Hukseflux SR30-M2-D1 User manual

Copyright by Hukseflux | manual v2203 | www.hukseflux.com | [e-mail]
USER MANUAL SR30-M2-D1
Digital Class A (secondary standard)
pyranometer with heating and tilt sensor
Hukseflux
Thermal Sensors
compliant with IEC
61724-1:2017 Class A

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Cautionary statements
Cautionary statements are subdivided into four categories: danger, warning, caution and
notice according to the severity of the risk.
DANGER
Failure to comply with a danger statement will lead to death or serious
physical injuries.
WARNING
Failure to comply with a warning statement may lead to risk of death or
serious physical injuries.
CAUTION
Failure to comply with a caution statement may lead to risk of minor or
moderate physical injuries.
NOTICE
Failure to comply with a notice may lead to damage to equipment or may
compromise reliable operation of the instrument.

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Contents
Cautionary statements 2
Contents 3
List of symbols 5
Introduction 6
1Ordering and checking at delivery 13
1.1 Ordering SR30-M2-D1 13
1.2 Included items 14
1.3 Quick instrument check 14
2Instrument principle and theory 15
2.1 Why a “spectrally flat” pyranometer? 18
2.2 Operating modes: heating and ventilation 20
2.3 Overview of remote diagnostics 21
2.4 Use of the tilt sensor 22
3Specifications of SR30-M2-D1 23
3.1 Specifications of SR30-M2-D1 23
3.2 Dimensions of SR30-M2-D1 29
4Standards and recommended practices for use 30
4.1 Classification standards 30
4.2 General use for solar radiation measurement 30
4.3 Specific use for outdoor PV system performance testing 31
4.4 Specific use in meteorology and climatology 31
4.5 General use for sunshine duration measurement 32
5Installation of SR30-M2-D1 33
5.1 Site selection and mechanical installation 33
5.2 Installation of the sun screen 35
5.3 Installation of optional mounts 36
5.4 Electrical installation 40
5.5 Internal protection 42
5.6 Connecting to an RS-485 network 42
5.7 Electrical isolation, grounding and shield connection 44
5.8 Cabling requirements 46
5.9 A PC as RS-485 master 47
6Communication with SR30-M2-D1 48
6.1 PC communication: Hukseflux Sensor Manager software 48
6.2 Network communication: getting started 48
6.3 Changing the device address and serial communication settings 50
7Use of remote diagnostics 51
7.1 Recommendations 51
7.2 Sensor body temperature 51
7.3 Tilt angle 52
7.4 Internal relative humidity 52
7.5 Heater current 52
7.6 Ventilator current 53
7.7 Ventilator speed 53

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8Making a dependable measurement 54
8.1 The concept of dependability 54
8.2 Reliability of the measurement 55
8.3 Repair and maintenance 56
8.4 Uncertainty evaluation 56
9Maintenance and trouble shooting 59
9.1 Recommended maintenance and quality assurance 59
9.2 Trouble shooting 60
9.3 Calibration and checks in the field 62
9.4 Data quality assurance 63
10 Appendices 65
10.1 Appendix on tools for SR30-M2-D1 65
10.2 Appendix on spare parts for SR30-M2-D1 65
10.3 Appendix on the ventilator 66
10.4 Appendix on standards for classification and calibration 67
10.5 Appendix on calibration hierarchy 67
10.6 Appendix on meteorological radiation quantities 69
10.7 Appendix on ISO and WMO classification tables 70
10.8 Appendix on ISO 9060:1990 classification no longer valid 72
10.9 Appendix on definition of pyranometer specifications 73
10.10 Appendix on terminology / glossary 75
10.11 Appendix on function codes, register and coil overview 76
10.12 Appendix on electromagnetic compatibility (EMC) testing 80
10.13 EU declaration of conformity 81

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List of symbols
Quantities Symbol Unit
Sensitivity S V/(W/m2)
Temperature T °C
Solar irradiance E W/m2
Plane of Array irradiance GiW/m2
Solar radiant exposure H W∙h/m2
Time in hours h h
Tilt angle relative to horizontal θh°
Relative humidity RH %
Pressure p bar
Temperature coefficient a 1/°C²
Temperature coefficient b 1/°C
Temperature coefficient c -
(see also appendix 10.6 on meteorological quantities)
Subscripts
extended RS-485 common mode range Vcm, max
DC isolation voltage (instrument body to signal ground) Viso
heater power Pheater
Acronyms
ASTM American Society for Testing and Materials
CRC Cyclic Redundancy Check
GHI Global Horizontal Irradiance
IEC International Electrotechnical Commission
ISO International Organization for Standards
LSW Least-Significant Word
MSW Most-Significant Word
POA Plane of Array
PV Photovoltaic
RPM Rounds-per-Minute
SCADA Supervisory Control And Data Acquisition
WMO World Meteorological Organization
Modbus®is a registered trademark of Schneider Electric, licensed to the Modbus Organization, Inc.

