Hukseflux SR20 User manual

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USER MANUAL SR20
Secondary standard pyranometer
Hukseflux
Thermal Sensors

SR20 manual v1713 2/43
Warning statements
Putting more than 12 Volt across the sensor wiring
can lead to permanent damage to the sensor.
Do not use “open circuit detection” when measuring
the sensor output.

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Contents
Warning statements 2
Contents 3
List of symbols 4
Introduction 5
1Ordering and checking at delivery 7
1.1 Ordering SR20 7
1.2 Included items 7
1.3 Quick instrument check 8
2Instrument principle and theory 9
3Specifications of SR20 12
3.1 Specifications of SR20 12
3.2 Dimensions of SR20 15
4Standards and recommended practices for use 16
4.1 Classification standard 16
4.2 General use for solar radiation measurement 16
4.3 General use for sunshine duration measurement 16
4.4 Specific use for outdoor PV system performance testing 17
4.5 Specific use in meteorology and climatology 17
5Installation of SR20 18
5.1 Site selection and installation 18
5.2 Installation of the sun screen 19
5.3 Electrical connection 20
5.4 Requirements for data acquisition / amplification 21
6Making a dependable measurement 22
6.1 The concept of dependability 22
6.2 Reliability of the measurement 23
6.3 Speed of repair and maintenance 24
6.4 Uncertainty evaluation 24
7Maintenance and trouble shooting 27
7.1 Recommended maintenance and quality assurance 27
7.2 Trouble shooting 28
7.3 Calibration and checks in the field 29
7.4 Data quality assurance 30
8Appendices 32
8.1 Appendix on cable extension / replacement 32
8.2 Appendix on tools for SR20 33
8.3 Appendix on spare parts for SR20 33
8.4 Appendix on standards for classification and calibration 34
8.5 Appendix on calibration hierarchy 35
8.6 Appendix on meteorological radiation quantities 36
8.7 Appendix on ISO and WMO classification tables 37
8.8 Appendix on definition of pyranometer specifications 38
8.9 Appendix on terminology / glossary 39
8.10 Appendix on converting resistance to temperature 40
8.11 EU declaration of conformity 41

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List of symbols
Quantities Symbol Unit
Voltage output U V
Sensitivity S V/(W/m2)
Sensitivity at reference conditions S0V/(W/m2)
Temperature T °C
Electrical resistance ReΩ
Solar irradiance E W/m2
Solar radiant exposure H W∙h/m2
Time in hours h h
Temperature coefficient a 1/°C²
Temperature coefficient b 1/°C
Temperature coefficient c -
Resistance of Pt100 RPt100 Ω
Pt100 coefficient A
Pt100 coefficient B
Resistance of 10 kΩthermistor Rthermistor Ω
Steinhart-Hart coefficient α
Steinhart-Hart coefficient β
Steinhart-Hart coefficient γ
(see also appendix 8.6 on meteorological quantities)
Subscripts
Not applicable

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Introduction
SR20 is a solar radiation sensor of the highest category in the ISO 9060 classification
system: secondary standard. SR20 pyranometer should be used where the highest
measurement accuracy is required.
SR20 measures the solar radiation received by a plane surface, in W/m2, from a 180o
field of view angle. SR20 enables you to attain the highest measurement accuracy and
excels in demanding applications.
The measured quantity, expressed in W/m2, is called “hemispherical” solar radiation.
SR20 pyranometer can be employed outdoors under the sun, as well as indoors with
lamp-based solar simulators. Its orientation depends on the application and may be
horizontal, tilted (for plane of array radiation) or inverted (for reflected radiation). In
combination with the right software, also sunshine duration may be measured.
Using SR20 is easy. It can be connected directly to commonly used data logging
systems. The irradiance, E, in W/m2is calculated by dividing the SR20 output, a small
voltage U, by the sensitivity S. The sensitivity is provided with SR20 on its calibration
certificate.
The central equation governing SR20 is: E = U/S (Formula 0.1)
SR20’s low temperature dependence makes it an ideal candidate for use under very cold
and very hot conditions. The temperature dependence of every individual instrument is
tested and supplied as a second degree polynomial. This information can be used for
further reduction of temperature dependence during post-processing. In case the
sensitivity is corrected for the instrument body temperature, the optional measurement
equation becomes:
E = U/(S0·(a·T² + b·T +c)) (Formula 0.2)
The temperature coefficients a, b, and c can be found on the calibration certificate of
each instrument.
SR20 is equipped with an internal temperature sensor. This can be either a Pt100 (T1
version) or a 10 kΩ thermistor (T2 version), as ordered. To calculate temperature in
degrees Celsius from resistance in Ohms, Formula 8.10.1 or 8.10.2 can be used. See the
dedicated chapter in the appendix of this manual for these equations.
The incorporated heater reduces measurement errors caused by early-morning dew
deposition. The instrument should be used in accordance with the recommended
practices of ISO, WMO and ASTM.

