Hukseflux

Thermal Sensors

USER MANUAL SR05-A1
Analogue second class pyranometer

Copyright by Hukseflux | manual v2316 | www.hukseflux.com | info@hukseflux.com

Warning statements
For proper instrument grounding: use SR05 with its
original factory-made SR05 cable. See chapter ongrounding and use of the shield.
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
Contents
List of symbols
Introduction
1
Ordering and checking at delivery
1.1
Ordering SR05
1.2
Included items
1.3
Quick instrument check2
Instrument principle and theory
3
Specifications of SR05-A1
3.1
Specifications SR05-A1
3.2
Dimensions of SR05-A1
4Standards and recommended practices for use
4.1
Classification standard
4.2
General use for solar radiation measurement
4.3
General use for sunshine duration measurement
4.4
Specific use for outdoor PV system performance testing
4.5
Specific use in meteorology and climatology
5Installation of SR05-A1
5.1
Site selection and installation
5.2
Mounting and levelling SR05
5.3
Installing SR05
5.4
Installing SR05 with its ball levelling and tube mount
5.5
Electrical connection of SR05-A1
5.6
Grounding and use of the shield
5.7
Using SR05-A1’s analogue millivolt ouput
6
Making a dependable measurement
6.1
The concept of dependability
6.2
Reliability of the measurement
6.3
Speed of repair and maintenance
6.4
Uncertainty evaluation
7
Maintenance and trouble shooting
7.1
Recommended maintenance and quality assurance
7.2
Trouble shooting
7.3
Calibration and checks in the field
7.4
Data quality assurance
8
Appendices8.1
Appendix on cable extension / replacement
8.2
Appendix on tools for SR05-A1
8.3
Appendix on spare parts for SR05-A1
8.4
Appendix on standards for classification and calibration
8.5
Appendix on calibration hierarchy
8.6
Appendix on meteorological radiation quantities
8.7
Appendix on ISO and WMO classification tables
8.8
Appendix on definition of pyranometer specifications
8.9
Appendix on terminology / glossary
8.10 EU declaration of conformity

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List of symbols
Quantities

SymbolUnit

Voltage output
Sensitivity
Solar irradiance
Temperature
Electrical resistanceSolar radiant exposure
Time in hours

U
S
E
T
Re
H
h

V
V/(W/m2)
W/m2°CΩW∙h/m2h(see also appendix 8.6 on meteorological quantities)
Subscripts
Not applicable

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Introduction
SR05 series is the most affordable range of pyranometers meeting ISO 9060 secondclass requirements. They are ideal for general solar radiation measurements in (agro-)meteorological networks and PV monitoring systems. SR05’s are easy to mount andinstall. Various outputs are available, both digital and analogue, for ease of integration.
SR05 pyranometer measures solar radiation received by a plane surface, in W/m2, from a
180 o field of view angle. Different configurations are available, depending on its
mounting and the output needed.
SR05 employs a thermopile sensor with black coated surface, one dome and an anodised
aluminium body with visible bubble level. SR05 series has a variety of industry standard
outputs, both digital and analogue:•••

Version SR05-D1A3: digital sensor with Modbus over RS-485 and analogue 0-1 V output
Version SR05-D2A2: digital sensor with Modbus over TTL and analogue 4–20 mA output
Version SR05-A1:
analogue sensor with analogue millivolt output

This user manual covers use of the analogue sensor in the SR05 series range:
SR05-A1. Specifications of this version differ from those of the digital versionsof model SR05: SR05-D1A3 and SR05-D2A2, offering various digital andanalogue outputs. For SR05-D1A3 and SR05-D2A2 use, consult the SR05 series
user manual.
SR05-A1 benefits:•••

Analogue millivolt output: easy implementation
Easy mounting and levelling
Pricing: second class pyranometers finally affordable for large networks

Using the analogue SR05-A1 is easy: the pyranometer can be connected directly tocommonly used data logging systems. The irradiance in W/m2 is calculated by dividing
the SR05-A1 output, a small voltage, by the sensitivity. This sensitivity is provided with
SR05-A1 on its calibration certificate.
The central equation governing SR05-A1 is: E = U/S(Formula 0.1)

Suggested use for SR05:•••

general solar radiation measurements(agro-)meteorological networks
PV power plant monitoring

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Optionally SR05 has a unique ball levelling mechanism with or without tube mount, foreasy installation.

Figure 0.1 On the left SR05-A1 analogue second class pyranometer with bubble level andM12-A cable connector in its standard configuration (3 metre cable standard included); on
the right SR05-A1 with optional ball levelling, for easy mounting and levelling on (non-)horizontal surfaces (included mounting screws not displayed)

Figure 0.2 SR05-A1 analogue second class pyranometer with optional ball levelling andtube mount for easy mounting and levelling on a tube (tube not included)
All SR05 versions should be used in accordance with the recommended practices of ISO,WMO and ASTM.

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The ASTM E2848 “Standard Test Method for Reporting Photovoltaic Non-Concentrator
System Performance” (issued end 2011) confirms that a pyranometer is the preferred
instrument for PV system performance monitoring. SR05-A1 pyranometer complies withthe requirements of this standard. For more information, see our pyranometer selection
guide.
WMO has approved the “pyranometric method” to calculate sunshine duration frompyranometer measurements in WMO-No. 8, Guide to Meteorological Instruments andMethods of Observation. This implies that SR05-A1 may be used, in combination withappropriate software, to estimate sunshine duration. This is much more cost-effective
than using a dedicated sunshine duration sensor. Ask for our application note.

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1

Ordering and checking at delivery

1.1

Ordering SR05

There is one standard configuration for SR05-A1:•
SR05-A1: with analogue millivolt output
standard cable length: 3 metres
Common options are:• longer cable (10, 20 metres). Specify total cable length• extension cable with connector pair (10, 20 metres). Specify total cable length• ball levelling• tube mount with ball levelling (for tube diameters 25 to 40 mm)
Ball levelling and tube mount are suited for retrofitting.
Table 1.1.1 Ordering codes for SR05-A1
VERSIONS OF SR05-A1 (part numbers), without cable
SR05-A1

analogue second class pyranometer, with millivolt output

CABLE FOR SR05, with female M12-A connector at sensor end, non-stripped on other end‘-03’ after SR05 part number‘-10’ after SR05 part number‘-20’ after SR05 part number
LEVELLING OPTIONS FOR SR05

standard cable length: 3 m
cable length: 10 m
cable length: 20 m

BL01
ball levelling, for levelling of SR05
TMBL01
tube mount with ball levelling, for mounting SR05 on a tube
CABLE EXTENSION FOR SR05, with male and female M12-A connectors
C06E-10
C06E-20

cable length: 10 m
cable length: 20 m

An extension cable (with connector pair) can be used in combination with a regular cable(with one connector at sensor end) to make alternative SR05 cable lengths possible.
Example: Cable length needed: 15 m. In this case, it is easiest to buy SR05 with a 20 m
cable and to cut it to desired length.
Example: Cable length needed: 30 m. In this case, it is easiest to buy SR05 with 10 m
cable and a cable extension of 20 m.

