EML SBS Manuale utente

UM-780-400-SBS Manual –V2.00

SBS Range Rain Gauge

User Manual

UM-780-400-SBS Manual –V2.00 2 | P a g e

PUBLISHED BY

Environmental Measurements Limited (EML)

7 Jupiter Court

Orion Business Park

North Shields NE29 7SE

United Kingdom

Visit our internet pages at http://www.emltd.net

©EML 2017

No part of this manual may be reproduced without any form or by any means, electronic or

mechanical (including photocopying), nor may its contents be communicated to a third party

without prior written permission of the copyright holder.

The contents are subject to change without prior notice.

Please observe that this manual does not create any legally binding obligation for EML

towards the customer or end user. All legally binding commitments and agreements are

included exclusively in the applicable supply contract or Conditions of Sale.

 
UM-780-400-SBS Manual –V2.00 3 | P a g e 
 
 
Table of Contents 
List of Figures ..........................................................................................................................................4 
List of Tables ...........................................................................................................................................4 
1. General Information .......................................................................................................................5 
About this Manual ..............................................................................................................................5 
Version Information........................................................................................................................5 
Related Manuals .............................................................................................................................5 
2. Introduction ....................................................................................................................................6 
3. Site and Installation Requirements.................................................................................................6 
Choosing a site....................................................................................................................................6 
Levelling the rain gauge......................................................................................................................7 
Alternative mounting options.............................................................................................................7 
4. Wiring Guidelines............................................................................................................................8 
Field replaceable dual reed switches..................................................................................................9 
Wiring for internal loggers..................................................................................................................9 
5. Operation........................................................................................................................................9 
Operation of the gauge.......................................................................................................................9 
6. Maintenance and Calibration .......................................................................................................10 
Basic Maintenance............................................................................................................................10 
Calibration.........................................................................................................................................11 
7. Specifications ................................................................................................................................12 
Gauge Specifications.........................................................................................................................12 
Cable Specifications (if fitted)...........................................................................................................13 
Appendix A –SBS500 products, accessories and spares ......................................................................14 
 
 
 

 
UM-780-400-SBS Manual –V2.00 4 | P a g e 
 
List of Figures 
Figure 1 - Levelling the Gauge.................................................................................................................7 
Figure 2 - SBS500 fitted to a pedestal as part of the EML system..........................................................8 
Figure 3 - Reed switch and resistor.........................................................................................................8 
Figure 4 - Filter and filter cap (left) / Nozzle delivering water into tipping bucket (right) .....................9 
Figure 5 - Internal photograph highlighting water drains.....................................................................10 
Figure 6 - SBS replaceable reed switch (left) / Empty socket to house one of the reed switches 
(centre) / reed switch being inserted into the empty socket...............................................................11 
 
 
List of Tables 
Table 1 - Document Revisions.................................................................................................................5 
Table 2 - Related Manuals ......................................................................................................................5 
Table 3 - Gauge Specifications..............................................................................................................12 
Table 4 - Cable Specifications (if fitted) ................................................................................................13 
Table 5 –SBS500 products....................................................................................................................14 
Table 6 - Accessories for the SBS500 ....................................................................................................14 
Table 7 - Spare parts for the SBS gauges ..............................................................................................15 
 

UM-780-400-SBS Manual –V2.00 5 | P a g e

1. General Information

About this Manual

This manual is intended as a general guide for installing, wiring and using the SBS range of rain gauges.

There are three models of SBS gauge, but the guidelines for each are the same so the generic term of

reference used is ‘SBS’. The information contained in this manual may not cover all aspects of SBS

applications. Please refer to associated equipment manuals or consult papers and technical notes on

the EML website (www.emltd.net).

