CNR1 Net Radiometer Revision: 5/11 C o p y r i g h t © 2 0 0 0 - 2 0 1 1 C a m p b e l l S c i e n t i f i c , I n c .
Warranty and Assistance PRODUCTS MANUFACTURED BY CAMPBELL SCIENTIFIC, INC. are warranted by Campbell Scientific, Inc. (“Campbell”) to be free from defects in materials and workmanship under normal use and service for twelve (12) months from date of shipment unless otherwise specified on the corresponding Campbell invoice. Batteries, fine-wire thermocouples, desiccant, and other consumables have no warranty.
CNR1 Table of Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. General Description.....................................................1 2. Sensor Specifications .................................................1 2.1 CNR1 Specifications ................................................................................1 2.2 CM3 Specifications .....................................................
CNR1 Table of Contents A. CNR1 Performance and Measurements under Different Conditions ........................................... A-1 B. Using the Heater...................................................... B-1 B.1 General Information ............................................................................ B-1 C. CR3000/CR5000 Program that Controls the Heater............................................................C-1 Figures 2-1. 3-1. 5-1. 5-2. 6-1. The Dimensions of the CNR1...................
CNR1 Net Radiometer 1. General Description The CNR1 Net Radiometer is intended for the analysis of the radiation balance of Solar and Far Infrared radiation. The most common application is the measurement of Net (total) Radiation at the earth's surface. The CNR1 design is such that both the upward-facing and the downwardfacing instruments measure the energy that is received from the whole hemisphere (180 degrees field of view). The output is expressed in Watts per square meter.
CNR1 Net Radiometer Cable length: Weight: Mounting arm attached to CNR1: 15 m (each cable) 4 kg 14.5” (37 cm) long 5/8” (1.6 cm) diameter FIGURE 2-1. The Dimensions of the CNR1 2.2 CM3 Specifications Specifications that are part of the ISO classification: 2 Response time 95%: 18 s Non-stability: < 1% change per year Non-linearity: Max. dev. 2.5% (0-1000 W m-2) Directional error: Max. 25 W m-2 at 1000 W m-2 Spectral selectivity: Max. dev.
CNR1 Net Radiometer Tilt response: Max. dev. 2% Overall ISO classification: second class Sensitivity: 10 - 35 µV/(W m-2) Impedance: 125 Ohm nominal Operating temperature: -40°C to +80°C Spectral range: 305-2800 nm (50% points) Expected signal range for atmospheric application: 0 - 15 mV typical Expected accuracy for daily sums: ± 10% Window heating offset: Max. 25 W m-2 at 1000 W m-2 normal incidence solar radiation 2.
CNR1 Net Radiometer Northern Hemisphere this implies that the Net Radiometer should be mounted south of the mast. It is suggested that the CNR1 is mounted at a height of at least 1.5 meters above the surface to avoid shading effects of the instruments on the soil and to promote spatial averaging of the measurement. If the instrument is H meters above the surface, 99% of the input of the lower sensors comes from a circular area with a radius of 10 H. Shadows or surface disturbances with radius < 0.
CNR1 Net Radiometer 3.1 Connecting and Using the Heater Only use the sensor’s heater when there is risk of dew forming on the sensors, especially for low power installations. Furthermore, the heater should be turned on and off infrequently because it may take some time for the sensor to come to thermal equilibrium.
CNR1 Net Radiometer 4.2 Measuring Far Infrared Radiation with the CG3 The downward-facing CG3 measures the Far Infrared radiation that is emitted by the ground. The upward-facing CG3 measures the Far Infrared radiation from the sky. As the sky is typically colder than the instrument, one can expect negative voltage signals from the upward-facing CG3. For this measurement, the Pt-100 output is required. The Equation 4.2 is used to calculate the Far Infrared irradiance of the sky and of the ground.
CNR1 Net Radiometer 4.4 Calculation of the Albedo for Solar Radiation The albedo is the ratio of incoming and reflected Solar radiation. It is a figure somewhere between 0 and 1. Typical values are 0.9 for snow, and 0.3 for grassland. To determine albedo, the measured values of the two CM3s can be used. The CG3s are not involved, as they do not measure Solar radiation. Do not use measured values when solar elevation is lower than 10 degrees above the horizon.
