Casella CEL Software for the Rainfall gauge system User Manual

Page 10

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 instruments 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

positioning. Both body and funnel are manufactured from aluminium alloy,

with an accurately machined septum ring with an aperture of 400 cm

The measurement accuracy for the various tip sizes is shown in Figure 2.

4.2

Construction

The rain gauge is manufactured entirely from non-corrosive materials. The

base and septum ring are cast in Aluminium Alloy LM25, heat treated and

protectively coated.

The outer ring and funnel are fabricated from aluminium alloy sheet and again

protectively coated. Stainless steel mesh is employed to protect the inlet and

outlet ports from the ingress of foreign bodies.

4.3

Preparing The Rain Gauge for Use

Each instrument is delivered ready calibrated to indicate either 0.1 mm, 0.2

mm or 0.5 mm of rainfall each time the bucket tips.

It is recommended that the rain gauge be installed in a location or enclosed

compound away from access by the general public.

Prepare a reasonably level site for the rain gauge paying due regard to the

following points:

No object should be nearer than four times its own height from the

bucket.

Do not locate the rain gauge in a hollow or on top of a hill.

Tall buildings or belts of trees can cause turbulence and gusts which

can increase or decrease the rain collected.

The surrounding soil should be capable of allowing the discharged

water to drain away freely.

Tipping Bucket

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Rainfall Logging System -

User Manual