Version Information

Table 1 - Document Revisions

EML Document Number:

Description:

UM-P-780-400

Version 1.00 - First Release, dated 16th June 2002

UM-P-780-400

Version 2.00 - Second Release, dated 25th July 2017

Related Manuals

Table 2 - Related Manuals

EML Document Number:

Description:

UM-780-400-SBS Manual –V2.00 6 | P a g e

2. Introduction

The SBS is EML’s recommended solution for Hydrological or meteorological professionals such as

National Met. Services, weather stations and flood warning systems. There are 3 funnel sizes available

which are recommended based on the environment in which they are installed. The SBS314 is ideal

for heavy rainfall regions, the SBS500 is favoured in a mixed climate such as Europe and the SBS1000

is particularly good in low, light rain areas. Aside from the funnel diameter all gauges are identical,

providing a robust and versatile instrument which is ideal for applications where data precision and

accuracy are of critical importance.

The SBS is available in White or Green. The internal tipping bucket mechanism has been designed to

maximise water flow and therefore to assure maximum performance repeatability.

Traditional cylinder-shaped rain gauges are inaccurate due to the effect of wind blowing over the

orifice. The physical presence of the gauge causes air to accelerate, carrying rainfall away from the

collecting vessel. The effect of this can be up to a 20% reduction in rainfall catch. The unique

aerodynamic shape of the EML range of scientific standard rain gauges reduces this effect, ensuring a

high level of confidence in the accuracy of our measurements.

3. Site and Installation Requirements

Choosing a site

A rain gauge site is often a compromise between exposure requirements and operational constraints.

The ideal site is level ground with a uniform scattering of objects in the surrounding area thus reducing

overall wind speeds. However, these objects should not be too large to cause eddying or high gusts to

occur near to the gauge, or so close to prevent rain from entering the gauge. The gauge should ideally

be no closer than at least twice the height of the obstruction. Although the SBS rain gauge is designed

to operate in higher wind speeds, care must still be taken to avoid over-exposing the gauge where

possible. Large expanses of open flat land should be avoided where possible. If the application is very

specific, such as monitoring a building site, then the siting of the rain gauge is largely prescribed by

use. Those users who wish to enquire more fully into rain gauge exposure are referred to the EML

website for more technical information and papers (www.emltd.net).

NOTES: No two rain gauge designs are ever likely to produce identical results, and even two identical

rain gauges can give slightly different catches even when sited close to each other.

If the gauge is to be operated in the area of livestock then a fence will almost always be required to

prevent damage from and to the animals.

WARNING! Remove packing piece! The tipping-bucket mechanism is immobilised before shipping to

prevent damage in transit. To release the mechanism for use, remove the funnel assembly from its

base by loosening the three screws and then lifting the funnel. Remove the piece of foam from under

the bucket mechanism. This foam may be saved and used whenever the rain gauge is transported.

UM-780-400-SBS Manual –V2.00 7 | P a g e

Levelling the rain gauge

The SBS can be mounted directly on to any flat surface, and securely fastened as desired. The gauge

must be levelled for correct operation, and it is important to ensure that the rim of the rain gauge is

levelled precisely, using a spirit level; failure to do this will result in a systematic error. Levelling is one

of the simplest means of improving accuracy of rainfall measurements. Although a small circular spirit

level is provided in the base of the rain gauge, this is provided only as a quick check system, always

level the rim of the funnel precisely and check regularly. The gauge is levelled by slackening the locking

nuts on the adjustable feet, adjust feet for level and tighten locking nuts (Figure 1). Pegs can be fitted

if necessary through the holes provided next to the adjusters.

Figure 1 - Levelling the Gauge

Alternative mounting options

It is not always possible to mount a rain gauge on the ground surface. Examples of applications which

make use of rain gauges mounted above the ground include; urban monitoring, areas prone to

ground-flooding and areas prone to snowfall. It should be noted that regardless of which option is

used to mount the gauge, it must be firmly fixed and not susceptible to vibration. Vibration may lead

to ‘false-tipping’ of the bucket mechanism and thus contribute to erroneous or inaccurate

measurements. There are options which can be used to mount the SBS above the ground.

The SBS can be purchased with a rain gauge pedestal and guy kit or a rain gauge pedestal only. An

example of this configuration is shown in Figure 2.

UM-780-400-SBS Manual –V2.00 8 | P a g e

Figure 2 - SBS500 fitted to a pedestal as part of the EML system

4. Wiring Guidelines

This section gives information on the wiring of SBS rain gauge.

