CNR4 Net Radiometer Revision: 11/10 C o p y r i g h t © 2 0 0 0 - 2 0 1 0 C a m p b e l l S c i e n t i f i c , I n c .
Warranty and Assistance The CNR4 NET RADIOMETER is warranted by Campbell Scientific, Inc. to be free from defects in materials and workmanship under normal use and service for twelve (12) months from date of shipment unless specified otherwise. Batteries have no warranty. Campbell Scientific, Inc.'s obligation under this warranty is limited to repairing or replacing (at Campbell Scientific, Inc.'s option) defective products.
CNR4 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 .................................................2 2.1 2.2 2.3 2.4 CNR4 Specifications ................................................................................3 Pyranometer Specifications ....................................
CNR4 Table of Contents 9. Maintenance and Recalibration ................................29 9.1 9.2 9.3 9.4 Cleaning Windows and Domes.............................................................. 29 Recalibration .......................................................................................... 30 Replacing the Drying Cartridge ............................................................. 30 Replacement Parts..................................................................................
CNR4 Table of Contents Tables 5-1. Resistance values versus CNR4's thermistor temperature in °C ...........11 5-2. Resistance values versus CNR4's Pt-100 temperature in °C .................12 6-1. Datalogger Connections for Differential Measurement ........................16 6-2. Datalogger Connections for Single-ended Measurement......................16 A-1. Typical output signals of CNR4 under different meteorological conditions. Explanation can be found in the text ........................... A-1 B-1.
CNR4 Table of Contents iv
CNR4 Net Radiometer 1. General Description The CNR4 is a four component net radiometer that measures the energy balance between incoming and outgoing radiation. The CNR4 net radiometer consists of a pyranometer pair, one facing upward, the other facing downward, and a pyrgeometer pair in a similar configuration. The pyranometer pair measures short-wave solar radiation, and the pyrgeometer pair measures long-wave far infrared radiation. The upper longwave detector of CNR4 has a meniscus dome.
CNR4 Net Radiometer 2. Sensor Specifications The CNR4 consists of two pyranometers, for measuring short-wave radiation, and of two pyrgeometers for measuring long-wave radiation. Two temperature sensors are available as standard, a thermistor and a Pt-100. The optional heater/ventilator unit CNF4-L is available. See Appendix B for more information on the CNF4-L. The properties of the CNR4 are mainly determined by the properties of the individual probes.
CNR4 Net Radiometer 2.1 CNR4 Specifications Sensor sensitivities: Four probes have unique sensitivity values. Please refer to the calibration sheets or label on the bottom of the sensor for the sensitivity values. Operating temperature: -40 to +80°C (-40 to 176°F) Operating humidity: 0 to 100 % RH Bubble level sensitivity: < 0.
CNR4 Net Radiometer 2.2 Pyranometer Specifications * indicates ISO specifications.
CNR4 Net Radiometer 2.3 Pyrgeometer Specifications Spectral range: 4.
CNR4 Net Radiometer 2.4.1 CNF4 Specifications Heater Power consumption: 10 W @ 12 Vdc (15 Ω) Ventilator Power consumption: 5 W @ 12 Vdc Supply voltage: 8 to 13.5 Vdc Weight: 1.11 lbs (0.5 kg) Operating temperature: -40 to +80°C 3. Installation For measurement of net radiation, it is most important that the instrument is located in a place that is representative of the entire area that one wishes to study.
CNR4 Net Radiometer NOTE Do not attempt to rotate the instrument using the sensor heads, or you may damage the sensors; use the mounting rod only. 4. Perform the fine levelling using the two spring-loaded levelling screws: one on the front and the other on the back of the bracket. FIGURE 3-1. Attaching the mounting rod to the CNR4 body.
CNR4 Net Radiometer FIGURE 3-2. Attaching the CNR4 onto the mounting rod (CSI p/n 26120) using vertical pole or horizontal crossarm. For installation in buildings or in solar energy applications, one will often have to mount the CNR4 parallel to the surface that is being studied. This may be in a tilted or a vertical position. The sensitivity of the radiometers will be affected, but only in a minor way. This is specified as the so-called tilt effect.
