Hukseflux IR20 User manual

Copyright by Hukseflux | manual v1604 | www.huksefluxusa.com | [email protected]
USER MANUAL IR20
Research grade pyrgeometer

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Warning statements
Putting more than 12 Volt across the sensor wiring
can lead to permanent damage to the sensor.
Do not use “open circuit detection”when measuring
the sensor output.

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Contents
Warning statements 2
Contents 3
List of symbols 4
Introduction 5
1Ordering and checking at delivery 8
1.1 Ordering IR20 8
1.2 Included items 8
1.3 Quick instrument check 9
2Instrument principle and theory 10
2.1 Pyrgeometer functionality 10
2.2 Solar and longwave radiation 10
2.3 IR20 pyrgeometer design 12
2.4 Typical measurement results 14
2.5 Optional heating 14
2.6 Optional shading 14
2.7 Use as a net radiation sensor 14
3Specifications of IR20 and IR20WS 15
3.1 Specifications of IR20 and IR20WS 15
3.2 Dimensions of IR20 18
4Standards and recommended practices for use 19
4.1 Site selection and installation 20
4.2 Installation of the sun screen 21
4.3 Electrical connection 22
4.4 Requirements for data acquisition / amplification 23
5Making a dependable measurement 24
5.1 The concept of dependability 24
5.2 Reliability of the measurement 25
5.3 Speed of repair and maintenance 26
5.4 Uncertainty evaluation 26
6Maintenance and trouble shooting 28
6.1 Recommended maintenance and quality assurance 28
6.2 Trouble shooting 29
6.3 Calibration and checks in the field 30
6.4 Data quality assurance 30
7Appendices 31
7.1 Appendix on cable extension / replacement 31
7.2 Appendix on tools for IR20 32
7.3 Appendix on spare parts for IR20 32
7.4 Appendix on standards for classification and calibration 32
7.5 Appendix on calibration hierarchy 33
7.6 Appendix on meteorological radiation quantities 35
7.7 Appendix on terminology / glossary 36
7.8 EU declaration of conformity 38

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List of symbols
Quantities Symbol Unit
Voltage output U V
Sensitivity S V/(W/m2)
Sensitivity at reference conditions S0V/(W/m2)
Temperature T °C
Equivalent blackbody radiative temperature T °C
Electrical resistance Re
Longwave irradiance E W/m2
Stefan–Boltzmann constant (5.67 x 10-8) σW/(m2∙K4)
temperature coefficient a 1/°C2
temperature coefficient b 1/°C
temperature coefficient c -
(see also appendix 7.6 on meteorological quantities)
Subscripts
sky relating to the atmosphere
surface relating to the ground surface
ambient relating to ambient air
body relating to the instrument body
sensor relating to the sensor

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Introduction
IR20 is a research grade pyrgeometer suitable for high-accuracy longwave irradiance
measurement in meteorological applications. IR20 is capable of measuring during both
day and night. In absence of solar radiation, model IR20WS offers even better accuracy
because of its wider spectral range.
IR20 measures the longwave or far-infra-red radiation received by a plane surface, in
W/m2, from a 180 ° field of view angle. In meteorological terms pyrgeometers are used
to measure “downward and upward longwave irradiance” (WMO definition). Longwave
radiation is the part of radiation that is not emitted by the sun. The spectral range of
longwave radiation is not standardised. A practical cut-on is in the range of 4 to 5 x 10-6 m.
IR20 has a dome with a solar blind filter with a cut-on at 4.5 x 10-6 m, making it suitable
for day- and night observations.
Model IR20WS has a wide spectral range with a cut-on at 1.0 x 10-6 m. It offers a
superior accuracy during night-time, when solar radiation is absent.
The main purpose of a pyrgeometer is to measure longwave radiation. As secondary
measurands, the sky temperature Tsky, and the equivalent surface temperature Tsurface
can be measured. Both are so-called equivalent blackbody temperatures, i.e.
temperatures calculated from pyrgeometer data, assuming the source behaves as a
blackbody with an emission coefficient of 1.
Using IR20 is easy. It can be connected directly to commonly used data logging systems.
The irradiance in W/m2is calculated by dividing the IR20 output, a small voltage, by the
sensitivity and taking in account the irradiated heat by the sensor itself (Planck’s law).
The sensitivity is provided with IR20 on its calibration certificate. Please note that the
IR20 sensitivity is corrected for temperature dependence in the measurement equation
by using 3 additional constants. These coefficients are provided as well.
The central measurement equation governing IR20 is:
E = U/(S0·(a·T² + b·T + c)) + σ·(T + 273.15)4(Formula 0.1)
S = S0·(a·T² + b·T + c) (Formula 0.2)
The instrument should be used in accordance with the recommended practices of WMO.
Suggested use for IR20 and IR20WS:
climatological networks
extreme climates (polar / tropical)
moving platforms (aircraft, buoys)
uncertainty assessment (IR20 + IR20WS)
calibration reference (IR20WS)

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Distinguishing features and benefits of IR20 are:
correction of temperature dependence by use of the measurement function. This is
far more accurate than temperature compensation in the instrument, especially at
very low and high temperatures. Every pyrgeometer is supplied with temperature
coefficients to enter into the equation.
high sensitivity. With sufficient input signal a typical datalogger no longer significantly
contributes to the uncertainty of the measurement.
low thermal-resistance of the sensor. Competing designs need a significant correction
for the difference in temperature between pyrgeometer body and sensor surface. For
IR20 this is not needed.
fast response time (3 s). A low response time is a benefit for measurements on
moving platforms such as aircraft and buoys.
on-board heater. Heating prevents condensation of water on the pyrgeometer dome
which, when occurring, leads to very large measurement errors.
instrument cut-on wavelength (5 %) and the two 50 % transmission points are
displayed on the product certificate for individual sensors.
Figure 0.1 IR20 research grade pyrgeometer with its sun screen removed
More about the instrument principle, theory and specifications can be found in the
following chapters.

