apogee SP-522 Pyranometer Owner’s Manual

apogee SP-522 Pyranometer

INTRODUCTION

Solar radiation at Earth’s surface is typically defined as total radiation across a wavelength range of 280 to 4000 nm (shortwave radiation). Total solar radiation, direct beam and diffuse, incident on a horizontal surface is defined as global shortwave radiation, or shortwave irradiance (incident radiant flux), and is expressed in Watts per square meter (W m-2, equal to Joules per second per square meter). Pyranometers are sensors that measure global shortwave radiation. Apogee SP-500 series pyranometers are blackbody thermopile pyranometers and are sensitive to most of the solar spectrum, thus eliminating spectral errors associated with silicon-cell pyranometers. The SP-522 is designed to measure incoming shortwave radiation and combines a diffuser with the blackbody detector and has calibrations traceable to Class A blackbody thermopile pyranometers traceable to the world radiation reference in Davos, Switzerland. Specifications compare favorably to specifications for World Meteorological Organization (WMO) moderate and good quality classifications and specifications for International Organization of Standardization (ISO) Class C and Class B classifications.
Typical applications of pyranometers include incoming shortwave radiation measurement in agricultural, ecological, and hydrological weather networks and solar panel arrays.
Apogee Instruments SP-522 pyranometers consist of a thermopile detector, acrylic diffuser, heater, and signal processing circuitry mounted in an anodized aluminum housing, and a cable to connect the sensor to a measurement device. Sensors are potted solid with no internal air space and are designed for continuous measurement of shortwave radiation in outdoor environments. The SP-522 model outputs a digital signal using Modbus RTU communication protocol over RS-232 or RS-485.

SENSOR MODELS

This manual covers the Modbus RTU protocol model SP-522 pyranometer sensor (in bold below). Additional models are covered in their respective manuals.

The sensor model number and serial number are located on the bottom of the sensor. If the manufacturing date of a specific sensor is required, please contact Apogee instruments with the serial number of the sensor.

SPECIFICATIONS

SP-522

ISO 9060:2018| Class C (previously known as second class )
Input Voltage Requirement| 5.5 to 24 V
Average Max Current Draw| 4 mA (heater off)

30 mA (heater on)

Calibration Uncertainty| ± 5 % (see Calibration Traceability below)
Measurement Repeatability| Less than 1 %
Long-term Drift

(Non-stability)

| Less than 2 % per year
Non-linearity| Less than 1 % (up to 2000 W m-2)
Field of View| 180°
Spectral Range| 385 to 2105 nm (wavelengths where the response is 50 % of maximum)
Directional (Cosine)

Response

| Less than 30 W m⁻² at 80° solar zenith
Temperature Response| Less than 5 % from -15 to 45 C
Zero Offset A| Less than 5 W m⁻²; Less than 10 W m⁻² (heated)
Zero Offset B| Less than 5  W m⁻²
Operating Environment| -50 to 80 C; 0 to 100 % relative humidity; can be submerged in water up to 30 m
Dimensions| 30.5 diameter, 37 mm height
Mass (with 5 m of cable)| 140 g
Cable| 5 m of four-conductor, shielded, twisted-pair wire; TPR jacket; pigtail lead wires; stainless

steel (316), M8 connector

Calibration Traceability

Apogee Instruments SP-500 series pyranometers are calibrated through side-by- side comparison to the mean of four transfer standard pyranometers (shortwave radiation reference) under high-intensity discharge metal halide lamps. The transfer standard pyranometers are calibrated through side-by-side comparison to the mean of at least two ISO-classified reference pyranometers under sunlight (clear sky conditions) in Logan, Utah. Each of four ISO-classified reference pyranometers is recalibrated on an alternating year schedule (two instruments each year) at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. NREL reference standards are calibrated to the World Radiometric Reference (WRR) in Davos, Switzerland.

DEPLOYMENT AND INSTALLATION

Mount the sensor to a solid surface with the nylon mounting screw provided. To accurately measure PPFD incidents on a horizontal surface, the sensor must be level. An Apogee Instruments model AL-100 Leveling Plate is recommended to level the sensor when used on a flat surface or be mounted to surfaces such as wood. To facilitate mounting on a mast or pipe, the Apogee Instruments model AL-120 Solar Mounting Bracket with Leveling Plate is recommended.

Important: Only use the nylon screw provided when mounting to insulate the non-anodized threads of the aluminum sensor head from the base to help prevent galvanic corrosion. For extended submersion applications, more insulation may be necessary. Contact Apogee tech support for details.

