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Campbell CM 21 Instruction Manual

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INSTRUCTION MANUAL
CM 21
PYRANOMETER

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  • Page 1 INSTRUCTION MANUAL CM 21 PYRANOMETER...
  • Page 2 WARRANTY AND ASSISTANCE This equipment is warranted by CAMPBELL SCIENTIFIC (CANADA) CORP. (“CSC”) 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 are not warranted.

  • Page 3: Important User Information

    IMPORTANT USER INFORMATION Reading this entire manual is recommended for full understanding of the use of this product. The exclamation mark within an equilateral triangle is intended to alert the user to the presence of important operating and maintenance instructions in the literature accompanying the instrument.

  • Page 4: Declaration Of Conformity

    According to EC guideline 89/336/EEC 73/23/EEC Kipp & Zonen B.V. Röntgenweg 1 2624 BD Delft Declare under our sole responsibility that the product Type: CM 21 Name: Pyranometer To which this declaration relates is in conformity with the following standards Imissions EN 50082-1...

  • Page 5: Table Of Contents

    INTRODUCTION PHYSICAL PRINCIPLES OF THE PYRANOMETER 1.2.1 Zero offsets 1.2.3 Directional error 1.2.4 Low temperature dependency of sensitivity 2 TECHNICAL DATA SPECIFICATIONS OF CM 21 PYRANOMETER ACCORDING TO ISO 9060 LISTING ACCURACY 3 INSTALLATION DELIVERY MECHANICAL INSTALLATION 3.2.1 Installation for measurement of global radiation 3.2.2 Installation for measurement of solar radiation on inclined surfaces 23...
  • Page 6 6 CALIBRATION INITIAL CALIBRATION RECALIBRATION CALIBRATION PROCEDURE AT KIPP & ZONEN 6.3.1 The facility 6.3.2 Procedure 6.3.3 Calculation 6.3.4 Zero offset 6.3.5 Traceability to World Radiometric Reference 7 FREQUENTLY ASKED QUESTIONS (FAQ’s) 8 TROUBLE SHOOTING 9 PART NUMBERS / SPARE PARTS / OPTIONS APPENDIX I CLASSIFICATION ACCORDING TO WMO GUIDE 1996 47 APPENDIX II...

  • Page 7: General Information

    • Low non-linearity. Like the CM 11 pyranometer, the CM 21 complies with the specifications for the best of three classes, “High quality”, as defined in the 'Guide to meteorological Instruments and Methods of Observation', sixth edition, 1996,...

  • Page 8: Physical Principles Of The Pyranometer

    Herein “high quality“ class is referred to as “secondary standard”. PHYSICAL PRINCIPLES OF THE PYRANOMETER The pyranometer CM 21 is provided with a thermal detector. This type of detector responds to the total power absorbed and theoretically it is non- selective as to the spectral distribution of the radiation.

  • Page 9: Zero Offsets

    1. GENERAL INFORMATION Figure 1 Construction details of a CM 21 pyranometer 1.2.1 Zero offsets Zero offset type B Heat flows in the sensing element e.g. due to rising or falling body temperature normally cause a spurious voltage., called zero offset. To compensate for this offset, a second non-illuminated element is installed, in which the same heat flow will arise.

  • Page 10: Directional Error

    The directional error is a combination of the error in zenith and azimuth directions. This Kipp & Zonen CM 21 pyranometer is manufactured with great care. Each pyranometer is constructed with selected glass domes. The glass...

  • Page 11: Low Temperature Dependency Of Sensitivity

    Before leaving the factory, the cosine response of each CM 21 is measured. At four zenith angles the cosine response versus two azimuth’s is determined. These values (40º and 70º) are stated on the calibration certificate, expressed as percentage deviation from the ideal proportionality and as absolute values (see appendix IV).

  • Page 13: Technical Data

    2. TECHNICAL DATA TECHNICAL DATA SPECIFICATIONS OF CM 21 PYRANOMETER ACCORDING TO ISO 9060 LISTING Spectral range: 305-2800 nm (50% points) 335-2200 nm (95% points) Sensitivity: between 7 and 17 µV/Wm Impedance: 40 -100 Ohm Response time: (95% response) 1.6 s (63% response)? Non-linearity: <...
  • Page 14 White plastic screen, ASA Drying cartridge, PMMA Weight: 930 g Cable length: 10 m Dimensions: W x H 150 x 95 mm. See figure 2 CM 21 specifications compared against the WMO 1996 qualification classes are shown in appendix I.
  • Page 15 2. TECHNICAL DATA 150 mm L = 10 m 6 mm Figure 2 CM 21 Pyranometer outline dimensions in mm.

