ARG100 Tipping Bucket Raingauge
2
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 raingauges
are given in HMSO (1956, 1982) and by Rodda (1967). Another useful text on
exposure and associated errors is Painter (1976).
2.2 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 Allen
screws with a 5/32" key.
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.
2.3 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 Rawl-
bolts. 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 (see Appendix A).
2.4 Levelling
If the raingauge is tilted by more than a few degrees, the bucket mechanism may
be thrown out of balance, significantly affecting its calibration. Furthermore,
during wind-driven rain the response of a gauge with a tilted funnel collector will
vary with wind direction.
Where a concrete slab is used, add sand underneath the slab to level the gauge. If
the gauge is mounted on a concrete base using Rawlbolts, add packing material
under the base before tightening the bolts. Use the internal bubble to check that
the base of the gauge (with the funnel removed) is level; as an additional check,
place a spirit level across the rim of the assembled ARG100.
3. Wiring
The raingauge is supplied with a 6m cable which may be extended if required. For
most applications the ARG100 may be connected directly to a pulse counting
input on the datalogger as shown in Figure 1. For a long cable, a significant
capacitance can exist between the conductors, which discharges across the reed
switch as it closes. As well as shortening the life of the switch, a voltage transient
may be induced in any other wires which run close to the raingauge cable each
time the gauge tips. A 100
Ω
resistor is fitted inside the gauge to protect the switch
from arcing and prevent transients.
