USER MANUAL IR02
Contents
1. Response time 95 18s Sensitivity nominal 15 x 10 V W m Sensitivity range 5 to 15 x 10 V W m Rated operating temperature range 40 to 80 C Temperature dependence lt 3 10 to 40 C Temperature sensor Pt100 Required sensor power zero passive sensor Heater 12 VDC 1 5 W see below for details Standard cable length 5m ir02 manual v1301 14 43 Smart Sensing SENSO 2 4 Typical measurement results Please note that the signal generated by an upfacing pyrgeometer usually has a negative sign The most important factors determining downward longwave irradiance are e ambient air temperature e Sky condition cloud cover e atmospheric moisture content Table 2 4 1 Expected pyrgeometer output U S at different ambient air temperatures Tambient and at different cloud conditions Under clear sky conditions the U S is around 100 W m while under cloudy conditions it will be close to O W m Also calculated the sky temperature Tsxy and the longwave downward irradiance E EXPECTED PYRGEOMETER OUTPUT CONDITIONS T ambient Sky condition U S T sky E C cloudy clear W m C W m 20 cloudy 0 20 232 20 clear sky 100 53 132 0 cloudy 0 0 314 0 clear sky 100 24 214 30 cloudy 0 30 477 30 clear sky 100 12 377 2 5 Optional heating A low power heater is located in the body of the pyrgeometer The heater is not necessarily switched on recommended oper2. 7 2 Dimensions of IRO2 TR 31 8 Appendices 34 8 1 X Appendix on cable extension replacement 34 8 2 Appendix on tools for IRO2 35 8 3 Appendix on spare parts for IRO2 35 8 4 Appendix on standards for classification and calibration 36 8 5 A Appendix on calibration hierarchy 36 8 6 Appendix on meteorological radiation quantities 38 8 7 Appendix on terminology glossary 39 8 8 Appendix on conditions of sale warranty and liability 40 8 9 EC declaration of conformity 41 irO2 manual 1301 3 43 Smart Sensing SENSOVAN T List of symbols Quantities Voltage output Sensitivity at reference conditions Temperature Equivalent blackbody radiative temperature Electrical resistance Longwave irradiance Stefan Boltzmann constant 5 67 x 10 see also appendix 8 6 on meteorological quantities Subscripts sky surface ambient body sensor irO2 manual 1301 Symbol oO am x3AA0cC Unit V W m W m W m K relating to the atmosphere relating to the ground surface relating to ambient air relating to the instrument body relating to the sensor 4 43 Smart Sensing SENSO ii Introduction IRO2 is a pyrgeometer suitable for longwave irradiance measurements in meteorological applications The instrument can be heated which improves measurement accuracy as it prevents dew deposition on its window IRO2 measures the longwave or far infra red radiation received by a plane surface
3. Check if the measurement function has been implemented properly Please note that each sensor has its own individual calibration factor and constants as documented in its production certificate Check the electrical resistance of the Pt100 This should be in the 100 Q range In case of use of the optional 10 kQ thermistor it should be in the 10 Q range Check if the pyrgeometer has a clean window Check the location of the pyrgeometer are there any obstructions sources that could explain the measurement result Check the condition of the wiring at the logger Check the cable condition looking for cable breaks Check the range of the data logger signal is usually negative this could be out of range or the amplitude could be out of range Check the data acquisition by applying a 1 x 105 V source to it in the 1 x 10 V range Look at the output Check if the output is as expected Check the data acquisition by short circuiting the data acquisition input with a 100 to 1000 Q resistor Look at the output Check if the output is close to 0 W m The sensor signal shows unexpected variations Check the presence of strong sources of electromagnetic radiation radar radio etc Check the condition of the shielding Check the condition of the sensor cable Check if the cable is not moving during the measurement The instrument shows internal condensation In case of condensation of droplets disassemble the instrument and
4. The World Meteorological Organization WMO is a specialised agency of the United Nations It is the UN system s authoritative voice on the state and behaviour of the earth s atmosphere and climate WMO publishes WMO No 8 Guide to Meteorological Instruments and Methods of Observation in which paragraph 7 4 covers measurement of total and long wave radiation For ultra high accuracy measurements the following manual may serve as a reference Baseline Surface Radiation Network BSRN Operations Manual Version 2 1 L J B McArthur April 2005 WCRP 121 WMO TD No 1274 This manual also includes chapters on installation paragraph 4 1 and calibration paragraph 8 4 irO2 manual 1301 18 43 Smart Sensing SENSOV ANT 4 1 Site selection and installation Table 4 1 1 Recommendations for installation of pyrgeometers Location the horizon should be as free from obstacles as possible Mechanical mounting thermal insulation preferably use connection by bolts to the bottom plate of the instrument A pyrgeometer is sensitive to thermal shocks Do not mount the instrument with the body in direct thermal contact to the mounting plate so always use the levelling feet also if the mounting is not horizontal do not mount the instrument on objects that become very hot black coated metal plates Instrument mounting with 2 bolts 2 x M5 bolt at 65 x 10 m centre to centre distance on north south axis connection through the pyrgeomet
5. We Hukseflux Thermal Sensors B V Elektronicaweg 25 2628 XG Delft The Netherlands in accordance with the requirements of the following directive 2004 108 EC The Electromagnetic Compatibility Directive hereby declare under our sole responsibility that Product model IR02 Type Pyrgeometer has been designed to comply and is in conformity with the relevant sections and applicable requirements of the following standards Emission EN 61326 1 2006 Immunity EN 61326 1 2006 Emission EN 61000 3 2 2006 Emission EN 61000 3 3 1995 2001 A2 2005 Kees VAN DEN BOS Director Delft April 10 2013 ir02 manual 1301 41 43 Smart Sensing SENSOVAN TS SMart T T 34 96 816 2005 Avda Benjamin Franklin 28 S jel S Ow A NI ra comercial sensovant com Parque Tecnol gico Valencia www sensovant com 46980 PATERNA
6. 5 m cable 0 5 kg Net weight including 5 m cable 0 3 kg Packaging box of 170 x 90 x 230 x 10 m ir02 manual 1301 15 43 Smart Sensing SENSO 3 Specifications of IRO2 3 1 Specifications of IRO2 IRO2 pyrgeometer measures the longwave irradiance received by a plane surface in W m72 from a 150 field of view angle which approximates the ideal 180 field of view angle In meteorological terms IRO2 measures downward and upward longwave irradiance Working completely passive using a thermopile sensor IRO2 generates a small output voltage proportional to the radiation balance between the instrument and the source it faces It can only be used in combination with a suitable measurement system The instrument is not subject to classification It should be used in accordance with the recommended practices of WMO IRO2 measures during both day and night For high accuracy measurements the user should consider to use the incorporated heater Table 3 1 1 Specifications of IRO2 IRO2 SPECIFICATIONS MEASURANDS Measurand longwave radiation Measurand in SI radiometry units longwave irradiance in W m Optional measurand sky temperature Optional measurand surface temperature Spectral range IRO2 4 5 to 40 x 10 m nominal see product certificate for individual value Solar offset lt 15 W m at 1000 W m global horizontal irradiance on the dome MAIN SPECIFICATIONS Field of view angle 150