CNR1 Net Radiometer As a rule of thumb, for ambient temperatures of about 20 degrees Celsius, one can say that one degree of temperature difference between two objects results in a 5 Watts per square meter exchange of radiative energy (infinite objects): 1 degree of temperature difference = 5 Watts per square meter (rule of thumb) 4.
CNR1 Net Radiometer FIGURE 5-1. CNR1 Schematic DATALOGGER EX1 4WPB100 10K 5H H 100 CNR1 5L L Red G 6H Yellow PT-100 6L Green Blue FIGURE 5-2.
CNR1 Net Radiometer The four radiation outputs can be measured using Differential or Single-Ended inputs on the datalogger. A differential voltage measurement (Instruction 2) is recommended because it has better noise rejection than a single-ended measurement. When differential inputs are used, jumper the low side of the to keep the signal in common mode range. input to AG or TABLE 5-1.
CNR1 Net Radiometer TABLE 5-3.
CNR1 Net Radiometer FIGURE 6-1. 4WPB100 Module 6.1 Calibration Factor Each CNR1 is provided with a ‘Certificate of Calibration’ by the manufacturer that shows the sensor serial number and ‘sensitivity’, or calibration factor. The serial number and sensitivity are also shown on a label attached to the sensor. The calibration factor is in units of μV/(W m-2), which needs to be converted to units of (W m-2)/mV for the multiplier parameter in the datalogger program.
CNR1 Net Radiometer 'CR1000 'Declare Variables and Units Public Batt_Volt Public CM3Up Public CM3Dn Public CG3Up Public CG3Dn Public CNR1TC Public CNR1TK Public NetRs Public NetRl Public Albedo Public UpTot Public DnTot Public NetTot Public CG3UpCo Public CG3DnCo Units Batt_Volt=Volts Units CM3Up=W/meter² Units CM3Dn=W/meter² Units CG3Up=W/meter² Units CG3Dn=W/meter² Units CNR1TC=Deg C Units CNR1TK=K Units NetRs=W/meter² Units NetRl=W/meter² Units Albedo=W/meter² Units UpTot=W/meter² Units DnTot=W/meter² U
CNR1 Net Radiometer 'Main Program BeginProg Scan(2,Sec,1,0) 'Default Datalogger Battery Voltage measurement Batt_Volt: Battery(Batt_Volt) 'CNR1 Net Radiometer measurements CM3Up, CM3Dn, CG3Up, CG3Dn, CNR1TC, CNR1TK, 'NetRs, NetRl, Albedo, UpTot, DnTot, NetTot, CG3UpCo, and CG3DnCo: * VoltDiff(CM3Up,1,mV25,1,True,0,_60Hz,100.0,0) * VoltDiff(CM3Dn,1,mV25,2,True,0,_60Hz,100.0,0) * VoltDiff(CG3Up,1,mV7_5,3,True,0,_60Hz,100.0,0) * VoltDiff(CG3Dn,1,mV7_5,4,True,0,_60Hz,100.
CNR1 Net Radiometer 'CR5000 Series Datalogger 'ANALOG INPUT '1H CM3 UP - downwelling shortwave radiation signal (red) '1L CM3 UP - downwelling shortwave radiation signal reference (blue) 'gnd CNR1 shield (clear) '2H '2L CM3 DOWN - upwelling shortwave radiation signal (white) CM3 DOWN - upwelling shortwave radiation signal reference (black) '3H '3L CG3 UP - downwelling longwave radiation signal (gray) CG3 UP - downwelling longwave radiation signal reference (yellow) '4H '4L CG3 DOWN - upwelling longwav
CNR1 Net Radiometer 'Define Data Tables DataTable(Table1,True,-1) DataInterval(0,60,Min,10) Average(1,CM3Up,FP2,False) Average(1,CM3Dn,FP2,False) Average(1,CG3Up,FP2,False) Average(1,CG3Dn,FP2,False) Average(1,CNR1TC,FP2,False) Average(1,CNR1TK,FP2,False) Average(1,NetRs,FP2,False) Average(1,NetRl,FP2,False) Average(1,Albedo,FP2,False) Average(1,UpTot,FP2,False) Average(1,DnTot,FP2,False) Average(1,NetTot,FP2,False) Average(1,CG3UpCo,FP2,False) Average(1,CG3DnCo,FP2,False) EndTable 'Main Program BeginProg
CNR1 Net Radiometer 6.2.3 Example 3, CR23X Program Using Differential Channels Program Example 3 requires six differential channels and the 4WPB100 module to measure the four radiation outputs and the Pt-100 temperature sensor.