  • Page 16: Accuracy

    This is especially convenient in connection with a programmable data acquisition system. For the CM 21 the effect of each parameter on the sensitivity can be shown separately, because the parameters show less interaction. The non-linearity error, the sensitivity variation with irradiance, is the same...
  • Page 17 2. TECHNICAL DATA The temperature dependence of the sensitivity is an individual function. For a given CM 21 the curve is somewhere in the region between the curved lines in figure 3. Figure 3 The curve of relative sensitivity variation with instrument temperature of a CM 21 pyranometer is in the shaded region.
  • Page 18 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Wavelength [nm] Figure 5 CM 21 Black absorbers relative absorption [%] Figure 6 1. Relative transmittance of two pyranometer domes. 2. Spectral distribution of solar radiation at sea level. Sun at...

  • Page 19: Installation

    In this case, and also if the contents are incomplete, your dealer should be notified in order to facilitate the repair or replacement of the instrument. The CM 21 pyranometer delivery will include the following items: CM 21 pyranometer White sun screen...

  • Page 20: Mechanical Installation

    (for example, by masts or exhaust pipes). Note that hot (over 200 degrees centigrade) exhausted gas will produce radiation in the spectral range of the CM 21 Pyranometer. The pyranometer should be distant from light-coloured walls or other objects likely to reflect sunlight onto it.
  • Page 21 2. Mounting The CM 21 pyranometer is provided with two holes for 5 mm bolts. Two stainless steel bolts and two nylon rings are provided. The pyranometer should first be secured lightly with the bolts to a mounting stand or platform (Shown in figure 7).
  • Page 22 Screw M5x80 Nylon insulator Washer M5 Nut M5 Figure 7 Mounting the pyranometer.

  • Page 23: Installation For Measurement Of Solar Radiation On Inclined Surfaces

    For easy levelling first use the screw nearest to the spirit level. When the CM 21 is placed horizontally using the spirit level, or when it is mounted with its base on a horizontal plane, the thermopile is horizontal within 0.05º.

  • Page 24: Installation For Measurement Of Reflected Global Radiation

    3. INSTALLATION 3.2.3 Installation for measurement of reflected global radiation In the inverted position the pyranometer measures reflected global radiation. According to the WMO the height should be 1-2 m above a surface covered by short cut grass. The mounting device should not interfere too much with the field of view of the instrument.

  • Page 25: Installation For Measurement Of Diffuse Radiation

    This can be done with the 2AP tracker, designed to track the sun under all weather conditions. More information about the combination of CM 21 and tracker is given in the 2AP tracker manual. Figure 9 2AP tracker with pyranometer Alternatively the use of a shadow ring is possible, however less accurate.

  • Page 26: Underwater Use

    R 3.2.6 Underwater use The CM 21 pyranometer is in principle watertight. However, the hemispherical water-glass and glass-air boundaries act as a negative lens. The parallel beam of direct solar radiation becomes strong divergent after the passage of the outer dome.

  • Page 27: Electrical Connection

    ELECTRICAL CONNECTION The CM 21 is provided with a 10 m cable with three leads and a shield covered with a black sleeve. The colour code is: plus blue minus white case The shield is isolated from the case, so no shield-current can exist. Shield and white lead may be connected to the same ground at the readout equipment.
  • Page 28 However, recorders with a variable voltage range can be set so that the result can be read directly in W/m Figure 11 Circuit diagram of the CM 21 pyranometer and connection to readout equipment. When an optional temperature sensor is built in (See specifications in...
  • Page 29 A considerable input bias current of the readout equipment can produce a voltage of several micro volts across the impedance of the pyranometer. The correct equipment “zero point” can be verified with a resistance replacing the pyranometer impedance at the input terminals. The pyranometer can also be connected to a computer or data acquisition system.

