Campbell ARG100 User manual

ARG100
Tipping Bucket
Raingauge
User Guide
Issued 30.11.10
Copyright ©1998-2010 Campbell Scientific Ltd.
CSL 78

Guarantee
This equipment is guaranteed against defects in materials and workmanship.
This guarantee applies for twelve months from date of delivery. We will
repair or replace products which prove to be defective during the guarantee
period provided they are returned to us prepaid. The guarantee will not apply
to:
•Equipment which has been modified or altered in any way without the
written permission of Campbell Scientific
•Batteries
•Any product which has been subjected to misuse, neglect, acts of God or
damage in transit.
Campbell Scientific will return guaranteed equipment by surface carrier
prepaid. Campbell Scientific will not reimburse the claimant for costs incurred
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obligation thereunder is in lieu of all other guarantees, expressed or implied,
including those of suitability and fitness for a particular purpose. Campbell
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Please inform us before returning equipment and obtain a Repair Reference
Number whether the repair is under guarantee or not. Please state the faults as
clearly as possible, and if the product is out of the guarantee period it should
be accompanied by a purchase order. Quotations for repairs can be given on
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employees and provide a safe working environment, in support of this policy a
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When returning equipment, the Repair Reference Number must be clearly
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Campbell Scientific Ltd,
Campbell Park, 80 Hathern Road,
Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone]
Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

PLEASE READ FIRST
About this manual
Please note that this manual was originally produced by Campbell Scientific Inc. primarily for the
North American market. Some spellings, weights and measures may reflect this origin.
Some useful conversion factors:
Area: 1 in2(square inch) = 645 mm2
Length: 1 in. (inch) = 25.4 mm
1 ft (foot) = 304.8 mm
1 yard = 0.914 m
1 mile = 1.609 km
Mass: 1 oz. (ounce) = 28.35 g
1 lb (pound weight) = 0.454 kg
Pressure: 1 psi (lb/in2) = 68.95 mb
Volume: 1 UK pint = 568.3 ml
1 UK gallon = 4.546 litres
1 US gallon = 3.785 litres
In addition, while most of the information in the manual is correct for all countries, certain information
is specific to the North American market and so may not be applicable to European users.
Differences include the U.S standard external power supply details where some information (for
example the AC transformer input voltage) will not be applicable for British/European use. Please
note, however, that when a power supply adapter is ordered it will be suitable for use in your country.
Reference to some radio transmitters, digital cell phones and aerials may also not be applicable
according to your locality.
Some brackets, shields and enclosure options, including wiring, are not sold as standard items in the
European market; in some cases alternatives are offered. Details of the alternatives will be covered in
separate manuals.
Part numbers prefixed with a “#” symbol are special order parts for use with non-EU variants or for
special installations. Please quote the full part number with the # when ordering.
Recycling information
At the end of this product’s life it should not be put in commercial or domestic refuse
but sent for recycling. Any batteries contained within the product or used during the
products life should be removed from the product and also be sent to an appropriate
recycling facility.
Campbell Scientific Ltd can advise on the recycling of the equipment and in some cases
arrange collection and the correct disposal of it, although charges may apply for some
items or territories.
For further advice or support, please contact Campbell Scientific Ltd, or your local agent.
Campbell Scientific Ltd, Campbell Park, 80 Hathern Road, Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone] Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

i
Contents
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1. Description...................................................................1
2. Installation and Siting .................................................1
2.1 Choice of Site...........................................................................................1
2.2 Unpacking................................................................................................2
2.3 Mounting..................................................................................................2
2.4 Levelling ..................................................................................................2
3. Wiring ...........................................................................2
3.1 Wiring to a Pulse Channel .......................................................................3
3.2 Wiring to a Control Port...........................................................................4
4. Datalogger Programming............................................4
4.1 Pulse Channel Example Programs...........................................................4
4.1.1 CR1000 Example Program.............................................................5
4.1.2 CR200(X) Series Example Program ..............................................5
4.1.3 CR10X Example Program..............................................................6
4.2 Control Port Example...............................................................................6
4.2.1 CR1000 Example Program.............................................................7
4.2.2 CR10X Example Program..............................................................8
5. Maintenance.................................................................8
6. Calibration....................................................................9
6.1 Static Adjustment and Calibration ...........................................................9
6.2 Dynamic Calibration................................................................................9
7. Advantages and Limitations of a Tipping
Bucket Gauge .........................................................11
Appendix
A. Optional RGB1 Levelling Baseplate..............................A-1
Figures 1. Wiring Diagram for ARG100....................................................................3
2. Arrangement for Setting and Calibrating the Raingauge.........................10
A-1. Installation of RGB1...........................................................................A-1
Tables 3-1. Wiring for Pulse Channel Input..............................................................3
3-2. Wiring for Control Port Input.................................................................4
4-1. Multipliers...............................................................................................4