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Figure 0.1 SR20 secondary standard pyranometer with its sun screen removed
Suggested use for SR20:
•PV system performance monitoring
•scientific meteorological observations
•reference instrument for comparison
•extreme climates (tropical / polar)
•sunshine duration measurement
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. SR20 pyranometer complies with the
requirements of this standard. For more information see our pyranometer selection
guide.
WMO has approved the “pyranometric method” to calculate sunshine duration from
pyranometer measurements in WMO-No. 8, Guide to Meteorological Instruments and
Methods of Observation. This implies that SR20 may be used, in combination with
appropriate software, to estimate sunshine duration. This is much more cost-effective
than using a dedicated sunshine duration sensor. Ask for our application note.
SR20’s output is analogue. Model SR20-D2 offers two other types of commonly used
irradiance outputs: digital via Modbus RTU over 2-wire RS-485 and analogue 4-20 mA
output (current loop).
This user manual covers SR20 use. Specifications of model SR20-D2, the digital
secondary standard pyranometer with Modbus RTU and 4-20 mA output, differ
from those of SR20. For SR20-D2 use, please consult the SR20-D2 user manual.

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1Ordering and checking at delivery
1.1 Ordering SR20
The standard configuration of SR20 is with 5 metres cable.
Common options are:
•Longer cable (in multiples of 5 m). Specify total cable length.
•Internal temperature sensor. This can be either a Pt100 or a 10 kΩ thermistor.
Specify respectively T1 or T2.
•Five silica gel bags in an air-tight bag for SR20 desiccant holder. Specify order
number DC01.
•VU01 ventilation unit.
1.2 Included items
Arriving at the customer, the delivery should include:
•pyranometer SR20
•sun screen
•cable of the length as ordered
•calibration certificate matching the instrument serial number
•product certificate matching the instrument serial number (including temperature
response and directional response test)
•any other options as ordered
Please store the certificates in a safe place.

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1.3 Quick instrument check
A quick test of the instrument can be done by using a simple hand held multimeter and a
lamp.
1. Check the electrical resistance of the sensor between the green (-) and white (+) wire.
Use a multimeter at the 1000 Ωrange. Measure the sensor resistance first with one
polarity, than reverse the polarity. Take the average value. The typical resistance of the
wiring is 0.1 Ω/m. Typical resistance should be the typical sensor resistance of 100 to
200 Ω plus 1.5 Ω for the total resistance of two wires (back and forth) of each 5 m.
Infinite resistance indicates a broken circuit; zero or a low resistance indicates a short
circuit.
2. Check if the sensor reacts to light: put the multimeter at its most sensitive range of
DC voltage measurement, typically the 100 x 10-3 VDC range or lower. Expose the sensor
to a strong light source, for instance a 100 W light bulb at 0.1 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.
3. Remove the sun screen, (see chapter on installation of the sun screen). Inspect the
bubble level.
4. Inspect the instrument for any damage.
5. Inspect if the humidity indicator is blue. Blue indicates dryness. The colour pink
indicates it is humid: in the latter case replace the desiccant (see chapter on
maintenance).

