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Hukseflux SR25-D2 User Manual

Digital secondary standard pyranometer with sapphire outer dome
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USER MANUAL SR25-D2
Digital secondary standard pyranometer
with sapphire outer dome
Copyright by Hukseflux | manual v1603 | www.huksefluxusa.com | info@huksefluxusa.com

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  • Page 1 USER MANUAL SR25-D2 Digital secondary standard pyranometer with sapphire outer dome Copyright by Hukseflux | manual v1603 | www.huksefluxusa.com | info@huksefluxusa.com...

  • Page 2: Warning Statements

    Putting more than 40 Volt across the sensor wiring of the current loop (4 to 20 mA) can lead to permanent damage to the sensor. For proper instrument grounding: use SR25-D2 with its original factory-made SR25-D2 cable. Using the same Modbus address for more than one device will lead to irregular behaviour of the entire network.

  • Page 3: Table Of Contents

    Site selection and installation Installation of the sun screen Electrical connection of SR25-D2: wiring diagram Grounding and use of the shield Using SR25-D2’s 4 to 20 mA output Connecting to an RS-485 network Connecting to a PC Communication with SR25-D2...
  • Page 4 Appendix on ISO and WMO classification tables Appendix on definition of pyranometer specifications 9.10 Appendix on terminology / glossary 9.11 Appendix on floating point format conversion 9.12 Appendix on function codes, register and coil overview 9.13 EU declaration of conformity SR25-D2 manual v1603 4/73...

  • Page 5: List Of Symbols

    Solar radiant exposure W∙h/m Time in hours Temperature coefficient 1/°C² Temperature coefficient 1/°C Temperature coefficient Output of 4-20 mA current loop Transmitted range of 4-20 mA output (see also appendix 9.7 on meteorological quantities) Subscripts Not applicable SR25-D2 manual v1603 5/73...

  • Page 6: Introduction

    SR25 with analogue millivolt output. For SR25 use, consult the SR25 user manual. By keeping the SR25-D2 outer dome free of dew and frost with help of the internal heater, data availability is highly increased over traditional pyranometers, whether these are ventilated or not.
  • Page 7 The connector, desiccant holder and sun screen fixation are very robust and designed for long term use. SR25-D2 uses a high-end 24-bit A/D converter. All parts are specified for use across SR25-D2’s entire rated operating temperature range.
  • Page 8 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 SR25-D2 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.

  • Page 9: Ordering And Checking At Delivery

     Longer cable (in multiples of 5 m). Specify total cable length.  Five silica gel bags in an air-thight bag for SR25-D2 desiccant holder. Specify order number DC01.  Adapted transmitted range for 4-20 mA output. Standard setting is 4 mA at 0 W/m and 20 mA at 1600 W/m .

  • Page 10: Quick Instrument Check

    (see chapter on maintenance). 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. SR25-D2 manual v1603 10/73...

  • Page 11: Instrument Principle And Theory

    Instrument principle and theory Figure 2.1 Overview of SR25-D2: cable (standard length 5 metres, optional longer cable) fixation of sun screen (thumb screw) glass inner dome thermal sensor with black coating sapphire outer dome sun screen humidity indicator desiccant holder...
  • Page 12 SR25-D2’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 , is called “hemispherical” solar radiation. The solar radiation spectrum extends roughly from 285 to 3000 x 10 m.
  • Page 13 North East South West ISO secondary standard directional response limit zenith angle [°] Figure 2.3 Directional response of a SR25-D2 pyranometer of 4 azimuth angles, compared to secondary standard limits SR25-D2 manual v1603 13/73...
  • Page 14 Specifications of SR25-D2 3.1 Specifications of SR25-D2 SR25-D2 measures the solar radiation received by a plane surface from a 180 field of view angle. This quantity, expressed in W/m , is called “hemispherical” solar radiation. SR25-D2 offers irradiance in W/m as a digital output and as a 4-20 mA output.
  • Page 15 Table 3.1.1 Specifications of SR25-D2 (continued) SR25-D2 ADDITIONAL SPECIFICATIONS Measurand hemispherical solar radiation Measurand in SI radiometry units irradiance in W/m Optional measurand sunshine duration Field of view angle 180 ° Output definition running average over 4 measurements, refreshed every 0.1 s...
  • Page 16 Table 3.1.1 Specifications of SR25-D2 (started on previous pages) 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 <...