1
ARG100 Raingauge
The ARG100 is a well-designed tipping bucket raingauge which combines durable construc-
tion with very reasonable cost. The gauge offers less resistance to air flow than most previous
designs, which helps to reduce the sampling errors that inevitably occur during wind-driven
rain. The gauge is manufactured for Campbell Scientific by Environmental Measurements
Ltd. (under licence from the Institute of Hydrology), and will provide many years of reliable
operation when carefully sited and installed.
1. Description
The ARG100 raingauge is constructed from UV-resistant, vacuum-moulded plas-
tic and consists of a base and an upper collecting funnel. The base splits into two
parts, the inner section supporting the tipping-bucket mechanism and the outer
providing protection and allowing the unit to be bolted firmly to a suitable
mounting plinth or concrete slab.
The tipping bucket arrangement is similar to most other gauges of this type;
precipitation is collected by the funnel and is passed to one of the two buckets
situated at either end of a short balance arm. The balance arm tips when the first
bucket is full, emptying this bucket and positioning the second under the funnel.
The tipping process repeats indefinitely as long as rain continues to fall, with each
tip corresponding to a fixed quantity of rainfall. At each tip, the moving balance
arm forces a magnet to pass a reed switch, causing contact to be made for a few
milliseconds. A two-core cable is used to connect the gauge to the datalogger
where the switch closures are counted.
The ARG100 is adjusted at manufacture to tip once for each 0.2 mm of rain (a
sensitivity of 0.25 mm/tip is optional). More information on gauge calibration is
given in Section 6.
2. Installation and Siting
2.1 Choice of Site
Site the gauge carefully, avoiding obvious sources of error such as nearby trees or
buildings. A useful ‘rule of thumb’ is that the distance between the gauge and any
obstruction should be at least as great as twice the height of the obstruction above
the ground. For standard meteorological sites in the UK, the Meteorological
Office specify the height at which the rim of a raingauge should be above a short
grass surface, and the ARG100 should be exposed similarly if measurements are
required for comparison with those from agrometeorological or synoptic sites.
No two raingauge designs are ever likely to produce identical
results, and identical raingauges can give slightly different catches
even when sited within a metre of each other.
Research has shown that a raingauge obstructs the flow of air and that the flow
accelerates and turbulence increases over the top of the funnel. This can cause less
rain to be collected in the funnel than otherwise would have fallen on the ground.
In most cases, this phenomenon is ignored but it may be corrected for
arithmetically or overcome physically by placing the gauge in a pit so that the rim
of the funnel is level with the ground. The pit is covered by a grating to simulate
NOTE

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 100Ωresistor is fitted inside the gauge to protect the switch
from arcing and prevent transients.

User Guide
3
Black
Clear
Yellow
(Shield)
ARG100
P
G or
Pulse
Port Control Port
C
+5V
No
Physical
connection
Figure 1 Wiring Diagram for ARG100
3.1 Wiring to a Pulse Channel
When Short cut software is used to generate the datalogger
program, the sensor should be wired to the channels shown on the
wiring diagram created by Short Cut.
The ARG100 is typically wired to a datalogger’s pulse channel (see Table 3-1).
Table 3-1. Wiring for Pulse Channel Input
Colour Description
CR800
CR1000
CR3000
CR5000
CR500
CR510
CR10(X)
21X
CR7
CR23X
CR200(X)
Series
Black Signal Pulse
Channel Pulse Channel Pulse Channel P_SW
Clear Signal
Return
G
Yellow Shield
NOTE