7. TERM DEFINITION REFERENCE Solar energy solar energy is the electromagnetic energy emitted by the sun Solar energy is or solar also called solar radiation and shortwave radiation The solar radiation incident radiation on the top of the terrestrial atmosphere is called extra terrestrial solar radiation 97 of which is confined to the spectral range of 290 to 3 000 x 10 m Part of the extra terrestrial solar radiation penetrates the atmosphere and directly reaches the earth s surface while part of it is scattered and or absorbed by the gas molecules aerosol particles cloud droplets and cloud crystals in the atmosphere The former is the direct component the latter is the diffuse component of the solar radiation ref WMO Hukseflux Hemispherical solar radiation received by a plane surface from a 180 field of view angle solid solar radiation angle of 2 n sr ref ISO 9060 Global solar the solar radiation received from a 180 field of view angle on a horizontal radiation surface is referred to as global radiation Also called GHI This includes radiation received directly from the solid angle of the sun s disc as well as diffuse sky radiation that has been scattered in traversing the atmosphere ref WMO Hemispherical solar radiation received by a horizontal plane surface ref ISO 9060 Plane of array also POA hemispherical solar irradiance in the plane of a PV array irradiance ref ASTM E2848 11 IEC 617
8. axes to highlight the longwave radiation Longwave radiation is mainly present in the 4 to 50 x 10 m range whereas solar radiation is mainly present in the 0 3 to 3 x 10 m range In practice the two are measured separately using pyrgeometers and pyranometers The downwelling longwave radiation essentially consists of several components 1 low temperature radiation from the universe filtered by the atmosphere The atmosphere is transparent for this radiation in the so called atmospheric window roughly the 10 to 15 x 10 m wavelength range 2 higher temperature radiation emitted by atmospheric gasses and aerosols 3 in presence of clouds or mist the low temperature radiation from the universe is almost completely blocked by the water droplets The pyrgeometer then receives the radiation emitted by the water droplets Upwelling longwave irradiance is measured with downfacing instruments These are presumably looking directly at the surface absorption and emission of the atmosphere is low over a short distance of around 2 m which behaves like a normal blackbody Hukseflux suggests calibrating downfacing instruments against a blackbody rather than having WISG as a reference ir02 manual 1301 10 43 Smart Sensing SENSO Table 3 1 1 Specifications of IRO2 continued ADDITIONAL SPECIFICATIONS Zero offset b response to 5 K h change lt 4 W m in ambient temperature Non stability lt
9. dry out the parts The instrument shows persistent internal condensation Arrange to send the sensor back to Hukseflux for diagnosis ir02 manual 1301 27 43 Smart Sensing SENSO 2 6 Maintenance and trouble shooting 6 1 Recommended maintenance and quality assurance IRO2 can measure reliably at a low level of maintenance in most locations Usually unreliable measurements will be detected as unreasonably large or small measured values As a general rule this means that regular visual inspection combined with a critical review of the measured data preferably checking against other measurements is the preferred way to obtain a reliable measurement Table 6 1 1 Recommended maintenance of IRO2 If possible the data analysis and cleaning 1 and 2 should be done on a daily basis MINIMUM RECOMMENDED PYRGEOMETER MAINTENANCE INTERVAL SUBJECT ACTION 1 1 week data analysis compare measured data to maximum possible maximum expected irradiance and to other measurements nearby redundant instruments Also historical seasonal records can be used as a source for expected values Look for any patterns and events that deviate from what is normal or expected 2 2 weeks cleaning use a soft cloth to clean the dome of the instrument persistent stains can be treated with soapy water or alcohol 3 6 months inspection inspect cable quality inspect cable glands inspect mounting position inspect cable clean instrume
10. during nighttime only irO2 manual 1301 21 43 Smart Sensing SENSOWAN TE 5 Making a dependable measurement 5 1 The concept of dependability A measurement with a pyrgeometer is called dependable if it is reliable i e measuring within required uncertainty limits for most of the time and if problems once they occur can be solved quickly The requirements for a measurement with a pyrgeometer may be expressed by the user as e required uncertainty of the measurement see following paragraphs e requirements for maintenance and repairs possibilities for maintenance and repair including effort to be made and processing time e arequirement to the expected instrument lifetime until it is no longer feasible to repair It is important to realise that the uncertainty of the measurement is not only determined by the instrument but also by the way it is used In case of pyrgeometers the measurement uncertainty as obtained during outdoor measurements is a function of e the instrument properties e the calibration procedure uncertainty e the presence of natural sunlight involving the instrument specification of solar offset e the measurement conditions such as tilting ventilation shading heating instrument temperature e maintenance mainly fouling and deposition of water e the environmental conditions such as temperature position of the sun presence of clouds horizon representativeness of the location
11. in W m from a field of view angle of approximately 150 Longwave radiation is the part of radiation that is not emitted by the sun The actual field of view angle of IRO2 is not the ideal 180 The reduction of this field of view makes it possible to offer an instrument at an attractive price level while the accuracy loss is relatively small IRO2 has a window with a solar blind filter with a cut on at 4 5 x 10 m making it suitable for day and night observations IRO2 pyrgeometer has a high sensitivity With sufficient input signal a typical datalogger no longer contributes to the uncertainty of the measurement IRO2 also houses an on board heater Heating prevents dew deposition and condensation which when occurring leads to very large measurement errors Using IRO2 is easy It can be connected directly to commonly used data logging systems The irradiance in W m is calculated by dividing the IRO2 output a small voltage by the sensitivity and taking in account the irradiated heat by the sensor itself Stefan Boltzmann law The sensitivity is provided with IRO2 on its calibration certificate The central measurement equation governing IRO2 is E U S o T 273 15 Formula 0 1 The instrument should be used in accordance with the recommended practices of the World Meteorological Organization WMO Suggested use for IRO2 e general meteorological observations e climatological networks e agricultural networks ir02 ma
