Campbell ARG100 User manual

INSTRUCTION MANUAL
ARG100 Tipping
Bucket Rain Gauge
"QSJM 201
Copyright © 2014
Campbell Scientific (Canada) Corp.

PLEASE READ FIRST
About this manual
Please note that this manual was originally produced by Campbell Scientific Inc. (CSI) primarily
for the US 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 US gallon = 3.785 litres
In addition, part ordering numbers may vary. For example, the CABLE5CBL is a CSI part
number and known as a FIN5COND at Campbell Scientific Canada (CSC). CSC Technical
Support will be pleased to assist with any questions.
About sensor wiring
Please note that certain sensor configurations may require a user supplied jumper wire. It is
recommended to review the sensor configuration requirements for your application and supply the jumper
wire is necessary.

i
Table of Contents
PDF viewers: These page numbers refer to the printed version of this document. Use the
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1. Description.................................................................1
2. Technical Specifications ...........................................1
3. Installation and Siting................................................2
3.1 Choice of Site.......................................................................................2
3.2 Unpacking............................................................................................2
3.3 Mounting..............................................................................................2
3.4 Levelling..............................................................................................3
4. Wiring..........................................................................3
4.1 Wiring to a Pulse Channel ...................................................................3
4.2 Wiring to a Control Port.......................................................................4
5. Datalogger Programming..........................................4
5.1 Pulse Channel Example Programs .......................................................5
5.1.1 CR1000 Example Program...........................................................5
5.1.2 CR200(X) Series Example Program.............................................5
5.1.3 CR10(X) Example Program..........................................................6
5.2 Control Port Example...........................................................................7
5.2.1 CR1000 Example Program...........................................................7
5.2.2 CR10(X) Example Program..........................................................8
6. Maintenance...............................................................8
7. Calibration..................................................................9
7.1 Static Adjustment and Calibration .......................................................9
7.2 Dynamic Calibration............................................................................9
8. Advantages and Limitations of a Tipping Bucket
Gauge .....................................................................11
9. References................................................................11

Table of Contents
ii
Figures
Figure 4-1 Wiring Diagram from ARG100..................................................... 3
Figure 7-1 Arrangement for Setting and Calibrating the Rain Gauge........... 10
Tables
Table 4-1 Wiring for Pulse Channel Input...................................................... 4
Table 4-2 Wiring for Control Port Input......................................................... 4
Table 5-1 Multipliers ...................................................................................... 4

1
ARG100 Rain Gauge
The ARG100 is a well-designed tipping bucket rain gauge which combines durable
construction 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 Canada
(Corp.) 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 rain gauge is constructed from UV-resistant, vacuum-moulded
plastic 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.
More information on gauge calibration is given in Section 7.
2. Technical Specifications
Funnel Diameter: 254 mm
Overall Height: 340 mm
Tip Sensitivity: Standard setting 0.20 mm of rain per tip
Typical Accuracy: 98% @ 20 mm/hr
96% @ 50 mm/hr
95% @ 120mm/hr
Maximum Rainfall Rate (with software correction): 500 mm/hr
Output: Contact closure at tip
Weight: 1.0 kg

ARG100 Tipping Bucket Rain Gauge
2
3. Installation and Siting
3.1 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.
No two rain gauge designs are ever likely to produce identical
results and identical rain gauges can give slightly different catches
even when sites within a meter of each other.
Research has shown that a rain gauge 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 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 rain gauges are given in HMSO (1956, 1982) and by Rodda
(1967). Another useful text on exposure and associated errors is Painter (1976).
3.2 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
screws.
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.
3.3 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
Anchorbolts. 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.
Note

ARG100 Tipping Bucket Rain Gauge
3
3.4 Levelling
If the rain gauge 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 Anchorbolts, 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.
4. Wiring
The rain gauge is supplied with custom cable length at the time of order. For
most applications the ARG100 may be connected directly to a pulse counting
input on the datalogger as shown in Figure 4-1. 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 rain gauge
cable each time the gauge tips. A 100:resistor is fitted inside the gauge to
protect the switch from arcing and prevent transients.
Figure 4-1 Wiring Diagram from ARG100
4.1 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 4-1).
Black
Clear
Yellow
(Shield)
ARG100
P
Gor
Pulse
Port Control Port
C
+5V
No
Physical
connection
Note

ARG100 Tipping Bucket Rain Gauge
4
Table 4-1 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
White
Signal
Return
G
Clear
Shield
G
4.2 Wiring to a Control Port
Dataloggers listed in Table 4-2 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 4-2 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
White
Signal
Return
5 V
5 V
5 V
5 V
Clear
Shield
G
The CR10 does not support the use of control port inputs with the Pulse Count
instruction.
5. 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 5-1).
Table 5-1 Multipliers
Rain Ga
uge
1 mm
ARG100
0.2
Note

ARG100 Tipping Bucket Rain Gauge
5
5.1 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.
5.1.1 CR1000 Example Program
'CR1000
'ARG100 Tipping
'
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
5.1.2 CR200(X) Series Example Program
'CR200(X) Series
'ARG100 Tipping
'
'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

ARG100 Tipping Bucket Rain Gauge
6
'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
5.1.3 CR10(X) 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

ARG100 Tipping Bucket Rain Gauge
7
5.2 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.
5.2.1 CR1000 Example Program
'CR1000
'ARG100 Tipping
'
'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 Rain Gauge
8
5.2.2 CR10(X) 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.
6. 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.

ARG100 Tipping Bucket Rain Gauge
9
2. Check that the gauge is still level.
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 inter-
vals (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.
7. Calibration
The sensitivity of the ARG100 is set at manufacture to approximately
0.2 mm/tip and each gauge is subsequently calibrated as described in Section
7.1. The calibration factor is given on a certificate and is also recorded on the
inside of the rain gauge. For precise measurements use this value in your
program instead of the nominal value of 0.2.
7.1 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
manufacturers 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.
7.2 Dynamic Calibration
1. Set up the gauge as illustrated in Figure 7-1, carefully levelled and
connected to the datalogger.
2. Fill the water container with 810.4 cm3of water for a 0.2 mm calibration.
This is usually achieved most precisely and consistently by weighing the
water on a scale 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

ARG100 Tipping Bucket Rain Gauge
10
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.
Shelf
Support Bench
Sink
Figure 7-1 Arrangement for Setting and Calibrating the Rain Gauge
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.

ARG100 Tipping Bucket Rain Gauge
11
8. 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). 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.
9. 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 rain gauge
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.

A-1
Appendix A. Optional RGB1 Levelling
Baseplate
The RGB1 levelling baseplate is only supplied with theARG100 raingauge when
specifically ordered. It is suitable for fast, semi-permanent installations on soft ground.
Install theRGB1asfollows:
1. Take the funnel assembly off theraingauge.
2. Drill out the three holes in the raingauge base to 6.5mm diameter and debur.
3. Screw one 6mm full nut on each stud and screw the studsinto thebaseplate flush
with the bottom surface. Tighten thenut up to the baseplatetolock thestudsin
position.
4. Screw on thelower plastic thumb nutsand slide the raingauge over thestuds until
it is sitting on top of the thumb nuts.
5. Complete the assembly as shown below for each stud.
6. Fix the baseplate to the ground using the four pegsprovided through the four
outer holes. If force is needed, remove the raingauge first, fit the base, and then
replace the raingauge.
7. Adjust thethumb nutsto level the gauge. Ensure that thethumb nutsare tightened
to secure the gauge.
8. Replace the funnel and check operation of the gauge.
Figure A-1 Installation of RGB1

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