ARM uses two different types of weighing buckets. Both operate by measuring the weight of liquid in a bucket as it changes over time, in order to calculate the precipitation amount and precipitation rate.
The weighing bucket in the Arctic uses three vibrating wire transducers that help to determine the weight. These weighing buckets use the datastream name [site]wbgeonor[facility].[data level]
Weighing buckets deployed in other locations (like AMF1, AMF2, SGP, and ENA) use a stainless steel loading cell with very high precision, that is protected against environmental influences and used as the sensor element. The orifice of the gauge is also heated, and when snow or ice occurs, the weight of its water is equal to the amount observed. The weight of the collection bucket is measured once per minute, and differences between the measurements as rain falls into the bucket determines the amount of rainfall that's occurred over the previous minute. These weighing buckets are called Pluvio2 and use the datastream name [site]wbpluvio2[facility].[data level]
The gauges used in the Arctic (currently OLI) are enclosed in a double alter sheild to decrease wind flow over the opening of the bucket and to increase the effeciency with which rain is caught. The gauges not used in the Arctic have a smaller wind sheld to serve the same purpose.
* For more information see the WB Instrument web page
Typically, weighing buckets deployed at both Arctic and non-Arctic locations use antifreeze and oil to prevent freezing and evaporation of liquid.
Currently, however, the weighing bucket deployed with AMF1 (ANX), unlike in warm climates, does not have oil floating on top of the water/antifreeze mixture. All oils that have been tried have not been up to the task. Without the oil to help prevent evaporation, the weight in the bucket can go down when evaporation occurs. This can sometimes give the appearance of negative rain amounts, or negative rain intensity.