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TIPPING BUCKET RAINFALL RECORDER


GENERAL

The principle of this type of recording gauge is very simple. A light metal container id divided into two compartments and is balanced in unstable equilibrium about a horizontal axis. The rain is led from a conventional collecting funnel into the uppermost compartment. As for the raingauge, the size of the opening of the collector is not really important, but a standard area of about  400cm² should probably found convenient.

The main advantage of this type of instrument is that it can have an electronic pulse output and can be recorded at a distance or for simultaneous recording of rainfall and river stage on a water stage recorder.
 
 

MEASUREMENT SPECIFICATIONS

After a predetermined amount of rain has fallen, the bucket became unstable in its present position and tips over to its other position of rest. The compartments of the container are so shaped that the water can now flow out of the lower one and leave it empty. Meanwhile, the rain falls into the newly positioned upper compartment. The movement of the bucket, as it tips over, is used to operate a relay contact and produce a record that consists of discontinuous steps. The distance between each step represents the time taken for a pre6specified amount of rain to fall. For many hydrological purposes, in particular for heavy rainfall areas and flood warning systems, 0.5 to 1.0 millimetre buckets are satisfactory.
 

CONDITIONS OF USE

All gauges in any area or country should have comparable exposures, and the same siting criteria should be applied to all. The gauge should be exposed with its orifice being horizontal over ground level. The height of the gauge orifice above the ground should be as low as possible because the wind velocity increases with height, but it should be high enough to prevent splash from the ground. A standard height of one metre is recommended.

When adequate conditions from the wind is not possible, individual objects should not be closer to the gauge than a distance equal to four times their height.
 

TECHNICAL SPECIFICATIONS

Ring collector with a sharp edge linked to a cone-shaped funnel with a sufficient slope to avoid splashing effects.
Opening area : 200cm² to 1000 cm²
Bucket volume : 20 ml (represents 0,5mm of rain for a 400cm² collector area)
Frequency of chart record (indicate on order) :
- drum recorder : daily, weekly,
- strip chart : 2 weeks to monthly or more (paper speed selectable from 1à to 20mm/h)
Stand housing