12. leads to a higher measurement reliability 5 3 Speed of repair and maintenance instrument lifetime Dependability is not only a matter of reliability but also involves the reaction to problems if the processing time of service and repairs is short this contributes to the dependability Hukseflux pyrgeometers are designed to allow easy maintenance and repair The main maintenance actions are e replacement of cabling and cable gland please note that with IRO2 the cable is potted inside the cable gland For optimisation of dependability a user should e estimate the expected lifetime of the instrument e design a schedule of regular maintenance e design a schedule of repair or replacement in case of defects When operating multiple instruments in a network Hukseflux recommends keeping procedures simple and having a few spare instruments to act as replacements during service recalibrations and repair Hukseflux pyrgeometers are designed to be suitable for the intended use for at least 5 years under normal meteorological conditions Factory warranty granting free of charge repair for defects that are clearly traceable to errors in production is 2 years The product expected lifetime is defined as the minimum number of years of employment with normal level of maintenance support until the instrument is no longer suitable for its intended use cannot be repaired For pyrgeometers the product expected lifetime depends heavily on
13. look out for any unrealistic values There are programs on the market that can semi automatically perform data screening See http www dqms com irO2 manual 1301 28 43 Smart Sensing SENSO 75 6 2 Trouble shooting Table 6 2 1 Trouble shooting for IRO2 The sensor does not give any signal Check the electrical resistance of the sensor between the green and white wire Use a multimeter at the 1000 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 O m Typical resistance should be the typical sensor resistance of 100 to 400 Q plus 1 5 Q 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 Check if the sensor reacts to heat put the multimeter at its most sensitive range of DC voltage measurement typically the 100 x 10 VDC range or lower Make sure that the sensor is at 20 C or lower Expose the sensor to a strong heat source at a short distance from the window of more than 50 C for instance a hot cup of coffee The signal should read positive and 1 x 10 V now In case of using your hand as a heat source the signal should be significantly lower Check the data acquisition by applying a 1 x 10 V source to it in the 1 x 10 V range The sensor signal is unrealistically high or low
14. the environmental conditions Examples of environments with reduced expected lifetime are areas with high levels of air pollution and areas with high levels of salt in the air Both cause enhanced corrosion It is not possible to give a generally applicable statement about expected lifetime In Hukseflux irO2 manual v1301 24 43 Smart Sensing SENSO experience it is not realistic to expect a lifetime longer than 10 years except in very dry environments such as very dry tropical or polar climates 5 4 Uncertainty evaluation The uncertainty of a measurement under outdoor or indoor conditions depends on many factors see paragraph 1 of this chapter It is not possible to give one figure for pyrgeometer measurement uncertainty The work on uncertainty evaluation is in progress There are several groups around the world participating in standardisation of the method of calculation The effort aims to work according to the guidelines for uncertainty evaluation according to the Guide to Expression of Uncertainty in Measurement or GUM The main ingredients of the uncertainty evaluation for pyrgeometers are e Calibration uncertainty which is in the order of 7 k 2 for upfacing instruments measuring downward longwave irradiance e Calibration uncertainty which is larger for other than upfacing instruments for downfacing instruments a blackbody calibration seems preferable Blackbody calibration will result in a lower sensitivit
15. 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 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 In the longwave spectrum the sky can be seen as a temperature source colder than ground level ambient air temperature with its lowest temperatures at zenith getting warmer closer to ambient air temperature at the horizon The uniformity of this longwave source is much better than that in the range of the solar spectrum where the sun is a dominant contributor The equivalent blackbody temperature as a function of zenith angle roughly follows the same pattern independent of the exact sky condition cloudy or clear This explains why for pyrgeometers the directional response is not very critical ir02 manual 1301 9 43 Smart Sensing SENSOWVANT xe 1 000 4 E N N gt downwelling a 0 100 longwave o solar x 9 Q i 0 010 4 5 E A T Q a n 0 001 1 10 100 wavelength x 10 56 m Figure 2 2 1 Atmospheric radiation as a function of wavelength plotted along two logarithmic
16. to 0 4 for vegetation up to 0 9 for fresh snow Angle of angle of radiation relative to the sensor measured from normal incidence varies incidence from 0 to 90 Zenith angle angle of incidence of radiation relative to zenith Equals angle of incidence for horizontally mounted instruments Azimuth angle angle of incidence of radiation projected in the plane of the sensor surface Varies from 0 to 360 0 is by definition the cable exit direction also called north west is 90 Sunshine sunshine duration during a given period is defined as the sum of that sub period duration for which the direct solar irradiance exceeds 120 W m ref WMO ir02 manual v1301 39 43 ar j 8 6 Appendix on meteorological radiation quantities A pyrgeometer measures longwave irradiance The time integrated total is called radiant exposure Table 8 6 1 Meteorological radiation quantities as recommended by WMO additional symbols by Hukseflux Thermal Sensor POA stands for Plane of Array irradiance The term originates from ASTM and IEC standards SYMBOL DESCRIPTION CALCULATION UNITS ALTERNATIVE EXPRESSION EX downward irradiance EX EQ X EN W m downward radiant exposure HX H X H X J m for a specified time interval EX upward irradiance EX E X E X W m upward radiant exposure Hg HiK J m W h m Change of for a specified time interval units E direct solar irradiance W m DNI D