  • Page 17: Specifications Of Sr25-D2

    Table 3.1.1 Specifications of SR25-D2 (started on previous pages) Principle of 4 to 20 mA output 2-wire current loop. note: 2 additional wires are needed for the main supply of the sensor Rated operating voltage range of 4 to 20 5.5 to 40 VDC...

  • Page 18: Dimensions Of Sr25-D2

    3.2 Dimensions of SR25-D2 M5 (2x) Figure 3.2.1 Dimensions of SR25-D2 in x 10 SR25-D2 manual v1603 18/73...

  • Page 19: Standards And Recommended Practices For Use

    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/m SR25-D2 manual v1603 19/73...

  • Page 20: Specific Use For Outdoor Pv System Performance Testing

    8.2.2 Pyranometric Method 4.4 Specific use for outdoor PV system performance testing SR25-D2 is very well applicable in outdoor PV system performance testing. See also Hukseflux model SR20-D2 “digital secondary standard pyranometer with Modbus RTU and 4-20 mA output”.

  • Page 21: Installation Of Sr25-D2

    Installation of SR25-D2 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.

  • Page 22: Installation Of The Sun Screen

    5.2 Installation of the sun screen SR25-D2’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.

  • Page 23: Electrical Connection Of Sr25-D2: Wiring Diagram

    Do not put more than 40 Volt across these wires. The internal heater is not necessarily used. The heater should be powered separately by 12 VDC (see appendix 9.1 on recommendations for using SR25-D2’s heater).

  • Page 24: Using Sr25-D2'S 4 To 20 Ma Output

    5.5 Using SR25-D2’s 4 to 20 mA output SR25-D2 gives users the option to use 4 to 20 mA output instead of its digital output. When using 4 to 20 mA output, please read this chapter first. When opting solely for SR25-D2’s digital output, please continue with the next chapter.
  • Page 25 Usually a 100 Ω shunt resistor (R) is used to convert the current to a voltage. SR25-D2 operates on a supply voltage of 5 to 30 VDC. In addition, 5.5 to 40 VDC is needed for the 4 -20 mA function.

  • Page 26: Connecting To An Rs-485 Network

    SR25-D2 is designed for a two-wire (half-duplex) RS-485 network. In such a network SR25-D2 acts as a slave, receiving data requests from the master. An example of the topology of an RS-485 two-wire network is shown in the figure below. SR25-D2 is powered from 5 to 30 VDC, whereas the heater is powered separately by 12 VDC.
  • Page 27 , RS-485 B / B’ green [ - ] data, RS-485 A / A’ SR25-D2 wire RS-485 network Figure 5.5.2 Connection of SR25-D2 to an RS-485 network. SR25-D2 is powered by an external power supply of 5 to 30 VDC. SR25-D2 manual v1603 27/73...

  • Page 28: Connecting To A Pc

    5.7 Connecting to a PC SR25-D2 can be accessed via a PC. In that case communication with the sensor is done via the user interface offered by the Sensor Manager software (see the next chapters) or by another Modbus testing tool.

