Hukseflux DR01, DR02, DR03 User Manual

Copyright by Hukseflux | manual v1609 | www.huksefluxusa.com | [e-mail]

USER MANUAL DR-SERIES

PYRHELIOMETERS

First class pyrheliometer DR01

Fast response first class pyrheliometer DR02

Compact fast response first class pyrheliometer DR03

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Warning statements

Putting more than 12 Volt across the sensor wiring
can lead to permanent damage to the sensor.

Do not use “open circuit detection” when measuring
the sensor output.

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Contents

Warning statements 2
Contents 3
List of symbols 4
Introduction 5
1 Ordering and checking at delivery 7

1.1 Ordering DR01, DR02 and DR03 7

1.2 Included items 7

1.3 Quick instrument check 8

2 Instrument principle and theory 9
3 Specifications of DR01 / DR02 / DR03 11

3.1 Specifications 11

3.2 Dimensions of DR01 & DR02 15

4 Standards and recommended practices for use 16

4.1 Classification standard 16

4.2 General use for solar radiation measurement 16

4.3 General use for sunshine duration measurement 17

4.4 Specific use in meteorology and climatology 17

5 Installation of pyrheliometers 18

5.1 Site selection and installation 18

5.2 Installation of the protection cap 18

5.3 Electrical connection 19

5.4 Requirements for data acquisition / amplification 20

6 Making a dependable measurement 21

6.1 The concept of dependability 21

6.2 Reliability of the measurement 22

6.3 Speed of repair and maintenance 23

6.4 Uncertainty evaluation 23

7 Maintenance and trouble shooting 28

7.1 Recommended maintenance and quality assurance 28

7.2 Trouble shooting 29

7.3 Calibration and checks in the field 30

7.4 Data quality assurance 30

8 DR03 31

8.1 Introduction DR03 31

8.2 Dimensions of DR03 32

9 Appendices 34

9.1 Appendix on cable extension / replacement 34

9.2 Appendix on optional chassis connector & cable connector 35

9.3 Appendix on tools for DR01 / DR02 / DR03 35

9.4 Appendix on spare parts for DR01 / DR02/ DR03 35

9.5 Appendix on standards for classification and calibration 36

9.6 Appendix on calibration hierarchy 37

9.7 Appendix on requirements for solar tracking 38

9.8 Appendix on meteorological radiation quantities 39

9.9 Appendix on ISO and WMO classification tables 40

9.10 Appendix on definition of pyrheliometer specifications 42

9.11 Appendix on terminology / glossary 43

9.12 Appendix on literature references 45

9.13 EC declaration of conformity 46

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List of symbols

Quantities Symbol Unit

Voltage output U V
Sensitivity S V/(W/m2)
Solar irradiance E W/m2

(see also appendix 9.8 on meteorological quantities)

Subscripts

Not applicable

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Introduction

DR01, DR02 and DR03 are high-accuracy direct normal irradiance (DNI) solar radiation
sensors, also known as pyrheliometers. The DR-series pyrheliometers comply with the
‘first class’ specifications of the ISO 9060 standard and the ‘good quality’ performance
level of WMO’s No. 8 Guide. Pyrheliometers are typically mounted on a solar tracker.

A unique product feature of all pyrheliometers in the DR-series is the heated window.
DR02 and DR03 are the fast-response versions of DR01. The difference is in detector
technology, resulting in a much faster response time (95 %) for DR02 and DR03: 2 s
instead of the traditional 12 s. DR02 has the same body and dimensions as DR01. DR03
is a compact version of DR02 pyrheliometer.

This manual is written for the standard model DR01; DR02 and DR03
specifications and operation are mentioned only in case these differ from
DR01’s. DR03, with its different dimensions, has a dedicated chapter in this
manual.

Figure 0.1 DR01 / DR02 pyrheliometer Figure 0.2 DR03 pyrheliometer

DR01 is a solar radiation sensor that is applied in high accuracy observations. It
measures the solar radiation received by a plane surface from a 5 ° full field of view
angle. This quantity, expressed in W/m2, is called ‘direct’ solar radiation or direct normal
irradiance (DNI). Pyrheliometers are generally employed outdoors under the sun. It is
necessary to keep the instrument pointed at the sun by using a two-axis tracker. Typical
DR01 applications include solar energy resource assessment, system performance
monitoring (in particular for concentrated solar energy) and scientific solar climate
observations.

DR01 pyrheliometer features a precision ground and polished quartz window, a
collimated tube and a thermopile sensor with black coated surface. It has an anodised

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aluminium body. DR01 also features a thermally isolated low-power heater in the window
assembly. The heater increases data availability, for instance by reducing measurement
errors caused by (early-morning) dew deposition. DR01 pyrheliometer is optionally
equipped with a temperature sensor and is optionally characterised for its temperature
response. This can be used to increase the accuracy of the measurement.

Using DR01 is easy. It can be connected directly to commonly used data logging
systems. The irradiance, E, in W/m2 is calculated by dividing the DR01 output, a small
voltage U, by the sensitivity S. The sensitivity is provided with DR01 on its calibration
certificate.

The central equation governing DR01 is:

E = U/S (Formula 0.1)

A pyrheliometer can also be used to measure sunshine duration. Sunshine duration
during a given period is defined as the sum of that sub-period for which the direct solar
irradiance exceeds 120 W/m2.

Suggested use for DR01:

 outdoor PV / CPV and CSP system performance monitoring
 solar energy surveys
 solar resource assessments
 meteorological networks

Applicable instrument classification standards are ISO 9060 and WMO-No. 8. Calibration
is traceable to WRR (World Radiometric Reference).

The instrument should be used in accordance with the recommended practices of ISO,
WMO and ASTM.

Various tracking solutions can be offered by Hukseflux. Please contact us for more
information on solar trackers.

Figure 0.3 Applications of DR01, DR02 and DR03 pyrheliometers, combined with SR20
pyranometers, in typical solar radiation monitoring stations

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1 Ordering and checking at delivery

1.1 Ordering DR01, DR02 and DR03

The standard configuration of DR01 is with 5 metres cable.

Common options are:

 Longer cable in multiples of 5 m, cable lengths above 20 m in multiples of 10 m.

Specify total cable length.

 Internal temperature sensor. This can be either a Pt100 or a 10 kΩ thermistor.

Specify respectively T1 or T2.

 Five silica gel bags in an air-thight bag for desiccant holder. Specify part number

DC01.

 Temperature dependence characterisation
 Improved temperature response

Standard DR01 / DR02 / DR03 pyrheliometers are equipped with a cable with cable
gland. Optionally the instrument may be ordered with a chassis connector and a cable
with connector. Please consult Hukseflux.

1.2 Included items

Arriving at the customer, the delivery should include:

 pyrheliometer DR01 / DR02 / DR03
 cable of the length as ordered
 product certificate matching the instrument serial number
 any other options as ordered

Please store the certificate in a safe place.

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1.3 Quick instrument check

A quick test of the instrument can be done by using a simple hand held multimeter and a
lamp.

1. Check the electrical resistance of the sensor between the green (-) and white (+) wire.
See chapter 5.3 on electrical connections. Use a multimeter at the 1000 Ω range.
Measure the sensor resistance first with one polarity, than reverse the polarity. Take the
average value. The typical resistance of the wiring is 0.1 Ω/m. Typical resistance should
be the typical sensor resistance of 400 to 500 Ω for DR01 and 150 to 250 Ω for DR02
and DR03, plus 1.5 Ω for the total resistance of two wires (back and forth) of each 5 m.
Infinite resistance indicates a broken circuit; zero or a low resistance indicates a short
circuit.

2. Check if the sensor reacts to light: put the multimeter at its most sensitive range of
DC voltage measurement, typically the 100 x 10-3 VDC range or lower. Expose the sensor
to a strong light source, for instance a 100 W light bulb at the front window. The signal
should read > 2 x 10-3 V now. Darken the sensor either by putting something over it or
switching off the light. The instrument voltage output should go down and within one
minute approach 0 V.

3. Inspect the instrument for any damage. Check if the sight is straight and aligned.

4. Inspect if the humidity indicator is blue. The colour pink indicates it is not dry but
humid: in the latter case replace the desiccant (see chapter on maintenance).

5. Optional: inspect the electrical resistance range of the internal temperature sensors

(for Pt100 in the 100 Ω range, for 10 kΩ thermistors in the 10 000 Ω range, in case of 3
wire or 4 wire connections of the Pt100 in the < 10 Ω range between connections at one

end).

Figure 1.3.1 DR01 first class pyrheliometer

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2 Instrument principle and theory

Figure 2.1 Overview of DR01:

(1) humidity indicator
(2) sights
(3) aperture tube
(4) protection cap
(5) window assembly with heater
(6) cable gland
(7) cable (standard length 5 metres cable, optional longer cable)

DR01’s scientific name is pyrheliometer. It measures the solar radiation received by a

plane surface from a 5 ° full field of view angle. In addition to the full field of view angle,
(the angle from the centre of the sensor to the edge of the aperture window) WMO
recommends in WMO manual 7.2 a slope angle (the angle from the side of the sensor to
the edge of the window aperture) of 1 °. The opening angle and slope angle together
with the sensor surface define the so-called acceptance function (see appendix on
terminology).

A pyrheliometer should measure ‘direct’ solar radiation, also called direct normal
irradiance or DNI. DNI is defined as the solar radiant flux collected by a plane unit
surface normal to the axis pointing towards the centre of the sun, within an optical
angular aperture. This aperture is characterized by the acceptance function (ref: IEA SHC
#46 and EU FP7 MACC-II projects, published by Blanc et al. (2014), see appendix on
terminology and appendix on literature references).
DNI is composed of the solar irradiance within the extent of the solar disk (half-angle

0.266 ° ± 1.7 %) plus some circumsolar radiation.

