ARG100 Tipping Bucket Rain Gauge
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3. Installation and Siting
3.1 Choice of Site
Site the gauge carefully, avoiding obvious sources of error such as nearby trees
or buildings. A useful ‘rule of thumb’ is that the distance between the gauge
and any obstruction should be at least as great as twice the height of the
obstruction above the ground.
No two rain gauge designs are ever likely to produce identical
results and identical rain gauges can give slightly different catches
even when sites within a meter of each other.
Research has shown that a rain gauge obstructs the flow of air and that the flow
accelerates and turbulence increases over the top of the funnel. This can cause
less rain to be collected in the funnel than otherwise would have fallen on the
ground. In most cases, this phenomenon is ignored but it may be corrected for
arithmetically or overcome physically by placing the gauge in a pit so that the
rim of the funnel is level with the ground. The pit is covered by a grating to
simulate the aerodynamic roughness of the ground surface while preventing
any splash into the funnel. There are obvious advantages with this method, but
it is not always practical. The body of the ARG100 has a profile which has
been designed to reduce drag and turbulence and it can therefore be sited
conventionally on exposed sites with some confidence. Further details on the
exposure of rain gauges are given in HMSO (1956, 1982) and by Rodda
(1967). Another useful text on exposure and associated errors is Painter (1976).
3.2 Unpacking
Unpack the ARG100 carefully. The tipping mechanism is immobilised before
shipping to prevent damage in transit. To release the mechanism:
1. Remove the funnel of the gauge from its base by unscrewing the three
screws.
2. Remove the small piece of tape which secures the balance arm to the
central post and check the bucket mechanism for freedom of movement.
3.3 Mounting
The ARG100 is a light-weight instrument and it must therefore be bolted down
securely. Three mounting holes are provided in the base of the gauge; access to
these is gained by simply pulling the inner section upwards (it may be
necessary to relieve the strain slightly by pushing a little more cable through
the rubber grommet).
If you need to mount the ARG100 on concrete, we recommend the use of
Anchorbolts. Alternatively, a concrete paving slab may be more convenient as
a base, in which case through-bolts or screws are suitable. Whichever is
chosen, we recommend the use of large washers to spread the load more evenly
around the mounting holes in the plastic base.
For fast, semi-permanent installations the optional RGB1 levelling baseplate
can be used.