  • Page 29: Communication With Sr25-D2

    The Hukseflux Sensor Manager software provides a user interface for communication between a PC and SR25-D2. It allows the user to locate, configure and test one or more SR25-D2’s and to perform simple laboratory measurements using a PC. The Sensor Manager’s most common use is for initial functionality testing and modification of the...
  • Page 30 6.1.3 Sensor Manager: main window Figure 6.1.3.1 Main window of the Sensor Manager When the Sensor Manager is started and a SR25-D2 is connected to the PC, the user can communicate with the instrument. If the instrument address and communication settings are known, the serial connection settings and the Modbus address can be entered directly.
  • Page 31 6.1.4 Sensor Manager: plotting data When the “Plot on Live Chart” button in the lower right corner is clicked the “Plot window” opens. A live graph is shown of the measurement with the selected instrument. SR25-D2 manual v1603 31/73...
  • Page 32 W/m . The Y-axis automatically scales to display the full measured range. Figure 6.1.4.1 Example of an SR25-D2 irradiance plot in the Sensor Manager 6.1.5 Sensor Manager: information about the instrument The main window shows the “Show details” button, giving access to the “Sensor details”...
  • Page 33 6.1.6 Sensor Manager: changing Modbus address and communication settings In the “Sensor details” window the “Change settings” function opens the “Change serial communication settings” window, as shown in the figure below. Figure 6.1.6.1 Change serial communication settings window in the Sensor Manager SR25-D2 manual v1603 33/73...

  • Page 34: Network Communication: Function Codes, Registers, Coils

    Example: During a calibration experiment, the result might be that SR25-D2 has an irradiance output in W/m that is 990, whereas the standard indicates it should be 970. The SR25-D2 output is in this example 2.06 % too high. The original sensitivity of 16.15 x 10 V/(W/m ) ought to be changed to 16.48, using registers 41 + 42.
  • Page 35 An Unsigned 32 bit integer can be calculated by the formula: (MSW x 2 )+LSW = U32. An example of such a calculation is available in the paragraph “Network communication: example master request to SR25-D2”. SR25-D2 manual v1603 35/73...
  • Page 36 Your data request may need an offset of +1 for each SR25-D2 register number, depending on processing by the network master. Example: SR25-D2 register number 7 + master offset = 7 + 1 = master register number 8. Consult the manual of the device acting as the local master.
  • Page 37 0.01 W/m². The value given must be divided by 100 to achieve the value in W/m². Hukseflux recommends using this data to achieve the highest accuracy. MSW and LSW should be read together in one request.
  • Page 38 Ω. Register 46 + 47, Sensor calibration date, last sensor calibration date, from which the sensitivity in register 41 and 42 was found, in YYYYMMDD. Register 61, Firmware version. Register 62, Hardware version. SR25-D2 manual v1603 38/73...
  • Page 39 PARAMETER DESCRIPTION OF CONTENT TYPE FORMAT NUMBER OF DATA 83 + 84 Directional response Directional response measurement date measurement date in YYYYMMDD Directional response measurement employee Register 83 to 85, these registers are for reference purposes. SR25-D2 manual v1603 39/73...
  • Page 40 Register 86 to 95, these registers are for reference purposes. Please note that if your data request needs an offset of +1 for each SR25-D2 register number, depending on processing by the network master, this offset applies to coils as well. Consult the manual of the device acting as the local master.
  • Page 41 After the measurement, a new value will be written into register 7. Requesting to write this coil with a high repetition rate will result in irregular behaviour of the sensor; the check must be executed as an exceptional diagnostics routine only. SR25-D2 manual v1603 41/73...

  • Page 42: Network Communication: Getting Started

    Modbus device. This usually consists of defining a request that can be broadcast by the master. If the SR25-D2 is not already defined as a standard sensor type on the network, contact the supplier of the network equipment to see if a library file for the SR25-D2 is available.

  • Page 43: Network Communication: Example Master Request To Sr25-D2

    For quality assurance also the sensor serial number, register 40 and the temperature in register 6, are useful. In this example a SR25-D2 has address 64. The example requests the solar radiation (temperature compensated) register 2 + 3, sensor serial number, register 40, and the temperature of the instrument register 6.
  • Page 44 [79][DA] = CRC, the checksum of the transmitted data Together, register 2 and 3 are representing the temperature compensated solar radiation output measured by SR25-D2. The MSW is in register 2 and the LSW in 3. The output has to be calculated by the formula: ((MSW x 2 ) + LSW)/100.
  • Page 45 [03] = Modbus function [02] = Number of bytes [0A][29] = Content of register 40, decimal equivalent = 2601 [43][35] = CRC Register 40 represents the sensors serial number. In this example the serial number is 2601. SR25-D2 manual v1603 45/73...