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Introduction
Welcome to the next level in solar radiation monitoring! The all-digital heated SR30-M2-D1
pyranometer offers the highest accuracy and highest data availability: using Recirculating
Ventilation and Heating (RVH
TM) technology, SR30 outperforms pyranometers equipped
with traditional ventilation systems. SR30 is the ideal instrument for use in PV system
performance monitoring and meteorological networks.
SR30 measures the solar radiation received by a plane surface, in W/m2, from a 180 o
field of view angle. SR30 is an ISO 9060 spectrally flat Class A (previously “secondary
standard”) pyranometer. It is employed where the highest measurement accuracy is
required. SR30 offers several advantages over competing pyranometers:
•Heated for best data availability: RVHTM technology outperforms traditional pyranometer
ventilation
•The first pyranometer compliant in its standard configuration with the IEC 61724-
1:2017 requirements for Class A PV monitoring systems
•Low cost of ownership: remote diagnostics and supported by a worldwide calibration
organisation
•Spectrally flat: WMO compliant, also suitable for Plane of Array, diffuse, and albedo
measurement
Figure 0.1 SR30-M2-D1 digital spectrally flat Class A pyranometer with heating and tilt sensor
NOTICE
This manual supports model SR30-M2-D1, the successor of SR30-D1.
Need support for the discontinued SR30-D1? Please refer to its separate manual.

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SR30 offers several advantages over competing pyranometers:
Heated for high data availability, featuring RVH
TM technology
High data availability is attained by heating of the outer dome using ventilation between
the inner and outer dome. This space forms a closed circuit together with the instrument
body; ventilated air is not in contact with ambient air. RVHTM – Recirculating Ventilation
and Heating – technology, developed by Hukseflux, suppresses dew and frost deposition
and is as effective as traditional ventilation systems, without the maintenance hassle and
large footprint.
•low power consumption: SR30-M2-D1 requires less than 3 W, compared to 10 W for
traditional ventilation systems
•low maintenance: SR30-M2-D1 does not require filter cleaning
RVHTM uses SR30’s built-in heater and ventilator. The dome of SR30 pyranometer is
heated by ventilating the space between the inner and outer dome. RVH TM is much more
efficient than traditional ventilation, where most of the heat is carried away with the
ventilation air. Recirculating ventilation is as effective in suppressing dew and frost
deposition at less than 3 W as traditional ventilation is at 10 W. RVHTM technology keeps
domes and sensor in perfect thermal equilibrium, which Plane of Array leads to a reduction
of zero offsets.
Compliant with IEC 61724-1:2017, Class A and B
IEC 61724-1: Photovoltaic System Performance Monitoring – Guidelines for
Measurement, Data Exchange and Analysis – requires ventilation and heating for Class A
monitoring. Only SR30 offers both, without the need for additional accessories. Most
competing pyranometers do not even comply with Class B, which requires heating.
“Spectrally flat” as required for PV monitoring and meteorology
The new ISO 9060:2018 version defines pyranometer classes A, B and C. The standard
also adds a new subclass, called “spectrally flat”. The vast majority of users needs to use
instruments of the spectrally flat subclass; only spectrally flat instruments measure with
high accuracy, also when a cloud obscures the sun, or when the irradiance includes
reflected radiation. These situations occur for example when you measure Global
Horizontal irradiance (GHI) under partly or fully cloudy skies, when you measure Plane of
Array (POA), albedo or net-radiation. Normal instruments, just of class A, B or C, and not
spectrally flat, only measure accurately under clear sunny skies.
Using "spectrally flat" instruments is essential because this ensures:
•you can measure accurately not only horizontally under clear-blue-sky but also
general GHI, POA, albedo and net radiation
•you comply with WMO requirements
•you can use the normal standardised ISO and WMO calibration procedures
•you can also measure separately the diffuse component only (creating a
diffusometer) with a shadow ring or shading ball, using the same instrument model.
•you can perform uncertainty evaluations with negligible (zero) spectral errors
See Section 2.1 in this manual for a more detailed explanation.