CNR4 Net Radiometer 5. Using the CNR4 in the Four Separate Components Mode In the four separate components mode configuration (measuring two shortwave radiation signals, two long-wave signals), all signals are measured separately. Calculation of net-radiation and albedo can be done on-line by the datalogger, or off-line by the user during post-processing, using the stored raw data. The two pyranometers will measure the short-wave radiation, both incoming and reflected.
CNR4 Net Radiometer colder. This means that for estimating the far infrared radiation that is generated by the object that is faced by the pyrgeometer, usually the sky or the soil, you will have to take the pyrgeometer temperature, T, into account. This is why the temperature sensors are incorporated in the CNR4's body near the pyrgeometer sensing element, and has, therefore, the same temperature as the pyrgeometer sensor surface.
CNR4 Net Radiometer The thermistor measurement can be done by the datalogger, using the half bridge measurement method which requires one voltage excitation and one single-ended analog channel. Alternatively, you can use the Pt-100 to make the temperature measurement. In order to make the temperature measurement, using the Pt-100 sensor, you will need one current excitation channel, and one differential analog channel. Please refer to Appendix C for a sample program to measure Pt-100. TABLE 5-1.
CNR4 Net Radiometer TABLE 5-2. Resistance values versus CNR4's Pt-100 temperature in °C. Temperature [°C] -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 Resistance [Ω] 88.22 88.62 89.01 89.40 89.80 90.19 90.59 90.98 91.37 91.77 92.16 92.55 92.95 93.34 93.73 94.12 94.52 94.91 95.30 95.69 96.09 96.48 96.87 97.26 97.65 98.04 98.44 98.83 99.22 99.
CNR4 Net Radiometer In the equation above, E is calculated according to the Equation 5-1. Albedo will always be smaller than 1. Checking this can be used as a tool for quality assurance of your data. If you know the approximate albedo at your site, the calculation of albedo can also serve as a tool for quality control of your measured data at a specific site. 5.
CNR4 Net Radiometer 5.7 Calculation of Net (Total) Radiation In the four separate components mode, net radiation, Rn, can be calculated using the individual sensor measurement results: Rn = {(E upper Pyranometer) - (E lower Pyranometer)} + {(E upper Pyrgeometer) - (E lower Pyrgeometer)} (5-8) Where E upper/lower pyranometers are calculated according to Equation 5-1, and E upper/lower pyrgeometers are calculated according to Equation 5-2. The terms with T cancel each other out. 6.
CNR4 Net Radiometer FIGURE 6-2. The marks on the end of the CNR4: S for SOLAR cable, and T for TEMP cable. The measurement details for Pt-100 sensor, including the wiring diagram and sample program are explained in the Appendix C of this manual. The four radiation outputs can be measured using differential or single-ended inputs on the datalogger. A differential voltage measurement is recommended because it has better noise rejection than a single-ended measurement.
CNR4 Net Radiometer FIGURE 6-4. Labels on the pigtail end of the TEMP cable. TABLE 6-1.
CNR4 Net Radiometer 7. Datalogger Programming The CNR4 outputs four voltages that typically range from 0 to 15 mV for the pyranometers, and ± 5 mV for the pyrgeometers. A differential voltage measurement is recommended because it has better noise rejection than a single-ended measurement. If differential channels are not available, singleended measurements can be used.
CNR4 Net Radiometer Average Corrected long-wave radiation (pyrgeometer up) Average Corrected long-wave radiation (pyrgeometer down) Average Short-wave net radiation Average Long-wave net radiation Average Albedo Average Net radiation 'CR1000 Series Datalogger ' 'CNR4 program 'This program measures CNR4 four-component net radiometer 'This program also measures the thermistor inside the CNR4 ' 'User must enter the sensitivity values for all four probes in the program and save/compile 'prior to downloading it
CNR4 Net Radiometer Public cnr4_T_C Public cnr4_T_K Public long_up_corr Public long_dn_corr Public Rs_net Public Rl_net Public albedo Public Rn 'CNR4 thermistor temperature in Celcius 'CNR4 thermistor temperature in Kelvin 'Downwelling long-wave radiation with temperature correction 'Upwelling long-wave radiation with temperature correction 'short-wave net radiation 'long-wave net radiation 'Albedo 'total net radiation Units logger_temp = degC Units batt_volt = volts Units short_up = W/m^2 Units short_dn
CNR4 Net Radiometer Average (1,Rl_net,IEEE4,False) Average (1,albedo,IEEE4,False) Average (1,Rn,IEEE4,False) EndTable DataTable (cnr4_ts,True,-1) DataInterval (0,1,Sec,10) CardOut (1,-1) Sample (4,cnr4(1),IEEE4) Sample (1,cnr4_T_K,IEEE4) EndTable BeginProg 'Load the multiplier values for the CNR4 cnr4_mult(1) = pyranometer_up_mult cnr4_mult(2) = pyranometer_dn_mult cnr4_mult(3) = pyrgeometer_up_mult cnr4_mult(4) = pyrgeometer_dn_mult Scan (1,Sec,3,0) PanelTemp (logger_temp,250) Battery (batt_volt) 'CNR4 ra
CNR4 Net Radiometer 7.2.2 Example 2, CR3000 Program Using Differential Measurements The Program Example 2 requires four differential channels to measure the four radiation outputs and one excitation channel and one single-ended channel to measure the thermistor. The program measures the sensors every 1 second, performs the on-line processing of the data and stores the following processed data to a data table called cnr4_data once every 60 minutes.