CNR1 Net Radiometer ;{CR23X} ;Program Example 1 for CR23X datalogger ; ;CNR1 sensitivity for program example = 7.30 uV/W/m^2 ;Multiplier for measurement instructions = 1000/7.30 = 136.99 ; ;*Table 1 Program 01: 2 Execution Interval (seconds) ;Measure CM3 Up and CM3 Down (shortwave radiation) ;Note: Multiplier (Parameter 5) will be different for each CNR1 1: Volt (Diff) (P2) 1: 2 2: 22+ 3: 1* 4: 1* 5: 136.
CNR1 Net Radiometer ;Net CM3 shortwave radiation = CM3 Up - CM3 Down 6: Z=X-Y (P35) 1: 1 2: 2 3: 7 X Loc [ CM3_up ] Y Loc [ CM3_dn ] Z Loc [ Net_Rs ] ;Net CG3 longwave radiation = CG3 Up - CG3 Down 7: Z=X-Y (P35) 1: 3 2: 4 3: 8 X Loc [ CG3_up ] Y Loc [ CG3_dn ] Z Loc [ Net_Rl ] ;Albedo = CM3 Down / CM3 Up 8: Z=X/Y (P38) 1: 2 2: 1 3: 9 X Loc [ CM3_dn ] Y Loc [ CM3_up ] Z Loc [ Albedo ] ;Net total radiation = (CM3 Up + CG3 Up) - (CM3 Down + CG3 Down) 9: Z=X+Y (P33) 1: 1 2: 3 3: 23 X Loc [ CM3_up ] Y L
CNR1 Net Radiometer 15: Z=X*Y (P36) 1: 25 X Loc [ scratch_1 ] 2: 27 Y Loc [ scratch_3 ] 3: 28 Z Loc [ scratch_4 ] 16: Z=X+Y (P33) 1: 3 X Loc [ CG3_up ] 2: 28 Y Loc [ scratch_4 ] 3: 11 Z Loc [ CG3_upCor ] 17: Z=X+Y (P33) 1: 4 X Loc [ CG3_dn ] 2: 28 Y Loc [ scratch_4 ] 3: 12 Z Loc [ CG3_dnCor ] ; ;Output data to final storage every 60 minutes 18: 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) 19: Real Time (P77) 1: 0220 Day,Hour/Minu
CNR1 Net Radiometer Wiring for Program Example 4 Color Function Red Blue White Black Grey or Orange Yellow Brown Green Shield CM3 Up Signal CM3 Up Reference CM3 Down Signal CM3 Down Reference CG3 Up Signal CG3 Up Reference CG3 Down Signal CG3 Down Reference Shield Example CR23X Program Channels Used SE1 SE2 SE3 SE4 Pt-100 Temperature Sensor Connections to 4WPB100 and Datalogger Color Function Red Blue Yellow Green Pt-100 Excitation + Pt-100 Excitation Pt-100 Signal + Pt-100 Signal - 4WPB100 H L G
CNR1 Net Radiometer ;Measure CNR1 temperature 3: Full Bridge w/mv Excit (P9) 1: 1 Reps 2: 22 50 mV, 60 Hz Reject, Slow, Ex Range 3: 22 50 mV, 60 Hz Reject, Slow, Br Range 4: 5 DIFF Channel 5: 1 Excite all reps w/Exchan 1 6: 4200 mV Excitation 7: 5 Loc [ Temp_C ] 8: 1 Mult 9: 0 Offset 4: Temperature RTD (P16) 1: 1 Reps 2: 5 R/R0 Loc [ Temp_C 3: 5 Loc [ Temp_C ] 4: 1.0 Mult 5: 0 Offset 5: Z=X+F (P34) 1: 5 2: 273.
