Kipp&Zonen CMA 6 Albedometers - Manual (Page 16)

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Instruction Manual - CMP/CMA series
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Throughout this manual the following symbols are used to indicate to the user important information.
General warning about conditions, other than those caused by high voltage electricity, which may result in physical
injury and/or damage to the equipment or cause the equipment to not operate correctly.
Note Useful information for the user
1.1 Product overview
According to International Standard ISO 9060:1990 and the World Meteorological Organisation (WMO) a pyranometer is the
designated type of instrument for the measurement of hemispherical (global or diffuse) solar radiation integrated over the
wavelength range from 0.3 to 3 µm (300 to 3000 nm). All pyranometers within the CMP series are compliant with one of the
classes specified by the international standard.
The albedo of a surface is the extent to which it diffusely reflects short-wave radiation from the sun in the wavelength range from
300 to 3000 nm. It is the ratio of the reflected radiation to the incoming radiation and varies from 0 (dark) to 1 (bright). As an
indication, albedo is about 0.15 for grass, 0.5 for dry sand and 0.8 for fresh snow.
CMA series albedometers consist of two pyranometers. The upper measures incoming global solar radiation and the lower
measures solar radiation reflected from the surface below. When the two signal outputs have been converted to irradiance in W/m²,
the albedo can be simply calculated.
This manual, together with the instruction sheets, provide information related to the installation, maintenance, calibration,
product specifications and applications of the CMP series pyranometers and CMA series albedometers.
If any questions should remain, please contact your local Kipp & Zonen representative or e-mail the Kipp & Zonen customer and
product support department at:
[email protected]
Please go to www.kippzonen.com for information about other Kipp & Zonen products, or to check for any updates to this manual.
1.1.1 The pyranometer and albedometer
The CMP series instruments are high quality radiometers designed for measuring short-wave irradiance on a plane surface
(radiant flux, W/m²) which results from the sum of the direct solar radiation and the diffuse sky radiation incident from the
hemisphere above the instrument. The CMA series also measures the amount of the incoming radiation which is reflected by the
surface below.
There are six models in the CMP series; CMP 3, CMP 6, CMP10, CMP 11, CMP 21 and CMP 22; and two models in the CMA series,
CMA 6 and CMA 11.
To achieve the required spectral and directional characteristics CMP series pyranometers and CMA series albedometers use
thermopile detectors and glass domes. They have built-in bubble levels and the pyranometers have adjustable levelling feet.
Snap-on sun shields reduce solar heating of the housings. Albedometers have a mounting rod fitted and an integral glare-
shield to prevent direct sunlight from below the horizon entering the lower pyranometer. The waterproof connectors have
gold-plated contacts.
The instruments are normally delivered with a waterproof plug pre-wired to a high quality signal cable, typically this is 10 m
long but other lengths are available. The instruments can also be ordered with a plug only, for the user to fit their own cable.
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CMP pyranometers and CMA albedometers do not require power to operate. Radiation falling onto the sensing element produces
a small analogue output voltage.
CMP 3 is smaller and lighter than the other CMP series pyranometers. It features a 64-junction thermopile sensing element with
a highly absorptive and spectrally flat black coating to capture incoming radiation and convert it to an electrical signal. This
detector is protected by a high quality glass dome which is 4 mm thick. The housing is completely sealed.
CMP 6 uses the same sensing element as CMP 3 but has improved performance due to the double glass dome construction and the
increased thermal mass of the larger housing. The glass used has better transmission of ultraviolet radiation than the CMP 3 glass.
The two high quality concentric domes, 2 mm thick, reduce directional error and improve thermal isolation. The radiometric
levelling is more accurate and CMP 6 has a drying cartridge with replaceable desiccant.
CMP10 and CMP 11 have a 32-junction thermopile sensing element which features faster response, better linearity and a wider
measurement range than the CMP 3 and CMP 6. CMP10 and CMP 11 have built-in temperature compensation. The CMP10 has
internal desiccant that lasts for 10 years and the CMP 11 has a removable drying cartridge.