ARG100 Tipping Bucket Raingauge
4
3.2 Wiring to a Control Port
Dataloggers listed in Table 3-2 have the capability of counting switch closures on
some of their control ports. When a control port is used, the return from the rain
gauge switch must be connected to +5 volts on the datalogger.
Table 3-2. Wiring for Control Port Input
Colour Description
CR800
CR1000
CR3000
CR500
CR510 CR10(X) CR23X
Black Signal Control
Port C2/P3 Control Port Control Port
Clear Signal
Return 5 V 5 V 5 V 5 V
Yellow Shield
The CR10 does not support the use of control port inputs with the Pulse Count
instruction.
4. Datalogger Programming
This section is for users who write their own programs. A
datalogger program to measure this sensor can be generated using
Campbell Scientific’s Short Cut Program Builder software. You do
not need to read this section to use Short Cut.
Precipitation is measured using a Pulse Count with a switch closure configuration
code. The multiplier used in the Pulse Count instruction determines the units in
which rainfall is reported (see Table 4-1).
Table 4-1. Multipliers
Rain Gauge 1 mm
ARG100 0.2
4.1 Pulse Channel Example Programs
The following example programs use a pulse channel to read the output from the
precipitation gauge. The CR1000 example will also work with the CR800,
CR850, CR3000, and CR5000. CR9000(X) programming is similar to the
CR1000 except it has an additional parameter in the PulseCount instruction to
specify the pulse module’s slot.
The CR10X program will also work with the CR500, CR510, CR10, 21X or
CR23X. CR7 programming is similar to the CR10X but has an additional
parameter in the PulseCount instruction to specify the slot that the Pulse Card is
in.
NOTE

User Guide
5
4.1.1 CR1000 Example Program
'CR1000
'ARG100 Tipping Blk > P1
' Clr > ground
Public Rain_mm
Units Rain_mm=mm
DataTable(Rain,True,-1)
DataInterval(0,60,Min,0)
Totalize(1,Rain_mm,FP2,0)
EndTable
BeginProg
Scan(1,Sec,1,0)
PulseCount(Rain_mm,1,1,2,0,0.2,0)
CallTable(Rain)
NextScan
EndProg
4.1.2 CR200(X) Series Example Program
'CR200(X) Series
'ARG100 Tipping Blk > P_SW
' Clr > ground
'Declare Variables and Units
Public Rain_mm
Units Rain_mm=mm
'Define Data Tables
DataTable(Rain,True,-1)
DataInterval(0,60,Min)
Totalize(1,Rain_mm,0)
EndTable
'Main Program
BeginProg
Scan(1,Sec)
'ARG100 Rain Gauge measurement Rain_mm:
PulseCount(Rain_mm,P_SW,2,0,0.2,0)
'Call Data Tables and Store Data
CallTable(Rain)
NextScan
EndProg

ARG100 Tipping Bucket Raingauge
6
4.1.3 CR10X Example Program
;{CR10X}
*Table 1 Program
01: 1.0000 Execution Interval (seconds)
1: Pulse (P3)
1: 1 Reps
2: 1 Pulse Channel 1
3: 2 Switch Closure, All Counts
4: 3 Loc [ Rain_mm ]
5: 0.2 Multiplier
6: 0 Offset
2: If time is (P92)
1: 0 Minutes (Seconds --) into a
2: 60 Interval (same units as above)
3: 10 Set Output Flag High (Flag 0)
3: Set Active Storage Area (P80)
1: 1 Final Storage Area 1
2: 101 Array ID
4: Real Time (P77)
1: 1220 Year,Day,Hour/Minute (midnight = 2400)
5: Totalize (P72)
1: 1 Reps
2: 3 Loc [ Rain_mm ]
*Table 2 Program
01: 0 Execution Interval (seconds)
*Table 3 Subroutines
End Program
4.2 Control Port Example
The following example programs use a control port to read the output from the
precipitation gauge. The CR1000 example will also work with the CR800,
CR850, and CR3000. The CR10X program will also work with the CR500,
CR510, or CR23X.