• Nylon Screw: 10-32×3/8
• Nylon Screw:**** 10-32×3/8
• Model: AL-100
• Model: AL-120

To minimize azimuth error, the sensor should be mounted with the cable pointing toward true north in the northern hemisphere or true south in the southern hemisphere. Azimuth error is typically less than 1 %, but it is easy to minimize by proper cable orientation.

In addition to orienting the cable to point toward the nearest pole, the sensor should also be mounted such that obstructions (e.g., weather station tripod/tower or other instrumentation) do not shade the sensor. Once mounted, the black cap should be removed from the sensor. The green cap can be used as a protective covering for the sensor when it is not in use.

CABLE CONNECTORS

Apogee sensors offer cable connectors to simplify the process of removing sensors from weather stations for calibration (the entire cable does not have to be removed from the station and shipped with the sensor). The ruggedized M8 connectors are rated IP68, made of corrosion-resistant marine-grade stainless- steel, and designed for extended use in harsh environmental conditions.

• Cable connectors are attached directly to the head.

Instructions

Pins and Wiring Colors: All Apogee connectors have six pins, but not all pins are used for every sensor. There may also be unused wire colors inside the cable. To simplify the datalogger connection, we remove the unused pigtail lead colors at the datalogger end of the cable. If a replacement cable is required, please contact Apogee directly to ensure ordering the proper pigtail configuration.

Alignment: When reconnecting a sensor, arrows on the connector jacket and an aligning notch ensure proper orientation.

• A reference notch inside the connector ensures proper alignment before tightening.

Disconnection for extended periods: When disconnecting the sensor for an extended period of time from a station, protect the remaining half of the connector still on the station from water and dirt with electrical tape or another method.

• When sending sensors in for calibration, only send the sensor head.

Tightening: Connectors are designed to be firmly finger-tightened only. There is an O-ring inside the connector that can be overly compressed if a wrench is used. Pay attention to thread alignment to avoid cross-threading. When fully tightened, 1-2 threads may still be visible.

WARNING: Do not tighten the connector by twisting the black cable or sensor head, only twist the metal connector (blue arrows).

• Finger-tighten firmly.

OPERATION AND MEASUREMENT

The SP-522 pyranometer has a Modbus output, where shortwave radiation is returned in digital format. Measurement of SP-522 pyranometers requires a measurement device with a Modbus interface that supports the Read Holding Registers (0x03) function.

Wiring

• White: RS-232 RX / RS-485 Positive
• Blue: RS-232 TX / RS-485 Negative
• Green: Select (Switch between RS-232 and RS-485)
• Black: Ground
• Red: Power +12 V

The Green wire should be connected to the Ground to enable RS-485 communication, or it should be connected to 12 V power for RS-232 communication. Text for the White and Blue wires above refers to the port that the wires should be connected.

Sensor Calibration

All Apogee Modbus thermopile pyranometers (model SP-522) has sensor-specific calibration coefficients determined during the custom calibration process. Coefficients are programmed into the sensors at the factory.

Modbus Interface

The following is a brief explanation of the Modbus protocol instructions used in Apogee SP-522 pyranometers. For questions on the implementation of this protocol, please refer to the official serial line implementation of the Modbus protocol: http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf (2006) and the general Modbus protocol specification: http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf (2012). Further information can be found at: http://www.modbus.org/specs.php

Overview

The primary idea of the Modbus interface is that each sensor exists at an address and appears as a table of values. These values are called Registers. Each value in the table has an associated index, and that index is used to identify which value in the table is being accessed.

Sensor addresses

Each sensor is given an address from 1 to 247. Apogee sensors are shipped with a default address of 1. If using multiple sensors on the same Modbus line, the sensor’s address will have to be changed by writing the Slave Address register.

Register Index

Each register in a sensor represents a value in the sensor, such as a measurement or a configuration parameter. Some registers can only be read, some registers can only be written, and some can be both read and written. Each register exists at a specified index in the table for the sensor. Often this index is called an address, which is a separate address from the sensor address but can be easily confused with the sensor address. However, there are two different indexing schemes used for Modbus sensors, though translating between them is simple. One indexing scheme is called one-based numbering, where the first register is given the index of 1, and is thereby accessed by requesting access to register 1. The other indexing scheme is called zero- based numbering, where the first register is given the index 0 and is thereby accessed by requesting access to register 0. Apogee Sensors use zero-based numbering. However, if using the sensor in a system that uses one-based numbering, such as using a CR1000X logger, adding 1 to the zero-based address will produce the one-based address for the registration.