CMP 21 is similar to the CMP 11 but has individually optimised temperature compensation and a sensor is fitted to monitor the
housing temperature. Each instrument is supplied with its own temperature and directional response for post-processing of
recorded data by the user. A Pt-100 temperature sensor can be ordered instead of the standard 10 kΩ thermistor.
CMP 22 has all the features of CMP 21 but uses two 4 mm thick very high quality quartz domes for a wider spectral range and reduced
thermal offsets. Because of the high optical quality and refractive index of these domes the directional error is greatly reduced.
CMA 6 is an albedometer comprised of two CMP 6 sensing element and dome assemblies in a single housing with two signal
outputs on one signal connector.
CMA 11 uses two of the same sensing elements as fitted to the CMP 11 pyranometer, for similarly improved performance over the CMA 6.
Features and specifications of the CMP and CMA instruments are explained later in this manual.
1.1.2 International Standards
CMP 3 exceeds the requirements of ISO 9060:1990 for a Second Class Pyranometer.
CMP 6 and CMA 6 are fully compliant with the requirements of ISO 9060:1990 for a First Class Pyranometer.
CMP10, CMP 11 and CMA 11 are fully compliant with the requirements of ISO 9060:1990 for a Secondary Standard Pyranometer.
CMP 21 and CMP 22 significantly exceed the requirements of ISO 9060:1990 for a Secondary Standard Pyranometer.
CMP series pyranometers and CMA series albedometers are calibrated in accordance with Annex A.3 of ISO 9847 ‘Calibration of
Field Pyranometers by Comparison to a Reference Pyranometer’. Annex A.3 refers to ‘Calibration Devices Using Artificial Sources’.
Calibrations are traceable to the World Radiometric Reference (WRR) in Davos, Switzerland.
CMP series pyranometers comply with IEC 60904-1 ‘Photovoltaic devices - Part 1: Measurement of Photovoltaic Current-Voltage
Characteristics’.
1.2 The CMP 3 pyranometer
1.3 The CMP10 pyranometer
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Please follow the instructions in this section carefully, and also refer to the instruction sheets, for the correct mechanical and
electrical installation of the CMP and CMA series radiometers.
2.1 Included with the product
Check the contents of the shipment for completeness (see below) and note whether any damage has occurred during transport. If
there is damage, a claim should be filed with the carrier immediately. In the case of damage and/or the contents are incomplete,
contact your local Kipp & Zonen representative or e-mail the Kipp & Zonen customer and product support department at:
[email protected]
Although all CMP and CMA radiometers are weather-proof and suitable for use in harsh environmental conditions, they have
some delicate mechanical parts. Please keep the original packaging for safe transport of the radiometer to the measurement
site, or for use when returning the radiometer for calibration.
The following items are included with CMP series pyranometers:
Pyranometer
Sun shield
Cable, pre-wired with connector (2, 4 or 8 pins) or connector only for customer cable
Calibration certificate (with temperature response and directional response for CMP 21 and CMP 22)
Instruction sheet
Pyranometer fixing kit CMP 3; 2 each of stainless steel M5 x 30, M5 x 40 and M5 x 50 mm screws, nut, flat washer
Pyranometer fixing kit CMP 6, CMP10, CMP 11, CMP 21 and CMP 22; 2 each of stainless steel M5 x 80 mm screw, nut, flat
washer, nylon insulation ring
2 Dessicant bags, except for CMP 3 (which is sealed) and CMP10 (desiccant lasts for 10 years, will be renewed every factory re-calibration)
CD-ROM with product documentation
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The following items are included with CMA series albedometers:
Albedometer with permanently fitted mounting rod
Sun shield
Cable, pre-wired with connector (4 pins) or connector only for customer cable
Calibration certificate
Instruction sheet
2 Dessicant bags
CD-ROM with product documentation
2.2 Tools required
The tools required to fit a CMP series pyranometer to a support are a 4 mm (M5 socket head screw) Allen key and an 8 mm (M5
nut) wrench/spanner. Tools required for the CMA series albedometers depend upon how the mounting rod will be attached to a
mast or wall (fittings are not included). Normally, the drying cartridge should be hand-tight, but a 16 mm or 5/8" open-ended
wrench/spanner can be used to loosen it.
