Kipp & Zonen CM 11 User manual

INSTRUCTION MANUAL
Kipp
Zonen
&
0305 201
PYRANOMETER / ALBEDOMETER
14
11
manual

IMPORTANT USER INFORMATION
1
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.
Should you have any comments on this manual we will be pleased to receive
them at: Kipp & Zonen B.V.
Röntgenweg 1 2624 BD Delft Holland
P.O. Box 507 2600 AM Delft Holland
Phone [phone]
Fax [phone]
Email [email protected]
Kipp & Zonen reserve the right to make changes to the specifications without
prior notice.
WARRANTY AND LIABILITY
Kipp & Zonen guarantees that the product delivered has been thoroughly tested
to ensure that it meets its published specifications. The warranty included in the
conditions of delivery is valid only if the product has been installed and used
according to the instructions supplied by Kipp & Zonen.
Kipp & Zonen shall in no event be liable for incidental or consequential
damages, including without limitation, lost profits, loss of income, loss of
business opportunities, loss of use and other related exposures, however
caused, arising from the faulty and incorrect use of the product.
User made modifications can affect the validity of the CE declaration.
COPYRIGHT©2000 KIPP & ZONEN
All rights reserved. No part of this publication may be reproduced,
stored in a retrieval system or transmitted in any form or by any means,
without permission in written form from the company.
Manual version: 0805

IMPORTANT USER INFORMATION
2
DECLARATION OF CONFORMITY
According to EC guideline 89/336/EEC 73/23/EEC
We Kipp & Zonen B.V.
Röntgenweg 1
2624 BD Delft
Declare under our sole responsibility that the product
Type: CM 11 / 14
Name: Pyranometer
To which this declaration relates is in conformity with the following standards
Imissions EN 50082-1 Group standard
Emissions EN 50081-1 Group standard
EN 55022
Safety standard IEC 1010-1
Following the provisions of the directive
R.E. Ringoir
Product management
KIPP & ZONEN B.V.

TABLE OF CONTENTS
3
TABLE OF CONTENTS
IMPORTANT USER INFORMATION...............................................................1
DECLARATION OF CONFORMITY ................................................................2
TABLE OF CONTENTS...................................................................................3
1. GENERAL INFORMATION ..................................................................5
1.1 Introduction.................................................................................................5
1.2 Physical principles......................................................................................6
1.2.1 Zero offsets ................................................................................................7
1.2.2 Spectral range and spectral selectivity......................................................9
1.2.3 Directional error....................................................................................... 11
1.2.4 Temperature dependence ...................................................................... 11
2. TECHNICAL DATA ............................................................................13
2.1 Specifications.......................................................................................... 13
2.1.1 Technical data of single version CM 11.................................................. 13
2.1.2 Technical data of albedo version CM 14................................................ 15
2.2 Accuracy.................................................................................................. 18
3. INSTALLATION..................................................................................21
3.1 Delivery ................................................................................................... 21
3.2 Mechanical installation............................................................................ 22
3.2.1 Installation for measurement of global radiation..................................... 22
3.2.2 Installation for measurement of solar radiation on inclined surfaces ..... 25
3.2.3 Installation for measurement of reflected global radiation...................... 26
3.2.4 Installationformeasurement ofdiffuse radiation..................................... 27
3.2.5 Installation for measurement of albedo .................................................. 27
3.2.6 Underwater use....................................................................................... 28
3.3 Electrical connection............................................................................... 29
3.3.1 Electrical connection CM 14................................................................... 31
4OPERATION.......................................................................................33
5MAINTENANCE..................................................................................35

TABLE OF CONTENTS
4
6CALIBRATION ...................................................................................37
6.1 Initial calibration....................................................................................... 37
6.2 Recalibration ........................................................................................... 37
6.3 Calibration procedure at Kipp & Zonen .................................................. 39
6.3.1 The facility............................................................................................... 39
6.3.2 Procedure................................................................................................ 39
6.3.3 Calculation............................................................................................... 40
6.3.4 Zero offset............................................................................................... 40
6.3.5 Traceability to World Radiometric Reference......................................... 41
7FREQUENTLY ASKED QUESTIONS (FAQ’S)..................................43
8TROUBLE SHOOTING.......................................................................45
9PART NUMBERS / SPARE PARTS / OPTIONS................................47
APPENDIX I CLASSIFICATION ACCORDING TO WMO GUIDE 1996.....49
APPENDIX II RADIOMETRIC LEVELLING.................................................51
APPENDIX III LIST OF WORLD AND REGIONAL RADIATION CENTRES53
APPENDIX IV RECALIBRATION SERVICE.................................................55