17. 1 9o change per year Non linearity lt 2 5 100 to 300 W m relative to 200 W m sensor to source exchange Measurement range 300 to 300 W m sensor to source exchange U S Tilt dependence 2 0 to 90 at 300 W m Sensor resistance range 100 to 400 Expected voltage output application for outdoor measurement of downward longwave irradiance 7 5 to 7 5 x 10 V Measurement function required E U S 0 T 273 15 programming Measurement function optional Ta EY 0 273 15 programming for sky temperature Measurement function optional Tsurface 4 273 15 programming for surface temperature Required readout 1 differential voltage channel or 1 single ended voltage channel input resistance gt 10 Q 1 temperature channel STANDARDS Standard governing use of the WMO No 8 Guide to Meteorological Instruments and instrument Methods of Observation seventh edition 2008 paragraph 7 4 measurement of total and long wave radiation MOUNTING CABLING TRANSPORT Standard cable length see options 5m Cable diameter 5 3x 10 m Cable replacement IRO2 cable is potted and cannot be replaced Instrument mounting 2 x M5 bolt at 65 x 10 m centre to centre distance on north south axis Levelling bubble level and adjustable levelling feet are included Levelling accuracy 0 4 bubble entirely in ring IP protection class IP 67 Gross weight including
18. 24 Direct solar radiation received from a small solid angle centred on the sun s disc on a given radiation plane ref ISO 9060 Terrestrial or radiation not of solar origin but of terrestrial and atmospheric origin and having longwave longer wavelengths 3 000 to 100 000 x 10 m In case of downwelling E X also radiation the background radiation from the universe is involved passing through the atmospheric window In case of upwelling E X composed of longwave electromagnetic energy emitted by the earth s surface and by the gases aerosols and clouds of the atmosphere it is also partly absorbed within the atmosphere For a temperature of 300 K 99 99 of the power of the terrestrial radiation has a wavelength longer than 3 000 x 10 m and about 99 per cent longer than 5 000 x 10 m For lower temperatures the spectrum shifts to longer wavelengths ref WMO World measurement standard representing the SI unit of irradiance with an uncertainty Radiometric of less than 0 3 see the WMO Guide to Meteorological Instruments and Reference Methods of Observation 1983 subclause 9 1 3 The reference was adopted by WRR the World Meteorological Organization WMO and has been in effect since 1 July 1980 ref ISO 9060 Albedo ratio of reflected and incoming solar radiation Dimensionless number that varies between 0 and 1 Typical albedo values are lt 0 1 for water from 0 1 for wet soils to 0 5 for dry sand from 0 1
19. Expose the sensor to a strong heat source at a short distance from the window of more than 50 C for instance a hot cup of coffee The signal should read positive and gt 1 x 10 V now In case of using your hand as a heat source the signal should be significantly lower 3 Inspect the bubble level 4 Check the electrical resistance of the Pt100 This should be in the 100 Q range In case of use of a 10 kQ thermistor it should be in the 10 Q range 5 Check the electrical resistance of the heater This should be in the 100 range 6 Inspect the instrument for any damage irO2 manual 1301 8 43 Smart Sensing SENSOVAN TE 2 Instrument principle and theory 2 1 Pyrgeometer functionality IRO2 s scientific name is pyrgeometer IRO2 measures the longwave or far infra red FIR radiation received by a plane surface in W m ideally from a 180 field of view angle In meteorological terms pyrgeometers are used to measure downward and upward longwave irradiance WMO definition In case of IRO2 the ideal 180 field of view angle has been reduced to 150 This makes it possible to offer an instrument at an attractive price level while the loss of accuracy is relatively small As secondary measurands the sky temperature 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
20. Smart Sensing SENSOWVAN TE USER MANUAL IRO2 Pyrgeometer with heater Smart Sensing 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 irO2 manual 1301 2 43 Smart Sensing SENSOV ANT Contents Warning statements 2 Contents 3 List of symbols 4 Introduction 5 1 Ordering and checking at delivery 7 1 1 Ordering IRO2 7 1 2 Included items 7 1 3 Quick instrument check 8 2 Instrument principle and theory 9 2 1 Pyrgeometer functionality 9 2 2 Solar and longwave radiation 9 2 3 IRO2 pyrgeometer design 11 2 4 Typical measurement results 13 2 5 Optional heating 13 2 6 Use as a net radiation sensor 13 3 Specifications of IRO2 14 3 1 Specifications of IRO2 14 3 2 Dimensions of IRO2 17 4 Standards and recommended practices for use 18 4 1 Site selection and installation 19 4 2 Electrical connection 20 4 3 Requirements for data acquisition amplification 21 5 Making a dependable measurement 22 5 1 The concept of dependability 22 5 2 Reliability of the measurement 23 5 3 Speed of repair and maintenance instrument lifetime 24 5 4 Uncertainty evaluation 25 6 Maintenance and trouble shooting 26 6 1 Recommended maintenance and quality assurance 26 6 2 Trouble shooting 27 6 3 Calibration and checks in the field 28 6 4 Data quality assurance 28 7 IRO2 TR 29 7 1 Introduction IRO2 TR 29
21. Therefore statements about the overall measurement uncertainty under outdoor conditions can only be made on an individual basis taking all these factors into account defined at Hukseflux as all factors outside the instrument that are relevant to the measurement such as the cloud cover presence or absence of direct radiation sun position the local horizon which may be obstructed or condition of the ground when inverted The environmental conditions also involve the question whether or not the measurement at the location of measurement is representative of the quantity that should be measured irO2 manual 1301 22 43 Smart Sensing SENSOVAN TE 5 2 Reliability of the measurement A measurement is reliable if it measures within required uncertainty limits for most of the time We distinguish between two causes of unreliability of the measurement e related to the reliability of the pyrgeometer and its design manufacturing calibration hardware reliability e related to the reliability of the measurement uncertainty measurement reliability which involves hardware reliability as well as condition of use Most of the hardware reliability is the responsibility of the instrument manufacturer The reliability of the measurement however is a joint responsibility of instrument manufacturer and user As a function of user requirements taking into account measurement conditions and environmental conditions the user will select an in
22. WAN TE 8 Appendices 8 1 Appendix on cable extension replacement IRO2 cable is potted and cannot be replaced The cable gland plus cable assembly may be completely removed and replaced by a similar assembly Please consult Hukseflux for instructions on cable preparation or use Hukseflux supplied parts IRO2 is equipped with one cable Keep the distance between data logger or amplifier and sensor as short as possible Cables act as a source of distortion by picking up capacitive noise In an electrically quiet environment the IRO2 cable can however be extended without problem to 100 meters If done properly the sensor signal although small will not significantly degrade because the sensor resistance is very low so good immunity to external sources and because there is no current flowing so no resistive losses Cable and connection specifications are summarised below NOTE the body of IRO2 contains connector blocks that can be used for the internal connection of a new cable See the chapter on electrical connections Table 8 1 1 Preferred specifications for cable extension of IRO2 General Please consult Hukseflux for instructions or use Hukseflux supplied parts Cable 8 wire shielded with copper core Sealing sealed at the sensor side against humidity ingress Core resistance lt 0 1 Q m Length cables should be kept as short as possible in any case the total cable length should be less than 100 m Out