User Guide
7
4.2.1 CR1000 Example Program
'CR1000
'ARG100 Tipping Blk > C4
' Clr > 5v
'Declare Variables and Units
Public BattV
Public Rain_mm
Units BattV = Volts
Units Rain_mm =mm
DataTable(OneMin,True,-1)
DataInterval(0,1,Min,10)
Totalize (1,Rain_mm,FP2,False)
EndTable
'Define Data Tables
DataTable(OneDay,True,-1)
DataInterval(0,1440,Min,10)
Minimum(1,BattV,FP2,False,False)
Totalize (1,Rain_mm,FP2,False) 'ARG100 tipping bucket
EndTable
'Main Program
BeginProg
Scan(5,Sec,1,0)
'Default Datalogger Battery Voltage measurement BattV
PanelTemp (PTemp,_50Hz)
Battery(BattV)
'ARG100 Rain Gauge measurement Rain_mm
PulseCount(Rain_mm,1,14,2,0,0.2,0)
'Call Data Tables and Store Data
CallTable(OneMin)
CallTable(OneDay)
NextScan
EndProg

ARG100 Tipping Bucket Raingauge
8
4.2.2 CR10X Example Program
;{CR10X}
;
*Table 1 Program
01: 1 Execution Interval (seconds)
1: Pulse (P3)
1: 1 Reps
2: 8 Control Port 8 (switch closure only) ;Black wire connect to C8
3: 2 Switch Closure, All Counts
4: 1 Loc [ Rain_mm ]
5. 0.2 Multiplier
6: 0 Offset
2: If time is (P92)
1: 0 Minutes (Seconds --) into a
2: 60 Interval (same units as above)
3: 10 Set Output Flag High (Flag 0)
3: Set Active Storage Area (P80)
1: 1 Final Storage Area 1
2: 101 Array ID
4: Real Time (P77)
1: 1220 Year,Day,Hour/Minute (midnight = 2400)
5: Totalize (P72)
1: 1 Reps
2: 1 Loc [ Rain_mm ]
*Table 2 Program
02: 0.0000 Execution Interval (seconds)
*Table 3 Subroutines
End Program
Output Instruction 72, Totalize, is used in the output section of the program to
output the total rainfall over the output interval. This section should be executed
every scan and not placed in a subroutine or conditional statement.
5. Maintenance
To ensure reliable and accurate measurements, we recommend that the following
checks be carried out every month if possible:
1. Inspect the funnel for any damage or blockage and check the integrity of the
connecting cable. At certain times of the year, leaves may accumulate in the
bottom of the funnel, clogging the filter and preventing the flow to the buckets
beneath, or reducing the flow rate to a slow drip. The obstruction is best
cleared by inverting the funnel (after removal from the base) and pouring
water back through from the spout beneath the collecting surface. Note that
the plastic filter in the bottom of the funnel is not removable on the ARG100.
2. Check that the gauge is still level. It is surprisingly easy for an apparently
immovable gauge to become tilted as a result of small ground movements,
vandalism or just inquisitive fingers.

User Guide
9
3. Check that the balance arm is free to move. This can be done by slowly
pouring a measured quantity of water (say 25 cm3) through the gauge and
counting the tips. It is worthwhile carrying this out at regular weekly intervals
(for example, every Monday at 0900) while leaving the gauge connected to the
datalogger. Providing a significant volume of water is used, these weekly
checks can easily be identified in the logged measurements. This simple
procedure confirms that the gauge is functioning, detects any marked change
in the calibration and (if carried out punctually) introduces an independent
time check into the records.
6. Calibration
The sensitivity of the ARG100 is set at manufacture to approximately 0.2 mm/tip
(optionally 0.25 mm/tip) and each gauge is subsequently calibrated as described
in Section 6.1. The calibration factor is given on a certificate and is also recorded
on the inside of the raingauge. For precise measurements use this value in your
program instead of the nominal value of 0.2.
6.1 Static Adjustment and Calibration
The following procedure is carried out during manufacture and may be repeated if
the calibration appears to have shifted:
1. Install the gauge over a sink unit as illustrated in Figure 2, ensuring that it is
correctly levelled.
2. Adjust the two calibration screws under the tipping buckets until the balance
arm tips in response to the correct amount of water dripped from a burette or
pipette (10.13 cm3for 0.2 mm sensitivity, 12.67 cm3 for 0.25 mm).
It is not possible to set the screws very precisely using this method, but it should
be done with as much care as possible. It is obviously very important to ensure
that both buckets tip in response to the same amount of water. Many manufac-
turers and users of tipping bucket gauges aim to adjust the bucket settings until
exactly the correct calibration is achieved. However, a dynamic test (see below) is
required to check this calibration precisely after each readjustment and the process
becomes very time-consuming. In any case, it is virtually impossible to get the
adjustments absolutely correct, and it is generally preferable to adjust the settings
as closely as is reasonably practical, and then to derive a calibration factor for
each gauge individually.
6.2 Dynamic Calibration
1. Set up the gauge as illustrated in Figure 2, carefully levelled and connected to
the datalogger.
2. Fill the water container with 810.4 cm3of water for a 0.2 mm calibration
(1013.4 cm3for a 0.25 mm setting). This is usually achieved most precisely
and consistently by weighing the water on a balance capable of measuring to
0.1 g (0.1 cm3). An alternative is to use a good quality graduated measuring
cylinder.
3. Allow the water to drip slowly into the gauge (allowing approximately 100
minutes for the container to empty). This is a rate equivalent to a rainfall of
10 mm/hour, as recommended in BS7843 Section 2.1 for calibration
purposes. At the end of this period approximately 80 tips will have occurred.
The exact number is obtained from the datalogger, together with a visual
inspection of what fraction of a ‘tip’ is left in whichever bucket is still filling
as the flow of water finishes.