  • Page 46: Making A Dependable Measurement

    * defined at Hukseflux as all factors outside the instrument that are relevant to the measurement such as the cloud cover (presence or absence of direct radiation), sun position, the local horizon (which may be obstructed) or condition of the ground (when tilted).

  • Page 47: Reliability Of The Measurement

    For first class and secondary standard models (for instance model SR11 first class pyranometer and SR25-D2 digital secondary standard pyranometer) extra desiccant (in a set of 5 bags in an air tight bag) is available.

  • Page 48: Speed Of Repair And Maintenance

    Dependability is not only a matter of reliability but also involves the reaction to problems; if the processing time of service and repairs is short, this contributes to the dependability. Hukseflux pyranometers are designed to allow easy maintenance and repair. The main maintenance actions are: ...
  • Page 49 3) A separate estimate has to be entered to allow for estimated uncertainty due to the instrument maintenance level. 4) The calibration uncertainty has to be entered. Please note that Hukseflux calibration uncertainties are lower than those of alternative equipment. These uncertainties are entered in measurement equation (equation is usually Formula 0.1: E = U/S), either as...
  • Page 50 Table 7.4.1.1 Preliminary estimates of achievable uncertainties of measurements with Hukseflux pyranometers. The estimates are based on typical pyranometer properties and calibration uncertainty, for sunny, clear sky days and well maintained stations, without uncertainty loss due to lack of maintenance and due to instrument fouling. The table specifies expanded uncertainties with a coverage factor of 2 and confidence level of 95 %.

  • Page 51: Maintenance And Trouble Shooting

    Maintenance and trouble shooting 8.1 Recommended maintenance and quality assurance SR25-D2 can measure reliably at a low level of maintenance in most locations. Usually unreliable measurements will be detected as unreasonably large or small measured values. As a general rule this means that regular visual inspection combined with a critical review of the measured data, preferably checking against other measurements, is the preferred way to obtain a reliable measurement.

  • Page 52: Trouble Shooting

    ISO 9847 or outdoors according to ISO9846 8.2 Trouble shooting Table 8.2.1 Trouble shooting for SR25-D2 (continued on next page) General Inspect the instrument for any damage. 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).

  • Page 53: Calibration And Checks In The Field

    The applicable standard is ISO 9847 “International Standard- Solar 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.

  • Page 54: Data Quality Assurance

    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 a pyranometer of a higher class, and 3) to connect both to the same electronics, so that electronics errors (also offsets) are eliminated.
  • Page 55 SR25-D2 manual v1603 55/73...

  • Page 56: Appendices

    9.1. 9.1.1 Recommendations on heater use in SR25-D2 SR25-D2 is equipped with an internal heater, which is not necessarily connected. The combined use of sapphire and internal heating keeps the outer dome dew- and frost-free. This highly increases data availability, while maintaining high measurement accuracy.
  • Page 57 [W/m²] Figure 9.1.2.2 nighttime offsets of ventilated pyranomers and SR25 versus net longwave radiation. SR25 has lower nighttime offset than the ventilated secondary standard pyranometers both when unheated and when heated SR25-D2 manual v1603 57/73...
  • Page 58 During a period of 26 days in spring 2015, the reduction in data availability due to dew deposition on domes was monitored for various sensor configurations. The Hukseflux outdoor test facility was used for this experiment. SR25 with heating had no reduction in data availability due to dew.

  • Page 59: Appendix On Cable Extension / Replacement

    9.2 Appendix on cable extension / replacement The sensor cable of SR25-D2 is equipped with a M16 straight connector. In case of cable replacement, it is recommended to purchase a new cable with connector at Hukseflux. An alternative is to choose for a Do-It-Yourself (DIY) approach; please ask for the DIY connector assembly guide.