1

2

3

2

4

5

6

7

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Summarising, DR01 is a radiometer designed to measure DNI (i.e. including some
circumsolar irradiance). It complies with the WMO recommended parameters for the
view-limiting geometry: a full opening angle of 5 °, and a slope angle of 1 °, and
therefore a limit angle of 4 °.

The solar radiation spectrum extends roughly from 285 to 3000 x 10-9 m. By definition a
pyrheliometer should cover that spectral range with a spectral selectivity that is as “flat”
as possible.

For a correct measurement DR01 should be pointed at the sun. It is usually mounted on
a solar tracker. For tracking requirements see the appendix on solar tracking.

In order to attain the proper directional and spectral characteristics, DR01
pyrheliometer’s main components are:

 a thermal sensor with black coating. It has a flat spectrum covering the 200 to 4000

x 10-9 m range. The coating absorbs all solar radiation and, at the moment of
absorption, converts it to heat. The heat flows through the sensor to the instrument
body. The thermopile sensor generates a voltage output signal that is proportional to
the solar irradiance.

 a quartz glass window. This window limits the spectral range from 200 to 4000 x 10

-9

m (cutting off the part above 4000 x 10-9 m)

 an aperture tube. The most important components of this tube are two apertures.

One at the detector and the other at the front window. These determine the opening­and slope angle.

 A heater incorporated in the window assembly. This reduces measurement errors

caused by (early-morning) dew deposition. Typically the heater is switched on at
night only. Some users have employed the heater in high-power operation to counter
frost deposition.

Pyrheliometers can be manufactured to different specifications and with different levels
of verification and characterisation during production. The ISO 9060 - 1990 standard,

“Solar energy - specification and classification of instruments for measuring
hemispherical solar and direct solar radiation”, distinguishes between 3 classes;

secondary standard (highest accuracy), first class (second highest accuracy) and second
class (third highest accuracy).

Due to the required spectral selectivity a secondary standard pyrheliometer can only be
made with a cavity-type sensor. In addition the calibration of a secondary standard
pyrheliometer must be done by periodic comparison with a primary standard radiometer.
For this reason commercially available thermopile pyrheliometers with a flat detector and
a window can only be first-class.

From first class to secondary standard, the achievable accuracy improves by a factor 2.

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3 Specifications of DR01 / DR02 / DR03

3.1 Specifications

DR01 measures the solar radiation received by a plane surface from a from a 5 ° full field
of view angle and a 1 ° slope angle, i.e. the acceptance function recommended by WMO.
This quantity, expressed in W/m2, is called ‘direct’ solar radiation or direct normal
irradiance (DNI). DNI can be used to calculate sunshine duration. Working completely
passive, using a thermopile sensor, DR01 generates a small output voltage proportional
to this flux. It can only be used in combination with a suitable measurement system and
a solar tracker to keep it continuously aimed at the sun. The window assembly contains a
heater which may be activated to prevent dew deposition. The instrument is classified
according to ISO 9060 and should be used in accordance with the recommended
practices of ISO, IEC, WMO and ASTM.

DR02 and DR03 are fast-response versions of DR01. DR03 is a compact version of DR02.

Table 3.1.1 Specifications of DR01 / DR02 / DR03 (continued on next pages)

DR01 / DR02 / DR03 MEASUREMENT SPECIFICTIONS:
LIST OF CLASSIFICATION CRITERIA OF ISO 9060*

ISO classification (ISO 9060: 1990)

first class pyrheliometer

WMO performance level (WMO-No-8,
seventh edition 2008)

good quality pyrheliometer

Response time (95 %)

DR01: 12 s (nominal)
DR02: 2 s (nominal)
DR03: 2 s (nominal)

Zero offset (response to 5 K/h
change in ambient temperature)

< ± 1 W/m2
Non-stability

< ± 0.5 % change per year

Non-Linearity

< ± 0.3 % (100 to 1000 W/m2)

Full field of view angle

5 °

Slope angle

1 °

Limit angle

4 ° (follows from full field of view angle and slope angle)

Spectral selectivity

< ± 1 % (0.35 to 1.5 x 10

-6

m)

Temperature response

< ± 1 % (-10 to +40 °C)
< ± 0.4 % (-30 to +50 °C)**

** with correction in dataprocessing if opted for internal
temperature sensor + temperature dependence
characterisation (see options)

Tilt response

< ± 0.5 % (0 to 90 ° at 1000 W/m2)

*For the exact definition of pyrheliometer ISO 9060 specifications see the appendix.

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Table 3.1.1 Specifications of DR01 / DR02 / DR03 (continued)

ADDITIONAL SPECIFICATIONS

Measurand

direct solar radiation
with the acceptance function recommended by WMO

Measurand in SI radiometry units

irradiance in W/m2

Optional measurand

sunshine duration

Measurement range

0 to 4000 W/m-2

Spectral range (50 % transmission
points)

200 to 4000 x 10-9 m
Sensitivity range

7 to 15 x 10-6 V/(W/m2)

Sensitivity (nominal)

10 x 10-6 V/(W/m2)

Rated operating temperature range

-40 to +80 °C

Rated operating relative humidity range

0 to 100 %

Sensor resistance range

DR01: 400 to 500 Ω
DR02: 150 to 250 Ω
DR03: 150 to 250 Ω

Required sensor power

zero (passive sensor)
see also heated window assembly

Expected voltage output

application under natural solar radiation: -0.1 to + 30
x 10-6 V

Measurement function / required
programming

E = U/S

Optional measurement function /
required programming for correction of
sensitivity as a function of instrument
body temperature

E = U/(S0·(a·T²+b·T+c))

Measurement function / required
programming for sunshine duration

if E > 120 W/m2 then SD = 1 else SD = 0

Required readout

1 differential voltage channel or 1 single ended
voltage channel, input resistance > 106 Ω

Optional readout

1 temperature channel in case optional temperature
sensor is present and used

Standards governing use of the
instrument

- WMO-No. 8; Guide to Meteorological Instruments
and Methods of Observation, chapter 7, measurement
of radiation, 7.2 measurement of direct solar radiation

- ASTM G183 - 05 Standard Practice for Field Use of
Pyranometers, Pyrheliometers and UV Radiometers

- WCRP - 121, WMO/TD-No. 1274:
BSRN operations manual version 2.1-2005

- WMO-No. 8; Guide to Meteorological Instruments
and Methods of Observation, chapter 8, measurement
of sunshine duration, 8.2.1 pyrheliometric method

Total sensor length including cap

DR01: 380 x10-3 m
DR02: 380 x10-3 m
DR03: 286 x10-3 m

Standard cable length (see options)

5 m

Cable diameter

5.3 x 10-3 m

Cable gland: cable diameter range

accepts cable diameters from 2.5 to 6.5 x 10-3 m

Cable replacement

cable can be removed and installed by the user
provided that the cable is sealed at the sensor side
against humidity ingress. Consult Hukseflux for
instructions or use Hukseflux-supplied parts

Mounting

DR01, DR02, DR03: mounting with 2 clamps around
the pyrheliometer tube Ø 38 x 10-3 m,
DR01, DR02: clamp to clamp distance of 214 x 10-3 m
max.
DR03: clamp to clamp distance of 120 x 10-3 m max.

.

.

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Table 3.1.1 Specifications of DR01 / DR02 / DR03 (continued)

IP protection class

IP67

Desiccant

Two bags of silica gel, 0.5 g, (35 x 20) x 10-3 m

Recommended desiccant replacement
interval

2 years
(typically at the moment of calibration)

Humidity indicator

blue when dry, pink when humid

SHIPPING

Gross weight including 5 m cable

1.0 kg

Net weight including 5 m cable

DR01: 0.9 kg
DR02: 0.9 kg
DR03: 0.8 kg

Packaging

box of (430x105x105) x 10-3 m

TRACKING AND ALIGNMENT

Required tracking

the instrument must be pointed at the sun centre

Required alignment

the pyrheliometer and the tracker should be aligned
using the pyrheliometer sight

Rated misalignment interval
(without impact on measurement
accuracy)

DR01: ± 0.5 °
DR02: ± 0.5 °
DR03: ± 0.3 °
from the sun centre, using the pyrheliometer sight as
a reference

Sight resolution

DR01: < 0.2 °
DR02: < 0.2 °
DR03: < 0.4 °
lightspot projection < 25 % off target hole

Sight sensitivity

DR01: 4 x 10-3 m/°
DR02: 4 x 10-3 m/°
DR03: 2 x 10-3 m/°

WINDOW ASSEMBLY WITH HEATER

Window assembly with heater

12 VDC, 0.5 W

Heater operation

the heater is not necessarily switched on;
recommended operation is to activate the heater
when the sun is below the horizon

Heater resistance

272 Ω

Steady state zero offset caused by 0.5W
heating

< 1 W/m2

Optional high power operation of the
heater to rapidly remove frost

24 VDC, 2 W

Steady state zero offset caused by high
power 2 W heating

< 4 W/m2

CALIBRATION
Calibration traceability

to WRR

Calibration hierarchy

from WRR through ISO 9059, applying a correction to
reference conditions

Calibration method

indoor comparison to a reference pyrheliometer

Calibration uncertainty

< 1.2 % (k = 2)

Recommended recalibration interval

2 years

Reference conditions

20 °C, horizontal mounting , irradiance level 1000
W/m2

Validity of calibration

based on experience the instrument sensitivity will not
change during storage. During use under exposure to
solar radiation the instrument “non-stability”
specification is applicable.