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Low cost of ownership
SR30 is an affordable spectrally flat Class A instrument and is designed for low cost of
ownership, which is mainly determined by costs of installation, on-site inspections,
servicing and calibration:
•low demand on infrastructure, SR30’s RVHTM requires less than 3 W power, compared
to 10 W for traditional ventilation systems
•reduction of unnecessary on-site inspection by remote diagnostics
•designed for efficient servicing; easy local diagnostics
•supported by an efficient calibration and maintenance organisation. Hukseflux offers
local support in the main global economies: USA, EU, China, India, SE Asia, Japan and
Brazil. Recalibration is recommended every 2 years, which is good practice in the industry.
Liabilities covered: test certificates
As required by ISO 9060 for Class A classification, each SR30 is supplied with test results
for the individual instrument:
•sensitivity
•directional response
•temperature response
•tilt sensor gains, offsets and temperature coefficients
Liabilities covered: test certificates
Improved electronics
Model SR30-M2-D1 is the successor of the popular SR30-D1 and offers improved
electronics design over its predecessor.
Figure 0.3 Two SR30 spectrally flat class A
pyranometers with digital output for GHI
(Global Horizontal Irradiance) and POA
(Plane of Array) PV monitoring measurement
Figure 0.2 Dew deposition and frost (as
in the photo): clear difference between a
non-heated pyranometer (back) and SR30
with RVHTM technology (front )

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Remote sensor diagnostics
Besides solar radiation, SR30 outputs sensor diagnostics, including:
•tilt angle
•sensor body temperature
•internal humidity
•internal pressure
•ventilator speed (RPM)
•ventilator current
•heater current
Remote diagnostics permits real-time status monitoring, reducing the need for
(un)scheduled field inspections.
Suggested use
Suggested use for SR30:
•PV system performance monitoring
•scientific meteorological observations
Diffuse radiation measurement
With its outstanding zero offset specifications, SR30 is also the instrument of choice for
high-accuracy diffuse radiation measurement.
Communication with a PC: Hukseflux Sensor Manager Software
For communication between a PC and SR30-M2-D1, the Hukseflux Sensor Manager
software can be used. It allows the user to plot and export data, and change the SR30-
M2-D1 Modbus address and its communication settings. Also, the digital outputs may be
viewed for sensor diagnostics.
See our separate Sensor Manager user manual.
Figure 0.4 User interface of the Sensor Manager, showing sensor diagnostics

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SR30 design
SR30 pyranometer employs a state-of-the-art thermopile sensor with black coated
surface, two domes and an anodised aluminium body. SR30 offers a digital output via
Modbus RTU over 2-wire RS-485. The pyranometer dome is heated by ventilating the
space between the inner and outer dome using RVHTM - Recirculating Ventilation and
Heating - technology.
Operating modes: heating and ventilation
The standard operating mode of SR30 is with heater and ventilator both [ON]. The power
consumption then is < 3 W. Alternatives are operation in medium power mode and in low
power mode. Heating and ventilation may be switched on and off by digital control. If the
heater is switched [OFF], SR30 operates in medium power mode. Operation at < 0.1 W,
in the low power mode, is possible by switching both the ventilator and heater [OFF].
Although zero offset will then increase slightly, overall performance will still comply with
the spectrally flat class A classification. In case there is no danger of deposition of dew or
frost, the medium power mode offers the most accurate measurement.
Options for mounting and levelling
There are several mounting options available for SR30: a levelling mount and a tube
levelling mount. They allow for simplified mounting, levelling and instrument exchange
on either a flat surface or a tube.
Figure 0.5Optional levelling mount (picture on the left); a practical spring-loaded mount
for easy mounting, levelling and instrument exchange on flat surfaces, and the optional
tube mount (picture on the right) including spring-loaded levelling upper clamp, lower
clamp for tube mounting and two sets of bolts.

