Casella CEL Tipping bucket rain gauge User Manual

Tipping Bucket Rain Gauges

User Manual

Tipping Bucket, Heated Tipping

Bucket Rain Gauges & Rain Gauge

That Meets The Requirements of

The UK Environmental Agency

Operator’s Handbook

HB 3166-06

Jan 2006

COPYRIGHT

The copyright in this document which contains proprietary information is vested in

CASELLA CEL. The contents of this document must not be used for purposes other

than that for which it has been supplied or reproduced or disclosed wholly or in part

without the prior written permission of

CASELLA CEL

CASELLA CEL

Regent House

Wolseley Road

Kempston

Bedford

MK42 7JY, U.K.

Phone: [phone]

Fax: [phone]

E-mail [e-mail]

Web: www.casellagmeasurement.com

CASELLA USA

17 Old Nashua Road #15

Amherst

NH 03031

U.S.A.

Toll Free: [phone]

Fax: [phone]

e-mail: [e-mail]

Web: www.casellausa.com

Contents

Tipping Bucket Rain Gauges

User Manual

TABLE OF CONTENTS

CONTENTS . . . . . . . . . . . . . . . . PAGE

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. PRINCIPAL OF OPERATION . . . . . . . . . . . . . . . . . . . . 4

3. CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4. PREPARATION FOR USE . . . . . . . . . . . . . . . . . . . . . . 6

4.1 Non Heated Versions . . . . . . . . . . . . . . . . . . . . 6

4.1.1 Standard Single Output Non-Heated Version . . . . . . . 6

4.1.2 Standard Dual Output Non-Heated Version . . . . . . . . 7

4.1.3 Dual Output Non-Heated Version That Meets the

Requirements of The UK Environmental Agency . . . . . 7

4.2 Heated Versions . . . . . . . . . . . . . . . . . . . . . . 8

4.2.1 Standard Single Output Heated Version . . . . . . . . . . 8

4.2.2 Standard Dual Output Heated Version . . . . . . . . . . . 9

4.2.3 Dual Output Heated Version that Meet the

Requirements of The UK Environmental Agency 9

4.3 General . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5. MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6. COUNTING BUCKET TIPS . . . . . . . . . . . . . . . . . . . . 12

6.1 Reed Switch Details

7. SERVICING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

8. SPECIFICATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

8.1 Common Specifications . . . . . . . . . . . . . . . . . 14

8.2 Heated Version - Additional Specifications . . . . . . . . 14

9. ORDERING INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

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Tipping Bucket Rain Gauges

User Manual

Introduction

1. INTRODUCTION

Casella Tipping Bucket Rain Gauges are reliable and extremely robust devices

that are intended for use as stand-alone sensors operating within an existing

logging system, such as the Casella Automatic or Portable Weather Stations.

Figure 1: The non-heated tipping bucket rain gauge with the

outer cover removed

Three versions of tipping bucket rain gauge are available:

¤ Standard non-heated version.

¤ Standard heated version for more severe weather conditions.

¤ Non-heated version constructed to meet the requirements of The UK

Environmental Agency.

¤ 200cm

2

versions are also available(these utilise a 0.1mm bucket

mechanism which relates to 0.2mm per tip).

¤ The non-heated version to meet the requirements of The UK

Environmental Agency has a dual output, while dual output versions

of the standard rain gauges are available for those users who need

independent outputs, for example to a counter and to a logger.

All versions now feature M6 bucket adjusting studs, while the version to

meet UK Environmental Agency requirements has a larger drop tube

diameter (5 mm), retained hexagonal headed long base-mounting screws to

raise the base plate above ground level and quick-release terminal blocks with

Mil Spec external connectors rated to IP67. When required, a heater can be

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Principle

Tipping Bucket Rain Gauge

Accuracy / 100 Tips

0

5

10

15

20

25

1 10 100 1000

Rain fall in mm/Hr

Error Per 100 Tips

0.1mm Tip

0.2mm Tip

0.5mm Tip

Max U.K

recorded -

Devon

Light Moderate Heavy

Classification

WMO 5%

Tipping Bucket Rain Gauges

User Manual

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

Page 4 of 16

Figure 2: Accuracy of 0.1 mm, 0.2 mm and 0.5 mm tip versions

Tipping Bucket Rain Gauges

Construction

User Manual

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

with an accurately machined septum ring with an aperture of 400 cm2.

(200cm2version is now also available)

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

3. 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.

The heater unit on heated rain gauges is operated via an adjustable thermo-

stat which controls the supply to two power resistors. The thermostat is

factory-set to switch the heater on at 3oC to ensure that the mechanism is

kept above freezing point.

The heater requires a 24 V AC supply, which can be obtained from the

isolated and fully protected -TR26 Mains Transformer available from Casella

CEL.

A cable carries the power to the heater and returns the signal from the

“tip” switch.

Page 5 of 16