CNR4 Net Radiometer '8H '8L CNR4 thermistor signal (white) 'gnd CNR4 thermistor signal reference (black) ' CNR4 thermistor shield (clear) ' 'VOLTAGE EXCITATION ' 'VX1 CNR4 thermistor voltage excitation (red) ' 'CNR4 sensor Public logger_temp, batt_volt Public cnr4(4) Alias cnr4(1) = short_up Alias cnr4(2) = short_dn Alias cnr4(3) = long_up Alias cnr4(4) = long_dn Public cnr4_T_C Public cnr4_T_K Public long_up_corr Public long_dn_corr Public Rs_net Public Rl_net Public albedo Public Rn 'CNR4 thermistor tem
CNR4 Net Radiometer 'CNR4 multipliers Public cnr4_mult(4) Const pyranometer_up_mult = 1000/pyranometer_up_sensitivity Const pyranometer_dn_mult = 1000/pyranometer_dn_sensitivity Const pyrgeometer_up_mult = 1000/pyrgeometer_up_sensitivity Const pyrgeometer_dn_mult = 1000/pyrgeometer_dn_sensitivity '(W/m^2/mV) '(W/m^2/mV) '(W/m^2/mV) '(W/m^2/mV) DataTable (cnr4_data,True,-1) DataInterval (0,60,Min,10) CardOut (1,-1) Minimum (1,batt_volt,FP2,0,False) Sample (1,logger_temp,FP2) Average (4,cnr4(1),IEEE4,False
CNR4 Net Radiometer 'Compute short-wave net radiation Rs_net = short_up - short_dn 'Compute long-wave net radiation Rl_net = long_up - long_dn 'Compute albedo albedo = short_dn/short_up 'Compute net radiation Rn = Rs_net + Rl_net CallTable cnr4_data CallTable cnr4_ts NextScan EndProg 7.2.
CNR4 Net Radiometer 'CR5000 Series Datalogger ' 'CNR4 program 'This program measures CNR4 four-component net radiometer 'This program also measures the thermistor inside the CNR4 ' 'User must enter the sensitivity values for all four probes in the program and save/compile 'prior to downloading it to the datalogger. 'Search for the text string "unique" to find places to enter the sensitivity values.
CNR4 Net Radiometer Public Rl_net Public albedo Public Rn 'long-wave net radiation 'Albedo 'total net radiation Units logger_temp = degC Units batt_volt = volts Units short_up = W/m^2 Units short_dn = W/m^2 Units long_up = W/m^2 Units long_dn = W/m^2 Units cnr4_T_C = deg_C Units cnr4_T_K = K Units long_up_corr = W/m^2 Units long_dn_corr = W/m^2 Units Rs_net = W/m^2 Units Rl_net = W/m^2 Units albedo = W/m^2 Units Rn = W/m^2 Dim Rs, Vs_Vx 'CNR4 sensitivities: refer to the Certificate of Calibration from Ki
CNR4 Net Radiometer DataTable (cnr4_ts,True,-1) DataInterval (0,1,Sec,10) CardOut (1,-1) Sample (4,cnr4(1),IEEE4) Sample (1,cnr4_T_K,IEEE4) EndTable BeginProg 'Load the multiplier values for the CNR4 cnr4_mult(1) = pyra_up_mult cnr4_mult(2) = pyra_dn_mult cnr4_mult(3) = pyrg_up_mult cnr4_mult(4) = pyrg_dn_mult Scan (1,Sec,3,0) PanelTemp (logger_temp,250) Battery (batt_volt) 'CNR4 radiation measurements VoltDiff (cnr4(1),4,mV20C,1,True ,0,_60Hz,cnr4_mult(1),0) 'CNR4 thermistor measurement BrHalf (Vs_Vx,1,mv
CNR4 Net Radiometer 8. Troubleshooting If there is no indication 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 short-wave and long-wave radiation.