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1.2

Included items

Arriving at the customer, the delivery should include:•••

pyranometer SR05-A1
cable of the length as ordered
product certificate matching the instrument serial number

Please store the certificate in a safe place.
When ordering mounting options BL01 or TMBL01 with SR05, the delivery should also
include:•BL01:
oball levellingo
4 mm hex keyo
1 x shimo
2 x M5x20 boltso
2 x M5 nuts•

TMBL01:oball levellingo
4 mm hex keyo
1 x shimo
2 x M5x20 boltso
2 x M5 nutsotube mounto
2 x M5x30 boltso
2 x M5x40 bolts

SR05-A1

SR05-A1 with BL01

SR05-A1 with TMBL01

Figure 1.2.1 From left to right: SR05-A1, SR05-A1 with mounting option BL01, andSR05-A1 with tube mounting option TMBL01(nuts and bolts, tools and certificates are not shown, tube itself is not included)

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1.3

Quick instrument check

A quick test of the instrument can be done by using a simple handheld multimeter and alamp.
1. Check the electrical resistance of the sensor between the grey (-) and white (+) wire.
Use a multimeter at the 200 Ω range. Measure the sensor resistance first with one
polarity, than reverse the polarity. Take the average value. The typical resistance of thewiring is 0.1 Ω/m. The measured resistance should be the typical sensor resistance of 40
to 80 Ω plus 1 Ω for the total resistance of two wires (back and forth) of each 3 m.
Infinite resistance indicates a broken circuit; zero or a low resistance indicates a shortcircuit.
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 0.1 m distance. The signal
should read > 2 x 10-3 V now. Darken the sensor either by putting something over it orswitching off the light. The instrument voltage output should go down and within one
minute approach 0 V.
3. If applicable, remove the optional sun screen, using the hex key (see chapter on
installation of the sun screen). Inspect the bubble level.
4. Inspect the instrument for any damage.

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2

Instrument principle and theory
4
3

5

6

2

1

7
12

11

10

9

8

Figure 2.1 Overview of SR05-A1 (shaded areas in exploded view show ball levelling mountand shim). Numbers 7 to 12 are included when ordering option BL01 or TMBL01:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)

cable (standard length 3 metres, optional longer cable)
connector
bubble level
thermal sensor with black coating
glass dome
sensor bodytube mount (included with TMBL01)
mounting screw (included with BL01 and TMBL01; requires 4 mm hex key)
shim (included with BL01 and TMBL01; needed for ball levelling mount)ball levelling mount (included with BL01 and TMBL01l)
countersunk set screw for levelling adjustment (included with BL01 and TMBL01;
requires 4 mm hex key)(12) opening for Ø 25 to Ø 40 mm tube when using ball levelling and tube mountSR05-A1 manual v2316

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SR05’s scientific name is pyranometer. A pyranometer measures the solar radiation
received by a plane surface from a 180 ° field of view angle. This quantity, expressed in
W/m2, is called “hemispherical” solar radiation. The solar radiation spectrum extends
roughly from 285 to 3000 x 10-9 m. By definition a pyranometer should cover thatspectral range with a spectral selectivity that is as “flat” as possible.
In an irradiance measurement by definition the response to “beam” radiation varies withthe cosine of the angle of incidence; i.e. it should have full response when the solar
radiation hits the sensor perpendicularly (normal to the surface, sun at zenith, 0 ° angle
of incidence), zero response when the sun is at the horizon (90 ° angle of incidence, 90 °zenith angle), and 50 % of full response at 60 ° angle of incidence.
A pyranometer should have a so-called “directional response” (older documents mention“cosine response”) that is as close as possible to the ideal cosine characteristic.
In order to attain the proper directional and spectral characteristics, a pyranometer’s
main components are:•a thermal sensor with black coating. It has a flat spectrum covering the 200 to 50000
x 10-9 m range, and has a near-perfect directional response. The coating absorbs all
solar radiation and, at the moment of absorption, converts it to heat. The heat flows
through the sensor to the sensor body. The thermopile sensor generates a voltage
output signal that is proportional to the solar irradiance.

•

a glass dome. This dome limits the spectral range from 285 to 3000 x 10-9 m (cutting
off the part above 3000 x 10-9 m), while preserving the 180 ° field of view angle.
Another function of the dome is that it shields the thermopile sensor from theenvironment (convection, rain).

Pyranometers can be manufactured to different specifications and with different levels of
verification and characterisation during production. The ISO 9060 - 1990 standard, “Solarenergy - specification and classification of instruments for measuring hemispherical solarand direct solar radiation”, distinguishes between 3 classes; secondary standard (highest
accuracy), first class (second highest accuracy) and second class (third highest
accuracy).
From second class to first class and from first class to secondary standard, the achievableaccuracy improves by a factor 2.

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relative spectral content /response [arbitrary units]

1.2
1

solar radiation

0.8

pyranometer
response

0.6
0.4
0.2
0
100

1000

10000

wavelength [x 10-9 m]

Figure 2.2 Spectral response of the pyranometer compared to the solar spectrum. The
pyranometer only cuts off a negligible part of the total solar spectrum.

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3

Specifications of SR05-A1

3.1

Specifications SR05-A1

SR05-A1 measures the solar radiation received by a plane surface from a 180 o field ofview angle. This quantity, expressed in W/m2, is called “hemispherical” solar radiation.
SR05-A1 offers irradiance in W/m2 as an analogue millivolt output. SR05-A1 is a passive
sensor and does not need a power supply. It can be connected directly to commonlyused data logging systems. The irradiance in W/m2 is calculated by dividing the SR05-A1
output, a small voltage, by the sensitivity. This sensitivity is provided with SR05-A1 on
its calibration certificate.
This user manual covers use of the analogue sensor in the SR05 series range:
SR05-A1. Specifications of this version differ from those of the digital versionsof model SR05: SR05-D1A3 and SR05-D2A2, offering various digital andanalogue outputs. For SR05-D1A3 and SR05-D2A2 use, consult the SR05 series
user manual.
The instrument is classified according to ISO 9060 and should be used in accordance withthe recommended practices of ISO, IEC, WMO and ASTM.
Table 3.1.1 Specifications of SR05-A1 (continued on next pages)
SR05 MEASUREMENT SPECIFICATIONS:LIST OF CLASSIFICATION CRITERIA OF ISO 9060*
ISO classification (ISO 9060: 1990)
WMO performance level (WMO-No. 8,seventh edition 2008)
Response time (95 %)Zero offset a (response to 200 W/m2
net thermal radiation)
Zero offset b (response to 5 K/hchange in ambient temperature)
Non-stability
Non-linearity
Directional response
Spectral selectivity
Temperature response
Tilt response

second class pyranometer
moderate quality pyranometer18 s< 15 W/m2 unventilated< ± 4 W/m2
< ± 1 % change per year
< ± 1 % (100 to 1000 W/m2)< ± 25 W/m2
< ± 5 % (0.35 to 1.5 x 10-6 m)< ± 3 % (-10 to +40 °C)< ± 2 % (0 to 90 ° at 1000 W/m2)*For the exact definition of pyranometer ISO 9060 specifications see the appendix.