For most applications, the rain gauge may be connected directly to a pulse counting input (contact

closure) on a data logger, but some care is needed if long cables are used. In a long cable 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 rain gauge cable each time the rain gauges tips. To help this situation, 100

resistors are pre-fitted to each of the reed switches (Figure 3), these will help protect the switches

from arcing and help prevent transients.

Figure 3 - Reed switch and resistor

UM-780-400-SBS Manual –V2.00 9 | P a g e

Field replaceable dual reed switches

SBS gauges are fitted with dual reed switches. This means that 2 data outputs can be logged using the

same tipping bucket mechanism. It is an important feature providing built-in redundancy which is

often critical for professional users such as National Meteorological Services. Another feature of the

reed switches is that they are replaceable in the field. They can simply be ‘clicked’ out of position and

replaced by a new reed switch. This process takes less than one minute and allows for easy servicing

of the gauge in the field. Using dual reed switches assures that the gauge remains operational after 1

has failed, allowing for maintenance to be carried out by field engineers. Reed switches can also be

replaced periodically as part of preventative maintenance.

Wiring for internal loggers

There are two black terminal blocks within the gauge casting. Each reed switches is connected to one

of these by two wires. To connect an internal data logger or counter, two wires have to be connected

to the black terminal block and taken to the contact closure input of your chosen logger. If two loggers

are to be used or if one logger is recording two measurements, then the process should be repeated

using the other black terminal block.

The type of measurement is contact closure (switch), therefore it does not matter which way round

the wires from the logger or counter are connected.

5. Operation

Operation of the gauge

Rainfall is measured by the well-proven tipping bucket method. Precipitation is collected by the funnel

and flows through a stainless-steel gauze filter, trapping and removing any leaves, dirt, etc. Figure 4.

Water then drips from the nozzle into one of the two halves of the tipping bucket.

The internal tipping bucket assembly rotates around precisions rolling pivot bearings. The balance

arm tips when the first bucket is full, emptying this rain water and positioning the second bucket under

the funnel. The tipping process repeats indefinitely as long as the rain continues to fall, with each tip

corresponding to a calibrated fixed quantity of rainfall. At each tip of the bucket the moving arm

forces the magnet past the reed switch causing contact to be made for a few milliseconds. As each

bucket side is used in turn, the outgoing water is drained away via outlets and discarded Figure 5.

Figure 4 - Filter and filter cap (left) / Nozzle delivering water into tipping bucket (right)

UM-780-400-SBS Manual –V2.00 10 | P a g e

Figure 5 - Internal photograph highlighting water drains

The exact calibration of each tip is pre-set by adjustable stops. Do not alter these stops unless as part

of a calibration exercise. A levelling bubble is provided as an aid to levelling of the rain gauge.

Connections to the reed switches are made via the connector terminals.

6. Maintenance and Calibration

Basic Maintenance

To ensure reliable and accurate measurements it is recommended that the following checks are

carried out at each visit to the rain gauge (if the gauge is still connected to a data logger and the logger

is operating, care must be taken to avoid tipping the bucket when carrying out these checks).

1. Inspect the funnel and filter for any damage or blockage. At certain times of the year,

particularly autumn, leaves may accumulate in the funnel, dirt and dust can also block the

filter preventing or reducing the flow rate to the buckets beneath. The leaves can easily be

removed from the funnel and the filter cleaned by removing the end cap from the filter tube,

remove the stainless-steel filter gauze carefully, clean and re-fit the filter and cap.

2. Check that the gauge is still level. Small movements may occur over time.

3. Remove and clean any dirt from the tipping bucket, being careful not to tip the bucket should

the rain gauge still be logging.

4. During any occasion when the rain gauge is disconnected from the logger, it is good practice

to check the balance arm of the tipping bucket for stiffness. The easiest way to do this in the

field is to try and balance the bucket in its centre position, it should be very difficult if not

impossible to achieve this, if the bucket balances easily then examine the bucket closely for

any dirt or wear on the pivot pin and bucket tubes.

Indice

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