CNR4 Net Radiometer 8.2 Testing the Pyrgeometer It is assumed that the zero offset is no more than a few watts per square meter (see second test in section 8.1). The CNR4 body and the ambient air should be at the same temperature as much as possible. Let the pyrgeometer rest for at least five minutes to regain its thermal equilibrium. Set the voltmeter to its most sensitive range. To test if the pyrgeometer is working properly, put your hand in front of the pyrgeometer.
CNR4 Net Radiometer 9.2 Recalibration For quality assurance of the measured data, the manufacturer recommends the CNR4 be recalibrated on a regular schedule by an authorized Kipp & Zonen calibration facility. The CNR4 should be recalibrated every two years. Alternatively, one can check the sensor calibration by letting a higher standard run parallel to it over a two-day period and, then, comparing the results. For comparison of pyranometers, one should use a clear day.
CNR4 Net Radiometer 9.4 Replacement Parts The following is the list of replacement parts for the CNR4 and CNF4 (heater/ventilator) available from Campbell Scientific. CSI Part Number Description CNR4CBL1-L Replacement CNR4 Solar Cable CNR4CBL2-L Replacement CNR4 Temperature Cable CNF4CBL-L Replacement CNF4 Cable 26006 Replacement Drying Cartridges 26010 Replacement Fan Filter (Set of 5). See Appendix B for fan filter replacement instruction.
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Appendix A. CNR4 Performance and Measurements under Different Conditions Below, Table A-1 shows 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 shows 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. CNR4 Performance and Measurements under Different Conditions FIGURE A-1. Different measurement conditions and signals.
Appendix A. CNR4 Performance and Measurements under Different Conditions upwelling signal (downward facing) pyrgeometer 30 Pyrgeometer: U‐emf / sensitivity [W/m²] Temp of instrument [°C] 20 10 0 ‐10 ‐20 ‐30 0:00:00 23:00:00 22:00:00 21:00:00 20:00:00 19:00:00 18:00:00 17:00:00 16:00:00 15:00:00 14:00:00 13:00:00 12:00:00 11:00:00 10:00:00 9:00:00 8:00:00 7:00:00 6:00:00 5:00:00 4:00:00 3:00:00 2:00:00 1:00:00 0:00:00 FIGURE A-3.
Appendix A. CNR4 Performance and Measurements under Different Conditions ⎡ E upper CG3 ⎤ Sky temperature = ⎢ ⎥ ⎣ 5.67 ⋅ 10 −8 ⎦ 1/ 4 ⎡ E lower CG3 ⎤ Ground Temperatur e = ⎢ ⎥ ⎣ 5.
Appendix B. CNF4 Heater/Ventilator NOTE Whenever the heater is used, the heating may cause errors in the measurement of the sensor temperature. Under most conditions the accuracy that is gained by heating will be larger than the errors that are introduced by heating. In both the pyranometer and the pyrgeometer, thermal sensors are used, and these sensors in principle measure a heat flow. For optimal performance, these sensors should be at thermal equilibrium with the ambient air.
Appendix B. CNF4 Heater/Ventilator Not available 10 Watt power 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 sunrise. The heater power can be controlled using one of the SW12V channels of the Campbell Scientific dataloggers. The heater’s current drain is approximately 850 mA at 12 Vdc (10 Watts).
Appendix B. CNF4 Heater/Ventilator B.2 Attaching the Optional CNF4 Heater/Ventilator Unit to CNR4 1. The CNF4 heater/ventilator unit comes with the following: the heater/ventilator, the white solar shield, three pan-head screws with washers, and four flat-head screws as shown in Figure B-1. FIGURE B-1.