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Pyrgeometers are not subject to a classification standard.
Calibration of pyrgeometers is usually traceable to the World Infrared Standard Group
(WISG). This calibration takes into account the spectral properties of typical downward
longwave radiation. As an option, calibration can be made traceable to a blackbody and
the International Temperature Scale of 1990 (ITS-90). This alternative calibration is
appropriate for measurements of upward longwave radiation (IR20 facing down).
See the specific paragraph in this manual about calibration and uncertainty assessment
for more information.
This manual is intended for users of both IR20 and IR20WS. The specifications of
IR20WS are identical to IR20’s except for its spectral range.
Figure 0.1 IR20WS research grade pyrgeometer

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1Ordering and checking at delivery
1.1 Ordering IR20
The standard configuration of IR20 is with 5 metres cable and a connector.
Common options are:
Longer cable (in multiples of 5 m). Specify total cable length.
Five silica gel bags in an air-thight bag for IR20 desiccant holder. Specify order
number DC01.
Optional calibration to blackbody (ITS-90).
IR20WS for the special wide spectrum model of IR20.
1.2 Included items
Arriving at the customer, the delivery should include:
pyrgeometer IR20 or IR20WS
cable of the length as ordered with connector
sun screen
product certificate matching the instrument serial number
calibration certificate matching the instrument serial number
temperature dependence report
any other options as ordered
Please store the certificates in a safe place.

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1.3 Quick instrument check
A quick test of the instrument can be done by using a simple hand held multimeter and a
thermal source.
1. Check the electrical resistance of the sensor between the green (-) and white (+) wire.
Use a multimeter at the 1000 Ω range. Measure the sensor resistance first with one
polarity, than reverse the polarity. Take the average value. The typical resistance of the
wiring is 0.1 Ω/m. Typical resistance should be the typical sensor resistance of 300 to
500 Ω plus 1.5 Ω for the total resistance of two wires (back and forth) of each 5 m.
Infinite resistance indicates a broken circuit; zero or a low resistance indicates a short
circuit.
2. Check if the sensor reacts to heat: put the multimeter at its most sensitive range of
DC voltage measurement, typically the 100 x 10-3 VDC range or lower. Make sure that
the sensor is at 25 °C or lower. Expose the sensor to a heat source at a short distance
from the window of more than 50 °C, for instance a heavy (> 5 kg) painted block of
metal, or a painted metal container holding hot water. Face the side of the container to
avoid condensation of water on the pyrgeometer window. Stir the water to attain
homogeneity. A painted surface will act as a blackbody in the far-infra-red (FIR),
irrespective of the visible colour. The signal should read positive and > 1 x 10-3 V now. In
case of using your hand as a heat source, the signal should be significantly lower.
3. Remove the sun screen (see chapter on installation of the sun screen). Inspect the
bubble level.
4. Check the electrical resistance of the thermistor. This should be in the 104Ω range.
5. Check the electrical resistance of the heater. This should be in the 100 Ω range.
6. Inspect the instrument for any damage.
7. Inspect if the humidity indicator is blue. Blue indicates dryness. The colour pink
indicates it is humid: in the latter case replace the desiccant (see chapter on
maintenance).

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2Instrument principle and theory
2.1 Pyrgeometer functionality
IR20’s scientific name is pyrgeometer. IR20 measures the longwave or far-infra-red (FIR)
radiation received by a plane surface, in W/m2, from a 180 ° field of view angle. In
meteorological terms pyrgeometers are used to measure “downward and upward
longwave irradiance” (WMO definition).
As secondary measurands, the sky temperature Tsky, and the equivalent surface (ground)
temperature Tsurface can be measured. Both are so-called equivalent blackbody radiative
temperatures, i.e. temperatures calculated from the pyrgeometer measurement
assuming these are uniform-temperature blackbodies with an emission coefficient of 1.
2.2 Solar and longwave radiation
Longwave radiation is the part of the radiation budget that is not emitted by the sun. The
spectral range of the longwave radiation is not standardised. A practical cut-on is in the
range of 4 to 5 x 10-6 m (see figure 2.2.1). In meteorology, solar- and longwave
radiation are typically measured as separate parameters. The instrument to measure
solar radiation is called pyranometer.
Figure 2.2.1 Atmospheric radiation as a function of wavelength plotted along two
logarithmic axes to highlight the longwave radiation. Longwave radiation is mainly
present in the 4 to 50 x 10-6 m range, whereas solar radiation is mainly present in the
0.3 to 3 x 10-6 m range. In practice, the two are measured separately using
pyrgeometers and pyranometers
0.001
0.010
0.100
1.000
110 100
spectral irradiance x 10-9 W/(m2/m)
wavelength x 10-6 m
downwelling
longwave
solar