Register Format

According to the Modbus protocol specification, Holding Registers (the type registers Apogee sensors contain) are defined to be 16 bits wide. However, when making scientific measurements, it is desirable to obtain a more precise value than 16 bits allows. Thus, several Modbus implementations will use two 16-bit registers to act as one 32-bit register. Apogee Modbus sensors use this 32-bit implementation to provide measurement values as 32-bit IEEE 754 floating-point numbers. Apogee Modbus sensors also contain a redundant, duplicate set of registers that use 16-bit signed integers to represent values as decimal-shifted numbers. It is recommended to use the 32-bit values, if possible, as they contain more precise values.

Communication Parameters

Apogee Sensors communicate using the Modbus RTU variant of the Modbus protocol. The default communication parameters are as follows:

• Slave address: 1
• Baud rate: 19200
• Data bits: 8
• Stop bits: 1
• Parity: Even
• Byte Order: Big-Endian (most significant byte sent first)

The baud rate and slave address are user-configurable. Valid slave addresses are 1 to 247. Since the address 0 is reserved as the broadcast address, setting the slave address to 0 will actually set the slave address to 1. (This will also reset factory-calibrated values and should NOT be done by the user unless otherwise instructed.)

Read only registers (function code 0x3)

Float Registers

0

1

| calibrated output watts
2

3

| detector millivolts
4

5

| Reserved for Future Use
6

7

| device status

(1 means the device is busy, 0 otherwise)

8

9

| firmware version
Integer Registers
40| calibrated output watts (shifted one decimal point to the left)
41| detector millivolts (shifted one decimal point to the left)
42| Reserved for Future Use
43| device status (1 means device is busy, 0 otherwise)
44| firmware version (shifted one decimal point to the left)

Read/Write registers (function codes 0x3 and 0x10)

Float Registers

16

17

| slave address
18

19

| model number*
20

21

| serial number*
22

23

| baud rate (0 = 115200, 1 = 57600, 2 = 38400, 3 = 19200, 4 = 9600, any

other number = 19200

24

25

| parity (0 = none, 1 = odd, 2 = even)
26

27

| number of stopbits
28

29

| multiplier*
30

31

| offset*
32

33

| running average
34

35

| heater status
Integer Registers
48| slave address
49| model number
50| serial number
51| baud rate (0 = 115200, 1 = 57600, 2 = 38400, 3 = 19200, 4 = 9600, any

other number = 19200)

52| parity (0 = none, 1 = odd, 2 = even)
53| number of stop bits
54| multiplier (shifted two decimal points to the left)
---|---
55| offset (shifted two decimal points to the left)
56| running average
57| heater status

• Registers marked with an asterisk (*) cannot be written to unless a specific procedure is followed. Contact Apogee Instruments to receive the procedure for writing these registers.

Write only registers (function code 0x10)

Integer Registers

190

| Writing to this register resets Coefficients to firmware defaults. (NOT factory calibrated values!) Slave Address

= 1, Model = 522, Serial = 1000, Baud = 3, Parity = 2,

Stopbits = 1, running average = 1

Packet Framing

Apogee sensors use Modbus RTU packets and tend to adhere to the following pattern:

Slave Address (1 byte), Function Code (1 byte), Starting Address (2 bytes), Number of Registers (2 bytes), Data Length (1 byte, optional) Data (n bytes, optional)

Modbus RTU packets use the zero-based address when addressing registers

For information on Modbus RTU framing, see the official documentation at http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf

Example Packets

An example of a data packet sent from the controller to the sensor using function code 0x3 reading register address 0. Each pair of square brackets indicates one byte.
[Slave Address][Function][Starting Address High Byte][Starting Address Low Byte][No of Registers High Byte][No of Registers Low Byte][CRC High Byte][CRC Low Byte] 0x01 0x03 0x00 0x00 0x00 0x02 0xC4 0x0B
An example of a data packet sent from the controller to the sensor using function code 0x10 writing a 1 to register 26. Each pair of square brackets indicates one byte.
[Slave Address][Function][Starting Address High Byte][Starting Address Low Byte][No of Registers High Byte][No of Registers Low Byte][Byte Count][Data High Byte][Data Low Byte][Data High Byte][Data Low Byte][CRC High Byte][CRC Low Byte] 0x01 0x10 0x00 0x1A 0x00 0x02 0x04 0x3f 0x80 0x00 0x00 0x7f 0x20.

MAINTENANCE AND RECALIBRATION

Blocking of the optical path between the target and detector can cause low readings. Occasionally, accumulated materials on the diffuser can block the optical path in three common ways:

1. Moisture or debris on the diffuser.
2. Dust during periods of low rainfall.
3. Salt deposit accumulation from the evaporation of sea spray or sprinkler irrigation water.

