Casella CEL Tipping bucket rain gauge - Manual (Page 4)

fitted to the base of this version (please consult the Casella CEL sales
department).
2. PRINCIPLE OF OPERATION
The rain gauges comprise a light weight injection moulded plastic divided
“tipping bucket” assembly with stainless steel pivot pins that rest upon
stainless steel pins in the support assembly. The use of pins produces a
rolling rather than pivoting motion when the bucket tips, which reduces the
likelihood of friction.
Rain collects in one side of the bucket, which tips once a predetermined
volume of water has been collected. The tipping action discharges the
collected water and positions the other side of the bucket under the
discharge nozzle ready for filling.
Each time the bucket is tipped, a magnet within the bucket moulding closes a
reed switch in the support assembly. The use of a sealed reed switch,
capable of indefinite operation, ensures the instrument has a long working
life. Each contact closure pulse represents a discrete amount of rainfall
appropriate to the instrument’s calibration. These “tipping” pulses may be
counted or recorded using a variety of methods, as described in Chapter 6.
The tipping bucket mechanism is mounted inside the body on a cast
aluminium-alloy base, incorporating a built-in spirit level to facilitate correct
Principle
Tipping Bucket Rain Gauge
Accuracy / 100 Tips
0
5
10
15
20
25
1 10 100 1000
Rain fall in mm/Hr
Er
ror
Pe
r10
0
Tips
0.1mm Tip
0.2mm Tip
0.5mm Tip
Max U.K
recorded -
Devon
Light Moderate Heavy
Classification WMO 5%
Figure 2: Accuracy of 0.1 mm, 0.2 mm and 0.5 mm tip versions
Page 4 of 16
Tipping Bucket Rain Gauges
User Manual