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Table 3.1.1 Specifications of DR01/DR02/DR03 (started on previous pages)

MEASUREMENT ACCURACY

Uncertainty of the measurement

statements about the overall measurement
uncertainty can only be made on an individual basis.
See the chapter on uncertainty evaluation

WMO ESTIMATE OF ACHIEVABLE MEASUREMENT UNCERTAINTY

Minute totals

± 1.8 % (k = 2)
(under typical conditions, well maintained, not taking
calibration uncertainty into account)

Hourly totals

± 1.5 % (k = 2)
(under typical conditions, well maintained, not taking
calibration uncertainty into account)

Daily totals

± 1.0 % (k = 2)
(under typical conditions, well maintained, not taking
calibration uncertainty into account)

VERSIONS / OPTIONS

Internal temperature sensor

measuring the body temperature:
version code = T1 for Pt100 DIN class A,
version code = T2 for thermistor 10 kΩ at 25 °C

longer cable, in multiples of 5 m, cable
lengths above 20 m in multiples of 10 m

option code = total cable length

Temperature dependence
characterisation

option code = TRC
< ± 1 % (-10 to +40 °C)

< ± 0.4 % (-30 to +50 °C) with correction in
dataprocessing

Improved temperature response

includes TRC
option code = ITR
< ± 0.5 % (-20 to +50 °C)

< ± 0.4 % (-30 to +50 °C) with correction in
dataprocessing

Adapted sensitivity range

DR01 only: the sensitivity range can be adapted to
customer requirements (to a lower range only)
option code = lower end - higher end of the allowed
range x 10-6 V/(W/m2)

Chassis connector and cable with
connector

M16 panel connector, male thread, 10-pole
Cable with M16 straight connector, female thread, 10­pole
option code = C

ACCESSORIES

Protection cap

spare protection cap

Bags of silica gel for desiccant

set of 5 bags in an air tight bag
option code = DC01

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3.2 Dimensions of DR01 & DR02

Figure 3.2.1 Dimensions of DR01 and DR02 in x 10-3 m. For DR03 dimensions see the
dedicated chapter on DR03.

380

215

50

Ø 38

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4 Standards and recommended practices

for use

Pyrheliometers are classified according to the ISO 9060 standard and the WMO-No. 8
Guide to Meteorological Instruments and Methods of Observation. In any application the
instrument should be used in accordance with the recommended practices of ISO, IEC,
WMO and / or ASTM.

4.1 Classification standard

Table 4.1.1 Standards for pyrheliometer classification. See the appendix for definitions

of pyrheliometer specifications, and a table listing the specification limits.

STANDARDS FOR INSTRUMENT CLASSIFICATION

ISO STANDARD

EQUIVALENT
ASTM STANDARD

WMO

ISO 9060:1990
Solar energy -- specification and
classification of instruments for
measuring hemispherical solar and
direct solar radiation

Not available

WMO-No. 8; Guide to
Meteorological Instruments
and Methods of Observation,
chapter 7, measurement of
radiation, 7.2 measurement
of direct solar radiation

4.2 General use for solar radiation measurement

Table 4.2.1 Standards with recommendations for instrument use in solar radiation

measurement

STANDARDS FOR INSTRUMENT USE FOR DIRECT SOLAR RADIATION

ISO STANDARD

EQUIVALENT
ASTM STANDARD

WMO

Not applicable

ASTM G183 - 05
Standard Practice for Field
Use of Pyranometers,
Pyrheliometers and UV
Radiometers

WMO-No. 8; Guide to
Meteorological Instruments
and Methods of Observation,
chapter 7, measurement of
radiation, 7.2 measurement
of direct solar radiation

WCRP - 121, WMO/TD-No.
1274: BSRN operations
manual version 2.1-2005

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4.3 General use for sunshine duration measurement

According to the World Meteorological Organization (WMO, 2003), sunshine duration
during a given period is defined as the sum of that sub-period for which the direct solar
irradiance exceeds 120 W/m2.
WMO has approved the “pyrheliometric method” to estimate sunshine duration from
pyrheliometer measurements (Chapter 8 of the WMO Guide to Instruments and
Observation, 2008). This implies that pyrheliometers may be used, in combination with
appropriate software to determine the threshold of 120 W/m2, to measure sunshine
duration.

Table 4.3.1 Standards with recommendations for instrument use in sunshine duration
measurement

STANDARDS FOR INSTRUMENT USE FOR SUNSHINE DURATION

WMO

WMO-No. 8; Guide to Meteorological Instruments and Methods of Observation, chapter 8,
measurement of sunshine duration, 8.2.1 Pyrheliometric Method

4.4 Specific use in meteorology and climatology

The World Meteorological Organization (WMO) is a specialised agency of the United
Nations. It is the UN system's authoritative voice on the state and behaviour of the
earth's atmosphere and climate. WMO publishes WMO-No. 8; Guide to Meteorological
Instruments and Methods of Observation, in which a table is included on “level of
performance” of pyrheliometers. Nowadays WMO conforms itself to the ISO classification
system.

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5 Installation of pyrheliometers

5.1 Site selection and installation

Table 5.1.1 Recommendations for installation of pyrheliometers

Location

The horizon should be as free from obstacles as
possible. Ideally there should be no objects between
the course of the sun and the instrument

Mechanical mounting / thermal insulation

preferably use the tube for clamping the instrument. A
pyrheliometer is sensitive to thermal shocks. Do not
mount the instrument on objects that become very
hot (black coated metal plates).

Performing a representative
measurement

the pyrheliometer measures the solar radiation in a
limited field of view. A representative measurement
requires that the instrument is accuractely pointing
towards the sun centre. A maximum deviation of
better than 0.75 ° is allowed (for DR01 and DR02 ±

0.5 ° relative to the pyrheliometer sight alignment, for
DR03 ± 0.3 ° ) before it results in measurement
errors.
Use the sight of the pyrheliometer as a reference.
See the chapter on uncertainty evaluation.

5.2 Installation of the protection cap

The protection cap can be installed and removed using a hex key (size 2.5 x 10-3 m).

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5.3 Electrical connection

In order to operate, a pyrheliometer should be connected to a measurement system,
typically a so-called datalogger. DR01 employs a passive sensor that does not need any
power. In case the heater is used, it consumes 1.5 W at 12 VDC.
Cables generally act as a source of distortion, by picking up capacitive noise. We
recommend keeping the distance between a datalogger or amplifier and the sensor as
short as possible. For cable extension, see the appendix on this subject.

The wiring electrical connection of your instrument can be found on its product
certificate.

Table 5.3.1 The electrical connection of DR01. In the standard DR01, only the signal and
heater wires are used. The table also shows connection of optional versions T1 and T2.
The heater is not necessarily used. The temperature sensor is not necessarily used.

PIN

WIRE

DR01

DR01-T1

DR01-T2

1

Red Pt100 [+]

10 kΩ thermistor [+]

2

Brown

Pt100 [+]

10 kΩ thermistor [+]

3

Yellow

Pt100 [−]

10 kΩ thermistor [−]

4

Blue Pt100 [−]

10 kΩ thermistor [−]

5

Pink

heater

heater

heater

6

Grey

heater

heater

heater

7

Green

signal [−]

signal [−]

signal [−]

8

White

signal [+]

signal [+]

signal [+]

9

Black

ground

ground

ground

Note 1: Pt100’s of optional version T1 may be connected in a 3-wire or 4-wire
configuration.
Note 2: 10 kΩ thermistors of optional version T2 are usually connected in a 2-wire
configuration.
Note 3: the heater is not necessarily connected. In case it is connected, the polarity of
the connection is not significant.
Note 4: signal wires are insulated from ground wire and from the sensor body. Insulation
resistance is tested during production and larger than 1 x 106 Ω.
Note 5: Ground is connected to the instrument body and the shield of the cable.

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Figure 5.3.2 Electrical diagram showing the internal wiring of DR01 and options with
body temperature measurement. The shield is connected to the instrument body.

5.4 Requirements for data acquisition / amplification

The selection and programming of dataloggers is the responsibility of the user. Please
contact the supplier of the data acquisition and amplification equipment to see if
directions for use with the DR01 are available. In case programming for similar
instruments is available, this can typically also be used. The irradiance signal of DR01
can usually be treated in the same way as other thermopile pyrheliometers and
pyranometers. Pyrheliometers usually have the same programming as heat flux sensors.

Table 5.4.1 Requirements for data acquisition and amplification equipment for DR01 in
the standard configuration

Capability to measure small voltage
signals

preferably: 5 x 10-6 V uncertainty
Minimum requirement: < 20 x 10-6 V uncertainty
(valid for the entire expected temperature range of the
acquisition / amplification equipment)

Capability for the data logger or the
software

to store data, and to perform division by the sensitivity to
calculate the solar irradiance.
E = U/S (Formula 0.1)

Data acquisition input resistance

> 1 x 106 Ω

Open circuit detection
(WARNING)

open-circuit detection should not be used, unless this is done
separately from the normal measurement by more than 5
times the sensor response time and with a small current
only. Thermopile sensors are sensitive to the current that is
used during open circuit detection. The current will generate
heat, which is measured and will appear as an offset.

Optional heating

the heater is not necessarily switched on; recommended
operation is to activate the heater when the sun is below the
horizon. Heating power is 12 VDC, 0.5 W at 12 VDC (the
heater is not necessarily active). Some users are operating
the heater at 24 V and 2 W to rapidly remove frost.

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6 Making a dependable measurement

6.1 The concept of dependability

A measurement with a pyrheliometer is called “dependable” if it is reliable, i.e. measuring
within required uncertainty limits, for most of the time and if problems, once they occur,
can be solved quickly.