Apogee Instruments pyranometers have a domed diffuser and housing for improved self-cleaning from rainfall, but active cleaning may be necessary. Dust or organic deposits are best removed using water, or window cleaner, and a soft cloth or cotton swab. Salt deposits should be dissolved with vinegar and removed with a cloth or cotton swab. Salt deposits cannot be removed with solvents such as alcohol or acetone. Use only gentle pressure when cleaning the diffuser with a cotton swab or soft cloth to avoid scratching the outer surface. The solvent should be allowed to do the cleaning, not mechanical force. Never use abrasive material or cleaner on the diffuser. Although Apogee sensors are very stable, nominal accuracy drift is normal for all research- grade sensors. To ensure maximum accuracy, we generally recommend sensors are sent in for recalibration every two years, although you can often wait longer according to your particular tolerances. To determine if your sensor needs recalibration, the Clear Sky Calculator (www.clearskycalculator.com) website and/or smartphone app can be used to indicate the total shortwave radiation incident on a horizontal surface at any time of day at any location in the world. It is most accurate when used near solar noon in the spring and summer months, where accuracy over multiple clear and unpolluted days is estimated to be ± 4 % in all climates and locations around the world. For best accuracy, the sky must be completely clear, as reflected radiation from clouds causes incoming radiation to increase above the value predicted by the clear sky calculator. Measured values of total shortwave radiation can exceed values predicted by the Clear Sky Calculator due to reflection from thin, high clouds and edges of clouds, which enhances incoming shortwave radiation. The influence of high clouds typically shows up as spikes above clear sky values, not a constant offset greater than clear sky values. To determine recalibration needs, input site conditions into the calculator and compare total shortwave radiation measurements to calculated values for a clear sky. If sensor shortwave radiation measurements over multiple days near solar noon are consistently different than calculated values (by more than 6 %), the sensor should be cleaned and re-leveled. If measurements are still different after a second test, email calibration@apogeeinstruments.com to discuss test results and the possible return of sensor(s).

This calculator determines the intensity of radiation falling on a horizontal surface at any time of the day in any location in the world. The primary use of this calculator is to determine the need for the recalibration of radiation sensors. It is most accurate when used near solar noon in th summer months.

Homepage of the Clear Sky Calculator. Two calculators are available: One for pyranometers (total shortwave radiation) and one for quantum sensors (photosynthetic photon flux density).

• Clear Sky Calculator for pyranometers. Site data are input in blue cells in the middle of the page and an estimate of total shortwave radiation is returned on the right-hand side of the page.

TROUBLESHOOTING AND CUSTOMER SUPPORT

Independent Verification of Functionality

If the sensor does not communicate with the datalogger, use an ammeter to check the current drain. It should be near 37 mA when the sensor is powered. Any current drain significantly greater than approximately 37 mA indicates a problem with the power supply to the sensors, wiring of the sensor, or sensor electronics.

Compatible Measurement Devices (Dataloggers/Controllers/Meters)

Any datalogger or meter with RS-232/RS-485 that can read/write float or integer values. An example datalogger program for Campbell Scientific dataloggers can be found at https://www.apogeeinstruments.com/content /Pyranometer-Modbus.CR1.

Cable Length

All Apogee sensors use shielded cable to minimize electromagnetic interference. For best communication, the shield wire must be connected to earth ground. This is particularly important when using the sensor with long lead lengths in electromagnetically noisy environments.

RS-232 Cable Length

If using an RS-232 serial interface, the cable length from the sensor to the controller should be kept short, no longer than 20 meters. For more information, see section 3.3.5 in this document: http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf

RS-485 Cable Length

If using an RS-485 serial interface, longer cable lengths may be used. The trunk cable can be up to 1000 meters long. The length of cable from the sensor to a tap on the trunk should be short, no more than 20 meters. For more information, see section 3.4 in this document: http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf

Troubleshooting Tips

• Make sure to use the green wire to select between RS-232 and RS-485.
• Make sure that the sensor is wired correctly (refer to wiring diagram).
• Make sure the sensor is powered by a power supply with a sufficient output (e.g., 12 V).
• Make sure to use the appropriate kind of variable when reading Modbus registers. Use a float variable for float registers and an integer variable for integer registers.
• Make sure the baud rate, stop bits, parity, byte order, and protocols match between the control program and the sensor. Default values are:
  • Baud rate: 19200
  • Stop bits: 1
  • Parity: Even
  • Byte order: ABCD (Big-Endian/Most Significant Byte First)
  • Protocol: RS-232 or RS-485

RETURN AND WARRANTY POLICY

RETURN POLICY

Apogee Instruments will accept returns within 30 days of purchase as long as the product is in new condition (to be determined by Apogee). Returns are subject to a 10 % restocking fee.

