The double-walled rain and snow gauge differs from the double-walled rain gauge only in that, in the former, all the parts required for processing snow into meltwater are duplicated; therefore, the time required for thawing is not lost for recording precipitation. (DIN 58 666)
The double-walled design reduces evaporation. Reducing evaporation error increases the measurement accuracy of the rain gauge.
Both devices should ideally be installed on level ground so that they are at least as far away from neighbouring buildings, trees or bushes as the height of these; this applies particularly to the weather side.
The collection container is suspended from the corresponding holder, which is screwed to a pole so that the collection area is horizontal and 1 m above ground level. A snow cross in the device prevents snow from being blown out by wind.
To measure the rain depth, the upper part is unhooked, the collecting vessel is removed from the lower part and emptied into the measuring cylinder. After a snowfall, the observer replaces the entire device with an empty one, carefully removing the snow cross from the filled one and inserting it into the other. The snow-filled collecting vessel is then brought into a warmer room and the collecting opening is closed with a lid. After the snow has melted, the meltwater depth can be determined as usual using the measuring cylinder, where each division corresponds to a precipitation depth of 1/10 mm. In unsettled weather, there is a possibility that the downdraft of atmospheric precipitation, which can occur due to eddies forming on the casing, can lead to a shortfall in the amount of precipitation collected compared to the amount actually fallen. Such incorrect measurements can be prevented with the Woelfle windshield, which consists of a ring 840 mm in diameter with 16 elastic shield leaves. A common bracket supports the device and windscreen, with four struts orienting the windscreen toward the collection surface. The entire device is mounted on a tubular column with a diameter of approximately 75 mm, which itself is generally not included in the scope of delivery.
Double-walled rain gauge according to Hellmann,
Collection area: 200 cm²
Material: stainless steel sheet
consisting of:
1 upper part with collecting ring
1 lower part
1 collecting can
1 holder
1 measuring cylinder RM25 T171 (for 10 mm rain height, divided into 0.1 mm rain height, according to DIN 58667B, material: plastic)
Dimensions: ø190 mm, height: 445 mm
Weight: approx. 3 kg
Double-walled rain and snow gauge according to Hellmann,
as above,
but consisting of:
2 upper parts with collecting ring
2 lower parts
2 collecting cans
2 snow crosses
1 protective cover
1 holder
1 measuring cylinder RM25 T171
Weight: 4.7 kg
The main features of the Hellmann rain gauge are:
- Collection area 200 cm²
- Material V2A
- low evaporation error
- easy operation
- high reliability
- maintenance-free