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Table 3.1.1 Specifications of SR05-A1 (continued)
SR05-A1 ADDITIONAL SPECIFICATIONS
Measurand
Measurand in SI radiometry units
Optional measurand
Field of view angle
Measurement range
Sensitivity range
Sensitivity (nominal)
Required sensor power
Expected voltage ouput
Measurement function / required
programming
Measurement function / optional
programming for sunshine duration
Rated operating temperature range
Spectral range(20 % transmission points)
Sensor resistance range
Required readout
Irradiance resolution
Standard governing use of the
instrument
Standard cable length (see options)
Cable diameter
Chassis connector
Chassis connector type
Cable connector
Cable connector type
Connector protection class
Cable replacement
Mounting (see options)Levelling (see options)Levelling accuracy
Desiccant
IP protection class
Gross weight
Net weightHEATING

hemispherical solar radiation
irradiance in W/m2
sunshine duration
180 °0 to 2000 W/m2
7 to 30 x 10-6 V/(W/m2)
10 x 10-6 V/(W/m2)
zero (passive sensor)
application under natural solar radiation: -0.1 to +50
x 10-3 V
E = U/S
programming according to WMO guide paragraph
8.2.2-40 to +80 °C
285 to 3000 x 10-9 m
40 to 80 Ω
1 differential voltage channel or 1 single ended
voltage channel, input resistance > 106 Ω
depends on readout equipment; 7 x 10-6 V datalogger
resolution is sufficient for 1 W/m2 resolution in
irradiance
ISO/TR 9901:1990 Solar energy -- Field pyranometers-- Recommended practice for use
ASTM G183 - 05 Standard Practice for Field Use of
Pyranometers, Pyrheliometers and UV Radiometers
3m
4.8 x 10-3 m
M12-A straight male connector, male thread, 5-pole
M12-A
M12-A straight female connector, female thread, 5pole
M12-A
IP67
replacement and extension cables with connector(s)can be ordered separately from Hukseflux
2 x M5 bolt at 46 mm centre-to-centre distance on
north-south axis, requires 4 mm hex key
bubble level is included< 0.6 ° bubble entirely in ringsilica gel, 1.0 g, in a HDPE bag, (25 x 45) mm
IP67
approx. 0.5 kg
approx. 0.5 kg

HeaterCALIBRATION

no heating

Calibration traceability
Calibration hierarchy

to WRR
from WRR through ISO 9846 and ISO 9847, applying
a correction to reference conditions
indoor calibration according to ISO 9847, Type IIc

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Table 3.1.1 Specifications of SR05-A1 (started on previous pages)
CALIBRATION
Calibration uncertainty
Recommended recalibration interval
Reference conditions
Validity of calibration< 2.4 % (k = 2)
2 years
20 °C, normal incidence solar radiation, horizontal
mounting, irradiance level 1000 W/m2
based on experience the instrument sensitivity will notchange during storage. During use under exposure tosolar radiation the instrument “non-stability”
specification is applicable.

MEASUREMENT ACCURACY AND RESOLUTION
Uncertainty of the measurement
WMO estimate on achievable accuracy
for daily sums (see appendix for adefinition of the measurement conditions)
WMO estimate on achievable accuracy
for hourly sums (see appendix for adefinition of the measurement conditions)
OPTIONS
Longer cable: 10,20 m
Cable with M12-A female connector on
sensor end, non-stripped on other end
Extension cable with connector pair:
10, 20 m. Cable with male and female
M12-A connectors
Ball levelling (BL01)

Tube mount with ball levelling (TMBL01)

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statements about the overall measurement
uncertainty can only be made on an individual basis.
see the chapter on uncertainty evaluation
10 %
20 %

option code = total cable length
option code = C06E-10 for 10 metres, C06E-20 for
20 metres
mountable on (non-)horizontal surfaces
with angle compensation up to 10 °; retrofittable; one
shim, two M5x20 mounting bolts and two M5 nuts
included; requires 4 mm hex key for levelling and 4mm hex key and 8 mm wrench for mounting
mountable on tubes Ø 25 to Ø 40 mm
with angle compensation up to 10 °; retrofittable;
one shim, two M5x30 and two M5x40 mounting bolts
included; requires 4 m hex key for levelling andmounting

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3.2

Dimensions of SR05-A1

Figure 3.2.1 Dimensions of SR05 in x 10-3 m. The bottom drawing shows the height of
SR05 combined with its optional ball levelling mount and the tube diameter required foruse with SR05’s optional tube mount. M5 mounting bolts and the countersunk set screw
require a 4 mm hex key for mounting and levelling.

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4

Standards and recommended practices
for use

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

4.1

Classification standard

Table 4.1.1 Standards for pyranometer classification. See the appendix for definitions ofpyranometer specifications, and a table listing the specification limits.
STANDARDS FOR INSTRUMENT CLASSIFICATIONISO STANDARD

EQUIVALENTASTM STANDARD

WMO

ISO 9060:1990
Solar energy -- specification andclassification of instruments formeasuring hemispherical solar anddirect solar radiation

Not available

WMO-No. 8; Guide toMeteorological Instruments
and Methods of Observation,
chapter 7, measurement ofradiation, 7.3 measurementof global and diffuse 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 HEMISPHERICAL SOLAR RADIATIONISO STANDARD

EQUIVALENTASTM STANDARD

WMO

ISO/TR 9901:1990
Solar energy -- Field
pyranometers -- Recommended
practice for use

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

WMO-No. 8; Guide toMeteorological Instruments
and Methods of Observation,
chapter 7, measurement ofradiation, 7.3 measurementof global and diffuse solar
radiation

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.

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WMO has approved the “pyranometric method” to estimate sunshine duration frompyranometer measurements (Chapter 8 of the WMO Guide to Instruments andObservation, 2008). This implies that a pyranometer may be used, in combination withappropriate software, to estimate sunshine duration. Ask for our application note.
Table 4.3.1 Standards with recommendations for instrument use in sunshine duration
measurement
STANDARDS FOR INSTRUMENT USE FOR SUNSHINE DURATIONWMO
WMO-No. 8; Guide to Meteorological Instruments and Methods of Observation, chapter 8,
measurement of sunshine duration, 8.2.2 Pyranometric Method

4.4

Specific use for outdoor PV system performance testing

Pyranometers are used for monitoring PV power plant efficiency, in order to measureincoming solar radiation independently from the PV system. Pyranometers can be placedin two positions:• plane of array (POA), parallel to the PV panels, for measurement of the in-plane
irradiance (also noted as Gi in IEC 61724-1)• horizontally, for measurement of the global horizontal irradiance (E, also noted as GHI
in IEC 61724-1)
SR05-A1 is applicable in outdoor PV system performance testing. See also Hukseflux
model SR20 “secondary standard pyranometer”.
Table 4.4.1 Standards with recommendations for instrument use in PV system
performance testing
STANDARDS ON PV SYSTEM PERFORMANCE TESTING
IEC / ISO STANDARD

EQUIVALENT ASTM STANDARD

IEC 61724-1; Photovoltaic system performancemonitoring – guidelines for measurement, dataexchange and analysis

ASTM 2848-11; Standard Test Method for
Reporting Photovoltaic Non-Concentrator
System Performance

COMMENT: Allows pyranometers or reference
cells according to IEC 60904-2 and -6.
Pyranometer reading required accuracy better
than 5% of reading (Par 4.1)

COMMENT: confirms that a pyranometer is thepreferred instrument for outdoor PV testing.
Specifically recommends a “first class”
pyranometer (paragraph A 1.2.1.)

COMMENT: equals JISC 8906 (JapaneseIndustrial Standards Committee)

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4.5

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 theearth'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 pyranometers. Nowadays WMO conforms itself to the ISO classification
system.

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5

Installation of SR05-A1

5.1

Site selection and installation

Table 5.1.1 Recommendations for installation of pyranometers
Location

the situation that shadows are cast on the instruments
is usually not desirable. The horizon should be as freefrom obstacles as possible. Ideally there should be no
objects between the course of the sun and the
instrument.

Mechanical mounting / thermal insulationpreferably use the ball levelling mount included with
BL01 and TMBL01 to mount SR05 to a (non-)horizontal surface. A pyranometer is sensitive tothermal shocks. Do not mount the instrument on
objects that become very hot (black coated metal
plates).