The requirements for a measurement with a pyrheliometer may be expressed by the user
as:

 required uncertainty of the measurement (see following paragraphs)
 requirements for maintenance and repairs (possibilities for maintenance and repair

including the effort to be made and the processing time)

 a requirement to the expected instrument lifetime (until it is no longer feasible to

repair)

It is important to realise that the uncertainty of the measurement is not only determined
by the instrument but also by the way it is used. See also ISO 9060 note 5. In case of
pyrheliometers, the measurement uncertainty as obtained during outdoor measurements
is a function of:

 the instrument class
 the calibration procedure / uncertainty
 the duration of instrument employment under natural sunlight (involving the

instrument stability specification)

 the measurement conditions (such as tilting, ventilation, shading, instrument

temperature)

 maintenance (cleaning of the window and verification of the alignment accuracy)
 the environmental conditions (such as atmospheric aerosol content, ambient air

temperature, position of the sun, presence of clouds, horizon, representativeness of
the location)*

Therefore, ISO 9060 says, “statements about the overall measurement uncertainty under

outdoor conditions can only be made on an individual basis, taking all these factors into
account”.

* defined at Hukseflux as all factors outside the instrument that are relevant to the
measurement such as the cloud cover (presence or absence of direct radiation), sun
position, the local horizon (which may be obstructed). The environmental conditions also
involve the question whether or not the measurement at the location of measurement is
representative of the quantity that should be measured. For pyrheliometers the spatial
distribution of circumsolar radiation, which is generated by optical scattering of direct
solar radiation of the sun, may be included in uncertainty estimates. There is a
contribution only in case there is a mismatch between the pyrheliometer’s acceptance
function and the acceptance function defined for the measurand.

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6.2 Reliability of the measurement

A measurement is reliable if it measures within required uncertainty limits for most of the
time. We distinguish between two causes of unreliability of the measurement:

 related to the reliability of the pyrheliometer and its design, manufacturing,

calibration (hardware reliability).

 related to the reliability of the measurement uncertainty (measurement reliability),

which involves hardware reliability as well as condition of use.

Most of the hardware reliability is the responsibility of the instrument manufacturer.
The reliability of the measurement however is a joint responsibility of instrument
manufacturer and user. As a function of user requirements, taking into account
measurement conditions and environmental conditions, the user will select an instrument
of a certain class, and define maintenance support procedures.

In many situations there is a limit to a realistically attainable accuracy level. This is due
to conditions that are beyond control once the measurement system is in place. Typical
limiting conditions are:

 the measurement conditions, for instance when working at extreme temperatures

when the instrument temperature is at the extreme limits of the rated temperature
range.

 the environmental conditions, for instance when installed at a sub-optimal

measurement location with obstacles in the path of the sun.

The measurement reliability can be improved by maintenance support. Important aspects
are:

 window fouling by deposition of dust, dew, rain or snow. Fouling results in undefined

measurement uncertainty (sensitivity and acceptance function are no longer defined).
This should be solved by regular inspection and cleaning.

 sensor instability. Maximum expected sensor aging is specified per instrument as its

non-stability in [% change / year]. In case the sensor is not recalibrated, the
uncertainty of the sensitivity gradually will increase. This is solved by regular
recalibration.

 moisture condensing under the pyrheliometer window resulting in a slow change of

sensitivity (within specifications). This is solved by regular replacement of desiccant
or by maintenance (drying the entire sensor). For pyrheliometers extra desiccant (in
a set of 5 bags in an air tight bag) is available.

Another way to improve measurement reliability is to introduce redundant sensors.

 The use of redundant instruments allows remote checks of one instrument using the

other as a reference, which leads to a higher measurement reliability.

 Data can also be compared to measurements by local meteorological stations.
 DNI data can often be compared to pyranometer measurements (global irradiance

and diffuse), assessing the uncertainty by looking if the totals match up.

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6.3 Speed of repair and maintenance

Dependability is not only a matter of reliability but also involves the reaction to
problems; if the processing time of service and repairs is short, this contributes to the
dependability.

Hukseflux pyrheliometers are designed to allow easy maintenance and repair. The main
maintenance actions are:

 replacement of desiccant
 replacement of cabling

For optimisation of dependability a user should:

 estimate the expected lifetime of the instrument
 design a schedule of regular maintenance
 design a schedule of repair or replacement in case of defects

When operating multiple instruments in a network Hukseflux recommends keeping
procedures simple and having a few spare instruments to act as replacements during
service, recalibrations and repair.

6.4 Uncertainty evaluation

The uncertainty of a measurement under outdoor or indoor conditions depends on many
factors, see paragraph 1 of this chapter. It is not possible to give one figure for
pyrheliometer measurement uncertainty. The work on uncertainty evaluation is “in
progress”. There are several groups around the world participating in standardisation of
the method of calculation. The effort aims to work according to the guidelines for

uncertainty evaluation (according to the “Guide to Expression of Uncertainty in
Measurement” or GUM).

6.4.1 Definition of the measurand

DR01 measures direct solar radiation with an acceptance function as recommended by
WMO (see also the appendix on the terminology).

In most measurements related to meteorology, solar energy resource assessment and PV
system performance monitoring, the required measurand equals the DR01 measurand.
In that case the acceptance function is perfect and there is no contribution of the
circumsolar radiation to the measurement uncertainty. However, in case the required
measurand acceptance function is different from that recommended by WMO, for
instance when estimating the input to Concentrated PV panels (CPV), this leads to
additional measurement uncertainty. See the next paragraph of an idea of the order of
magnitude.

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6.4.2 Contributions from circumsolar radiation

DR01 measures by definition direct solar radiation with an acceptance function as
recommended by WMO. (see also the appendix on the terminology). The measurement
includes a certain amount of circumsolar radiation.

Table 6.4.2.1 contributions from the circumsolar radiation to the DNI measurement with
a pyrheliometer with a 5 ° full field of view angle. The contribution is estimated for
different aerosol types, different amounts of aerosol and different solar zenith angles.
The total amount of aerosol is defined by spectral optical thickness at a wavelength of
550 x 10-9 m. Optical thicknesses are 0.05, 0.2 and 0.4 respectively. Corresponding
Linke turbidity factors are 1.8, 3.4 and 5.4 respectively. Desert-type environments, not
in this table, are in between urban and continental. Source: adaptation of ISO 1959,
Annex A, Table A1

ATMOSPHERIC
AEROSOL

SOLAR
ZENITH
ANGLE

DNI FROM THE
SUN

solar disk only

CIRCUMSOLAR
RADIATION

as percentage of DNI
when measured with
acceptance function
recommended by
WMO

[type]

[amount]

[°]

[W/m2]

[%]

urban

low

30
985

0.1

medium

872

0.3

high

746

0.5

low

70
736

0.1

medium

555

0.5

high

389

1.2

continental
(background)

low

30
979

0.4

medium

851

0.8

high

707

1.8

low

70
735

0.7

medium

514

2.4

high

328

4.1

maritime

low

30
972

0.7

medium

826

2.8

high

668

5.2

low

70
711

1.6

medium

473

6.6

high

275

12.9

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6.4.3 Instrument classification, and approaches to uncertainty evaluation

The standard covering instrument specification, ISO 9060, defines pyrheliometer
classification in 3 categories or classes, according to their quality of manufacture and
level of quality assurance during production.

An “accuracy class” is defined according to the International Vocabulary of Metrology,

VIM paragraph 4.25, as a class of measuring instruments or measuring systems that
meet stated metrological requirements that are intended to keep measurement errors or
instrumental uncertainties within specified limits under specified operating conditions.

[2]

Instrument manufacturers can only supply an instrument according certain specifications,
with a certain initial calibration uncertainty. They are not in control of the other factors
determining the measurement uncertainty. This is the user’s own responsibility.

When making an uncertainty evaluation, the general approach is laid down in GUM. The
link between the classification and GUM is specified in VIM paragraph 2.29: a way to
obtain non-statistical, type B evaluation of measurement uncertainty is “obtained from
the accuracy class of a verified measuring instrument”.

A user of solar radiation sensors therefore has several options:

1) To make a full analysis according to GUM, and all local circumstances; the latter is
found in the following paragraph.

2) to use a generalised uncertainty evaluation based on analogy of instrument class,
calibration, maintenance and environmental conditions.

6.4.4 Evaluation of measurement uncertainty under outdoor conditions

Hukseflux actively participates in the discussions about pyrheliometer measurement
uncertainty; we also provide spreadsheets, reflecting the latest state of the art, to assist
our users in making their own evaluation. Application of this spread sheet is at the user’s
own risk. The input to the assessment is summarised:

1) The formal evaluation of uncertainty should be performed in accordance with ISO 98-3
Guide to the Expression of Uncertainty in Measurement, GUM.

2) The specifications of the instrument according to the list of ISO 9060 classification of
pyranometers and pyrheliometers are entered as limiting values of possible errors, to be
analysed as type B evaluation of standard uncertainty per paragraph 4.3.7. of GUM. A
priori distributions are chosen as rectangular.

3) A separate estimate has to be entered to allow for estimated uncertainty due to the
instrument maintenance level.

4) The calibration uncertainty has to be entered. Please note that Hukseflux calibration
uncertainties are lower than those of alternative equipment. These uncertainties are
entered in measurement equation (equation is usually Formula 0.1: E = U/S), either as
an uncertainty in E (zero offsets, directional response) in U (voltage readout errors)
or in S (tilt error, temperature dependence, calibration uncertainty).