2.3 Location and support
The Instruction sheets contain all the outline information necessary for the correct installation of the radiometers. Further
details for specific types of installation and application are given later in this section.
Check the condition of the desiccant and replace before installation, if necessary; for example after a long storage period.
Not required for CMP 3. The CMP10 internal desiccant is operational 10 years after the last calibration date as mentioned on
the instrument label and calibration certificate.
2.4 Installation for measurement of horizontal global irradiance
The following steps must be carefully taken for optimal performance of the instrument.
2.4.1 Location
Ideally, the site for the radiometer should be free from any obstructions to the hemispherical view from the plane of the sensing
element. If this is not possible, the site should be chosen in such a way that any obstruction over the azimuth range between
earliest sunrise and latest sunset should have an elevation not exceeding 5 ° (the apparent sun diameter is 0.5 °)
This is important for an accurate measurement of the direct solar radiation component. The diffuse solar radiation is less
influenced by obstructions near the horizon. For instance, an obstruction with an elevation of 5 ° over the whole azimuth range
of 360 ° decreases the downward diffuse solar radiation by only 0.8%.
It is evident that the radiometer should be located in such a way that a shadow will not be cast upon it at any time (for example
by masts). Note that hot exhaust gas (> 100 °C) from ventilation ducts will produce some radiation in the spectral range of the
radiometer and cause an offset in the measurements. The radiometer should be distant from light-coloured walls or other
objects likely to reflect sunlight onto it, or emitting short-wave radiation.
The radiometer should be readily accessible for cleaning the outer dome, checking that it is level and inspecting the desiccant.
2.4.2 Mounting
The CMP pyranometer is provided with two holes for 5 mm screws. Two each of stainless steel screws, washers and nuts are
provided in the fixing kit, and two nylon insulation rings (except for CMP 3). The pyranometer should first be secured lightly with
the screws to a solid and stable mounting stand or platform, as shown below. The nylon insulators are important to prevent
corrosion between the stainless steel screws and the aluminium pyranometer housing (they are not supplied with CMP 3, where
mounting through the base flange is less critical).
The mounting stand temperature may vary over a wider range than the air temperature. Temperature fluctuations of the
pyranometer body can produce offset signals, therefore it is recommended to isolate the pyranometer thermally from the
mounting stand by placing it on its three feet. However, ensure that there is a good electrical contact with the ground to conduct
away currents in the cable shield induced by lightning.
Note After recalibration and/or reinstallation ensure that the nylon insulators are refitted.
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CMA albedometers are fitted with a mounting rod with a flat on the top surface that is pre-aligned with the horizontal axis of the
radiometer. The rod is 16 mm diameter and extends approximately 300 mm beyond the sun shield. The CMB 1 mounting bracket
can be used for fixing the mounting rod to a mast, pole or wall. Also refer to the requirements in 2.6 and 2.7 for the measurement
of reflected radiation and albedo.
CMP 3 has an accessory mounting rod which screws into the base flange of the pyranometer. The rod is 12 mm diameter and
300 mm long and can be used with the CMB 1 mounting bracket.
CMF 1 and CMF 2 mounting fixtures for unventilated or ventilated (respectively) CMP series pyranometers have similar mounting
rods to the albedometers and can also be used with the CMB 1.
2.4.3 Orientation
In principle no special orientation of the instrument is required, although the World Meteorological Organisation (WMO) recommends
that the signal lead (connector) is pointed towards the nearest pole, to minimise heating of the electrical connections. This is also
where any mounting pole, or other support, should be located in order that shadows do not fall on the instrument.