GENERAL INFORMATION
5
1. GENERAL INFORMATION
1.1 INTRODUCTION
The pyranometer CM 11 is designed for measuring the irradiance
(radiant-flux, Watt/m2) on a plane surface, which results from the
direct solar radiation and from the diffuse radiation incident from the
hemisphere above.
Because the CM 11 exhibits no tilt dependence it can measure solar
radiation on surfaces inclined as well.
In the inverted position reflected solar radiation can be measured.
The albedometer CM 14 is based on two CM 11 sensors and is
suitable for the measurement of net global radiation and/or albedo
over surfaces of different nature (see chapter 5 for installation).
For measuring the diffuse component of solar radiation only, the direct
solar component can be shielded semi-automatically from the
pyranometer by the Kipp & Zonen shadow ring CM 121, and fully
automatically by the 2AP tracker with shading system.
The CM 11 pyranometer complies with the specifications for 'High
quality', the best of three classes, as published in the 'Guide to
meteorological Instruments and Methods of Observation', Eight
edition, 1996, of the World Meteorological Organization (WMO) -
Geneva - Switzerland.
The WMO classification list is adopted, improved and extended by the
International Standard Organization ISO and published as ISO 9060.
This standard is one of a series of standards specifying methods and
instruments for the measurement of solar radiation.
In this manual the specifications of accuracy are listed according the
ISO 9060, in which the CM 11 is classified as a “secondary standard”
list.

GENERAL INFORMATION
6
1.2 PHYSICAL PRINCIPLES
The pyranometer CM 11 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. This implies that the naked thermal detector is also sensitive
to long wave infrared radiation (thermal radiation λ> 3000 nm) from
the environment. (e.g. the inner dome)
The radiant energy is absorbed by a black painted disk. The heat
generated flows through a thermal resistance to the heat sink (the
pyranometer body). The temperature difference across the thermal
resistance of the disk is converted into a voltage.
The rise of temperature is easily affected by wind, rain and thermal
radiation losses to the environment ('cold' sky). Therefore the detector
is shielded by two glass domes. Glass domes allow equal transmitting
of the direct solar component for every position of the sun on the
celestial sphere. The spectral range of the pyranometer is limited by
the transmission of the glass. See figure 3. A desiccator in the body
prevents dew on the inner side of the domes, which can cool down
considerably, at clear windless nights.
Construction details (See figure 1)
The sensing element of the pyranometer CM 11 is a black painted
ceramic (Al2O3) disk. 100 thermocouples forming a thermopile are
imprinted on it using thick film techniques. Only the border of the disk
is in good thermal contact with the pyranometer body (heat sink), and
along this border the 100 cold junctions are located. The 100 hot
junctions are near the centre in a rotational symmetric arrangement.
This fact plus a proper levelling of the sensor related to the spirit level
results in a low azimuth error.
When the pyranometer is illuminated, the absorbed radiation results in
a radial heat flow to the border of the disk. The temperature in the
centre of the disk will rise due to its thermal resistance. The thermal