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5) In uncertainty analysis for pyrheliometers, the location and date of interest is entered.
The course of the sun is then calculated, and the direct and diffuse components are
estimated, based on a model.

6) In uncertainty analysis for modern pyrheliometers: tilt dependence often is so low that
one single typical observation may be sufficient.

7) In case of special measurement conditions, typical specification values are chosen.
These should for instance account for the measurement conditions and environmental
conditions (clear sky / cloudy, working temperature range).

8) Among the various sources of uncertainty, some are “correlated”; i.e. present during
the entire measurement process, and not cancelling or converging to zero when
averaged over time; the off-diagonal elements of the covariance matrix are not zero.
Paragraph 5.2 of GUM.

9) Among the various sources of uncertainty, some are “uncorrelated”; cancelling or
converging to zero when averaged over time; the off-diagonal elements of the covariance
matrix are zero. Paragraph 5.1 of GUM.

10) Among the various sources of uncertainty, some are “not included in analysis”; this
applies for instance to the spectral response for pyranometers and pyrheliometers
because it is already taken into account in the calibration process.

11) in case the required measurand acceptance function is different from that
recommended by WMO, for instance when estimating the input to Concentrated PV
panels (CPV), this leads to additional measurement uncertainty.

The following two tables show results by Hukseflux and WMO; the latter without entering
calibration uncertainty.

Table 6.4.4.1 Preliminary estimate of the achievable uncertainty of measurements with
first class pyrheliometers. The estimate is based on typical pyrheliometer properties and
a typical calibration uncertainty, for sunny, clear sky days and well maintained stations,
without uncertainty loss due to lack of maintenance, circumsolar radiation and due to
instrument fouling. The table specifies expanded uncertainties with a coverage factor of 2
and confidence level of 95 %.
Estimates are based on 1 s sampling. IMPORTANT NOTE: there is no international
consensus on uncertainty evaluation of pyrheliometer measurements, so this table
should not be used as a formal reference. The uncertainty hardly shows any dependence
of time of day or season. (contrary to pyranometers).The measurement around solar
noon is more accurate because of the contribution of absolute uncertainty sources.

Pyrheliometer
class
(ISO 9060)

Season

AOD

uncertainty
minute totals
at solar noon

uncertainty
hourly totals
at solar noon

uncertainty
daily totals

first class

summer

mid-latitude

2.8 %

2.8 %

2.9 %

pole

2.8 %

2.8 %

2.8 %

winter

mid-latitude

2.8 %

2.8 %

2.9 %

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Table 6.4.4.2 Estimate of achievable uncertainties of measurements with first class
pyrheliometers according to WMO-No.-8, seventh edition, 2008. Copy from WMO Guide

7.2.1: The estimated uncertainties are based on the following assumptions: (a)
Instruments are well-maintained, correctly aligned and clean; (b) 1 min and 1 h figures
are for clear-sky irradiances at solar noon; (c) Daily exposure values are for clear days at
mid-latitudes. IMPORTANT NOTE: According to 7.3.2.5 the achievable uncertainty does
not include any calibration errors. IMPORTANT NOTE: Achievable accuracy is not part of
the GUM vocabulary.

Interval

Achievable uncertainty

Achievable uncertainty (95% confidence
level) daily totals

± 1.0 %

Achievable uncertainty (95% confidence
level) hourly totals

± 1.5 %

Achievable uncertainty (95% confidence
level) minute totals

± 1.8 %

6.4.5 Calibration uncertainty

Our latest calibration method results in an uncertainty of the sensitivity of less than

1.2 %. The user may receive an instrument with a lower uncertainty. See the calibration
report for the exact value.

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7 Maintenance and trouble shooting

7.1 Recommended maintenance and quality assurance

DR01 is typically used for high-accuracy measurements and cannot measure reliably at a
low level of maintenance. As a general rule this means that regular cleaning of the
window and visual inspection of alignment accuracy combined with a critical review of the
measured data, preferably checking against other measurements, is the preferred way to
obtain a reliable measurement.

Table 7.1.1 Recommended maintenance of DR01. If possible the data analysis, tracker
inspection and cleaning (1 and 2) should be done on a daily basis.

MINIMUM RECOMMENDED PYRHELIOMETER MAINTENANCE

INTERVAL

SUBJECT

ACTION

1

0.5 week

cleaning

use a soft cloth to clean the window of the instrument,
persistent stains can be treated with soapy water or alcohol

tracking

Inspect tracking and alignment, make adjustments if
necessary

2

1 week

data analysis

compare measured data to maximum possible / maximum
expected irradiance and to other measurements nearby
(redundant instruments). Also historical seasonal records can
be used as a source for expected values. Analyse night time
signals. These may be slightly positive due to heating. Look
for any patterns and events that deviate from what is normal
or expected.

3

6 months

inspection

inspect cable quality, inspect cable glands, inspect mounting
position, inspect cable, clean instrument, clean cable, inspect
levelling, inspect mounting connection, inspect interior of
window for condensation, inspect desiccant

4

2 years

desiccant
replacement

desiccant replacement

5 recalibration

recalibration by side-by-side comparison to a higher standard
instrument in the field according to ISO 9059

6 lifetime
assessment

judge if the instrument should be reliable for another 2 years,
or if it should be replaced

7

6 years

parts
replacement

if applicable / necessary replace the parts that are most
exposed to weathering; cable, cable gland.
NOTE: use Hukseflux approved parts only.

8 internal
inspection

if applicable: open instrument and inspect / replace o-rings;
dry internal cavity around the circuit board

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7.2 Trouble shooting

Table 7.2.1 Trouble shooting for DR01

The sensor
does not give
any signal

Check the electrical resistance of the sensor between the green
(-) and white (+) wire. Use a multimeter at the 1000 Ω range. Measure the sensor
resistance first with one polarity, than reverse the polarity. Take the average
value. The typical resistance of the wiring is 0.1 Ω/m. Typical resistance should be
the typical sensor resistance of 400 to 500 Ω (150 to 250 Ω for DR02 and DR03)
plus 1.5 Ω for the total resistance of two wires (back and forth) of each 5 m.
Infinite resistance indicates a broken circuit; zero or a low resistance indicates a
short circuit.
Check if the sensor reacts to light: put the multimeter at its most sensitive range
of DC voltage measurement, typically the 100 x 10-3 VDC range or lower. Expose
the sensor to strong light source, for instance a 100 W light bulb at the front
window. The signal should read > 2 x 10-3 V now. Darken the sensor either by
putting something over it or switching off the light. The instrument voltage output
should go down and within one minute approach 0 V.
Check the data acquisition by applying a 1 x 10-6 V source to it in the
1 x 10-6 V range.

The sensor
signal is
unrealistically
high or low.

Note that night-time signals may be slightly positive (up to 1 W/m2 at low power,
up to 4 W/m2 at high power) when heating.
Check if the pyrheliometer has a clean window.
Check the tracking accuracy in the presence of sun. The dot projected by the sight
on the target hole should be no more than 100 % off target (the dot has a 2 x 10-3
m diameter, the target hole also has a 2 x 10-3 m diameter; 100 % off target
means that the dot is projected outside the target hole).
Check if the right calibration factor is entered into the algorithm. Please note that
each sensor has its own individual calibration factor, as documented on its
calibration certificate.
Check if the voltage reading is divided by the calibration factor in review of the
algorithm.
Check the condition of the wiring at the logger.
Check the cable condition looking for cable breaks.
Check the range of the data logger; signal can be negative (this could be out of
range) or the amplitude could be out of range.
Check the data acquisition by applying a 1 x 10-6 V source to it in the
1 x 10-6 V range. Look at the output. Check if the output is as expected.
Check the data acquisition by short circuiting the data acquisition input with a 100
Ω resistor. Look at the output. Check if the output is close to 0 W/m2.

The sensor
signal shows
unexpected
variations

Check the presence of strong sources of electromagnetic radiation (radar, radio
etc.)
Check the condition of the shielding.
Check the condition of the sensor cable.
Check if the cable is not moving during the measurement

The
instrument
shows internal
condensation

Arrange to send the sensor back to Hukseflux for diagnosis or find a local qualified
partner to perform diagnostics.

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7.3 Calibration and checks in the field

Recalibration of field pyrheliometers is typically done by comparison in the field to a
reference pyrheliometer. The applicable standard is ISO 9059 “International Standard­Solar Energy- calibration of field pyrheliometers by comparison to a reference
pyrheliometer”.

At Hukseflux an indoor calibration according to the same standard is used.

In case of field comparison; ISO allows use of sensors of the same class. Hukseflux
recommends also using the same model, because an intercomparison of similar
instruments has the advantage that they suffer from the same offsets and contributions
of circumsolar radiation.
ISO recommends to perform field calibration during several days; 2 to 3 days under
cloudless conditions. In order to limit the influence of turbidity and aerosols Hukseflux
suggests to using hourly totals near solar noon.

Hukseflux main recommendations for field intercomparisons are:

1) to take high solar irradiance measurements at solar noon as a reference and not the
entire day.

2) to take a reference of the same brand and type as the field pyrheliometer or a
pyrheliometer of a higher class.

3) to connect both to the same electronics, so that electronics errors (also offsets) are
eliminated.

4) to mount all instruments on the same platform, so that they have the same body
temperature.

8) to correct deviations of more than ± 0.2 %. Lower deviations should be interpreted as
acceptable and should not lead to a revised sensitivity.

