark on a strip chart recorder 25 indicating an increment of rainfall, and by determining the number of increments during a period of time, the rainfall rate is calculated.

From the above description, it will be readily apparent to those skilled in the art that the gauge of the present invention has advantages over conventional tipping-bucket type rain gauges in that its accuracy is determined by physical dimensions, while at the same time, its operation is independent of temperature effects and the impurity content of the collected rain water. Furthermore, the sensitivity of the gauge allows the measurement of rainfall rates in the range of 0.3 mm/h to 33 mm/h which normally would not be detected.

It should be pointed out that while the figures disclose what is at present considered to be the preferred embodiments of the subject invention, this disclosure is made by way of illustration only and is not meant to be interpreted in a limiting sense, since when desirable other modifications and alterations may be resorted to by those skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims. Accordingly,