23. WISG A typical uncertainty of S is 4 2 k 2 CORRECTION OF WORKING STANDARD IR20 CALIBRATION TO STANDARDISED REFERENCE CONDITIONS Correction from test conditions of the standard to reference conditions No corrections are applied Reference conditions are horizontal mounting atmospheric longwave irradiance clear sky nights 20 C OUTDOOR IRO2 WORKING STANDARD CALIBRATION AT HUKSEFLUX Calibration of working standard IRO2 150 degrees field of view angle pyrgeometer at Hukseflux INDOOR PRODUCT CALIBRATION Calibration of products i e pyrgeometers of type IRO2 Indoor side by side comparison to a working standard IRO2 pyrgeometer under an infra red blackbody source CALIBRATION UNCERTAINTY CALCULATION ISO 98 3 Guide to the Expression of Uncertainty in Measurement GUM Determination of combined expanded uncertainty of calibration of the product including uncertainty of the working standard uncertainty of correction uncertainty of the method transfer error The coverage factor must be determined at Hukseflux we work with a coverage factor k 2 Hukseflux specifies a calibration uncertainty of lt 7 k 2 ir02 manual 1301 37 43 Smart Sensing 8 4 Appendix on standards for classification and calibration Unlike pyranometers pyrgeometers are not subject to a system of classification At Hukseflux we distinguish between normal pyrgeometers like mod
24. ation is to activate the heater when there is a risk of dew deposition 2 6 Use as a net radiation sensor Two pyrgeometers mounted back to back may be used to measure net longwave radiation Net longwave radiation is defined as downwelling minus upwelling longwave irradiance In case the two instruments are thermally coupled the body temperatures of the instruments are identical In that case the body temperature cancels from the equation for the net radiation However for calculation of sky temperature and surface temperature the instrument temperature still needs to be measured See also model NRO1 a 4 component net radiometer irO2 manual 1301 13 43 Smart Sensing SENSOVANT A pyrgeometer should have a so called directional response older documents mention cosine response that is as close as possible to the ideal cosine characteristic In order to attain the proper directional and spectral characteristics a pyrgeometer s main components are a thermal sensor with black coating It has a flat spectrum covering the 0 3 to 50 x 10 m range and has a near perfect directional response The coating absorbs all longwave radiation and at the moment of absorption converts it to heat The heat flows through the sensor to the sensor body The thermopile sensor generates a voltage output signal that is proportional to the irradiance exchange between sensor and source The sensor not only absorbs but also irradiates heat a
25. ave irradiance measurement MEASUREMENT ACCURACY Uncertainty of the measurement statements about the overall measurement uncertainty can only be made on an individual basis See the chapter on uncertainty evaluation Achievable uncertainty 95 9o confidence level daily totals 15 Hukseflux own estimate VERSIONS OPTIONS Longer cable in multiples of 5 m option code total cable length Calibration optional to blackbody ITS 90 4 20 mA transmitter creating a 4 20 mA output signal option code TR with adapted housing standard setting is 4 x 10 A at 300 W m and 20 x 10 A at 100 W m heater and internal temperature sensor directly connected to cable wire for specifications see the chapter on IRO2 TR Internal temperature sensor Longer cable in multiples of 5 m measuring the body temperature version code T1 for Pt100 DIN class A version code T2 for thermistor 10 kQ at 25 C option code total cable length irO2 manual 1301 16 43 Smart Sensing SENSOV ANT 3 2 Dimensions of IRO2 78 46 e 22 M5 2x 65 Figure 3 2 1 Dimensions of IRO2 in 10 m ir02 manual 1301 17 43 Smart Sensing 4 Standards and recommended practices for use Pyrgeometers are not subject to standardisation
26. cted sensor aging is specified per instrument as its non stability in change year In case the sensor is not recalibrated the uncertainty of the sensitivity gradually will increase This is solved by regular recalibration e moisture condensing under pyrgeometer domes resulting in a slow change of sensitivity within specifications For non serviceable sensors like Hukseflux flat window pyrgeometers such as model IRO2 this may slowly develop into a defect For research grade model IR20 extra desiccant in a set of 5 bags in an air tight bag is available irO2 manual 1301 23 43 Smart Sensing SENSO One of the larger errors in the daytime measurement of downwelling longwave irradiance is the offset caused by solar radiation the solar offset Errors due to solar offset are of the order of 15 W m at 1000 W m global horizontal irradiance For ultra high accuracy measurements this offset can be reduced by around 60 by shading which means preventing the direct radiation to reach the instrument Shading is typically done by using a shading disk on a solar tracker Shading is often applied with research grade pyrgeometers like Hukseflux model IR20 The overall accuracy of model IRO2 does not justify use of shading Another way to improve measurement reliability is to introduce redundant sensors e The use of redundant instruments allows remote checks of one instrument using the other as a reference which
27. e for product or working hours is 24 months Hukseflux does not accept any liability for losses or damages related to use of the supplied products See the appendix and Hukseflux General Conditions of Sale for detailed statements on warranty and liability 1 2 Included items Arriving at the customer the delivery should include pyrgeometer IRO2 e cable of the length as ordered e product certificate matching the instrument serial number e any other options as ordered Please store the certificate in a safe place ir02 manual 1301 7 43 Smart Sensing SENSOVANTI 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 Q 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 Q m Typical resistance should be the typical sensor resistance of 100 to 400 Q plus 1 5 Q 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 VDC range or lower Make sure that the sensor is at 20 C or lower