7.4 Data quality assurance

Quality assurance can be done by:

 analysing trends in solar irradiance signal
 plotting the measured irradiance against mathematically generated expected values
 comparing irradiance measurements between sites
 analysis of night time signals

The main idea is that one should look out for any unrealistic values. There are programs
on the market that can automatically perform data screening:

See http://www.dqms.com

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8 DR03

8.1 Introduction DR03

DR03 is a high accuracy direct (normal incidence) solar radiation sensor with a short
response time and a relatively small size. DR03’s compact size improves compatibility
with small sized trackers.

Specifications of DR03 can be found in the general specification table.
The specification of DR03 deviates from DR01 in:

 dimensions
 response time
 size
 weight
 required tracking accuracy / rated misalignment range

Figure 8.1.1 DR03 compact fast response first class pyrheliometer

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8.2 Dimensions of DR03

Figure 8.2.1 Overview of DR03:

(1) humidity indicator
(2) sights
(3) aperture tube
(4) protection cap
(5) window assembly with heater
(6) cable gland
(7) cable (standard length 5 metres cable, optional longer cable)

Figure 8.2.2 Dimensions of DR03 in x 10-3 m

1

2

3

2

4

5

6

7

120

Ø 38

286

50

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9 Appendices

9.1 Appendix on cable extension / replacement

The standard sensor cable can be removed and installed by the user provided that the
cable is sealed at the sensor side against humidity ingress. Please consult Hukseflux for
instructions on cable preparation or use Hukseflux-supplied parts.

DR01 is equipped with one cable. Keep the distance between data logger or amplifier and
sensor as short as possible. Cables act as a source of distortion by picking up capacitive
noise. In an electrically “quiet” environment the DR01 cable can however be extended
without problem to 100 meters. If done properly, the sensor signal, although small, will
not significantly degrade because the sensor resistance is very low (so good immunity to
external sources) and because there is no current flowing (so no resistive losses).
Cable and connection specifications are summarised below.

NOTE: the body of DR01 contains connector blocks that can be used for the internal
connection of a new cable. See the chapter on electrical connections. Usually it is easier
to connect a new extended cable inside the pyrheliometer body cable than to make a
good (weatherproof) connection to an existing cable.

Table 9.1.1 Preferred specifications for cable extension of DR01

General

please consult Hukseflux for instructions or use Hukseflux-supplied parts.

Cable

8-wire, shielded, with copper conductors (at Hukseflux 8-wire shielded
cable is used, of which 2 wires are used for signal transmission, 2 for
heating and optionally 2 to 4 for the temperature sensor)

Sealing

sealed at the sensor side against humidity ingress

Core resistance

< 0.1 /m

Outer diameter

± 2.5 to 6.5 x 10-3 m (to fit cable gland)

Length

cables should be kept as short as possible, in any case the total cable
length should be less than 100 m

Outer sheet

specified for outdoor use
(for good stability in outdoor applications)

Connection

either solder the new cable core and shield to the original sensor cable,
and make a waterproof connection using cable shrink, or use gold plated
waterproof connectors. Always connect shield.

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9.2 Appendix on optional chassis connector & cable connector

Table 9.2.1 specification of optional connectors

Chassis connector

M16 panel connector, male thread, 10-pole

Chassis connector type

HUMMEL AG 7.840.200.000 panel connector, front
mounting, short version

Cable connector

M16 straight connector, female thread, 10-pole

Cable connector type

HUMMEL AG 7.810.300.00M straight connector,
female thread, for cable 3 to 6 x 10-3 m, special
version

Connector protection class

IP 67 / IP 69 K per EN 60 529 (connected)

Cable replacement

replacement cables with connector can be ordered
separately from Hukseflux

9.3 Appendix on tools for DR01 / DR02 / DR03

Table 9.3.1 Specifications of tools for DR01/DR02/ DR03

tooling required for protection cap fixation and removal

hex key 2.5 x 10-3 m

tooling required for window assembly and backside fixation
and removal

hex key 3 x 10-3 m
tooling required for cable gland fixation and removal

spanner size 15 x 10-3 m

tooling required for desiccant holder fixation and removal

spanner size 20 x 10-3 m

tooling required for wire fixation and removal
(internal wiring inside DR01 body)

screwdriver blade width 2 x 10-3 m

9.4 Appendix on spare parts for DR01 / DR02/ DR03

 protection cap DR01
 DR01 cable (specify length in multiples of 5 m), sealed at one end
 cable gland DR01
 o-ring DR01

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9.5 Appendix on standards for classification and calibration

Both ISO and ASTM have standards on instrument classification and methods of
calibration. The World Meteorological Organisation (WMO) has largely adopted the ISO
classification system.

Table 9.5.1 Pyrheliometer standardisation in ISO and ASTM.

STANDARDS ON INSTRUMENT CLASSIFICATION AND CALIBRATION

ISO STANDARD

EQUIVALENT ASTM STANDARD

ISO 9060:1990 Solar energy -- Specification
and classification of instruments for measuring
hemispherical solar and direct solar radiation

not available
Comment: work is in progress on a new ASTM
equivalent standard

Comment: a standard “Solar energy --Methods
for testing pyranometer and pyrheliometer

characteristics” has been announced in ISO

9060 but is not yet implemented.

not available
ISO 9846:1993 Solar energy -- Calibration of
a pyranometer using a pyrheliometer

ASTM G167 - 05 Standard Test Method for
Calibration of a Pyranometer Using a
Pyrheliometer

ISO 9847:1992 Solar energy -- Calibration of
field pyranometers by comparison to a
reference pyranometer

ASTM E 824 -10 Standard Test Method for
Transfer of Calibration from Reference to Field
Radiometers

ASTM G207 - 11 Standard Test Method for
Indoor Transfer of Calibration from Reference to
Field Pyranometers

ISO 9059:1990 Solar energy -- Calibration of
field pyrheliometers by comparison to a
reference pyrheliometer

ASTM E 816 Standard Test Method for
Calibration of Pyrheliometers by Comparison to
Reference Pyrheliometers

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9.6 Appendix on calibration hierarchy

The World Radiometric Reference (WRR) is the measurement standard representing the
Sl unit of irradiance. Use of WRR is mandatory when working according to the standards
of both WMO and ISO. ISO9874 states under paragraph 1.3: the methods of calibration
specified are traceable to the WRR. The WMO manual states under paragraph 7.1.2.2:
the WRR is accepted as representing the physical units of total irradiance.

The worldwide homogeneity of the meteorological radiation measurements is guaranteed
by the World Radiation Center in Davos Switzerland, by maintaining the World Standard
Group (WSG) which materialises the World Radiometric Reference.

See www.pmodwrc.ch

The Hukseflux standard is traceable to an outdoor WRR calibration. During the outdoor
calibration the sun is typically at 20 to 60° zenith angle, and the total irradiance at a 700
to 900 W/m2 level.

Table 9.6.1 Calibration hierarchy for pyrheliometers

WORKING STANDARD CALIBRATION AT PMOD / WRC DAVOS

Calibration of working standard pyrheliometers:
Method: ISO 9059, outdoor. This working standard has an uncertainty “uncertainty of

standard”. The working standard has been calibrated under certain “test conditions of the
standard”. The working standard has traceability to WRR world radiometric reference.

CORRECTION OF (WORKING) STANDARD CALIBRATION TO STANDARDISED
REFERENCE CONDITIONS

Correction from “test conditions of the standard” to “reference conditions” i.e. to horizontal
position and 20 °C, using known (working) standard pyrheliometer properties: non linearity,
offsets, temperature dependence). This correction has an uncertainty; “uncertainty of
correction”.
Current practice is not to enter any corrections except for temperature dependence.
At Hukseflux we call the working standard pyrheliometer “standard”.

INDOOR PRODUCT CALIBRATION

Calibration of product, i.e. pyrheliometers:
Method: Calibration according to Hukseflux internal procedure DRC02. This method employs
solar radiation generated by a lamp source.
This calibration has an uncertainty associated with the method.

CALIBRATION UNCERTAINTY CALCULATION

ISO 98-3 Guide to the Expression of Uncertainty in Measurement, GUM Determination of
combined expanded uncertainty of calibration of the product, including uncertainty of the
working standard, uncertainty of correction, uncertainty of the method (transfer error). The
coverage factor must be determined; at Hukseflux we work with a coverage factor k = 2.

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9.7 Appendix on requirements for solar tracking

For a correct measurement the DR01 should be pointed at the sun. It usually mounted
on a solar tracker.Theoretically the alignment accuracy of a pyrheliometer should be
better than the slope angle minus the full angle of the solar disk, i.e within 0.5 °.
However, in practice a wider misalignment interval may be tolerated.
ISO 9059-1990 paragraph 5.3.2 specifies that a misalignment of the slope angle minus

0.25 ° is permitted. With Hukseflux pyrheliometers that would allow 0.75 ° pointing
error, which is rounded off to < 0.7 °.
An independent simulation in the BSRN operations manual figure 4.7 indicates that a
pointing error of < 0.7 ° does not lead to significant measurement errors.

During production, the optical axis of the pyrheliometer is aligned with its sights. In
outdoor operation the tracker is on its turn aligned along the zenith axis with its own
level, and in the azimuth direction with the pyrheliometer sights. The latter is typically
done using the sun as a source. The resolution (i.e. the ability to meaningfully distinguish
between measurement results) of the DR01 and DR02 sights is 0.2 °. This means that if
the pyrheliometer sight is used as a reference, the tracking accuracy should remain
within 0.6 °.

Hukseflux therefore specifies a rated misalignment interval (i.e. without impact on
pyrheliometer measurement accuracy) of ± 0.5 ° from the sun centre using the
pyrheliometer sight as a reference.

The sight resolution of DR03 is 0.4 ° so the rated misalignment interval for DR03 is
± 0.3 ° from the sun centre using the pyrheliometer sight as a reference.