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2Instrument principle and theory
Figure 2.1 Overview of SR20:
(1) cable (standard length 5 metres, optional longer cable)
(2) fixation of sun screen (thumb screw)
(3) inner dome
(4) thermal sensor with black coating
(5) outer dome
(6) sun screen
(7) humidity indicator
(8) desiccant holder
(9) levelling feet
(10) bubble level
(11) connector
1
2
345
6
7
8
9
10
11

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SR20’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” (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 the
environment (convection, rain).
•a second (inner) glass dome: For a secondary standard 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 offsets.
Pyranometers can be manufactured to different specifications and with different levels of
verification and characterisation during production. The ISO 9060 - 1990 standard, “Solar
energy - specification and classification of instruments for measuring hemispherical solar
and direct solar radiation”, distinguishes between 3 classes; secondary standard (highest
accuracy), first class (second highest accuracy) and second class (third highest
accuracy).
From second class to first class and from first class to secondary standard, the achievable
accuracy improves by a factor 2.

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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.
Figure 2.3 Directional response of a SR20 pyranometer of 4 azimuth angles, compared
to secondary standard limits
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
-4%
-2%
0%
2%
4%
0 20 40 60 80
Deviation from ideal cosine behaviour [%]
zenith angle [°]
North
East
South
West
ISO secondary
standard
directional
response limit

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3Specifications of SR20
3.1 Specifications of SR20
SR20 is a pyranometer of the highest category in the ISO 9060 classification system:
secondary standard. It measures the solar radiation received by a plane surface from a
180ofield of view angle. This quantity, expressed in W/m2, is called “hemispherical” solar
radiation. Working completely passive, using a thermopile sensor, SR20 generates a
small output voltage proportional to this flux. It can only be used in combination with a
suitable measurement system.
SR20 has an onboard heater and a temperature sensor. Heating the sensor, measuring
the body temperature and using the correction of the temperature response, all
contribute to the dependability and accuracy of the measurement. However, also when
not using these features, SR20 still complies with the secondary standard requirements.
The instrument should be used in accordance with the recommended practices of ISO,
IEC, WMO and ASTM.
Table 3.1.1 Specifications of SR20 (continued on next pages)
SR20 MEASUREMENT SPECIFICATIONS:
LIST OF CLASSIFICATION CRITERIA OF ISO 9060*
ISO classification (ISO 9060: 1990)
secondary standard pyranometer
WMO performance level (WMO-No. 8,
seventh edition 2008)
high quality pyranometer
Response time (95 %)
3 s
Zero offset a (response to 200 W/m2
net thermal radiation)
5 W/m2 unventilated
2.5 W/m
2
ventilated
Zero offset b (response to 5 K/h
change in ambient temperature)
< ± 2 W/m
2
Non-stability
< ± 0.5 % change per year
Non-linearity
< ± 0.2 % (100 to 1000 W/m2)
Directional response
< ± 10 W/m2
Directional response test of individual
instrument
report included
Spectral selectivity
< ± 3 % (0.35 to 1.5 x 10-6 m)
Temperature response
< ± 1 % (-10 to +40 °C)
< ± 0.4 % (-30 to +50 °C) with correction in data-
processing
Temperature response of individual
instrument
report included
Tilt response
< ± 0.2 % (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 SR20 (continued)
SR20 ADDITIONAL SPECIFICATIONS
Measurand
hemispherical solar radiation
Measurand in SI radiometry units
irradiance in W/m2
Optional measurand
sunshine duration
Field of view angle
180 °
Measurement range
0 to 4000 W/m2
Sensitivity range
7 to 25 x 10-6 V/(W/m2)
Sensitivity (nominal)
15 x 10-6 V/(W/m2)
Expected voltage output application under natural solar radiation: -0.1 to + 50
x 10
-3
V
Measurement function / required
programming
E = U/S
Optional measurement function /
required programming for correction of
sensitivity as a function of instrument
body temperature
E = U/(S0·(a·T²+b·T+c))
Measurement function / optional
programming for sunshine duration
programming according to WMO guide paragraph
8.2.2
Required readout 1 differential voltage channel or 1 single ended
voltage channel, input resistance > 10
6
Ω
Internal temperature sensor measuring the body temperature:
version code = T1 for Pt100 DIN class A,
version code = T2 for thermistor 10 kΩ at 25 °C
Optional readout 1 temperature channel in case the temperature sensor
is used
Rated operating temperature range
-40 to +80 °C
Sensor resistance range
50 to 100 Ω
Required sensor power
zero (passive sensor)
Spectral range
(20 % transmission points)
285 to 3000 x 10
-9
m
Standard governing use of the
instrument
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
Standard cable length (see options)
5 m
Cable diameter
5.3 x 10-3 m
Chassis connector
M16 panel connector, male thread, 10-pole
Chassis connector type
HUMMEL AG 7.840.200.000 panel connector, front
mounting, short version
Cable connector
M16 straight connector, female thread, 10-pole
Cable connector type
HUMMEL AG 7.810.300.00M straight connector,
female thread, for cable 3 to 6 x 10-3 m, special
version
Connector protection class
IP 67 / IP 69 K per EN 60 529 (connected)
Cable replacement replacement cables with connector can be ordered
separately from Hukseflux
Mounting
2 x M5 bolt at 65 x 10-3 m centre-to-centre distance
on north-south axis, or 1 x M6 bolt at the centre of
the instrument, connection from below under the
bottom plate of the instrument
Levelling
bubble level and adjustable levelling feet are included
Levelling accuracy
< 0.1° bubble entirely in ring
Desiccant
two bags of silica gel, 0.5 g, 35 x 20 mm
Humidity indicator
blue when dry, pink when humid
IP protection class
IP 67