28. el IRO2 and research grade pyrgeometers like IR20 and IR20WS The term research grade is used to indicate that this instrument has the highest attainable specifications 8 5 Appendix on calibration hierarchy Hukseflux pyrgeometers are traceable to the World Infrared Standard Group WISG WISG is composed of a group of pyrgeometers The calibration hierarchy of Hukseflux IRO2 is from WISG through Hukseflux internal calibration procedures The calibration of the IRO2 working standard involves outdoor comparison at Hukseflux of the IRO2 working standard to a working standard of a higher level a pyrgeometer of model IR20 calibrated against the WISG IRO2 pyrgeometers are calibrated using an indoor procedure under an infra red source blackbody The WISG group of instruments is maintained by World Radiation Center WRC in Davos Switzerland An absolute sky scanning radiometer provides the absolute longwave irradiance reference Comparisons between the reference and the WISG are performed on a regular basis to maintain the WISG and supervise its long term stability It is essential that these intercomparisons take place under various sky conditions but the predominant condition is a clear sky which means that the validity of WISG calibration is a clear sky spectrum Typical exchange between pyrgeometer and sky is in the 70 to 120 W m irO2 manual 1301 36 43 Smart sensing SENSOVANT 8 9 EC declaration of conformity CE
29. er flange Performing a representative the pyrgeometer measures the solar radiation in the measurement plane of the sensor This may require installation in a tilted or inverted position The sensor surface sensor bottom plate should be mounted parallel to the plane of interest In case a pyrgeometer is not mounted horizontally or in case the horizon is obstructed the representativeness of the location becomes an important element of the measurement See the chapter on uncertainty evaluation Levelling in case of horizontal mounting only use the bubble level and levelling feet Instrument orientation by convention with the cable exit pointing to the nearest pole so the cable exit should point north in the northern hemisphere south in the southern hemisphere Installation height in case of inverted installation WMO recommends a distance of 1 5 m between soil surface and sensor reducing the effect of shadows and in order to obtain good spatial averaging ir02 manual v1301 19 43 Smart Sensing SENSO 4 2 Electrical connection In order to operate a pyrgeometer should be connected to a measurement system typically a so called datalogger IRO2 is a passive sensor that does not need any power Cables generally act as a source of distortion by picking up capacitive noise We recommend keeping the distance between a datalogger or amplifier and the sensor as short as possible For cable extension see the appendix on t
30. er sheet specified for outdoor use Connection either solder the new cable core and shield to the original sensor cable and make a waterproof connection using cable shrink or use gold plated waterproof connectors Always connect shield ir02 manual v1301 34 43 Smart Sensing 8 2 Appendix on tools for IRO2 Table 8 2 1 Specifications of tools for IRO2 tooling required for cable gland fixation and removal spanner size 15 x 10 m tooling required for wire fixation and removal screwdriver blade width 2 x 10 m internal wiring inside IRO2 body tooling for removal of bottom cap locking plug plate for slot of 15 by 2 x 10 m 5 EURO CENT coin 8 3 Appendix on spare parts for IRO2 e Levelling feet set of 3 socket head cap screw M5 x 20 Aluminium e IRO2 cable specify length in multiples of 5 m potted to cable gland e Bottom cap of IRO2 with O ring locking plug M32 x 1 5 plus O ring 47 x 2 irO2 manual 1301 35 43 Smart Sensing SENSOVANTT WISG World Infra Red Standard Group Group of pyrgeometers maintained by PMOD Davos Switzerland that forms the reference for calibration of pyrgeometers WISG is traceable to international standards through an absolute sky scanning radiometer WISG has been formally recognised by the World Meteorological Organisation WMO as interim WMO Pyrgeometer Infrared Reference Sky equivalent blackbody radiative temperature of the sky i e the temperature temperature calcu
31. his subject Table 4 2 1 The electrical connection of IRO2 The heater is not necessarily used The temperature sensor must be used PIN WIRE IRO2 White Pt100 un Pt100 Pt100 heater heater ground signal AN OU KR N Grey signal Note 1 optional 10 kQ thermistors are internally connected in a 4 wire configuration like the Pt100 but usually connected to electronics used in 2 wire configuration Note 2 the heater is not necessarily connected In case it is connected the polarity of the connection is not important Note 3 signal wires are insulated from ground wire and from the sensor body Insulation resistance is tested during production and larger than 1 x 1050 Note 4 ground is connected to the connector the sensor body and the shield of the wire Housing Thermopile Temperature sensor Heater Lf Figure 4 2 1 Electrical diagram of the internal wiring of IRO2 The shield is connected to the sensor body ir02 manual 1301 20 43 Smart Sensing 4 3 Requirements for data acquisition amplification The selection and programming of dataloggers is the responsibility of the user Please contact the supplier of the data acquisition and amplification equipment to see if directions for use with the IRO2 are available In case programming for similar instruments is available this can typically also be used IRO2 can usually be treated in the same way as other thermopile p
32. ing instruments are thermally coupled the temperature measurement and also its uncertainty cancel from the equation ir02 manual 1301 25 43 Smart Sensing SENSOW AN TS Table 7 1 1 Specifications of IRO2 TR IRO2 TR SPECIFICATIONS Description pyrgeometer with heater and with 4 20 mA transmitter Transmitted range 300 to 100 W m Output signal 4 to 20x 107A Principle 2 wire current loop Supply voltage 7 2 to 35 VDC Options adapted transmitted range longer cable in multiples of 5 m Mounting 2 x M5 bolt at 65 mm centre to centre distance on north south axis or 1 x M6 bolt at the centre of the instrument connection from below under the bottom plate of the instrument Table 7 1 2 Requirements for data acquisition and amplification equipment with the IRO2 TR configuration Capability to measure 4 20 mA or measure currents or measure voltages The IRO2 TR has a 4 20 mA output as well as a temperature sensor see next row which both must be read out Concerning the 4 20 mA signal there are several possibilities to handle this signal It is important to realise that the signal wires not only act to transmit the signal but also act as power supply Some dataloggers have a 4 20 mA input In that case the connection can be directly made Some dataloggers have the capability to measure currents In some cases the datalogger accepts a voltage input Usually a 100 Q precision res