Some trackers employ active control with a sun sensor:

The BSRN operations manual in 2.2.1.1 recommends a tracker with a 4-quadrant sun
sensor. The tracker accuracy is recommended to be < 0.1 °. However, this is not a
requirement for pyrheliometers, which can operate with a 0.75 ° pointing error or
a 0.5 ° detectable misalignment.
Verbal communication with the editor of the BSRN manual, B. Forgan, in October 2015
confirmed that the specified tracking accuracy is a requirement for operation of sun
photometers. The BSRN manual will be adapted to correct this mistake.

In case a sun sensor is used, this sensor typically controls tracking as soon as the direct
solar irradiance is above a certain level. In that case the pyrheliometers should be
aligned with the sun sensor, and the rated solar tracking range, defined for passive
tracking based on calculation, may be relaxed. In case we use a sun sensor with < 0.1 °
misalignment, this is much better than required for pyrheliometers.
Please note that sun sensors must be regularly cleaned to be dependable. The 4­quadrant type sun sensor also needs regular recalibration to make sure that the
individual drift of the 4 quadrants is compensated for.

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9.8 Appendix on meteorological radiation quantities

A pyrheliometer measures irradiance. The time integrated total is called radiant

exposure. In solar energy radiant exposure is often given in W∙h/m2.

Table 9.8.1 Meteorological radiation quantities as recommended by WMO (additional
symbols by Hukseflux Thermal Sensor). POA stands for Plane of Array irradiance. The
term originates from ASTM and IEC standards.

SYMBOL

DESCRIPTION

CALCULATION

UNITS

ALTERNATIVE
EXPRESSION

E↓

downward irradiance

E↓ = E

g

↓ + E

l

↓

W/m2

H↓

downward radiant exposure
for a specified time interval

H↓ = Hg↓ + H

l

↓

J/m2

W∙h/m2

Change of
units

E↑

upward irradiance

E↑ = E

g

↑ + El ↑

W/m2

H↑

upward radiant exposure
for a specified time interval

H↑ = H

g

↑ + Hl ↑

J/m2

W∙h/m2

Change of
units

E

direct solar irradiance
normal to the apparent
solar zenith angle

W/m2

DNI

Direct
Normal
Irradiance

E0

solar constant

W/m2

E

g

↓

h

global irradiance;
hemispherical irradiance on
a specified, in this case
horizontal surface.*

Eg↓ = E cos θh + Ed↓

W/m2

GHI

Global
Horizontal
Irradiance

E

g

↓

t

global irradiance;
hemispherical irradiance on
a specified, in this case
tilted surface.*

E

g

↓ = E∙cos θ

t

+

E

d

↓ t + E

r↑ t

***

W/m2

POA

Plane of
Array

E

d

↓

downward diffuse solar
radiation

W/m2

DHI

Diffuse
Horizontal
Irradiance

E

l

↑, El ↓

upward / downward long­wave irradiance

W/m2
Er↑

reflected solar irradiance

W/m2

E*

net irradiance

E* = E↓ – E↑

W/m2

T↓

apparent surface
temperature**

º C or K

T↑

apparent sky
temperature**

º C or K
SD

sunshine duration

h

θ is the apparent solar zenith angle θh relative to horizontal, θt relative to a tilted surface

g = global, l = long wave, t = tilted *, h = horizontal*
* distinction horizontal and tilted by Hukseflux,
** T symbols introduced by Hukseflux,
*** contributions of E

d

↓ t and E

r↑ t

are E

d

↓ and E

r↑

both corrected for the tilt angle of the

surface

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9.9 Appendix on ISO and WMO classification tables

Table 9.9.1 Classification table for pyrheliometers per ISO 9060 and WMO.

NOTE: WMO specification of response time, zero offset, non-stability and spectral
selectivity are different from that of ISO. WMO does not specify a second class or
moderate quality pyrheliometer. Hukseflux conforms to the ISO limits. WMO also
specifies achievable accuracies. ISO finds this not to be a part of the classification system
because it also involves calibration. Please note that WMO achievable accuracies are for
clear days at mid latitudes and that the uncertainty estimate does not include uncertainty
due to calibration*.

ISO CLASSIFICATION** TABLE

ISO CLASS

SECONDARY
STANDARD

FIRST CLASS

SECOND CLASS
Specification limit

Response time (95 %)

15 s

20 s

30 s

Zero offset (response to 5 K/h in ambient
temperature)

± 1 W/m2

± 3 W/m2

± 6 W/m2

Non stability (change per year)

± 0.5 %

± 1 %

± 2 %
Non linearity (100 to 1000 W/m2)

± 0.2 %

± 0.5 %

± 2 %

Spectral selectivity
(350 to 1 500 x 10-9 m)

± 0.5 %

± 1 %

± 5 %
Temperature response (interval of 50 K)**

± 1 %

± 2 %

± 10 %

Tilt response
(0 to 90 ° at 1000 W/m2)

± 0.2 %

± 0.5 %

± 2 %

Traceability: maintained by periodic
comparison

with primary
standard
pyrheliometer

with secondary
standard
pyrheliometer
or better

with a fist class
pyrheliometer
or better

Full field of view angle (recommended)

5 °

5 °

5 °

Slope angle (recommended)

1 °

1 °

1 °

ISO TRACKING RECOMENDATIONS****

Rated non-alignment interval (without
impact on measurement accuracy) for 1 °
slope angle

< 0.75 ° from
the sun centre

< 0.75 ° from
the sun centre

< 0.75 ° from
the sun centre

CONFORMITY TESTING***

ISO 9060

individual
instrument only:
all specs must
comply
may be qualified
as primary
standard

group
compliance

group
compliance

continued on next page

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started on previous page

ADDITIONAL WMO SPECIFICATIONS (DEVIATING FROM ISO 9060)

WMO CLASS

HIGH QUALITY

GOOD
QUALITY

MODERATE
QUALITY

WMO: response time (95 %)

15 s

30 s

WMO: spectral selectivity
(300 to 3 000 x 10-9 m)

± 0.5 %

± 1 %

Not applicable

WMO: zero offset (response to 5 K/h in
ambient temperature)

± 2 W/m2

± 4 W/m2

Not applicable
WMO: non stability (change per year)

± 0.1 %

± 0.5 %

Not applicable

WMO: achievable accuracy for daily sums*

± 0.5 %

± 1.0 %

Not applicable

WMO: achievable accuracy for hourly sums*

± 0.7 %

± 1.5 %

Not applicable

WMO: achievable accuracy for minute sums*

± 0.9 %

± 1.8 %

Not applicable

WMO: resolution
(smallest detectable change)

± 0.51 W/m2

± 1 W/m2

Not applicable

* WMO 7.2.1: The estimated uncertainties are based on the following assumptions: (a)
instruments are well-maintained, correctly aligned and clean; (b) 1 min and 1 h figures
are for clear-sky irradiances at solar noon; (c) daily exposure values are for clear days at
mid-latitudes. WMO 7.3.2.5: Table 7.5 lists the expected maximum deviation from the
true value, excluding calibration errors.
** At Hukseflux we use the expression ± 1 % instead of a range of 2 %.
*** an instrument is subject to conformity testing of its specifications. Depending on the
classification, conformity compliance can be proven either by group- or individual
compliance. A specification is fulfilled if the mean value of the respective test result does
not exceed the corresponding limiting value of the specification for the specific category
of instrument.
**** ISO 9059 Solar energy - Calibration of field pyrheliometers by comparison to a
reference pyrheliometer paragraph 5.3.2 allows slope angle minus 0.25 °, which is
rounded off to 0.7 °. See also paragraph 2.1 on requirements for tracking.

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9.10 Appendix on definition of pyrheliometer specifications

Table 9.10.1 Definition of pyrheliometer specifications

SPECIFICATION

DEFINITION

SOURCE

Response time
(95 %)

time for 95 % response. The time interval between the instant
when a stimulus is subjected to a specified abrupt change and the
instant when the response reaches and remains within specified
limits around its final steady value.The response time is a measure
of the thermal inertia inherent in the stabilization period for a final
reading.

ISO
9060­1990
WMO

1.6.3

Zero offset b:
(5 K/h in ambient
temperature)

response to 5 K/h change in ambient temperature.
Zero offsets are a measure of the stability of the zero-point.

ISO
9060­1990

Non stability
(change per
year)

percentage change in sensitivity per year. The dependence of
sensitivity resulting from ageing effects which is a measure of the
long-term stability.

ISO
9060­1990

Non linearity
(100 to 1000
W/m2)

percentage deviation from the sensitivity at 500 W/m

2

due to the

change in irradiance within the range of 100 W/m

2

to 1000 W/m2.
Non-linearity has an overlap with directional response, and
therefore should be handled with care in uncertainty evaluation.

ISO
9060­1990

Spectral
selectivity (350
to 1500 x 10-9 m)
(WMO 300 to
3000 x 10-9 m)

percentage deviation of the product of spectral absorptance and
spectral transmittance from the corresponding mean within the
specified spectral range. Spectral selectivity is a measure of the
spectral selectivity of the sensitivity.

ISO
9060­1990

Temperature
response
(interval of 50 K)

percentage deviation of the sensitivity due to change in ambient
temperature within an interval of 50 K the temperature of the
pyrheliometer body.

ISO
9060­1990

Tilt response
(0 ° to 90 ° at
1000 W/m2)

percentage deviation from the sensitivity at 0 ° tilt (horizontal)
due to change in tilt from 0 ° to 90 ° at 1000 W/m

2

irradiance. Tilt
response describes changes of the sensitivity due to changes of
the tilt angle of the receiving surface.