  • Page 31: Operation

    4. OPERATION OPERATION After completing the installation the pyranometer will be ready for operation. The irradiance value (E ) can be simply computed by dividing the output ↓ Solar signal (U ) of the pyranometer by its sensitivity (S ) formula 1, or by ensitivity multiplication of the voltage value with the reciprocal of the sensitivity.

  • Page 33: Maintenance

    5. MAINTENANCE MAINTENANCE Once installed the pyranometer needs little maintenance. The outer dome must be cleaned and inspected regularly, e.g. every morning. On clear windless nights the outer dome temperature of horizontally placed pyranometers will decrease, even to the dew point temperature of the air, due to IR radiation exchange with the cold sky.
  • Page 34 The rubber ring is normally coated with a silicon grease (Vaseline will also do) to make the seal even better. If the rubber ring looks dry apply some grease to it. Check that the metal spring that retains the drying cartridge applies enough force.

  • Page 35: Calibration

    6. CALIBRATION CALIBRATION INITIAL CALIBRATION The ideal pyranometer should always have a constant ratio of voltage output to irradiance level (outside the instrument in the plane of the sensing element). This ratio is called sensitivity (S ) or responsivity. ensitivity The sensitivity figure of a particular pyranometer is unique.
  • Page 36 for recalibration the use of the recalibration form in appendix VII is recommended. Accurate calibrations can also be done outdoors under clear conditions by reference to a standard pyrheliometer. Many National Weather Services have calibration facilities. Their standard pyrheliometer is compared with the World Radiometric Reference (maintained at Davos, Switzerland) embodied by several absolute pyrheliometers (black body cavity type).

  • Page 37: Calibration Procedure At Kipp & Zonen

    6. CALIBRATION CALIBRATION PROCEDURE AT KIPP & ZONEN 6.3.1 The facility The artificial sun is a good quality film sun (Osram) fed by an AC voltage stabiliser. It embodies a 1000 W tungsten-halogen lamp with compact filament. The built-in ventilator allows continuous operation. Behind the lamp is a diffuse reflector with a diameter of 7.5 cm.

  • Page 38: Calculation

    The irradiance at position 1 (pyranometer 'a') may be slightly different from that at position 2 (pyranometer 'b') due to asymmetry in the lamp optics etc. Therefore the pyranometers are interchanged and the whole procedure is repeated. We get another pair of values: A' and B'. 6.3.3 Calculation The sensitivity of the unknown pyranometer is calculated with the formula 2: ⋅...

  • Page 39: Traceability To World Radiometric Reference

    6. CALIBRATION 6.3.5 Traceability to World Radiometric Reference Working standard pyranometers are maintained at Kipp & Zonen. Each standard pyranometer is characterised. Linearity, temperature dependence curve and directional response are well known. The working standard pyranometers are calibrated each year at the World Radiation Centre in Davos, Switzerland, periodically according to the component method.

  • Page 41: Frequently Asked Questions (Faq's)

    7. FREQUENTLY ASKED QUESTIONS FREQUENTLY ASKED QUESTIONS (FAQ’s) The most frequently asked questions are listed below. For an update refer to the Kipp & Zonen web page: http://www.kippzonen.com Negative output during night time measurements? This error is related to the zero offset type A. Normally this zero offset is present when the inner dome has a different temperature from the cold junctions of the sensor.
  • Page 42 Maximum and minimum irradiation quantities? Due to possible reflection from clouds the global irradiance at sea level can rise above the extraterrestrial irradiance of 1367 W/m at the top of the atmosphere. Values up to 1500 W/m have been reported due to focussing effects of clouds.

  • Page 43: Trouble Shooting

    8 TROUBLE SHOOTING TROUBLE SHOOTING The following contains a procedure for checking the instrument in case it appears that it does not function as it should. Trouble shooting: Output signal fails or shows improbable results: Check the wires, whether they are proper connected to the readout equipment.

  • Page 45: Part Numbers / Spare Parts / Options

    Part no. Measuring/compensating cell in housing covered by inner glass dome 0305-161 Outer glass dome 50 mm with metal ring 0305-162 Rubber ring for outer glass dome of CM 21 2132-426 Screen (plastic) 0305-166 Levelling screw (2 required per pyranometer) 0012-117...
  • Page 46 Description Part no. Mounting plate for 4 unventilated sensors (2 upper and 2 lower) 0012 092 10 meters cable extension and connectors 0305 666 15 meters cable extension and connectors 0305 631 20 meters cable extension and connectors 0305 632 25 meters cable extension and connectors 0305 633 30 meters cable extension and connectors...