33. ion hits the sensor perpendicularly normal to the surface 0 angle of incidence zero response when the source is at the horizon 90 angle of incidence 90 zenith angle and 50 of full response at 60 angle of incidence irO2 manual 1301 11 43 Smart Sensin SENSO T Table 3 1 1 Specifications of IRO2 started on previous pages HEATING Heater operation the heater is not necessarily switched on recommended operation is to activate the heater when there is a risk of dew deposition Required heater power 1 5 W at 12 VDC Heater resistance 95 Q Steady state zero offset caused by 0 W m heating CALIBRATION Calibration traceability to WISG Optional traceability to blackbody ITS 90 Calibration hierarchy from WISG through Hukseflux internal calibration procedure employing a blackbody Calibration method indoor calibration under a blackbody by comparison reference pyrgeometer traceable to WISG Calibration uncertainty lt 7 k 2 Recommended recalibration interval 2 years Reference conditions horizontal mounting atmospheric longwave irradiance clear sky nights 20 C Validity of calibration based on experience the instrument sensitivity will not change during storage During use under exposure to solar radiation the instrument non stability specification is applicable Hukseflux recommends ITS 90 traceable calibration for upward longw
34. irect normal to the apparent Normal solar zenith angle Irradiance Eo solar constant W m global irradiance EN Ecos Op W m GHI Global hemispherical irradiance on Horizontal a specified in this case Irradiance horizontal surface EQ global irradiance E W Ecos 0 W m POA Plane of hemispherical irradiance on E M EX Array a specified in this case tilted surface E W downward diffuse solar W m DHI Diffuse radiation Horizontal Irradiance upward downward W m longwave irradiance EW reflected solar irradiance W m Ex net irradiance EX EN W m T surface equivalent blackbody radiative temperature of the surface Tsky equivalent blackbody radiative temperature of the sky SD sunshine duration H 0 is the apparent solar zenith angle relative to horizontal 6 relative to a tilted surface g global longwave t tilted h horizontal distinction horizontal and tilted from Hukseflux T symbols introduced by Hukseflux contributions of E4 X and are Eqa Xand E N both corrected for the tilt angle of the surface ir02 manual 1301 38 43 Smart Sensing SENSOVANT Table 8 5 1 Calibration hierarchy for pyrgeometers with 150 field of view angle WORKING STANDARD IR20 CALIBRATION AT PMOD WRC DAVOS Calibration of working standard IR20 180 field of view angle pyrgeometers traceable to
35. istor is used to convert the current to a voltage this will then be in the 0 4 to 2 VDC range This resistor must be put in the wire of the sensor In the two latter cases the user must check that the low side of the input channel is connected to ground and the high side to a positive voltage in the required range Capability to measure temperatures ir02 manual 1301 Depending on the version this may be Pt100 or a 10 kQ thermistor 30 43 Smart Sensing SENSOVAN Ti 7 IRO2 TR 7 1 Introduction IRO2 TR As a version of IRO2 Hukseflux offers model IRO2 TR a pyrgeometer with heater and 4 20 mA transmitter IRO2 TR houses a 4 20 mA transmitter for easy read out by dataloggers commonly used in the industry Using IRO2 TR is easy The pyrgeometer can be connected directly to commonly used data logging systems The irradiance in W m is calculated by using the transmitter s output and the temperature reading The latter can either be a Pt100 or a 10 kQ thermistor depending on the ordered version In IRO2 TR s standard configuration the 4 to 20 mA output corresponds to a transmitted range of 300 to 100 W m This range can be adjusted at the factory upon request Figure 7 1 1 RO2 TR pyrgeometer with heater and 4 20 mA transmitter ir02 manual 1301 29 43 Smart Sensing SENSOW AN TE 6 3 Calibration and checks in the field Recalibration of field pyrgeometers is typically done by comparison in the fie
36. lated from pyrgeometer data measuring downwelling longwave radiation assuming the sky behaves as a blackbody with an emission coefficient of 1 Surface equivalent blackbody radiative temperature of the surface i e the temperature temperature calculated from pyrgeometer data measuring upwelling longwave radiation assuming the ground behaves as a blackbody with an emission coefficient of 1 8 8 Appendix on conditions of sale warranty and liability Delivery of goods is subject to Hukseflux General Conditions of Sale Hukseflux has the following warranty and liability policy Hukseflux guarantees the supplied goods to be new free from defects related to bad performance of materials and free from faults that are clearly related to production and manufacturing Warranty on products is valid until 24 months after transfer of ownership The warranty does not apply if the application involves significant wear and tear if it involves use outside the specified range of application or if it involves accidental damage or misuse The warranty expires when anyone other than Hukseflux makes modifications to or repairs the products Hukseflux is in no event liable for damages to its customers or anyone claiming through these customers associated to the goods or services it supplies ir02 manual 1301 40 43 Smart Sensing SENSOVANTT 8 7 Appendix on terminology glossary Table 8 7 1 Definitions and references of used terms
37. ld to a reference pyrgeometer There is no standard for this procedure Hukseflux recommendation for re calibration if possible perform calibration indoor by comparison to an identical or a higher class reference instrument under nighttime as well as daytime conditions Use nighttime data only to determine S Hukseflux main recommendations for field intercomparisons are 1 perform field calibration during several days 2 to 3 days and if possible under cloudless conditions 2 to take a reference of the same brand and type as the field pyrgeometer or a pyrgeometer of a higher class and 3 to connect both to the same electronics so that electronics errors also offsets are eliminated 4 to mount all instruments on the same platform so that they have the same body temperature 5 to analyse downward irradiance values at nighttime only to determine S 6 to analyse the daytime data independently and look at the residuals between the calibration reference and calibrated instrument as a function of solar irradiance The solar offset can serve as a quality indicator of the pyrgeometer filter condition 6 4 Data quality assurance Quality assurance can be done by e analysing trends in longwave irradiance signal e plotting the measured irradiance against mathematically generated expected values e comparing irradiance measurements between sites e analysis of daytime signals against solar irradiance The main idea is that one should
38. nt clean cable inspect levelling change instrument tilt in case this is out of specification inspect mounting connection 4 2 years recalibration recalibration by side by side comparison to a higher standard instrument in the field 5 lifetime judge if the instrument should be reliable for another 2 years assessment or if it should be replaced 6 6 years parts if applicable necessary replace the parts that are most replacement exposed to weathering cable amp cable gland sun screen NOTE use Hukseflux approved parts only 7 internal if applicable open instrument and inspect replace O rings inspection dry internal cavity around the circuit board 8 recalibration recalibration by side by side comparison to a higher standard instrument at the manufacturer or a reference institute Also recalibrate the temperature sensor ir02 manual 1301 26 43 Smart Sensing SENSOVANTT 7 2 Dimensions of IRO2 TR Figure 7 2 1 Overview of IR02 TR 1 2 3 4 5 6 7 8 cable standard length 5 metres optional longer cable cable gland window with solar blind filter sensor below window sensor body transmitter housing levelling feet bubble level ir02 manual 1301 31 43 Smart Sensing SENSO 32 Figure 7 2 2 Dimensions of IRO2 TR in 10 m ir02 manual 1301 32 43 Smart Sensing SENSOVAN TS irO2 manual 1301 33 43 Smart Sensing SENSO