2.4.4 Levelling
Accurate measurement of the global radiation requires proper levelling of the detector surface. Level the instrument by turning
the two adjustable feet to bring the bubble of the spirit level centrally within the marked ring. For easy levelling, first use the
screw nearest to the spirit level.
Note It is ideal that the bubble should be completely within the marked ring. However, in fact, the pyranometer is level
within the specified accuracy when the bubble is at least half within the ring.
2.4.5 Securing
Fix the pyranometer tightly with the two stainless steel bolts. For albedometers tighten the mounting rod fixings. Ensure that
the radiometer maintains the correct levelled position when it is secured.
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2.4.6 Fitting the connector and cable
Locate the plug correctly in the radiometer socket, it only fits one way, and push it in. Screw the plug locking ring hand-tight.
Over-tightening may damage the waterproof seal. Secure the cable so that it cannot blow in the wind or cause a shadow on the
instrument.
Note The cable should be arranged with a curve below the instrument so that water drips off, rather than running along
the cable up to the connector.
2.4.7 Fitting the sun shield
Finally, clip on the sun shield to prevent excessive heating of the radiometer body. The bubble level is visible through the top
of the sun shield for routine checks and the shield ‘tail’ helps to protect the connector.
2.5 Installation for measurement of tilted global irradiance
When a pyranometer is mounted on a large flat tilted surface the temperature of this surface can rise considerably (more than
10 °C) above air temperature. It improves the measurement accuracy when the body is thermally isolated by its feet from the
surface. This promotes thermal equilibrium between the dome(s) and the housing and decreases zero offsets. It is advised to
pre-adjust the levelling feet on a horizontal surface for easy mounting of the instrument parallel to the inclined surface.
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For accurately and securely fixing a pyranometer at an angle to a surface an adjustable tilt mounting kit is available. See Accessories
in chapter 3.
2.6 Installation for measurement of reflected global irradiance
In the inverted position the pyranometer measures reflected global radiation. The
height above the surface (H) depends upon its roughness. The WMO recommends
a height of 1 m to 2 m above a uniform surface covered by short grass.
The mounting device should not interfere significantly with the field of view of
the instrument. The mounting plate above the pyranometer prevents excessive
heating of the housing by downwards solar radiation. CMF 1 or CMF 2 mounting
fixtures can be used. The accessory glare screen kit has an angle of 5 ° and is
fitted to the pyranometer to prevent direct illumination of the domes by the sun
at sunrise and sunset. It does not fit the CMP 3.
Thermal offset signals generated in the pyranometer are 5 times more significant
in the measurement of reflected radiation due to the lower irradiance level.
The mast shown intercepts a fraction D/2πS. of the radiation coming from the
ground. In the most unfavourable situation (sun at zenith) the pyranometer
shadow decreases the signal by a factor R²/H².
As a guide, a black shadow below the pyranometer with a radius of 0.1 x H decreases the signal by 1%, and 99 % of the signal
will originate from an area with a radius of 10 x H.
2.7 Installation for measurement of albedo
An albedometer consists of two identical pyranometers that measure the
incoming global solar radiation and the radiation reflected from the surface
below. Albedo is the ratio of the two irradiances, and varies from 0 (dark) to
1 (bright).
Two CMP 3’s can be mounted back to back with the standard fixing kit, and
the accessory mounting rod screwed into one of them, to make a second
class albedometer.
For two of the larger CMP pyranometers a mounting fixture is required. The
CMF 1 is used for unventilated pyranometers and the CMF 2 for ventilated
instruments. The glare screen kit should be fitted to the lower pyaranometer.
The requirements for installation of the upper pyranometer are the same as
for horizontal global irradiance. The requirements for installation of the
lower pyranometer are the same as for reflected global irradiance.
The same principles apply to the CMA 6 and CMA 11 albedometers, which already have an upper sun shield and an integrated
lower glare screen and mounting rod.