  • Page 47: Appendix Iclassification According To Wmo Guide 1996

    APPENDIX I CLASSIFICATION ACCORDING TO WMO GUIDE 1996 High Good Moderate Characteristics CM 21 quality quality quality Secondary ISO 9060 classification First class Second class standard Response time (95 percent response) < 15 s < 30 s < 60 s Zero offset: <±...
  • Page 49 APPENDIX II RADIOMETRIC LEVELLING This must be done in the laboratory by mounting the instrument on a stand that can be rotated around an axis that is accurately vertical and passes through the centre of the receiving surface. The instrument then is illuminated by a lamp so that radiation falls at an elevation of approximately 15º...

  • Page 51: Appendix Iii

    APPENDIX III LIST OF WORLD AND REGIONAL RADIATION CENTRES World Radiation Centres Davos (Switzerland) St. Petersburg (Russia) Regional Radiation Centres Region I Africa: Cairo (Egypt) Khartoum (Sudan) Kinshasa (Zaire) Lagos (Nigeria) Tamanrasset (Algeria) Tunis (Tunisia) Region II Asia: Poona (India) Tokyo (Japan) Region III South America:...

  • Page 53: Appendix Iv Pyranometer Measurement Report

    APPENDIX IV PYRANOMETER MEASUREMENT REPORT Routine measurement of directional error during final inspection. Mean cosine error of each new CM 21 pyranometer is measured by a simple routine. The pyranometer base is placed against the vertical turntable of a goniometer in the parallel (0,5º) beam of a sun simulator.
  • Page 54 PYRANOMETER MEASUREMENT REPORT Relative cosine error at azimuth angle Angle North West South East -0.27% 0.30% 0.38% -0.18% 0.61% -0.62% 0.66% 1.09% 0.10% 0.62% Absolute cosine error for 1000 W/m beam radiation Angle North West South East -2.04 W/m 2.32 W/m 2.89 W/m -1.40 W/m 3.06 W/m...

  • Page 55: Appendix Vthermistor Specifications

    APPENDIX V THERMISTOR SPECIFICATIONS YSI thermistor 44031 Resistance versus Temperature in ° C Resistance Resistance Resistance Temperature Temperature Temperature Ω Ω Ω Ω Ω Ω Ω Ω Ω Ω Ω Ω [ °C ] [ °C ] [ °C ] 135200 29490 8194...

  • Page 57: Appendix Vi Pt-100 Specifications

    APPENDIX VI PT-100 SPECIFICATIONS Pt-100 Resistance versus Temperature in ºC Resistance Resistance Resistance Temperature Temperature Temperature Ω Ω Ω Ω Ω Ω Ω Ω Ω Ω Ω Ω [ °C ] [ °C ] [ °C ] 88.22 100.00 111.67 88.62 100.39 112.06...

  • Page 59: Appendix Vii Recalibration Service

    APPENDIX VII RECALIBRATION SERVICE Pyranometers, UV-meters, Pyrgeometers & Sunshine duration sensors Kipp & Zonen solar radiation measurement instruments comply with the most demanding international standards. In order to maintain the specified performance of these instruments, Kipp & Zonen recommends calibration of their instruments at least every two years.
  • Page 61 RECALIBRATION FORM NAME COMPANY/INSTITUTE ADDRESS POSTCODE +CITY COUNTRY PHONE I would like to receive a price list for recalibration I would like to submit my instruments for recalibration Type/Model: Qty: Requested delivery time I intend to send the instruments to Kipp &...
  • Page 63 RECALIBRATION FORM NAME COMPANY/INSTITUTE ADDRESS POSTCODE +CITY COUNTRY PHONE I would like to receive a price list for recalibration I would like to submit my instruments for recalibration Type/Model: Qty: Requested delivery time I intend to send the instruments to Kipp &...
  • Page 65 RECALIBRATION FORM NAME COMPANY/INSTITUTE ADDRESS POSTCODE +CITY COUNTRY PHONE I would like to receive a price list for recalibration I would like to submit my instruments for recalibration Type/Model: Qty: Requested delivery time I intend to send the instruments to Kipp &...

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