Instrument mounting with 2 bolts

2 x M5 bolt at 46 mm centre-to-centre distance on
north-south axis, connection through the sensor
bottom in SR05’s standard configuration.
with BL01 ball levelling option: 2 x M5 bolt at 46 mm
centre-to-centre distance, connection through balllevelling mount, M5x20 bolts and M5 nuts included.
with TMBL01 ball levelling on tube mount option: 2 x
M5 bolt at 46 mm centre-to-centre distance,
connection through tube and ball levelling mount,M5x30 and M5x40 bolts included.

Performing a representative
measurement

the pyranometer measures the solar radiation in theplane of the sensor. This may require installation in atilted or inverted position. The black sensor surface(sensor bottom plate) should be mounted parallel tothe plane of interest.
In case a pyranometer is not mounted horizontally orin case the horizon is obstructed, therepresentativeness of the location becomes animportant element of the measurement. See thechapter on uncertainty evaluation.

Levellingin case of horizontal mounting use the bubble leveland optionally the ball levelling mount. The bubble
level is visible and can be inspected at all times.

Instrument orientationby convention with the cable exit pointing to thenearest pole (so the cable exit should point north in
the northern hemisphere, south in the southernhemisphere).

Installation heightin case of inverted installation, WMO recommends a
distance of 1.5 m between soil surface and sensor(reducing the effect of shadows and in order to obtain
good spatial averaging).

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5.2

Mounting and levelling SR05

SR05 in its standard configuration is equipped with a visible bubble level and two mounting
holes. For easy mounting and levelling on a (non-)horizontal surface, SR05’s optional balllevelling, included with BL01 and TMBL01, is recommended. Ball levelling offers:••••

easy levellingeasy cable orientationeasy instrument exchangeeasy mounting (mounting screws and nuts included)

When installing SR05, ball levelling allows SR05 to rotate 360 ° and to tilt up to 10 °. This
allows compensation for up to a ten degree angle when installing on a non-horizontal
surface. A 4 mm hex key (un)locks the ball levelling mechanism. When using a tube or rod
for installing SR05, the optional tube mount, included with TMBL01, is recommended.
Combined with ball levelling it allows mounting to a 25 to 40 mm diameter tube with thesame ease of levelling and instrument exchange.

SR05

SR05 with BL01

SR05 with TMBL01

Figure 5.2.1 From left to right: SR05 in its standard configuration with 3 metre cable;with optional ball levelling for easy mounting and levelling on a (non-)horizontal surface;with optional ball levelling and tube mount for easy installation on a 25 to 40 mm
diameter tube. Mounting screws are included with the ball levelling and / or tube mount.

5.3

Installing SR05

SR05 without ball levelling and tube mounting options can be mounted using two M5bolts (not included). For the required screw lengths, 5 to 7 mm should be added to thethickness of the user’s mounting platform. See the chapter on required tooling.

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5.4

Installing SR05 with its ball levelling and tube mountTwo M5x20 bolts and two M5 nuts are included with SR05’s BL01 (and TMBL01) balllevelling option. These screws are to be used to mount SR05 with its ball levelling to a(non-)horizontal surface when mounting SR05 with BL01.
Two M5x30 bolts and two M5x40 screws are included with SR05’s TMBL01’s tube mountwith ball levelling option. These screws are to be used to clamp both ball levelling andtube mount to a 25 to 40 mm diameter tube. For tube diameters larger than or equal to
33 mm, use the M5x40 bolts instead of the M5x30 bolts for a secure fit.
The unique ball head mechanism of SR05’s ball levelling mount is used to level SR05.
When ordering ball levelling with SR05, it is delivered separately from SR05.
In case SR05 is not attached to its ball levelling mount yet, the user has to ensure a shimis placed properly in the centre of the bottom plate of SR05 before mounting andlevelling. The shim allows smooth levelling and is shown top left in Figure 5.4.1. Follow
steps 1 to 5 in Section 5.4.1 for placing the shim. Once a shim is in place, follow steps 6
to 9 in Section 5.4.2 to mount and level SR05 with its BL01 or TMBL01 ball levelling
option. See Section 5.4.3 for removing the ball levelling mount and its shim.

Figure 5.4.1 On the left SR05’s ball levelling including shim (mounting bolts not
displayed) and on the right SR05 placed on the ball levelling mount. Loosen the
countersunk set screw on SR05’s side to unlock, allowing placement of the ball head and
SR05 levelling, and tighten it to lock the ball head mechanism. A 4 mm hex key is the
only tool needed to place and remove the ball levelling and to allow and disallow levelling
adjustment. The shim, included when ordering ball levelling, allows for smooth levellingand should be positioned properly in the centre of the bottom plate of SR05.

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5.4.1 Placing SR05’s ball levelling shim
When ordering SR05 pyranometer and its optional ball levelling or when exchanging a
SR05 sensor on a ball levelling mount (retrofitting), the user has to ensure a dedicatedshim is placed properly in the centre of the bottom plate of SR05. The aluminium shimensures a secure fit between SR05 and ball levelling and allows the ball head to rotatesmoothly for easy levelling. The shim, a loose set screw, a 4 mm hex key, two M5x20
mounting bolts and two M5 nuts are included when ordering the BL01 or TMBL01 balllevelling mount.

Figure 5.4.1.1 Line drawing indicating placement of the aluminium shim and photoshowing the shim properly positioned in the centre of SR05’s bottom plate. Note theposition of the protruding ledge when placing the shim.
The shim can be placed into SR05’s bottom plate following these steps:
1)

If your SR05 has a small black plastic cover cap on the countersunk set screw
opening on SR05’s side, remove it. A small flathead screwdriver may be used. Theninsert the loose set screw with a 4 mm hex key by turning the hex key clockwise
until the screw is only slightly protruding (sticking out).

2)

Hold SR05 in one hand, the shim in the other.

3)

Ensure the orientation of the shim fits with that of SR05’s bottom plate. Note theposition of the protruding ledge (see Figure 5.5.1).

4)

Pinch the shim slightly in order to reduce its diameter and to make it fit easily into
SR05’s bottom plate.

5)

While pinching, push the shim into its position on SR05’s bottom plate. The shim isplaced.

Continue with the following section for mounting and levelling SR05 with ball levelling.

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5.4.2 Mounting and levelling SR05 with BL01 or TMBL01
When the shim is properly in place (see steps 1 to 5), SR05 can be mounted and levelledusing BL01 or TMBL01. Continue with the following steps:
6)

Mount the ball levelling to a surface or platform with its M5 bolts and nuts. See
chapter on tooling required.

7)

SR05, with its shim positioned, can now be placed on the ball levelling mount.
Gently push the sensor onto the ball head until it clicks.

8)

The ball head can be rotated 360 ° and allows angle compensation on nonhorizontal surfaces up to 10 °.

9)When SR05 is mounted and levelled, judging by its bubble level, lock the ball headmechanism by turning the set screw clockwise with a 4 mm hex key until it istightened. The set screw should be countersunk and not protruding (not sticking out).

A similar approach is followed when levelling SR05 on its tube mount in the field:

1) judge bubble level and cable orientation 2) loosen set screw to tilt and rotate SR053) tighten set screw to lock ball levelling4) SR05 is mounted and levelled

Figure 5.4.2.1 Levelling steps for SR05 when mounted on tube mount with ball levelling

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5.4.3 Removing the ball levelling mount and its shim
1)

Loosen SR05’s countersunk set screw with a 4 mm hex key by turning the hex key
counter clockwise until the screw is slightly protruding (sticking out).

2)

Hold SR05 in one hand, the ball levelling mount in the other.