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Table 3.1.1 Specifications of SR20 (started on previous pages)
Gross weight including 5 m cable
1.2 kg
Net weight including 5 m cable
0.85 kg
Packaging
box of 200 x 135 x 225 mm
HEATING
Heater operation
the heater is not necessarily switched on;
recommended operation is to activate the heater
when the sun is below the horizon
Required heater power
1.5 W at 12 VDC (the heater is not necessarily active)
Heater resistance
95 Ω
Steady state zero offset caused by
heating
0 to -8 W/m2
CALIBRATION
Calibration traceability
to WRR
Calibration hierarchy from WRR through ISO 9846 and ISO 9847, applying
a correction to reference conditions
Calibration method
indoor calibration according to ISO 9847, Type IIc
Calibration uncertainty
< 1.2 % (k = 2)
Recommended recalibration interval
2 years
Reference conditions
20 °C, normal incidence solar radiation, horizontal
mounting, irradiance level 1000 W/m
2
Validity of calibration
based on experience the instrument sensitivity will not change during storage. During use under exposure to
solar radiation the instrument “non-stability”
specification is applicable.
MEASUREMENT ACCURACY
Uncertainty of the measurement
statements about the overall measurement
uncertainty can only be made on an individual basis.
See the chapter on uncertainty evaluation
WMO estimate on achievable accuracy
for daily sums (see appendix for a
definition of the measurement conditions)
2 %
WMO estimate on achievable accuracy
for hourly sums (see appendix for a
definition of the measurement conditions)
3 %
VERSIONS / OPTIONS
Digital output via Modbus RTU protocol
and 4-20 mA output (current loop)
option code = D2
for specifications see the SR20-D2 user manual
Longer cable, in multiples of 5 m
option code = total cable length
ACCESSORIES
Ventilation unit
VU01
Separate amplifiers
AC100 and AC420
Hand-held read-out unit
LI19
Bags of silica gel for desiccant
set of 5 bags in an air tight bag
option code = DC01

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3.2 Dimensions of SR20
Figure 3.2.1 Dimensions of SR20 in x 10-3 m.
85
M6
M5 (2x)
Ø 150
65

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4Standards 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 the
recommended 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 of
pyranometer specifications, and a table listing the specification limits.
STANDARDS FOR INSTRUMENT CLASSIFICATION
ISO STANDARD EQUIVALENT
ASTM STANDARD
WMO
ISO 9060:1990
Solar energy -- specification and
classification of instruments for
measuring hemispherical solar and
direct solar radiation
Not available
WMO-No. 8; Guide to
Meteorological Instruments
and Methods of Observation,
chapter 7, measurement of
radiation, 7.3 measurement
of 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 RADIATION
ISO STANDARD EQUIVALENT
ASTM 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 UV
Radiometers
WMO-No. 8; Guide to
Meteorological Instruments
and Methods of Observation,
chapter 7, measurement of
radiation, 7.3 measurement
of 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.