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Spring-loaded levelling
When opting for one of the levelling mounts, SR30 is easily mounted and levelled using
the mount’s spring-loaded centre bolt and SR30’s adjustable levelling feet.
Figure 0.6Optional levelling mount allows spring-loaded levelling
Figure 0.7 PMF series pyranometer mounting fixtures can be used for easy installation of
pyranometers. On the left, PMF01 pyranometer mounting fixture with one SR30, and on the
right PMF02 with two SR30 pyranometers. Both fixtures allow mounting in Plane of Array for
PV system performance monitoring and meteorological applications.
See also
•SRA30 albedometer consisting of two SR30’s
•SR05, an economical solution often used for monitoring small scale PV systems
•PMF series mounting fixtures
•consult our pyranometer selection guide
•introduction of SR30 on our YouTube channel
•environmental impact analysis of SR30
•why ventilate and heat pyranometers
•view our complete range of solar sensors

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Cabling
The standard cable length is 5 m. Optionally cables of 10 and 20 m are supplied. It is
good practice to keep cables as short as possible; see chapter on cabling requirements.
Figure 0.8SR30-M2-D1 standard cable with M12-A female connector on sensor end. On
the opposite end (not visible), the cable is terminated with removed sheath over 0.15 m;
stranded copper conductors with plastic insulators, stripped ends with ferrules. Its length is
5 metres standard and it is available in 10 and 20 metres too.
SR30-M2-D1 is designed for use in SCADA (Supervisory Control And Data Acquisition)
systems, supporting Modbus RTU (Remote Terminal Unit) protocol over RS-485. In these
networks the sensor operates as a Modbus RTU slave. SCADA systems are often
implemented in photovoltaic solar energy (PV) systems and meteorological networks.
Using SR30-M2-D1 in a network is easy. Once the Modbus address and communication
settings have been configured and is connected to a power supply, the instrument can be
used in RS-485 networks. The user should have sound knowledge of the Modbus
communication protocol when installing sensors in a network.
The instrument should be used in accordance with the recommended practices of ISO,
WMO and ASTM.
The recommended calibration interval of pyranometers is 2 years. The registers
containing the applied sensitivity and the calibration history of SR30-M2-D1 are fully
accessible for users. This allows the user to choose his own local calibration service. The
same feature may be used for remotely controlled re-calibration of pyranometers in the
field. Ask Hukseflux for information on this feature and on ISO and ASTM standardised
procedures for field calibration.

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1Ordering and checking at delivery
1.1 Ordering SR30-M2-D1
The standard configuration of SR30-M2-D1 is with 5 metres cable.
Common options are:
•longer cable; 10 and 20 metres
•levelling mount. Specify article number LM01
•tube levelling mount with set of bolts. Includes LM01. Specify article number TLM01
Table 1.1.1 Ordering codes for SR30
VERSIONS OF SR30 (part numbers)
SR30-M2-D1
digital spectrally flat Class A (secondary standard)
pyranometer, with heating, internal ventilation, tilt sensor
and Modbus over RS-485 output
SR30-M2-D1-LM01
digital spectrally flat Class A (secondary standard)
pyranometer, with heating, internal ventilation, tilt sensor,
Modbus over RS-485 output and with levelling mount, for
spring-loaded levelling and mounting SR30 on a surface
SR30-M2-D1-TLM01
digital spectrally flat Class A (secondary standard)
pyranometer, heating, internal ventilation, tilt sensor,
Modbus over RS-485 output and with tube levelling mount,
for spring-loaded levelling and mounting SR30 on a tube
CABLES FOR SR30
with M12-A female connector on sensor end, and on the opposite end cable terminated
with removed sheath over 0.15 m; stranded copper conductors with plastic insulators,
stripped ends with ferrules.
‘-05’ after SR30 part number
standard cable length: 5 m
‘-10’ after SR30 part number
cable length: 10 m
‘-20’ after SR30 part number
cable length: 20 m
CABLE WITH CONNECTOR PAIR
with male and female M12-A connectors
C07E-20
cable length: 20 m

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1.2 Included items
Arriving at the customer, the delivery should include:
•pyranometer SR30-M2-D1
•sun screen
•cable of the length as ordered
•product certificate matching the instrument serial number, including:
ocalibration certificate
otemperature response test report
odirectional response test report
otilt sensor test report
•any other options as ordered
For SR30-M2-D1-LM01, also
•spring-loaded levelling mount
For SR30-M2-D1-TLM01, also
•spring-loaded levelling mount
•lower clamp to mount SR30 to a tube or mounting rod
•2 sets of bolts for different tube diameters
Please store the certificates in a safe place.
The latest version of the Hukseflux Sensor Manager can be downloaded via
www.hukseflux.com/downloads.
1.3 Quick instrument check
A quick test of the instrument can be done by connecting it to a PC and installing the
Sensor Manager software. See the chapters on installation and PC communication for
directions. Please note that a separate power supply is required; the sensor cannot be
powered from a USB port.
1. At power–up the signal may have a temporary output level different from zero; an
offset. Let this offset settle down; it is a normal part of the power-up procedure.
2. Check if the sensor reacts to light: expose the sensor to a strong light source, for
instance a 100 W light bulb at 0.1 m distance. The signal should read > 100 W/m2now.
Darken the sensor either by putting something over it or switching off the light. The
instrument irradiance output should go down and within one minute approach 0 W/m2.
3. Inspect the bubble level, compare to the tilt angle output.
4. Verify heater current, ventilator speed, internal humidity.
5. Inspect the instrument for any damage.
6. Check the instrument serial number as indicated by the software against the label on
the instrument and against the certificates provided with the instrument.