CNR1 Net Radiometer 8. Troubleshooting If there is no clue as to what may be the problem, start performing the following "upside-down test", which is a rough test for a first diagnosis. It can be performed both outdoors and indoors. Indoors, a lamp can be used as a source for both Solar and Far Infrared radiation.
CNR1 Net Radiometer 8.2 Testing of the CG3 It is assumed that the amplifier circuit is the same as the one used for the CM3, and that its zero offset is no more than a few watts per square meter, let us say 5 Watts per square meter just as an example (see second test in 7.1). The pyrgeometer, the mounting plate, and ambient air should be at the same temperature as much as possible. Let the CG3 rest for at least five minutes to regain its thermal equilibrium. Set the voltmeter to its most sensitive range.
Appendix A. CNR1 Performance and Measurements under Different Conditions Below, Table A-1, shows an indication of what one might typically expect to measure under different meteorological conditions. The first parameter is day and night. At night, the Solar radiation is zero. The second column indicates if it is cloudy or clear. A cloud acts like a blanket, absorbing part of the Solar radiation, and keeping Net Far Infrared radiation close to zero. The third parameter is ambient temperature.
Appendix A. CNR1 Performance and Measurements under Different Conditions TABLE A-1. Typical output signals of CNR1 under different meteorological conditions. Explanation can be found in the text.
Appendix B. Details about Using the Heater NOTE Whenever the heater is used, the heating may cause errors in the measurement of the sensor temperature, see chapter 1.1.2.3. in the Kipp and Zonen CNR1 manual (http://www.kippzonen.com/?download/85182/CNR+1+Net+Ra diometer+-+Manual+(English).aspx), two degrees typical, and zero offsets in the CM3 (10 Watts per square meter typical). Under most conditions the accuracy that is gained by heating will be larger than the errors that are introduced by heating.
Appendix B. Details about Using the Heater For decisions about heating one can make the following diagram: Not available 12 VDC, 6 VA available? DO NOT HEAT Available Consider options below Not Available DO NOT HEAT (CSI recommendation) Clock and relay available? Available Heat from 1 hour before the sunset until 1 hour after the sunset The maximum allowable power for the heater is 50 VA. In case of snow or frost one might also consider heating at a higher level than the usual 6 VA.
Appendix C. CR3000/CR5000 Program that Controls the Heater This program applies power to the CNR1 heater using the SW12V relay controller and the pulse width modulation instruction (PWM ()). The program below uses the dew point value. The datalogger calculates dew point using the relative humidity (RH) measurements provided by the HMP45C Temperature/Relative Humidity probe. Enter 0 degrees C as the set point for the heater when a temperature/RH probe is not used.
Appendix C.
Appendix C. CR3000/CR5000 Program that Controls the Heater Alias nr01(3) = Rs_downwell Alias nr01(4) = Rs_upwell Alias nr01(5) = Rl_downwell Alias nr01(6) = Rl_upwell Alias nr01(7) = t_nr01 Alias nr01(8) = Rl_down_meas Alias nr01(9) = Rl_up_meas Units panel_temp = C Units batt_volt = V Units t_hmp = C Units rh_hmp = percent Units e_hmp = kPa Units nr01 = W/m^2 Units albedo = unitless Units t_nr01 = K 'Net radiometer heater control variables.
Appendix C. CR3000/CR5000 Program that Controls the Heater BeginProg Scan (1,Sec,0,0) 'Control the net radiometer heater. PWM (duty_cycle,4,250,mSec) 'Datalogger panel temperature. PanelTemp (panel_temp,250) 'Measure battery voltage. Battery (batt_volt) 'Measure the HMP45C temperature and relative humidity. VoltDiff (t_hmp,1,mV1000C,5,TRUE,200,250,0.1,-40) VoltDiff (rh_hmp,1,mV1000C,6,TRUE,200,250,0.1,0) 'Measure NR 01 Net Radiometer.
Appendix C. CR3000/CR5000 Program that Controls the Heater Case Else duty_cycle = 0.01 EndSelect Else duty_cycle = 0.
Appendix C.
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