ISO
9060­1990

Sensitivity

the change in the response of a measuring instrument divided by
the corresponding change in the stimulus.

WMO

1.6.3

Spectral range

the spectral range of radiation to which the instrument is
sensitive. For a normal pyrheliometer this should be in the 0.3 to 3
x 10-6 m range. Some pyrheliometers with coloured glass windows
have a limited spectral range.

Hukseflux
Full field of view
angle

(also opening angle) twice the angle between the centre of the
sensor and the view limiting front aperture, 2 arctan (ra/L) with ra
the radius of the aperture at the front window and L the distance
sensor to aperture.

Hukseflux
/ ISO
9060­1990

Slope angle

the angle from the sensor edge to the view limiting front aperture
at the same side, arctan [(ra - rr)/L] with ra the radius of the
aperture, rr the radius of the sensor, and L the distance sensor to
aperture.

Hukseflux
/ ISO
9060­1990

Limit angle

the angle from the sensor edge to the view limiting front aperture
at the opposite side. (ref: IEA SHC #46 and EU FP7 MACC-II
projects, published by Blanc et al. 2014)

Hukseflux
/ ISO
9060­1990

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9.11 Appendix on terminology / glossary

Table 9.11.1 Definitions and references of used terms

TERM

DEFINITION (REFERENCE)

Solar energy
or solar
radiation

solar energy is the electromagnetic energy emitted by the sun. Solar energy is
also called solar radiation and shortwave radiation. The solar radiation incident
on the top of the terrestrial atmosphere is called extra-terrestrial solar radiation;
97 % of which is confined to the spectral range of 290 to 3 000 x 10-9 m. Part of
the extra-terrestrial solar radiation penetrates the atmosphere and directly
reaches the earth’s surface, while part of it is scattered and / or absorbed by the
gas molecules, aerosol particles, cloud droplets and cloud crystals in the
atmosphere. The former is the direct component, the latter is the diffuse
component of the solar radiation. (ref: WMO, Hukseflux)

Hemispherical
solar radiation

solar radiation received by a plane surface from a 180 ° field of view angle (solid
angle of 2 π sr).(ref: ISO 9060)

Global solar
radiation

the solar radiation received from a 180 ° field of view angle on a horizontal
surface is referred to as global radiation. Also called GHI. This includes radiation
received directly from the solid angle of the sun’s disc, as well as diffuse sky
radiation that has been scattered in traversing the atmosphere. (ref: WMO)
Hemispherical solar radiation received by a horizontal plane surface.
(ref: ISO 9060)

Plane-of-array
irradiance

also POA: hemispherical solar irradiance in the plane of a PV array.
(ref: ASTM E2848-11 / IEC 61724)

Direct solar
radiation

radiation received from a small solid angle centred on the sun’s disc, on a given
plane. (ref: ISO 9060)

Terrestrial or
Longwave
radiation

radiation not of solar origin but of terrestrial and atmospheric origin and having
longer wavelengths (3 000 to 100 000 x 10-9 m). In case of downwelling E

l

↓ also

the background radiation from the universe is involved, passing through the
”atmospheric window”. In case of upwelling E

l

↑, composed of long-wave

electromagnetic energy emitted by the earth’s surface and by the gases, aerosols

and clouds of the atmosphere; it is also partly absorbed within the atmosphere.
For a temperature of 300 K, 99.99 % of the power of the terrestrial radiation has
a wavelength longer than 3 000 x 10-9 m and about 99 per cent longer than
5 000 x 10-9 m. For lower temperatures, the spectrum shifts to longer
wavelengths. (ref: WMO)

World
Radiometric
Reference
(WRR)

measurement standard representing the Sl unit of irradiance with an uncertainty
of less than ± 0.3 % (see the WMO Guide to Meteorological Instruments and
Methods of Observation, 1983, subclause 9.1.3). The reference was adopted by
the World Meteorological Organization (WMO) and has been in effect since 1 July

1980. (ref: ISO 9060)

Albedo

ratio of reflected and incoming solar radiation. Dimensionless number that varies
between 0 and 1. Typical albedo values are: < 0.1 for water, from 0.1 for wet
soils to 0.5 for dry sand, from 0.1 to 0.4 for vegetation, up to 0.9 for fresh snow.

Angle of
incidence

angle of radiation relative to the sensor measured from normal incidence (varies
from 0° to 90°).

Zenith angle

angle of incidence of radiation, relative to zenith. Equals angle of incidence for
horizontally mounted instruments

Azimuth angle

angle of incidence of radiation, projected in the plane of the sensor surface.
Varies from 0 ° to 360 °. 0 is by definition the cable exit direction, also called
north, east is + 90 °. (ASTM G113-09)

Sunshine
duration

sunshine duration during a given period is defined as the sum of that sub-period
for which the direct solar irradiance exceeds 120 W/m2. (ref: WMO)

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The IEA SHC #46 and EU FP7 MACC-II projects (Blanc et al. 2014) concluded that the
ISO and WMO definitions are insufficiently clear and suggest the following new and
refined definitions:

Table 9.11.2 Proposed new and not yet formally accepted pyrheliometer-related
definitions as suggested by IEA SHC #46 and EU FP7 MACC-II projects, published by
Blanc et al. 2014, compared to ISO and WMO

TERM

PROPOSED NEW DEFINITION (REFERENCE)

Pyrheliometer

radiometer designed for measuring the irradiance which results from the solar
radiant flux from a well-defined solid angle the axis of which is perpendicular to
the plane receiver surface. (ref: WMO)

Pyrheliometer

a radiometer designed to measure DNI (i.e. including some circumsolar
irradiance). Recommended parameters for the view-limiting geometry are a full
opening angle of 5 °, and a slope angle of 1 °, and therefore a limit angle of 4 °.
(ref: IEA SHC #46 and EU FP7 MACC-II projects, published by Blanc et al. 2014)

Direct solar
radiation

DNI, the solar radiant flux collected by a plane unit surface normal to the axis
pointing towards the centre of the Sun, within an optical angular aperture. This
aperture is characterized by an acceptance function. (ref: IEA SHC #46 and EU
FP7 MACC-II projects, published by Blanc et al. 2014)

Direct solar
radiation

radiation received from a small solid angle centred on the sun’s disc, on a given

plane. (ref: ISO 9060)

Direct solar
radiation
from the Sun

DNI from the Sun, the solar radiant flux collected by a plane unit surface normal
to the axis pointing towards centre of the Sun, within the extent of the solar disk
only (half-angle S = 0.266 ° ± 1.7 %), with a perfect radially symmetric
rectangular acceptance function. (ref: IEA SHC #46 and EU FP7 MACC-II
projects, published by Blanc et al. 2014)

Acceptance
function

the acceptance function of an optical angular aperture: the fraction of the total
radiant flux that is collected by an optical angular aperture, as a function of the
off-axis angles. The geometrically perfect acceptance function is equal to one up
to the slope angle, and equals zero for off-axis angles larger than the limit angle.
(ref: IEA SHC #46 and EU FP7 MACC-II projects, published by Blanc et al. 2014)

Pyrheliometer
acceptance
function

The acceptance function of a pyrheliometer: the fraction of the total radiant flux
that is collected by the combination of sensor and optical angular aperture, as a
function of the off-axis angles. (ref: IEA SHC #46 and EU FP7 MACC-II projects,
published by Blanc et al. 2014)

Opening angle

(also full field of view angle): twice the angle between the centre of the sensor
and the view limiting front aperture. (ref: IEA SHC #46 and EU FP7 MACC-II
projects, published by Blanc et al. 2014)

Limit angle

the angle from the sensor edge to the view limiting front aperture at the opposite
side. (ref: IEA SHC #46 and EU FP7 MACC-II projects, published by Blanc et al.

2014)

Slope angle

the angle from the sensor edge to the view limiting front aperture at the same
side. (ref: IEA SHC #46 and EU FP7 MACC-II projects, published by Blanc et al.

2014)

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9.12 Appendix on literature references

1. Blanc et al. (2014) Direct normal irradiance related definitions and applications; the
circumsolar issue, Solar Energy, Volume December 2014, pp. 561-577

2. ISO (1990), ISO 9060-Solar energy - Specification and classification of instruments for
measuring hemispherical solar and direct solar radiation, first edition

3. ISO / IEC (1995), GUIDE 98-3 Uncertainty of measurement — Part 3: Guide to the
expression of uncertainty in measurement (GUM:1995), also published as JCGM
100:2008, published on internet, accessed 15-JAN-2014

4. JCGM (2008), JCGM 200:2008 International vocabulary of metrology — Basic and
general concepts and associated terms (VIM), published on internet, accessed 15-JAN­2014

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9.13 EC declaration of conformity

We, Hukseflux Thermal Sensors B.V.
Delftechpark 31
2628 XJ Delft
The Netherlands

in accordance with the requirements of the following directive:

2004/108/EC The Electromagnetic Compatibility Directive

hereby declare under our sole responsibility that:

Product model: DR01, DR02, DR03
Product type: Pyrheliometer

has been designed to comply and is in conformity with the relevant sections and
applicable requirements of the following standards:

Emission: EN 61326-1 (2006)
Immunity: EN 61326-1 (2006)
Emission: EN 61000-3-2 (2006)
Emission: EN 61000-3-3 (1995) + A1 (2001) + A2 (2005)
Report: 08C01340RPT01, 06 January 2009

Eric HOEKSEMA
Director
Delft
January 15, 2014

© 2016, Hukseflux Thermal Sensors B.V.

www.hukseflux.com

Hukseflux Thermal Sensors B.V. reserves the right to change specifications without notice.