WARRANTY POLICY

What is Covered

All products manufactured by Apogee Instruments are warranted to be free from defects in materials and craftsmanship for a period of four (4) years from the date of shipment from our factory. To be considered for warranty coverage an item must be evaluated by Apogee. Products not manufactured by Apogee (spectroradiometers, chlorophyll content meters, EE08-SS probes) are covered for a period of one (1) year.

What is Not Covered

The customer is responsible for all costs associated with the removal, reinstallation, and shipping of suspected warranty items to our factory. The warranty does not cover equipment that has been damaged due to the following conditions:

1. Improper installation or abuse.
2. Operation of the instrument outside of its specified operating range.
3. Natural occurrences such as lightning, fire, etc.
4. Unauthorized modification.
5. Improper or unauthorized repair.

Please note that nominal accuracy drift is normal over time. Routine recalibration of sensors/meters is considered part of proper maintenance and is not covered under warranty.

Who is Covered

This warranty covers the original purchaser of the product or other party who may own it during the warranty period.

What Apogee Will Do At no charge Apogee will:

1. Either repair or replace (at our discretion) the item under warranty.
2. Ship the item back to the customer by the carrier of our choice.

Different or expedited shipping methods will be at the customer’s expense.

How To Return An Item

1. Please do not send any products back to Apogee Instruments until you have received a Return Merchandise Authorization (RMA) number from our technical support department by submitting an online RMA form at www.apogeeinstruments.com/tech-support-recalibration-repairs/. We will use your RMA number for tracking of the service item. Call 435-245-8012 or email echsupport@apogeeinstruments.com-with-questions.
2. For warranty evaluations, send all RMA sensors and meters back in the following condition: Clean the sensor’s exterior and cord. Do not modify the sensors or wires, including splicing, cutting wire leads, etc. If a connector has been attached to the cable end, please include the mating connector otherwise, the sensor connector will be removed in order to complete the repair/recalibration. Note: When sending back sensors for routine calibration that have Apogee’s standard stainless-steel connectors, you only need to send the sensor with the 30 cm section of cable and one-half of the connector. We have mating connectors at our factory that can be used for calibrating the sensor.
3. Please write the RMA number on the outside of the shipping container.
4. Return the item with freight pre-paid and fully insured to our factory address shown below. We are not responsible for any costs associated with the transportation of products across international borders.

Apogee Instruments, Inc. 721 West 1800 North Logan, UT 84321, USA

1. Upon receipt, Apogee Instruments will determine the cause of failure. If the product is found to be defective in terms of operation to the published specifications due to a failure of product materials or craftsmanship, Apogee Instruments will repair or replace the items free of charge. If it is determined that your product is not covered under warranty, you will be informed and given an estimated repair/replacement cost.

PRODUCTS BEYOND THE WARRANTY PERIOD

For issues with sensors beyond the warranty period, please contact Apogee at techsupport@apogeeinstruments.com to discuss repair or replacement options.

OTHER TERMS

The available remedy of defects under this warranty is for the repair or replacement of the original product, and Apogee Instruments is not responsible for any direct, indirect, incidental, or consequential damages, including but not limited to loss of income, loss of revenue, loss of profit, loss of data, loss of wages, loss of time, loss of sales, accruement of debts or expenses, injury to personal property, or injury to any person or any other type of damage or loss. This limited warranty and any disputes arising out of or in connection with this limited warranty (“Disputes”) shall be governed by the laws of the State of Utah, USA, excluding conflicts of law principles and excluding the Convention for the International Sale of Goods. The courts located in the State of Utah, USA, shall have exclusive jurisdiction over any Disputes.

This limited warranty gives you specific legal rights, and you may also have other rights, which vary from state to state and jurisdiction to jurisdiction, and which shall not be affected by this limited warranty. This warranty extends only to you and cannot by transferred or assigned. If any provision of this limited warranty is unlawful, void or unenforceable, that provision shall be deemed severable and shall not affect any remaining provisions. In case of any inconsistency between the English and other versions of this limited warranty, the English version shall prevail.

This warranty cannot be changed, assumed, or amended by any other person or agreement.

APOGEE INSTRUMENTS, INC.

• 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
• TEL: 435-792-4700
• FAX: 435-787-8268
• WEB: APOGEEINSTRUMENTS.COM

Copyright © 2021 Apogee Instruments, Inc.

References

• Recalibration and Repair | Apogee Instruments
• Clear Sky Calculator | Apogee Instruments Inc.
• Clear Sky Calculator | Apogee Instruments Inc.
• apogeeinstruments.com/content/Pyranometer-Modbus.CR1

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