Appendix B. CNF4 Heater/Ventilator 2. Attach the heater/ventilator unit unto the bottom of the CNR4 sensor, using the three pan-head screws and washers, as shown in Figure B-2. Make sure that the pyranometer and the pyrgeometer windows are not scratched during the installation. FIGURE B-2. Attaching the CNF4 to CNR4 using pan-head screws and washers.
Appendix B. CNF4 Heater/Ventilator 3. Make sure the cables are cleared from the edges of the CNF4, as shown in Figure B-3, and place the white solar shield over it. Use the four flat-head screws provided to complete the solar shield installation to the CNF4, as shown in Figure B-4 and B-5. FIGURE B-3. Making sure the cables are clear from the edges. FIGURE B-4. CNF4 solar shield and four flat-head screws.
Appendix B. CNF4 Heater/Ventilator FIGURE B-5. Attaching the solar shield to CNF4 using four flat-head screws. 4. Once the CNF4 heater/ventilator unit is attached to the bottom side of the CNR4, the CNF4 will cover the label that contains the serial number and the sensitivity values for the four sensors. Affix the extra label that came with the sensor to the bottom side of the CNF4’s anodized aluminium base so that the label is in a visible location. See Figure B-6 below. FIGURE B-6.
Appendix B. CNF4 Heater/Ventilator B.3 Wiring The following table shows the recommended datalogger wiring for using the CNR4 sensor with the CNF4 heater/ventilator while making the differential measurement. TABLE B-1.
Appendix B. CNF4 Heater/Ventilator B.4 Example B, CR3000 Datalogger Program with Heater/Ventilator Control The Program Example B measures the four radiation outputs, thermistor temperature, and controls the ventilator and heater, using SW12V-1 and SW12V-2 channels on the CR3000, respectively. In this example program, the ventilator and heater can be turned on or off by manually setting the flag(1) and flag(2) high or low, respectively.
Appendix B.
Appendix B. CNF4 Heater/Ventilator Dim Rs, Vs_Vx 'CNR4 sensitivities: refer to the Certificate of Calibration from Kipp & Zonen for sensitivity values 'for each probes, and enter them below. Const pyranometer_up_sensitivity = 15.35 'unique sensitivity for upper pyranometer '(microV/W/m^2) Const pyranometer_dn_sensitivity = 15.41 'unique sensitivity for lower pyranometer '(microV/W/m^2) Const pyrgeometer_up_sensitivity = 8.
Appendix B. CNF4 Heater/Ventilator 'CNR4 thermistor measurement BrHalf (Vs_Vx,1,mv5000,16,Vx1,1,2500,True ,0,250,1.0,0) Rs = 1000*(Vs_Vx/(1-Vs_Vx)) cnr4_T_C = 1/(1.0295e-3+2.391e-4*LN(Rs)+1.568e-7*(LN(Rs))^3)-273.15 'Convert CNR4 temperature to Kelvin cnr4_T_K = cnr4_T_C+273.15 'Correct the long-wave radiation values from pyrgeometers long_up_corr = long_up+5.67e-8*cnr4_T_K^4 long_dn_corr = long_dn+5.
Appendix B. CNF4 Heater/Ventilator pulling it straight out. Inspect the fan inside for any object that might impede the fan’s rotation. Upon completing the inspection, put the filter and the cover back in place. B.5.3 Replacing the Filter for the Ventilator The filter needs to be checked for every 6 to 12 months. Remove the black cover at the bottom side of the ventilator by prying it open with a small flathead screw driver or by pulling it straight out.
Appendix C. CR3000 Program for Measuring Pt-100 Temperature Sensor The program example C measures the Pt-100 sensor for the body temperature of the CNR4. This program requires four differential channels to measure the four radiation outputs, and one current excitation channel and one differential channel for Pt-100 measurement.
Appendix C. CR3000 Program for Measuring Pt-100 Temperature Sensor 'CR3000 Series Datalogger ' 'CNR4 program 'This program measures CNR4 four-component net radiometer 'This program also measures the Pt-100 sensor inside the CNR4 ' 'User must enter the sensitivity values for all four probes in the program and save/compile 'prior to downloading it to the datalogger. 'Search for the text string "unique" to find places to enter the sensitivity values.
Appendix C.
Appendix C.
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