3)

Separate SR05 from the ball levelling mount by gently pulling out the ball levelling
mount. Make sure the glass dome is protected at all times.

When (TM)BL01’s ball head is not inserted in SR05, the shim makes a minor rattlingnoise when moving SR05. This is normal, caused by mechanical freedom between thetwo parts.
The shim can be removed from SR05’s bottom plate by hand with the assistance of asmall flathead screwdriver. See the chapter on tooling required. Let the screwdrivergently tip the shim out. When removing or placing the shim, make sure the glass dome isprotected at all times.

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5.5

Electrical connection of SR05-A1

This user manual covers use of the analogue sensor in the SR05 series range:
SR05-A1. Specifications of this version differ from those of the digital versionsof model SR05: SR05-D1A3 and SR05-D2A2, offering various digital andanalogue outputs. For SR05-D1A3 and SR05-D2A2 use, consult the SR05 series
user manual.
In order to operate, a pyranometer should be connected to a measurement system,
typically a so-called datalogger. SR05-A1 is a passive sensor that does not need any
power. 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.
Table 5.5.1 Wiring diagram of SR05-A1
PIN

WIRE

SR05-A1
analogue millivolt output

1

Brown

not connected

4

Black

not connected

3

Blue

not connected

2

White

signal [+]

5

Grey

signal [—]YellowshieldNote 1: at the connector-end of the cable, the shield is connected to the connector housing

5.6

Grounding and use of the shield

Grounding and shield use are the responsibility of the user. The cable shield (called shieldin the wiring diagram) is connected to the aluminium instrument body via the connector.
In most situations, the instrument will be screwed on a mounting platform that is locallygrounded. In these cases the shield at the cable end should not be connected at all.
When a ground connection is not obtained through the instrument body, for instance inlaboratory experiments, the shield should be connected to the local ground at the cableend. This is typically the ground of the datalogging system. In exceptional cases, forinstance when both the instrument and a datalogger are connected to a small size mast,
the local ground at the mounting platform is the same as the network ground. In suchcases ground connection may be made both to the instrument body and to the shield at
the cable end.

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5.7

Using SR05-A1’s analogue millivolt ouput

Using the analogue SR05-A1 is easy: the pyranometer can be connected directly tocommonly used data logging systems. The irradiance in W/m2 is calculated by dividing
the SR05-A1 output, a small voltage, by the sensitivity. This sensitivity is provided with
SR05-A1 on its calibration certificate.
The central equation governing SR05-A1 is: E = U/S(Formula 0.1)

5.7.1 Requirements for data acquisition / amplification
SR05-A1 is a passive sensor that does not need any power. In order to operate, apyranometer should be connected to a measurement system, typically a so-called
datalogger. The selection and programming of dataloggers is the responsibility of theuser. Please contact the supplier of the data acquisition and amplification equipment to
see if directions for use with the SR05-A1 are available. In case programming for similar
instruments is available, this can typically also be used. SR05-A1 can usually be treatedin the same way as other thermopile pyranometers. Pyranometers usually have the same
programming as heat flux sensors.
When using SR05-A1 combined with read-out unit / datalogger LI19, please consult theLI19 manual as well.
Table 5.7.1 Requirements for data acquisition and amplification equipment for SR05-A1
in its 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 theacquisition / amplification equipment)

Capability for the data logger or thesoftwareto 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 ΩOpen circuit detection(WARNING)

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

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6

Making a dependable measurement

6.1

The concept of dependability

A measurement with a pyranometer 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 pyranometer 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 effort to be made and processing time)a requirement to the expected instrument lifetime (until it is no longer feasible torepair)

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

the instrument classthe 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 (mainly fouling)
the environmental conditions*

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 themeasurement such as the cloud cover (presence or absence of direct radiation), sunposition, the local horizon (which may be obstructed) or condition of the ground (whentilted). The environmental conditions also involve the question whether or not themeasurement at the location of measurement is representative of the quantity thatshould be measured.

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6.2

Reliability of the measurement

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

related to the reliability of the pyranometer 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 accountmeasurement conditions and environmental conditions, the user will select an instrumentof 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. Typicallimiting 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-optimalmeasurement location with obstacles in the path of the sun.
other environmental conditions, for instance when assessing PV system performanceand the system contains panels at different tilt angles, the pyranometermeasurement may not be representative of irradiance received by the entire PV
system.

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

•

•

dome fouling by deposition of dust, dew, rain or snow. Fouling results in undefinedmeasurement uncertainty (sensitivity and directional error 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, theuncertainty of the sensitivity gradually will increase. This is solved by regular
recalibration.
moisture condensing under pyranometer domes resulting in a slow change ofsensitivity (within specifications). This is solved by regular replacement of desiccantor by maintenance (drying the entire sensor) in case the sensor allows this. For nonserviceable sensors like most second class pyranometers, this may slowly develop
into a defect. For first class and secondary standard models (for instance model SR11
first class pyranometer and SR20-D2 digital secondary standard pyranometer) extra
desiccant (in a set of 5 bags in an air tight bag) is available.

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

the use of redundant instruments allows remote checks of one instrument using theother as a reference, which leads to a higher measurement reliability.
in PV system performance monitoring, in addition to instruments measuring in theplane of array, horizontally placed instruments are used for the measurement of
global radiation. Global irradiance data enable the user to compare the local climate
and system efficiency between different sites. These data can also be compared tomeasurements by local meteorological stations.

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 thedependability.
Hukseflux pyranometers 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 maintenancedesign 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 duringservice, recalibrations and repair.

6.4

Uncertainty evaluation

The uncertainty of a measurement under outdoor or indoor conditions depends on manyfactors, see paragraph 1 of this chapter. It is not possible to give one figure forpyranometer measurement uncertainty. The work on uncertainty evaluation is “inprogress”. 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).

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6.4.1 Evaluation of measurement uncertainty under outdoor conditions
Hukseflux actively participates in the discussions about pyranometer measurement
uncertainty; we also provide spreadsheets, reflecting the latest state of the art, to assist
our users in making their own evaluation. 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 ofpyranometers and pyrheliometers are entered as limiting values of possible errors, to beanalysed 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 areentered 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) orin S (tilt error, temperature dependence, calibration uncertainty).
5) In uncertainty analysis for pyranometers, 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; the angle of incidence of direct radiation is a major factor
in the uncertainty.
6) In uncertainty analysis for modern pyrheliometers: tilt dependence often is so low thatone 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 (shaded / unshaded,ventilated/ unventilated, horizontal / tilted) 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 covariancematrix are zero. Paragraph 5.1 of GUM.
10) Among the various sources of uncertainty, some are “not included in analysis”; thisapplies for instance to non-linearity for pyranometers, because it is already included in
the directional error, and the spectral response for pyranometers and pyrheliometers
because it is already taken into account in the calibration process.