2.8 Installation for measurement of horizontal diffuse irradiance
For measuring the diffuse radiation from the sky, the direct solar radiation
must be blocked from the pyranometer dome(s).
A static shadow ring can be used to intercept the direct solar radiation. This
requires frequent manual adjustment as the sun’s arc in the sky changes. At
times the shadow ring also intercepts a significant proportion of the diffuse
sky radiation. Therefore, post-processing of the recorded data is necessary to
correct for this.
Kipp & Zonen produces a universal shadow ring, model CM 121, which is
suitable for use at all latitudes.
The alternative to a shadow ring is to use a two-axis automatic sun tracker,
such as one of the Kipp & Zonen SOLYS 2 or 2AP. The sun tracker uses location
and time information to calculate the position of the sun and point at it
accurately under all weather conditions.
The sun tracker can be fitted with a small sphere mounted on an articulated
shading assembly. The shadow of the sphere is adjusted to cover the
pyranometer dome(s) completely and it will then be shaded correctly
throughout the year without adjustment.
2.9 Electrical connections
As standard CMP pyranometers and CMA albedometers are supplied with a waterproof connector pre-wired to 10 m of high quality
yellow cable with 2, 4 or 8 wires and a shield covered with a black sleeve. Longer cables of 25 m and 50 m length are available as
options and 100 m on special request. The colour code of the wires and the connector pin numbers are shown below and on the
instruction sheets.
Note Where the cable needs to be longer than 50 m, the AMBOX 4 to 20 mA signal amplifier is recommended.
2.9.1 Pyranometer connections
CMP 3, CMP 6, CMP10 and CMP 11 are fitted with a 2-pin connector and 2-wire shielded cable. CMP 21 and CMP 22 are fitted with
a 4-pin connector and 4-wire shielded cable, the 2 extra connections are for the standard 10 kΩ thermistor temperature sensor
signal. CMP 21 and CMP 22 with the optional Pt-100 temperature sensor are fitted with an 8-pin connector and 8-wire shielded
cable, two wires are not used.
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2.9.2 Albedometer connections
CMA 6 and CMA 11 are fitted with a 4-pin connector and 4-wire shielded cable.
2.9.3 Grounding
The shield of the cable is connected to the aluminium radiometer housing through the connector body. Preferably,
secure the radiometer with its levelling screws to a metal support with a good connection to ground (e.g. by using
a lightning conductor) and do not connect the cable shield.
If there is no good ground connection at the pyranometer, the shield at the cable end should be connected to
ground at the readout equipment. Lightning can induce high voltages in the shield but these will be led off at the
pyranometer or readout equipment.
2.9.4 Radiation signal output
The radiometers produce a low-level analogue voltage output. Each radiometer (each ‘half’ of an albedometer) has a unique
sensitivity, which is given on the serial number label on the instrument and on the calibration certificate.
The sensitivity is in the range of 5 to 20 µV/W/m².
Therefore, to accurately measure changes in irradiance of 1 W/m² the data logger or data acquisition system requires a total
input measurement uncertainty (error) of 5 µV, or less; including noise, offsets, resolution, temperature effects, etc.
The maximum irradiance under natural sunlight is unlikely to exceed 1500 W/m².
The signal output can be connected to a single-ended or differential measurement system input.
Note The input impedance of the readout equipment should be > 1 MΩ.
Note The output signal can be negative at night-time. This is normal and is not a fault (see section 7.2).
2.9.5 Temperature signal output
The CMP 21 and CMP 22 are fitted with an internal temperature sensor close to the cold-junction of the thermopile sensing
element. Recording this signal allows post-processing of the radiation signal data to remove the small effect of temperature
changes not compensated for by the internal circuit. The individual temperature response of each CMP 21 and CMP 22 is provided
with the calibration certificate.
For the standard 10 kΩ thermistor temperature sensor the conversion from resistance to temperature is given in Appendix C.
For the optional Pt-100 temperature sensor the conversion from resistance to temperature is given in Appendix D.