39. nual 1301 5 43 Smart Sensing SENSO Figure 0 1 JRO2 pyrgeometer with heater Calibration of pyrgeometers used for downward longwave radiation is 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 with IRO2 pyrgeometers facing down Model IRO2 TR houses a 4 20 mA transmitter for easy read out by dataloggers commonly used in the industry For more information see the chapter on IRO2 TR ir02 manual 1301 6 43 SENSOVAN TI 1 Ordering and checking at delivery 1 1 Ordering IRO2 The standard configuration of IRO2 is with 5 metres cable Common options are Longer cable in multiples of 5 m Specify total cable length e IRO2 TR pyrgeometer with heater and 4 20 mA transmitter Standard setting is 4 mA at 300 W m and 20 mA at 100 W m Specify setting and total cable length e Internal temperature sensor This can be either a Pt100 standard configuration or a 10 kQ thermistor optional Specify respectively T1 or T2 e Optional calibration to blackbody ITS 90 Supply of products is subject to Hukseflux General Conditions of Sale The product warranty involving repair or replacement without charg
40. s a blackbody a silicon window This dome limits the spectral range from 1 0 to 40 x 10 m cutting off the part below 1 0 x 10 m while preserving as much as possible the ideal 180 field of view angle Another function of the window or dome is that it shields the thermopile sensor from the environment convection rain a solar blind interference coating deposited on the window this coating limits the spectral range It now becomes 4 5 to 40 x 10 m cutting off the part below 4 5 x 10 m Pyrgeometers can be manufactured to different specifications and with different levels of verification and characterisation during production Hukseflux also manufactures higher accuracy pyrgeometers see pyrgeometer model IR20 irO2 manual 1301 12 43 Smart Sensing SENSOVANTT 2 3 IRO2 pyrgeometer design Figure 2 3 1 Overview of IRO2 pyrgeometer 1 2 3 4 5 6 7 8 cable standard length 5 metres optional longer cable cable gland window with solar blind filter sensor below window sensor body levelling feet mounting hole bubble level By definition a pyrgeometer should not measure solar radiation and in the longwave have a spectral selectivity that is as flat as possible In an irradiance measurement by definition the response to beam radiation varies with the cosine of the angle of incidence i e it should have full response when the radiat
41. strument of a certain class and define maintenance support procedures In many situations there is a limit to a realistically attainable accuracy level This is due to conditions that are beyond control once the measurement system is in place Typical limiting conditions are e the measurement conditions for instance when working at extreme temperatures when the instrument temperature is at the extreme limits of the rated temperature range e the environmental conditions for instance when installed at a sub optimal measurement location with obstacles in the field of view e the environmental conditions for instance when assessing net radiation the downfacing pyrgeometer measurement may not be representative of irradiance received in that particular area The measurement reliability can be improved by maintenance support Important aspects are e dome fouling by deposition of dust dew rain or snow With pyrgeometers the most important source of unreliability is deposition of water on the dome Water completely blocks the longwave radiation flux between sensor and sky In particular at clear nights this causes very large errors Water deposition under clear sky nighttime conditions can largely be prevented by using the instrument heater Fouling results in undefined measurement uncertainty sensitivity and directional error are no longer defined This should be solved by regular inspection and cleaning e sensor instability Maximum expe
42. y S than WISG traceable calibraton Errors due to water deposition at clear nights these completely block the longwave irradiance exchange between pyrgeometer and may cause the signal U S to change from a large negative value 100 W m to around O W m Water deposition at clear nights may largely be avoided by using the on board heater of IRO2 e Errors due to solar offset which is of the order of 15 W m at 1000 W m global horizontal irradiance This uncertainty is not taken into account in the WISG calibration of the reference instrument Errors due to the choice of the cut on wavelength of the pyrgeometer Depending on the atmospheric water content the pyrgeometer will block a variable percentage of the downward longwave irradiance This causes an uncertainty of the sensitivity S With IRO2 this uncertainty is already taken into account in the WISG calibration of the reference instrument e Errors due to instrument non stability This is now estimated at 1 9o change per year The main factor in instrument non stability is the aging of the pyrgeometer solar blind filter e Errors due to the temperature measurement T For this a Pt100 or optional 10 thermistor must be read out Required accuracy of the readout is 0 2 C which results in around 1 W m uncertainty of the irradiance measurement To this the uncertainty of the thermistor itself should be added In measurement of net radiation in case the upfacing and downfac
43. yrgeometers Table 4 3 1 Requirements for data acquisition and amplification equipment for IRO2 in the standard configuration Capability to measure small voltage preferably better than 5 x 10 V uncertainty signals Minimum requirement 20 x 10 V uncertainty valid for the entire expected temperature range of the acquisition amplification equipment Capability for the data logger or the to store data and to perform division by the sensitivity to software calculate the longwave irradiance E U S o T 273 15 Formula 0 1 see also optional measurands Data acquisition input resistance gt 1x10 Q Open circuit detection open circuit detection should not be used unless this is done WARNING separately from the normal measurement by more than 5 times the sensor response time and with a small current only Thermopile sensors are sensitive to the current that is used during open circuit detection The current will generate heat which is measured and will appear as an offset Capability to measure temperature a Pt100 or optional thermistor must be read out Required accuracy of the readout is 0 2 C which results in around 1 W m uncertainty of the irradiance measurement Capability to power the heater IRO2 has a 12 VDC 1 5 W heater on board which may OPTIONAL optionally be activated to keep the instrument above dew point Some users prefer to have the heater on full time others prefer to switch it on
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