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Table 6.4.1.1 Preliminary estimates of achievable uncertainties of measurements with
Hukseflux pyranometers. The estimates are based on typical pyranometer properties andcalibration uncertainty, for sunny, clear sky days and well maintained stations, without
uncertainty loss due to lack of maintenance and due to instrument fouling. The tablespecifies 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 pyranometer measurements, so this table should
not be used as a formal reference.
Pyranometer
class(ISO 9060)
secondarystandard

first classsecond classseasonlatitudeuncertainty
minute totals
at solar noon

uncertainty
hourly totals
at solar noon

uncertainty
daily totals

summermid-latitude

2.7 %

2.0 %

1.9 %

winterequatorpole
mid-latitude

2.6 %
7.9 %
3.4 %

1.9 %
5.6 %
2.5 %

1.7 %
4.5 %
2.7 %

summermid-latitude

4.7 %

3.3 %

3.4 %

equator

4.4 %

3.1 %

2.9 %

pole

16.1%

11.4 %

9.2 %wintermid-latitude

6.5 %

4.5 %

5.2 %

summermid-latitude

8.4 %

5.9 %

6.2 %

equator

7.8 %

5.5 %

5.3 %

pole

29.5 %

21.6 %

18.0 %

mid-latitude

11.4 %

8.1 %

9.9 %

(SR05 series)
winter

6.4.2 Calibration uncertainty
New calibration procedures were developed in close cooperation with PMOD World
Radiation Center in Davos, Switzerland. The latest calibration method results in an
uncertainty of the sensitivity of less than 2.4 %, compared to typical uncertainties ofhigher than 3.5 % for this pyranometer class. See the appendix for detailed information
on calibration hierarchy.

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7

Maintenance and trouble shooting

7.1

Recommended maintenance and quality assurance

SR05-A1 can measure reliably at a low level of maintenance in most locations. Usuallyunreliable measurements will be detected as unreasonably large or small measured
values. As a general rule this means that regular visual inspection combined with acritical review of the measured data, preferably checking against other measurements, isthe preferred way to obtain a reliable measurement.
Table 7.1.1 Recommended maintenance of SR05-A1. If possible the data analysis andcleaning (1 and 2) should be done on a daily basis. (continued on next page)
MINIMUM RECOMMENDED PYRANOMETER MAINTENANCE
INTERVALSUBJECTACTION1

1 weekdata analysis

compare measured data to maximum possible / maximum
expected irradiance and to other measurements nearby(redundant instruments). Also historical seasonal records canbe used as a source for expected values. Analyse night time
signals. These signals may be negative (down to - 5 W/m2 on
clear windless nights), due to zero offset a. In case of use with
PV systems, compare daytime measurements to PV system
output. Look for any patterns and events that deviate fromwhat is normal or expected

22 weeks

cleaning

use a soft cloth to clean the dome of the instrument,
persistent stains can be treated with soapy water or alcohol3

6 months

inspection

inspect cable quality, inspect connectors, inspect mounting
position, inspect cable, clean instrument, clean cable, inspectlevelling, change instrument tilt in case this is out ofspecification, inspect mounting connection, inspect interior ofdome for condensation

4

2 years

desiccantreplacement

desiccant is specified to last for minimum 2 years. In case theuser wants to replace desiccant himself, this is at own risk andshould only be executed in an ESD-safe work environment.
The bottom plate of SR05 should be removed by unscrewing 3
x T10 screws with a Torx 10 screwdriver. The desiccant bag istaped on the bottom plate of SR05. Care should be taken
when mounting the bottom plate on SR05

5

2 years

recalibration

recalibration by side-by-side comparison to a higher standard
instrument in the field according to ISO 9847

lifetime
assessment

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

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

6

7

6 years

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MINIMUM RECOMMENDED PYRANOMETER MAINTENANCE (continued)
8

internal
inspection

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

9

recalibration

high-accuracy recalibration indoors according to ISO 9847 or
outdoors according to ISO 9846

7.2

Trouble shooting

7.2.1 Trouble shooting SR05-A1
Table 7.2.2.1 Trouble shooting for SR05-A1 (continued on next page)The sensor
does not give
any signal

Check the electrical resistance of the sensor between the grey(-) and white (+) wire. Use a multimeter at the 200 Ω range. Measure the sensor
resistance first with one polarity, than reverse the polarity. Take the averagevalue. The typical resistance of the wiring is 0.1 Ω/m. The measured resistanceshould be the typical sensor resistance of 40 to 80 Ω plus 1 Ω for the total
resistance of two wires (back and forth) of each 3 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 rangeof 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 1 x 10-1 m
distance. 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. Check the condition of
the connectors (on chassis as well as the cable).

The sensor
signal isunrealisticallyhigh or low.

Note that night-time signals may be negative (down to -5 W/m2 on clear windlessnights), due to zero offset a.
Check if the pyranometer has clean domes.
Check the location of the pyranometer; are there any obstructions that could
explain the measurement result.
Check the orientation / levelling of the pyranometer.
Check if the right calibration factor is entered into the algorithm. Please note thateach sensor has its own individual calibration factor, as documented in its
calibration certificate.
Check if the voltage reading is divided by the calibration factor in review of thealgorithm. Check the condition of the wiring at the logger.
Check the cable condition looking for cable breaks. Check the condition of theconnectors (on chassis as well as the cable). Check the range of the data logger;
signal can be negative (this could be out of range) or the amplitude could be outof range. Check the data acquisition by applying a 1 x 10-6 V source to it in the1 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 100Ω resistor. Look at the output. Check if the output is close to 0 W/m2.

The sensor
signal shows
unexpectedvariations

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

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The dome
Arrange to send the sensor back to Hukseflux for diagnosis.
shows internal
condensation

7.3

Calibration and checks in the field

Recalibration of field pyranometers is typically done by comparison in the field to areference pyranometer. The applicable standard is ISO 9847 “International StandardSolar Energy- calibration of field pyranometers by comparison to a reference
pyranometer”. At Hukseflux an indoor calibration according to the same standard is used.
Hukseflux recommendation for re-calibration:
if possible, perform calibration indoor by comparison to an identical reference instrument,
under normal incidence conditions. The recommended calibration interval ofpyranometers is 2 years.
In case of field comparison; ISO recommends field calibration to a higher classpyranometer. Hukseflux suggests also allowing use of sensors of the same model andclass, because intercomparisons of similar instruments have the advantage that they
suffer from the same offsets. It is therefore just as good to compare to pyranometers of
the same brand and type as to compare to an instrument of a higher class. ISO
recommends to perform field calibration during several days; 2 to 3 days under cloudlessconditions, 10 days under cloudy conditions. In general this is not achievable. In order toshorten the calibration process Hukseflux suggests to allow calibration at normal
incidence, using hourly totals near solar noon.
Hukseflux main recommendations for field intercomparisons are:1) to take normal incidence as a reference and not the entire day.
2) to take a reference of the same brand and type as the field pyranometer or apyranometer of a higher class, and
3) to connect both to the same electronics, so that electronics errors (also offsets) areeliminated.
4) to mount all instruments on the same platform, so that they have the same bodytemperature.
5) assuming that the electronics are independently calibrated, to analyse radiation values
at normal incidence radiation (possibly tilting the radiometers to approximately normal
incidence), if this is not possible to compare 1 hour totals around solar noon forhorizontally mounted instruments.
6) for second class radiometers, to correct deviations of more than ± 10 %. Lower
deviations should be interpreted as acceptable and should not lead to a revised
sensitivity.
7) for first class pyranometers, to correct deviations of more than ± 5 %. Lower
deviations should be interpreted as acceptable and should not lead to a revised
sensitivity.

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8) for secondary standard instruments, to correct deviations of more than ± 3 %. 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 programson the market that can semi-automatically perform data screening. See for more
information on such a program: www.dqms.com.

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8

Appendices8.1

Appendix on cable extension / replacement

The sensor cable of SR05-A1 is equipped with a M12-A straight connector. In case ofcable replacement, it is recommended to purchase a new cable with connector at
Hukseflux. In case of cable extension, it is recommended to purchase an extension cablewith connector pairs at Hukseflux. Please note that Hukseflux does not provide support
for Do-It-Yourself connector- and cable assembly.
SR05-A1 is equipped with one cable. Keep the distance between data logger or amplifierand sensor as short as possible. Cables act as a source of distortion by picking up
capacitive noise. In an electrically “quiet” environment the SR05-A1 cable can however
be extended without problem to 100 metres. 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 noresistive losses).
Connector and cable specifications are summarised on the next page.