SR20 manual v1713 17/43
WMO has approved the “pyranometric method” to estimate sunshine duration from
pyranometer measurements (Chapter 8 of the WMO Guide to Instruments and
Observation, 2008). This implies that a pyranometer may be used, in combination with
appropriate 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 DURATION
WMO
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
SR20 is very well applicable in outdoor PV system performance testing. See also model
SR20-D2 “digital secondary standard pyranometer with Modbus RTU and 4-20 mA
output” and SR12 “first class pyranometer for solar energy test applications”.
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; Photovoltaic system performance
monitoring – guidelines for measurement, data
exchange and analysis
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: equals JISC 8906 (Japanese
Industrial Standards Committee)
ASTM 2848-11; Standard Test Method for
Reporting Photovoltaic Non-Concentrator
System Performance
COMMENT: confirms that a pyranometer is the
preferred instrument for outdoor PV testing.
Specifically recommends a “first class”
pyranometer (paragraph A 1.2.1.)
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 the
earth's atmosphere and climate. WMO publishes WMO-No. 8; Guide to Meteorological
Instruments and Methods of Observation, in which a table is included on “level of
performance” of pyranometers. Nowadays WMO conforms itself to the ISO classification
system.

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5Installation of SR20
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 free
from obstacles as possible. Ideally there should be no
objects between the course of the sun and the
instrument.
Mechanical mounting / thermal insulation
preferably use connection by bolts to the bottom plate of the instrument. A pyranometer is sensitive to
thermal shocks. Do not mount the instrument with the
body in direct thermal contact to the mounting plate
(so always use the levelling feet also if the mounting
is not horizontal), 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 65 x 10-3 m centre to centre distance
on north-south axis, connection from below under the
bottom plate of the instrument.
Instrument mounting with one bolt 1 x M6 bolt at the centre of the instrument,
connection from below under the bottom plate of the
instrument.
Performing a representative
measurement the pyranometer measures the solar radiation in the plane of the sensor. This may require installation in a
tilted or inverted position. The black sensor surface
(sensor bottom plate) should be mounted parallel to
the plane of interest.
In case a pyranometer is not mounted horizontally or
in case the horizon is obstructed, the
representativeness of the location becomes an
important element of the measurement. See the
chapter on uncertainty evaluation.
Levelling in case of horizontal mounting only use the bubble
level and levelling feet. For inspection of the bubble
level the sun screen must be removed.
Instrument orientation by convention with the cable exit pointing to the
nearest pole (so the cable exit should point north in
the northern hemisphere, south in the southern
hemisphere).
Installation height
in 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 Installation of the sun screen
SR20’s sun screen can be installed and removed by using the dedicated thumb screw.
See item 2 of the drawing below. The thumb screw can be turned without tools for
fixation or loosening of the sun screen, as visualised below. Once the thumb screw has
turned the sun screen loose, the screen can be lifted off manually. After removal the user
may inspect the bubble level, item 10 of the drawing, and remove the cable / connector,
item 11.
Figure 5.2.1 Installation and removal of SR20’s sun screen
1
2
345
6
7
8
9
10
11

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5.3 Electrical connection
In order to operate, a pyranometer should be connected to a measurement system,
typically a so-called datalogger. SR20 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 5.3.1 The electrical connection of SR20 versions T1 and T2. The heater is not
necessarily used. The temperature sensor is not necessarily used.
PIN WIRE SR20-T1 SR20-T2
2 Red Pt100 [+] 10 kΩ thermistor [+]
3 Pink Pt100 [+] 10 kΩ thermistor [+]
6 Blue Pt100 [−] 10 kΩ thermistor [−]
8 Grey Pt100 [−] 10 kΩ thermistor [−]
1 Brown heater heater
4 Yellow heater heater
9 Black ground ground
7 White signal [+] signal [+]
5 Green signal [−] signal [−]
Note 1: Pt100’s of version T1 may be connected in a 3-wire of 4-wire configuration.
Note 2: 10k thermistors of version T2 are usually connected in a 2-wire configuration.
Note 3: the heater is not necessarily connected. In case it is connected, the polarity of
the connection is not important.
Note 4: signal wires are insulated from ground wire and from the sensor body. Insulation
resistance is tested during production and larger than 1 x 106Ω.
Note 5: ground is connected to the connector, the sensor body and the shield of the wire.
Figure 5.3.1 Electrical diagram of the internal wiring of SR20. The shield is connected to
the sensor body.