ARG100 Tipping Bucket Raingauge
10
Shelf
Support Bench
Sink
Figure 2 Arrangement for Setting and Calibrating the Raingauge
If N is the number of tips (together with the fractional part left in the one bucket),
the calibration factor (CF) is then
CF = 0.2 (optionally 0.25) x 80/N
For example, if N = 78.8, then
CF = 0.2 (optionally 0.25) x 80/78.8
= 0.203 mm/tip
The amount of rainfall in any particular interval is obtained by multiplying the
number of recorded tips by the calibration factor.
This type of dynamic calibration gives repeatable results indoors, but it is not a
true representation of the gauge’s sensitivity to natural precipitation. Useful
results can be obtained by comparing the output from the ARG100 with the
catches from a standard ‘Snowdon pattern’ gauge (HMSO, 1956) sited nearby; if
this comparison is carried out with care, a calibration factor for natural rainfall
can be calculated from the slope of a graphical plot of (number of tips) against
(catch from Snowdon gauge in mm).

User Guide
11
7. Advantages and Limitations of a Tipping Bucket
Gauge
Gauges which operate on the tipping bucket principle provide a digital output,
which simplifies connection to a datalogger. The pulses returned during rainfall
may be counted over any time interval desired allowing accurate determination of
the rainfall rate (this variable, sometimes called ‘intensity’, is frequently used in
soil erosion studies and is relevant to some aspects of crop pathology).
When the ARG100 is used primarily to measure rainfall rates, the resolution of
the gauge may be too coarse to detect the significant changes in rate which nor-
mally occur from minute to minute in moderately heavy rain. In this case the
gauge may be adjusted to improve the resolution slightly (see Section 6.1);
alternatively, the bucket volume may be reduced by adding plasticine (or possibly
candle wax). It is generally much more satisfactory and convenient to improve the
resolution by increasing the collecting area of the gauge. This can be achieved by
attaching a funnel with a diameter greater than 25.5 cm over the instrument and
avoids the need for internal modifications.
A tipping bucket gauge responds to discrete quanta of rainfall, and the accuracy
and reproducibility of this quantum are determined not only by factors such as
friction in the bearings, etc. but also by the rate of fill of the buckets. When the
rainfall rate is high, a bucket may start to tip when the necessary volume of water
has been collected, but while the bucket is moving away from the funnel outlet, an
extra volume will have been collected and lost through spillage. The resulting
degradation in accuracy is of the order of 4% at rainfall rates of 25 mm/hr and 8%
at 133 mm/hr for most gauges (Parkin et al, 1982). This is important when results
from gauges of different designs are compared. These errors worsen when gauge
sensitivity is increased. It follows that gauge design is always a compromise
between the need for good resolution and good overall accuracy in rainfall totals.
References
HMSO (1956) Handbook of Meteorological Instruments, Part 1, Met.0. 577.
HMSO (1982) Observers Handbook, Met.0. 933.
Painter, R.D. (1976) in Methods of Plant Ecology pp 369-410. Ed. by
S.B.Chapman, Blackwell Scientific Press, Oxford
Parkin, D.A., King, W.D. and Shaw, D.E. (1982) An automatic raingauge
network for a cloud seeding experiment J.Appl.Meteorol. p 228.
Rodda, J.C., (1967) The rainfall measurement problem Proc. IAHS Gen. Ass.
Bern, IAHS Pub. No. 78, 215-231