EML SBS User manual

UM-780-400-SBS Manual –V2.00
SBS Range Rain Gauge
User Manual

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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.

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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

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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

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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:

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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.

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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.

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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

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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)

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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.

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5. As mentioned in section 4, the SBS gauges are equipped with two removable reed switches
per gauge. Figure 6 shows a removable reed switch (left), the empty housing socket (centre)
and the process of connecting the reed switch (right). The other reed switch can be seen
directly opposite the empty socket in the middle picture. The two arms in between the reed
switches are the magnets which pass the reed switches when the bucket tips, causing a
contact closure. To remove a reed switch, insert a small flat screwdriver into the catch on the
white connector. The reed switch has been constructed with an IP67 waterproof connector
and is completely potted to produce a robust replaceable accessory. (Note: IP67 means Dust
Tight (6) and Immersion up to 1m (7)).
PLEASE NOTE: A spares kit is available with filter, cap, and screws. Contact EML sales
([email protected]t) for more information.
Calibration
The sensitivity of the rain gauge is accurately calibrated during the manufacturing to a nominal
0.2mm/tip using a purpose-built calibration rig supplying an adjustable constant head of water
allowing accurate calibration of the rain gauge. Each rain gauge is supplied with its own calibration
figure to three decimal places. All gauges are calibrated to a tolerance of 2% of the 0.2mm tip value.
A re-calibration and overhaul service is also offered to customers; EML recommends re-calibration
every 12 to 24 months depending on applications.
For information on how we calibrate the rain gauges see British Standards document BS 7843-1:2012
and the CIMO Guide to Meteorological Instruments and Methods of Observation (Chapter 6). These
documents describe the processes of bucket balancing, static calibration at a fixed intensity, and
dynamic calibration using variable intensities
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.

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7. Specifications
Gauge Specifications
Table 3 - Gauge Specifications
Technical Specifications
Resolution
0.1/0.2/0.5mm
0.005/0.01/0.02inch
WMO Compliant
Yes
Output
Contact Closure (Reed Switch)
Typical Accuracy
99% up to 120mm/hr
Rainfall Intensity
SBS314 (0-1750 mm/hr),
SBS500 (0-1200mm/hr),
SBS1000 (0-600mm/hr),
With mathematical correction over 120mm/hr - contact EML
Operating Temperature
1°C - 70°C
Funnel Diameter
SBS314 (20cm), SBS500 (25.2cm), SB1000 (35.7cm)
Funnel Area
SBS314 (314cm2),
SBS500 (500cm2),
SBS1000 (1000cm2)
Height
SBS314 (43.5-46.5cm),
SBS500 (46.0-49.0cm),
SBS1000 (53.0-56.0cm)
Weight
SBS314 (5.5Kg),
SBS500 (6Kg),
SBS1000 (7.5Kg)
Colour
White (or Green on request)

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Cable Specifications (if fitted)
The standard cable used in all extended versions (on request) of the rain gauge is a single twisted pair
of 7/0.25mm (22awg) tinned copper conductors, insulated with polyethylene, wrapped in an
aluminised tape with a 7/0.25mm tinned drain wire and a PVC outer sheath.
Table 4 - Cable Specifications (if fitted)
Technical Specifications
Temperature Range
-30°C to +70°C
Overall diameter
4.6 mm
Char. impedance
85 
Capacitance/metre
154 pF
Equivalents
Alpha 2401
Belden 8761
UL style2092

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Appendix A –SBS500 products, accessories and spares
Table 5 –SBS500 products
Product code
Description
P-780-400
SBS500 Rain gauge
P-780-401
SBS500/H (12v) Rain gauge
P-780-402
SBS500/H (24v) Rain gauge
P-780-404
SBS500 Rain gauge (0.01 inch)
P-780-405
SBS314 Rain gauge
P-780-4051
SBS314-S Syphon Rain gauge
P-780-406
SBS314/H (12v) Rain gauge
P-780-407
SBS314/H (24v) Rain gauge
P-780-408
SBS314 Rain gauge - 0.5mm/tip (Specials - Built to Order)
P-780-4081
SBS314 Rain gauge (0.01 inch)
P-780-409
SBS314 Rain gauge (0.02 inch) - (Specials - Built to Order)
P-780-410
SBS1000 Rain gauge
P-780-411
SBS1000/H (12v) Rain gauge
P-780-412
SBS1000/H (24v) Rain gauge
P-780-4121
SBS1000 Rain gauge (0.005 inch)
Table 6 - Accessories for the SBS500
Product code
Description
P-780-188
Rain gauge Pedestal + Guy Kit
P-780-189
ARG/SBS Pedestal

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Table 7 - Spare parts for the SBS gauges
Product code
Description
P-780-415
SBS Bucket Assembly
P-780-425
SBS Reed Switches
P-780-430
SBS Casting Assembly
P-780-450
SBS500 Funnel Assembly
P-780-451
SBS1000 Funnel Assembly
P-780-453
SBS314 Funnel Assembly
P-780-490
Spares Kit (includes funnel screws, filter material and
filter cap)