R102/R102H-C Tipping Bucket Raingauge

13 Pages·1999·0.09 MB·English

R102/R102H-C
Tipping Bucket
Raingauge
User Guide
Issued 10.8.98
ª
Copyright 1998 Campbell Scientific Ltd.

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 in removing and/or reinstalling equipment. This guarantee and the
Company’s obligation thereunder is in lieu of all other guarantees,
expressed or implied, including those of suitability and fitness for a
particular purpose. Campbell Scientific is not liable for consequential
damage.
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 request.
When returning equipment, the Repair Reference Number must be clearly
marked on the outside of the package.
Note that goods sent air freight are subject to Customs clearance fees
which Campbell Scientific will charge to customers. In many cases, these
charges are greater than the cost of the repair.

Campbell Scientific Ltd,
Campbell Park, 80 Hathern Road,
Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone]
Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

Contents
1. Description................................................................. 1
2. Installation and Siting................................................ 1
2.1 Choice of Site...........................................................................................1
2.2 Unpacking................................................................................................2
2.3 Mounting..................................................................................................2
3. Wiring.......................................................................... 2
3.1 Optional Heater........................................................................................3
4. Programming.............................................................. 4
5. Maintenance............................................................... 4
6. Calibration.................................................................. 5
7. Advantages and Limitations of a
Tipping Bucket Gauge............................................... 6
Figures
1. Wiring Diagram for R102..........................................................................3
2. Dynamic Calibration of R102....................................................................6
Tables
1. Pin Descriptions of 6-pin Connector..........................................................4

R102/R102H-C Tipping Bucket Raingauge
The R102 is a high-quality robust tipping bucket raingauge constructed from stainless steel
and non-ferrous metals. The precision bucket mechanism uses stainless steel pivot pins to
reduce friction and a magnetic reed switch to count the pulses. When carefully sited and
installed the R102 will provide many years of reliable operation.
As an optional extra, the R102 can be supplied with a heater which consumes approximately
1.5A from a 12V AC/DC power supply. A thermostat brings the heater into operation when
the temperature inside the gauge approaches freezing point. The heater can also be supplied
as a conversion kit to convert an existing R102 to an R102H-C.
1. Description
The tipping bucket arrangement is similar to most other gauges of this type; pre-
cipitation 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 briefly. A
screened cable is used to connect the gauge to the datalogger where the switch
closures are counted.
The R102 is adjusted at manufacture to tip once for each 0.2mm of rain.
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 R102 should be exposed similarly if measurements are
required for comparison with those from agrometeorological or synoptic sites.
NOTE No two raingauge designs are ever likely to produce identical re-
sults, 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 ar-
ithmetically 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. Further details on the exposure of raingauges are given in HMSO (l956,
l982) and by Rodda (l967). Another useful text on exposure and associated errors
is Painter (l976).
The surrounding soil should be capable of allowing the discharge water to drain
away freely.
R102/R102H-C Tipping Bucket Raingauge
2.2 Unpacking
Unpack the R102 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 the key provided.
2. Remove the packing material which secures the balance arm to the pivot
posts and check the bucket mechanism for freedom of movement.
2.3 Mounting
Connections to the R102 are made via a 6-pin waterproof connector. One half is
mounted underneath the gauge and the cable is supplied attached to the mating
half. Connect the cable as follows:
1. Pick up the base and hold it upside down.
CAUTION Do not rest the base upside down as this may damage the
components.
2. While holding the base in one hand, attach the cable with the other by
aligning the two halves of the connector and tightening the locking ring.
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. Set the base level by adjusting the feet and checking
against the integral spirit level. When the base is level tighten the locking nuts to
hold the feet in position.
The R102 can be used for temporary installations without bolting down. For
permanent installation or where high wind speeds are likely it must be bolted to a
firm foundation; a small paving slab is ideal. If required bolt the R102 down as
follows:
1. Drill three holes to align with the fixing lugs in the base.
2. If you need to mount the R102 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.
Finally, reassemble the raingauge. As an additional check, place a spirit level
across the rim of the assembled R102.
3. Wiring
The raingauge is supplied with a 4-core 6m cable which may be extended if
required.
NOTE The red and black wires are only used if a heater is fitted.
CAUTION If you extend the cable, ensure that the heater wires are
screened from the wires connected to the reed switch. This
will prevent the false detection of rainfall when the heater
switches on or off.
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User Guide
For most applications the R102 may be connected directly to a pulse counting
input on the datalogger, but some care is needed if the raingauge lead has been
lengthened appreciably. For a long cable, a significant capacitance can exist be-
tween 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. The
inclusion of a l00W resistor close to the gauge will protect the switch from arcing
and prevent transients (Figure 1). We recommend this modification if leads longer
than 30m are used with the raingauge.
R102
Green
P
White
G or
Shield wire
(a) Normal Configuration
R102
100W
Green
P
White
G or
Shield wire
(b) With 100• Resistor Fitted by User for Long Cable
Figure 1 Wiring Diagram for R102
3.1 Optional Heater
The R102 can be supplied fitted with a thermostatically controlled heater. A
conversion kit is also available for retrospective fitting to existing units. The
thermostat senses the internal temperature of the gauge and, as the temperature
approaches zero, switches on the heater. The heater allows the gauge to operate
down to approximately -6°C.
NOTE The heater is not guaranteed to melt heavy ice concentrations or
snow which has filled the funnel area.
Raingauges fitted with a heater (model R102H-C) use the red and black
conductors for the connection of a 12V AC/DC supply. The heater can be
powered from any 12V AC/DC supply. Connect the red to the positive and the
black wire to the negative.
The pin descriptions of the 6-pin connector are given in Table 1 for reference.
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R102/R102H-C Tipping Bucket Raingauge
Table 1 Pin Descriptions of 6-pin Connector
Pin Internal Connection External Connection
A Reed switch (white) Green to datalogger
B Reed switch (white) White to datalogger
C Thermostat (white) 12V supply positive (red) *
D Thermostat (yellow) 12V supply negative (black) *
E not used -
F not used -
- not connected Shield wire to datalogger ground
* Red and black used for R102H-C only.
4. Programming
A tipping bucket raingauge is monitored with the Pulse Count instruction
(Instruction 3) configured for Switch Closure. Counts from long intervals are
used, as the final output desired is total rainfall (obtained with Instruction 72,
Totalize). If counts from long intervals were discarded, less rainfall would be
recorded than was actually measured by the gauge (assuming there were counts in
the long intervals). Output is desired in millimetres of precipitation. The gauge is
calibrated for a 0.2mm tip, so a multiplier of 0.2 is used.
PROGRAM
01: P 3Pulse
01: 1Rep
02: 1Pulse Input Chan
03: 2Switch closure
04: 11Loc [:RAIN mm ]
05: 0.2Mult
06: 0Offset
NOTE CR10/10X users wanting to use the pulse counters for other sensors
can program the rainfall measurement using an interrupt subroutine
which uses a control port for monitoring the rainguage (see example
in the datalogger manual).
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. If you need to remove the filter to
clean it, first remove the top of the gauge by unscrewing the three Allen screws.
Reach inside the cylinder and unscrew the inlet nozzle, thus allowing the filter to
be withdrawn from the top.
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.
3. Check that the balance arm is free to move. This can be done by slowly
pouring a measured quantity of water (say 250cm3) through the gauge and count-
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