  • Page 60: Appendix On Tools For Sr25-D2

    Table 9.2.1 Preferred specifications for SR25-D2 cable replacement and extension General replacement please order a new cable with connector at Hukseflux or choose for a DIY approach. In case of DIY replacement by the user see connector specifications below and ask for the DIY connector assembly guide...

  • Page 61: Appendix On Spare Parts For Sr25-D2

     O-ring SR25-D2 NOTE: Outer dome, level and sensor of SR25-D2 cannot be supplied as spare parts. In case of possible damage to the SR25-D2, after repair the instrument must be tested to verify performance within specification limits. This is required by ISO 9060.

  • Page 62: Appendix On Standards For Classification And Calibration

    Indoor Transfer of Calibration from Reference to Field Pyranometers ISO 9059:1990 Solar energy -- Calibration of ASTM E 816 Standard Test Method for field pyrheliometers by comparison to a Calibration of Pyrheliometers by Comparison to reference pyrheliometer Reference Pyrheliometers SR25-D2 manual v1603 62/73...

  • Page 63: Appendix On Calibration Hierarchy

    (transfer error). The coverage factor must be determined; at Hukseflux we work with a coverage factor k = 2. SR25-D2 manual v1603...

  • Page 64: Appendix On Meteorological Radiation Quantities

    In solar energy radiant exposure is often given in W∙h/m Table 9.7.1 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.

  • Page 65: Appendix On Iso And Wmo Classification Tables

    WMO 7.3.2.5: Table 7.5 lists the expected maximum deviation from the true 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 the classification, conformity compliance can be proven either by group- or individual compliance.

  • Page 66: Appendix On Definition Of Pyranometer Specifications

    1.6.3 reading. Zero offset a: response to 200 W/m net thermal radiation (ventilated). (200 W/m Hukseflux assumes that unventilated instruments have to specify 9060- thermal the zero-offset in unventilated – worst case – conditions. 1990 radiation ) Zero offsets are a measure of the stability of the zero-point.

  • Page 67: Appendix On Terminology / Glossary

    The former is the direct component, the latter is the diffuse component of the solar radiation. (ref: WMO, Hukseflux) Hemispherical solar radiation received by a plane surface from a 180° field of view angle (solid solar radiation angle of 2 π...

  • Page 68: Appendix On Floating Point Format Conversion

    9.11 Appendix on floating point format conversion For efficient use of microcontroller capacity some registers in the SR25-D2 contain data in a float or floating point format. In fact, a floating point is an approximation of a real number represented by a number of significant digits (mantissa) and an exponent. For implementation of the floating point numbers, Hukseflux follows the IEEE 754 standard.

  • Page 69: Appendix On Function Codes, Register And Coil Overview

    0x10 Write Multiple Registers Your data request may need an offset of +1 for each SR25-D2 register number, depending on processing by the network master. Example: SR25-D2 register number 7 + master offset = 7 + 1 = master register number 8. Consult the manual of the device acting as the local master.
  • Page 70 YYYYMMDD Directional response measurement employee Temperature response In x 0.01 % 87 + 88 Polynomial temperature Float coefficient a 89 + 90 Polynomial temperature Float coefficient b 91 + 92 Polynomial temperature Float coefficient c SR25-D2 manual v1603 70/73...
  • Page 71 Up to five 16 bit registers can be requested in one request. If requesting six or more registers, use multiple requests. Please note that if your data request needs an offset of +1 for each SR25-D2 register number, depending on processing by the network master, this offset applies to coils as well.

  • Page 72: Eu Declaration Of Conformity

    Emission: IEC/EN 61000-6-1, Class B, RF emission requirements, IEC CISPR11 and EN 55011 Class B requirements Immunity: IEC/EN 61000-6-2 and IEC 61326 requirements Report: SR25-D2, 04 December 2015 Eric HOEKSEMA Director Delft 10 March, 2016 SR25-D2 manual v1603 72/73...
  • Page 73 © 2016, 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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