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2Instrument principle and theory
Figure 2.0.1 Overview of SR30:
(1) cable (standard length 5 metres, optional longer cable)
(2) connector
(3) sun screen
(4) bubble level
(5) bubble level window
(6) outer dome
(7) inner dome
(8) thermal sensor with black coating
(9) internal ventilation vents
(10) quick release system of sun screen
(11) instrument body
(12) levelling feet
(13) optional spring-loaded levelling mount
(14) optional tube mount
(15) screws included with tube mount
12
3
678910
5
4
11
12
13
14
15

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SR30’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 that
spectral range with a spectral selectivity that is as “flat” as possible.
In an irradiance measurement by definition the response to “beam” radiation varies with
the 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” that is as close as possible to the ideal
cosine characteristic (older documents mention the term “cosine response” instead).
In order to attain the proper directional and spectral characteristics, SR30’s main
components are:
•a thermal sensor with black coating. It has a flat spectrum covering the (200 to
50 000) 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 and from the sensor body to the
environment. The thermopile sensor generates a voltage output signal that is
proportional to the solar irradiance.
•in case of SR30, the analogue thermopile voltage is converted by the instrument
electronics to a digital signal. In this process the temperature dependence of the
thermopile is compensated. SR30-M2-D1 uses high-end conversion electronics with a
very small temperature dependence and excellent long-term stability.
•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 the
environment (convection, rain).
•a second (inner) glass dome: For a spectrally flat Class A pyranometer, two domes
are used, and not one single dome. This construction provides an additional “radiation
shield”, resulting in a better thermal equilibrium between the sensor and inner dome,
compared to using a single dome. The effect of having a second dome is a strong
reduction of instrument thermal offsets.
•a heater and ventilator: in order to reduce dew deposition and frost on the outer dome
surface, SR30 has a built-in heater and ventilator. The heater is attached to the sensor
body. The ventilation air circulates inside the body and between the domes. The
combination of ventilation and heating keeps the domes in thermal equilibrium with the
thermopile sensor and above dew point. When ventilation is [ON], zero offsets are very
low.

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•a tilt sensor: this sensor measures tilt with a ± 1 ° uncertainty and a short-term
resolution, or detection limit, of 0.1 °. This is sufficient to monitor incidents that
change the instrument tilt.
Pyranometers can be manufactured to different specifications and with different levels of
verification and characterisation during production. The ISO 9060:2018 standard, “Solar
energy - specification and classification of instruments for measuring hemispherical solar
and direct solar radiation”, distinguishes between 3 classes; spectrally flat Class A
(highest accuracy), Class B (second highest accuracy) and Class C (third highest
accuracy).
From class C to class B and from class B to class A, the achievable accuracy improves
roughly by a factor 2.
Figure 2.0.2 Spectral response of the pyranometer compared to the solar spectrum. The
pyranometer only cuts off a negligible part of the total solar spectrum.
0
0.2
0.4
0.6
0.8
1
1.2
100 1000 10000
relative spectral content /
response [arbitrary units]
wavelength [x 10-9 m]
solar radiation
pyranometer
response