Figure 8.1.1 On the left the SR05-A1 cable with M12-A female connector on sensor end.
The cable is non-stripped on the other end. Its length is 3 metres standard and available
in 10 and 20 metres too. On the right Hukseflux extension cable with connector pairs,with male and female M12-A connectors, available in 10 and 20 metres.

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Table 8.1.1 Specifications for SR05-A1 cable replacement and extension
General replacement

please order a new cable with connector at Hukseflux

General cable extension

please order an extension cable with connector pairs at Hukseflux

Connectors usedchassis: M12-A straight male connector, male thread, 5-pole
manufacturer: Binder
cable: M12-A straight female connector, female thread, 5-pole
manufacturer: Binder
The shield is electrically connected to the connector

Cable

5-wire, shielded
manufacturer: Binder

Lengthcables should be kept as short as possible

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8.2

Appendix on tools for SR05-A1

Table 8.2.1 Specifications of tools for SR05-A1
CONFIGURATIONTOOLSINCLUDED

tooling required for mounting SR05
without ball levelling

two M5 bolts
applicable screwdrivernonotooling required for mounting SR05
with ball levellinghex key 4 mm
wrench size 8 mm for M5 nuts

yesnotooling required for mounting SR05
with tube mounthex key 4 mm

yestooling required for levelling SR05
with ball levelling and tube mounthex key 4 mm

yestooling required for tipping the aluminium
shim out of SR05’s bottom panel position

screwdriver blade width 2 to 4
mm

no

8.3
•
•
•
•
•
•
•
•
•
•
•

Appendix on spare parts for SR05-A1

SR05-A1 cable with female M12-A connector on sensor end, non-stripped on otherend (3, 10, 20 m). Specify cable lengthSR05-A1 extension cable with connector pair, with male and female M12-A
connectors, (10, 20 m). Specify extension cable length
Ball levelling (order number BL01)
Tube mount (order number TM01)
Tube mount with ball levelling (order number TMBL01)
Shim for ball levelling mountCountersunk set screw for ball levelling mount2 x M5x40 mounting bolt
2 x M5x30 mounting bolt
2 x M5x20 mounting bolt with 2 x M5 nut
Desiccant (silica gel, 1.0 g, in a HDPE bag)

NOTE: Dome, level and sensor of SR05 cannot be supplied as spare parts

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8.4

Appendix on standards for classification and calibration

Both ISO and ASTM have standards on instrument classification and methods ofcalibration. The World Meteorological Organisation (WMO) has largely adopted the ISOclassification system.
Table 8.4.1 Pyranometer standardisation in ISO and ASTM.
STANDARDS ON INSTRUMENT CLASSIFICATION AND CALIBRATIONISO STANDARD

EQUIVALENT ASTM STANDARD

ISO 9060:1990 Solar energy -- Specificationand 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 pyrheliometercharacteristics” has been announced in ISO
9060 but is not yet implemented.

not available

ISO 9846:1993 Solar energy -- Calibration ofa pyranometer using a pyrheliometer

ASTM G167-05 Standard Test Method for
Calibration of a Pyranometer Using a
PyrheliometerISO 9847:1992 Solar energy -- Calibration offield pyranometers by comparison to areference pyranometer

ASTM E 824-10 Standard Test Method forTransfer 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 offield pyrheliometers by comparison to areference pyrheliometer

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

not available

ASTM G213-17 Standard Guide for Evaluating
Uncertainty in Calibration and Field
Measurements of Broadband Irradiance with
Pyranometers and Pyrheliometers

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8.5

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 standardsof 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 guaranteedby 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. Some small
corrections are made to transfer this calibration to the Hukseflux standard conditions:sun at zenith and 1000 W/m2 irradiance level. During the outdoor calibration the sun istypically at 20 to 40° zenith angle, and the total irradiance at a 700 W/m2 level.
Table 8.5.1 Calibration hierarchy for pyranometers
WORKING STANDARD CALIBRATION AT PMOD / WRC DAVOS
Calibration of working standard pyranometers:
Method: ISO 9846, type 1 outdoor. This working standard has an uncertainty “uncertainty ofstandard”. The working standard has been calibrated under certain “test conditions of thestandard”. The working standard has traceability to WRR world radiometric reference.
CORRECTION OF (WORKING) STANDARD CALIBRATION TO STANDARDISEDREFERENCE CONDITIONSCorrection from “test conditions of the standard” to “reference conditions” i.e. to normal
incidence and 20 °C:
Using known (working) standard pyranometer properties: directional, non linearity, offsets,temperature dependence). This correction has an uncertainty; “uncertainty of correction”.
At Hukseflux we also call the working standard pyranometer “standard”.
INDOOR PRODUCT CALIBRATION
Calibration of products, i.e. pyranometers:
Method: according to ISO 9847, Type IIc, which is an indoor calibration.
This calibration has an uncertainty associated with the method.
(In some cases like the BSRN network the product calibration is with a different method; forexample again type 1 outdoor)
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 theworking 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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8.6

Appendix on meteorological radiation quantities

A pyranometer measures irradiance. The time integrated total is called radiant exposure.
In solar energy radiant exposure is often given in W∙h/m2.
Table 8.6.1 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.
SYMBOLDESCRIPTIONCALCULATION

UNITS

E↓

downward irradianceE↓ = Eg ↓ + El↓

W/m2

H↓

downward radiant exposure
for a specified time intervalH↓ = Hg↓ + Hl ↓

J/m2

E↑

upward irradianceE↑ = Eg ↑ + El ↑

W/m2

H↑

upward radiant exposure
for a specified time intervalH↑ = Hg↑ + Hl ↑J/m2

W∙h/m2

Change ofunitsE

direct solar irradiancenormal to the apparent
solar zenith angle
solar constant

W/m2

DNI

DirectNormalIrradiance

E0
Eg ↓ hEg ↓ tEd ↓global irradiance;
hemispherical irradiance ona specified, in this casehorizontal surface.*
global irradiance;
hemispherical irradiance ona specified, in this casetilted surface.*
downward diffuse solar
radiation

W/m2
Eg↓ = E cos θh + Ed↓

W/m2

GHI

GlobalHorizontal
Irradiance

Eg ↓ = E∙cos θt +Ed ↓ t + Er↑ t ***

W/m2

POA

Plane of
Array

W/m2

DHI

DiffuseHorizontal
IrradianceEl ↑, El ↓upward / downward longwave irradiance

W/m2

Er↑

reflected solar irradiance

W/m2

E*

net irradianceT↓apparent surface
temperature**apparent sky
temperature**
sunshine duration

T↑
SD

ALTERNATIVE
EXPRESSION

E* = E↓ – E↑

W/m2
ºC or KºC or Kh

θ is the apparent solar zenith angle θh relative to horizontal, θt relative to a tilted surfaceg = global, l = long wave, t = tilted *, h = horizontal**
distinction horizontal and tilted from Hukseflux,**
T symbols introduced by Hukseflux,*** contributions of Ed ↓ t and Er↑ t are Ed ↓ and Er↑ both corrected for the tilt angle of thesurfaceSR05-A1 manual v2316

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8.7

Appendix on ISO and WMO classification tables

Table 8.7.1 Classification table for pyranometers per ISO 9060 and WMO.
NOTE: WMO specification of spectral selectivity is different from that of ISO. Hukseflux
conforms to the ISO limits. WMO also specifies expected 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 CLASSSECONDARYSTANDARD