GENERAL INFORMATION
7
resistance of the Al2O3substrate is relatively low. E.g. an irradiance of
1000 W/m2results in a rise of centre temperature of 3 °C only and a
voltage of 4-6 mV. Natural convection inside the inner dome due to
this temperature difference appeared to be small and when tilting a
pyranometer CM 11, no change of sensitivity is observed.
1.2.1 Zero offsets
The following definition of zero offsets is used:
When the sensor does not absorb radiation with wavelengths in the
spectral range of the instrument and there still is a signal, we call it
zero offset. Two types of zero offset are distinguished.
Zero offset type B
This zero offset arises when the body (heat sink) temperature
increases or decreases. This results in a temperature difference
between cold junctions (connected to the heat sink) and the hot
junctions due to the heat flow necessary to load or unload the sensor
heat capacity. In the CM 11 there is principally no zero offset B
because there is a second non-illuminated compensation element.
See figure 1.
Other heat flows in the sensing element e.g. due to rising or falling
body temperature cause spurious voltage, sometimes called zero
offsets. See Appendix II. To compensate for one of these offsets, a
second non-illuminated element is installed, in which the same heat
flow will arise. By anti-series arrangement of both elements the
spurious voltage is cancelled out greatly. The white plastic screen
reduces the body temperature variations due to solar radiation and
(cold) rain showers.
Zero offset type A
This zero offset is present when the inner dome has another
temperature than the cold junctions of the sensor. Practically this is
always the case when there is a clear sky. Because of the low
effective sky temperature (<0 °C) the earth surface emits roughly
100 W/m2long wave infrared radiation upwards. The outer glass

GENERAL INFORMATION
8
dome of a pyranometer also has this emission and is cooling down
several degrees below air temperature (the emissivity of glass for the
particular wavelength region is nearly 1). The emitted heat is attracted
from the body (by conduction in the dome), from the air (by wind) and
from the inner dome (through infrared radiation). The inner dome is
cooling down too and will attract heat from the body by conduction
and from the sensor by the net infrared radiation again. The latter heat
flow is opposite to the heat flow from absorbed solar radiation and
causes the well known zero depression at night of approximately -5
W/m2. This negative zero offset is also present on a clear day,
however, hidden in the solar radiation signal.
Figure 1 Approximate construction of Kipp & Zonen pyranometer CM 11.
During indoor measurements with a solar simulator, the inner dome
can become warmer than the pyranometer body due to net thermal
radiation from the lamp housing. A positive zero offset A is the result.
The zero offset A can be checked by placing a light and IR reflecting
cap over the pyranometer. A thin aluminium foil cap covering only the
dome seems to be the best solution. The response to solar radiation

GENERAL INFORMATION
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will decay with a time constant 1/e of 4s, but the dome temperature
will go to equilibrium with a time constant of several minutes. So after
one minute the remaining signal is the main part of the last zero offset
A.
Good ventilation of domes and body is the solution to decrease zero
offset A. Kipp & Zonen advises CV 2 for optimal ventilation and
suppression of zero offset type A. Using the CV 2 zero offset type A
will be less than 7 W/m2.
SUMMARIZED: Zero offset is the result of lack of thermal equilibrium
in the instrument.
Upper values of zero offset in CM 11
Zero offset A: 7 W/m2response to 200 W/m2thermal radiation
(ventilated domes)
12 W/m2response to 200 W/m2thermal radiation (no
ventilation)
Zero offset B: < 3 W/m2response to 5 °C/hr change of body
temperature
1.2.2 Spectral range and spectral selectivity
Spectral selectivity is the product of spectral absorptance of the black
coating (see figure 2) and spectral transmittance of the glass domes
(see figure 3).
Shifts in the solar spectrum, due to changes from clear to overcast
sky, are mainly in the mid of the spectral range. No significant spectral
selectivity errors have to be expected. E.g. at a sun's elevation of 30°
(airmass 2) only 1% of the solar radiation has wavelengths below 335
nm and only 1% of the solar radiation has wavelengths above 2200
mm.

GENERAL INFORMATION
10
Figure 2 Spectral reflectance of Carbon black coating as measured in a
UV/VIS/NIR spectrophotometer with integrating sphere attachment.

GENERAL INFORMATION
11
Figure 3 1. Relative spectral transmittance of two pyranometer domes. (Four
surface reflections and index change with wavelength are taken
into account).
2. Spectral distribution of solar radiation at sea level. Sun at zenith
(Airmass 1).
1.2.3 Directional error
The directional response is an individual feature and depends on
imperfections of the glass domes and angular reflection properties of
the black paint.
1.2.4 Temperature dependence
For a given heat flow the sensitivity of the pyranometer is a function of
the thermal conductivity of the substrate and of the thermo-electric
power of the thermocouple material. These physical quantities show
temperature dependency, and a thermistor is applied in the electric
circuit to keep the sensitivity constant at least for temperatures
between -10 °C and + 40 °C. See figure 9.