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Figure 2.0.3 Directional response of an SR30 pyranometer of 4 azimuth angles,
compared to spectrally flat Class A limits
2.1 Why a “spectrally flat” pyranometer?
ISO 9060:2018 defines classes A, B and C. The standard also defines a subclass, called
"spectrally flat". The vast majority of users needs to use instruments of the spectrally flat
subclass; only spectrally flat instruments measure with high accuracy, also when a cloud
obscures the sun, or when the irradiance includes reflected radiation. These situations
occur when measuring Global Horizontal Irradiance (GHI) under partly or fully cloudy
skies, Plane of Array (POA) and albedo or net-radiation. Instruments of class A, B or C
that are not spectrally flat only measure accurately under clear sunny skies in a
horizontal position.
Compliance with the spectrally flat subclass also means the instrument complies with
WMO guide and keeps continuity with the 1990 version of ISO 9060. The classification
"spectrally flat" may be added to the name of the class if the instrument fulfils spectral
criteria as in the WMO guide and ISO 9060:1990 (the preceding version of the same
standard dating from 1990) secondary standard pyranometers (i.e. spectral selectivity
(350 to 1500) x 10-9 m: < ± 3 % with 2 % guard band).
The spectral error of ISO 9060:2018 is defined as "Clear sky global horizontal irradiance
spectral error". This error is valid under a clear sky on a sunny day. This is not the
common spectrum in normal application in solar renewable energy and it is also not the
common spectrum in meteorological application. Even for frequently occurring situations,
-4
-3
-2
-1
0
1
2
3
4
020 40 60 80
deviation from ideal cosine response
[%]
zenith angle [°]
South
West
East
North
ISO 9060
specification limit
secondary standard
pyranometer
specification limit
spectrally flat Class A
pyranometer

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for example when a cloud obscures the direct sun or under a cloudy sky, the
measurement error with a normal class A, B or C pyranometer is undefined. This is why
almost all users need a "spectrally flat" pyranometer, for which this error is negligible.
To conclude, specifying "spectrally flat" is essential because this ensures:
•you can measure accurately not only clear-blue-sky (with direct solar radiation) GHI
in a horizontal position, but also when a cloud obscures the sun, blue sky diffuse only,
cloudy sky diffuse, reflected, Plane of Array, POA, for Photovoltaic solar panels,
albedo or net radiation for meteorology.
•you comply with WMO: spectrally flat Class A and B instruments comply with the
WMO spectral requirements of high quality pyranometers as well as with the WMO
network requirement to measure not only global horizontal but also reflected
radiation. Normal Class A and B instruments do not comply with WMO requirements.
•you can use the normal standardised ISO and WMO calibration procedures, and can
benefit from relatively low-cost indoor calibrations. For normal class A, B and C
instruments this is not possible.
•you comply with the WMO Guide to Meteorological Instruments and Methods of
Observation, and the preceding ISO 9060 version of 1990, attain continuity of
performance and specifications.
•you can also measure separately the diffuse component only (creating a
diffusometer) for example with a shadowring or shading ball, using the same
instrument model.
•you can perform uncertainty evaluations with negligible (zero) spectral errors under
all conditions, because they are calibrated out.
Figure 2.1.1 Recirculating ventilation and heating between the inner- and outer dome is
much more power-efficient than traditional ventilation systems.

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2.2 Operating modes: heating and ventilation
A unique feature of SR30-M2-D1 is its built-in heater and ventilator. In practice, this is as
effective against dew and frost deposition as using traditional ventilation systems.
The heater is attached to the sensor body. Heat is generated inside the sensor body. The
ventilator circulates air inside the body and between the domes. The combination of
ventilation and heating keeps the domes in thermal equilibrium with the sensor and the
entire instrument above dew point. When ventilation is [ON], zero offsets are very low.
There are 3 operation modes: standard, medium power and low power mode.
In standard operating mode, both heater and ventilator are [ON], in medium power
mode, only the ventilator is [ON], in low power mode both are [OFF]. Table 2.1.1 gives
an overview of these settings and our recommendations for use.
Table 2.2.1 Possible user scenarios for the heater and ventilator
Operating
mode
heater
status
ventilator
status
power use
(at 12 VDC)
comment
standard
[ON]
[ON]
< 3.0 W
factory default
recommended settings
N/A
[ON]
[OFF]
do not use these settings, spectrally
flat Class A specifications will not be
met
medium
power
[OFF]
[ON]
< 0.65 W
this mode offers the most accurate
measurement results because the
sensitivity to thermal fluctuations of
the environment is smaller
recommended over the [OFF] [OFF]
setting, because it reduces the
thermal sensor offset
low power
[OFF]
[OFF]
< 0.1 W
spectrally flat Class A performance is
also guaranteed with these settings
Heating when used in combination with ventilation does not affect the classification
specifications and the measurement accuracy.
When using the heater without ventilation spectrally flat Class A specifications will not be
met, because of a heating-induced offset.
In case that there is no danger of deposition of dew or frost, the medium power mode
(using the ventilator but not the heater) offers the most accurate measurements over
short time intervals. Averages on the minute time scale produce the same result as in
the standard operating mode. The measurement in medium power mode is less sensitive
to thermal shocks (rapid changes of the sensor body temperature) and is less noisy.