FIRST CLASSSECOND
CLASS

15 s+ 7 W/m2

30 s+ 15 W/m2

60 s+ 30 W/m2± 2 W/m2± 4 W/m2± 8 W/m2± 0.8 %
± 0.5 %
± 10 W/m2± 1.5 %
±1%
± 20 W/m2±3%±3%± 30 W/m2

Spectral selectivity (350 to 1 500 x 10-9 m)(WMO 300 to 3 000 x 10-9 m)

±3%

±5%

± 10 %

Temperature response (interval of 50 K)**

2%

4%

8%

Tilt response(0 to 90 ° at 1000 W/m2)± 0.5 %

±2%

±5%

WMO CLASSHIGH QUALITY

GOOD QUALITY

WMO: achievable accuracy for daily sums*

2%

5%

MODERATEQUALITY
10 %WMO: achievable accuracy for hourly sums*

3%

8%

20 %

WMO: achievable accuracy for minute sums*

not specified

not specified

not specified

WMO: resolution(smallest detectable change)

1 W/m2

5 W/m2

10 W/m2

individual
instrument only:
all specs mustcomplygroup
compliancegroup
compliance

Specification limit
Response time (95 %)Zero offset a (response to 200 W/m2 net
thermal radiation)
Zero offset b (response to 5 K/h in ambient
temperature)
Non-stability (change per year)
Non-linearity (100 to 1000 W/m2)
Directional response

ADDITIONAL WMO SPECIFICATIONSCONFORMITY TESTING***
ISO 9060* 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 thetrue value, excluding calibration errors.
** At Hukseflux the expression ± 1 % is used instead of a range of 2 %.
*** an instrument is subject to conformity testing of its specifications. Depending on theclassification, conformity compliance can be proven either by group- or individualcompliance. 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 categoryof instrument.

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8.8

Appendix on definition of pyranometer specifications

Table 8.8.1 Definition of pyranometer specifications
SPECIFICATION

DEFINITION

SOURCE

Response time
(95 %)

time for 95 % response. The time interval between the instantwhen a stimulus is subjected to a specified abrupt change and theinstant when the response reaches and remains within specified
limits around its final steady value.The response time is a measureof the thermal inertia inherent in the stabilization period for a final
reading.
response to 200 W/m2 net thermal radiation (ventilated).
Hukseflux assumes that unventilated instruments have to specify
the zero-offset in unventilated – worst case – conditions.
Zero offsets are a measure of the stability of the zero-point.
Zero offset a is visible at night as a negative offset, the instrument
dome irradiates in the far infra red to the relatively cold sky. This
causes the dome to cool down. The pyranometer sensor irradiates
to the relatively cool dome, causing a negative offset. Zero offset
a is also assumed to be present during daytime.
response to 5 K/h change in ambient temperature.
Zero offsets are a measure of the stability of the zero-point.

ISO
90601990
WMO
1.6.3

Zero offset a:(200 W/m2 net
thermalradiation )Zero offset b:(5 K/h in ambient
temperature)
Non-stability(change per
year)
Non-linearity(100 to 1000
W/m2)
Directional
response

Spectralselectivity (350
to 1500 x 10-9 m)(WMO 300 to3000 x 10-9 m)
Temperature
response(interval of 50 K)
Tilt response(0° to 90° at
1000 W/m2)
Sensitivity
Spectral range

percentage change in sensitivity per year. The dependence ofsensitivity resulting from ageing effects which is a measure of thelong-term stability.
percentage deviation from the sensitivity at 500 W/m2 due to thechange in irradiance within the range of 100 W/m2 to 1000 W/m2.
Non-linearity has an overlap with directional response, andtherefore should be handled with care in uncertainty evaluation.
the range of errors caused by assuming that the normal incidence
sensitivity is valid for all directions when measuring from any
direction a beam radiation whose normal incidence irradiance is1000 W/m2 . Directional response is a measure of the deviations
from the ideal “cosine behaviour” and its azimuthal variation.
percentage deviation of the product of spectral absorptance andspectral transmittance from the corresponding mean within 350 x
10-9 m to 1500 x 10-9 m and the spectral distribution of irradiance.
Spectral selectivity is a measure of the spectral selectivity of thesensitivity.
percentage deviation of the sensitivity due to change in ambient
temperature within an interval of 50 K the temperature of thepyranometer body.
percentage deviation from the sensitivity at 0° tilt (horizontal) due
to change in tilt from 0° to 90° at 1000 W/m2 irradiance. Tilt
response describes changes of the sensitivity due to changes of
the tilt angle of the receiving surface.
the change in the response of a measuring instrument divided by
the corresponding change in the stimulus.
the spectral range of radiation to which the instrument issensitive. For a normal pyranometer this should be in the 0.3 to 3
x 10-6 m range. Some pyranometers with coloured glass domes
have a limited spectral range.

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ISO
90601990

ISO
90601990
ISO
90601990
ISO
90601990
ISO
90601990
ISO
90601990
ISO
90601990
ISO
90601990
WMO
1.6.3
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8.9

Appendix on terminology / glossary

Table 8.9.1 Definitions and references of used terms
TERM
Solar energy
or solarradiation

Hemisphericalsolar radiation
Global solar
radiation

Plane-of-array
irradianceDirect solar
radiation
Terrestrial or
Longwaveradiation

World
Radiometric
Reference(WRR)
AlbedoAngle ofincidence
Zenith angle
Azimuth angle
Sunshineduration

DEFINITION (REFERENCE)
solar energy is the electromagnetic energy emitted by the sun. Solar energy isalso 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 ofthe extra-terrestrial solar radiation penetrates the atmosphere and directly
reaches the earth’s surface, while part of it is scattered and / or absorbed by thegas molecules, aerosol particles, cloud droplets and cloud crystals in theatmosphere. The former is the direct component, the latter is the diffuse
component of the solar radiation. (ref: WMO, Hukseflux)
solar radiation received by a plane surface from a 180° field of view angle (solid
angle of 2 π sr).(ref: ISO 9060)
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)
also POA: hemispherical solar irradiance in the plane of a PV array.
(ref: ASTM E2848-11 / IEC 61724)
radiation received from a small solid angle centred on the sun’s disc, on a given
plane. (ref: ISO 9060)
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 El ↓ also
the background radiation from the universe is involved, passing through the”atmospheric window”. In case of upwelling El ↑, 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)
measurement standard representing the Sl unit of irradiance with an uncertaintyof less than ± 0.3 % (see the WMO Guide to Meteorological Instruments andMethods 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)
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 radiation relative to the sensor measured from normal incidence (varies
from 0° to 90°).
angle of incidence of radiation, relative to zenith. Equals angle of incidence forhorizontally mounted instruments
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 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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8.10 EU 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:
2014/30/EU

The Electromagnetic Compatibility Directive

hereby declare under our sole responsibility that:
Product model:
Product type:SR05-A1
Pyranometerhas been designed to comply and is in conformity with the relevant sections andapplicable requirements of the following standards:
Emission:
Immunity:
Emission:
Emission:
Report:EN 61326-1 (2006)
EN 61326-1 (2006)
EN 61000-3-2 (2006)
EN 61000-3-3 (1995) + A1 (2001) + A2 (2005)
08C01340RPT01, 06 January 2009

Kees VAN DEN BOS
Director
Delft
18 August, 2017

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© 2023, Hukseflux Thermal Sensors B.V.
www.hukseflux.com
Hukseflux Thermal Sensors B.V. reserves the right to change specifications without notice.

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