GENERAL INFORMATION
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TECHNICAL DATA
13
2. TECHNICAL DATA
2.1 SPECIFICATIONS
2.1.1 Technical data of single version CM 11
Performance
Spectral range: 310-2800 nm (50% points)
340-2200 nm (95% points)
Sensitivity: between 4 and 6 µV/Wm-2
Impedance: 700 -1500 Ohm
Response time: < 15 s (95% response)
< 24 s (99% response)
Non-linearity: < 0.6% (< 1000 W/m2)
Temperature dependence
of sensitivity: < 1% (-10 0C to +40 0C)
Directional error: < 10 W/m2 (beam 1000 W/m2)
Tilt error < 0.25% (beam 1000 W/m2)
Zero-offset due to FIR < 7 W/m2at 200 W/m2 net thermal
(Ventilated with CV 2) radiation
Zero-offset due to temp. changes < 2 W/m2at 5 K/h temp. change
Operating temperature -40 0C to +80 0C
Viewing angle: 2 πsr

TECHNICAL DATA
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Irradiance: 0 - 1400 W/m2(max. 4000 W/m2)
Non-stability: < 0.5% sensitivity change per year
Spectral selectivity ±2% (0,35 µm to 1,5 µm)
Construction
Receiver paint: Carbon black
Glass domes: Schott N-K5 optical glass 2 mm
thick, 30 mm and 50 mm outer
diameter
Desiccant: Silica gel
Spirit level: Sensitivity 0.1°(bubble half out of
the ring) Coincide with base of the
instrument.
Detector surface and base are
coplanar within 0.1°
Materials: Anodised aluminium case, seawater
proof quality.
Stainless steel screws corrosion free
mounted.
Anodised aluminium levelling
screws.
White plastic screen, ASA/PC
Drying cartridge, PMMA
Weight: 830 g
Cable length: 10 m
Dimensions: W x H 150 x 95 mm. See figure 4

TECHNICAL DATA
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2.1.2 Technical data of albedo version CM 14
•The general technical data of the CM 11 pyranometer also apply to
the albedometer CM 14
•Sensors of equal sensitivity
•Conical lower screen, which prevents illumination of the lower
glass dome at sunrise and sunset
Impedance Depends on connection
Weight, including rod 1.9 kg
Cable length 10 m
Dimensions See figure 6

TECHNICAL DATA
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Figure 5 Kipp & Zonen pyranometer CM 11 outline dimensions in mm.

TECHNICAL DATA
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Figure 6 Kipp & Zonen albedometer CM 14 outline dimensions in mm.

TECHNICAL DATA
18
2.2 ACCURACY
Unfortunately the sensitivity is cross-correlated to a number of
parameters as temperature, level of irradiance, vector of incidence,
etc. The upper limiting values of the resulting sensitivity variations are
listed in the specifications. It classifies the pyranometer CM 11 as a
'secondary standard' according to the classification of the World
Meteorological Organization.
Normally, the supplied sensitivity figure is used to calculate the
irradiances. If the conditions differ from calibration conditions, errors in
the calculated
irradiances must be expected.
For a secondary standard instrument the WMO expects maximum
errors in the hourly radiation totals of 3%. In the daily total an error of
3% is expected, because some response variations cancel out each
other if the integration period is long.
These errors can be reduced further if the actual sensitivity of the
pyranometer is used by the conversion of voltage to irradiance. The
actual sensitivity can be calculated when it is a well-known function of
simply measured parameters (sometimes called transfer function or
sensitivity function). This is especially convenient in connection with a
programmable data acquisition system.
For the CM 11 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
equal for any given CM 11. See figure 7.

TECHNICAL DATA
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Figure 7 Non-linearity (sensitivity variation with irradiance) of Kipp & Zonen
pyranometer CM 11.
The temperature dependence of the sensitivity is an individual function. For
a given CM 11 the curve is somewhere in the shaded region of figure 8.
Figure 8 The curve of relative sensitivity variation with instrument temperature
of a pyranometer CM 11 is in the shaded region. A typical curve is
drawn.
The directional error is the summation of the azimuth and zenith error and is
commonly given in W/m2. Figure 9 shows the maximum relative zenith error in
any azimuth direction for the CM 11.