Apogee Instruments SP-522 User manual

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: [phone] | FAX: [phone] | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2022 Apogee Instruments, Inc.
OWNER’S MANUAL
PYRANOMETER
Models SP-522
Rev: 10-Feb-2022

TABLE OF CONTENTS

CERTIFICATE OF COMPLIANCE
EU Declaration of Conformity
This declaration of conformity is issued under the sole responsibility of the manufacturer:
Apogee Instruments, Inc.
721 W 1800 N
Logan, Utah 84321
USA
for the following product(s):
Models: SP-522
Type: Pyranometer
The object of the declaration described above is in conformity with the relevant Union harmonization legislation:
2014/30/EU Electromagnetic Compatibility (EMC) Directive
2011/65/EU Restriction of Hazardous Substances (RoHS 2) Directive
2015/863/EU Amending Annex II to Directive 2011/65/EU (RoHS 3)
Standards referenced during compliance assessment:
EN 61326-1:2013 Electrical equipment for measurement, control, and laboratory use –EMC requirements
EN 50581:2012 Technical documentation for the assessment of electrical and electronic products with respect to
the restriction of hazardous substances
Please be advised that based on the information available to us from our raw material suppliers, the products
manufactured by us do not contain, as intentional additives, any of the restricted materials including lead (see
note below), mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB), polybrominated
diphenyls (PBDE), bis (2-ethylhexyl) phthalate (DEHP), butyl benzyl phthalate (BBP), dibutyl phthalate (DBP), and
diisobutyl phthalate (DIBP). However, please note that articles containing greater than 0.1 % lead concentration
are RoHS 3 compliant using exemption 6c.
Further note that Apogee Instruments does not specifically run any analysis on our raw materials or end products
for the presence of these substances, but we rely on the information provided to us by our material suppliers.
Signed for and on behalf of:
Apogee Instruments, February 2022
Bruce Bugbee
President
Apogee Instruments, Inc.

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.
Model
Signal
SP-522
Modbus
SP-510
Self-powered
SP-610
Self-powered
A sensor’s model number and serial number are
located on the bottom of the sensor.

SPECIFICATIONS
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 are 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.
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 at
1000 W m-2
Less than 3 % (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 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

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.
DEPLOYMENT AND INSTALLATION
Mount the sensor to a solid surface with the nylon mounting screw provided. To accurately measure PPFD incident
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 being 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.
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.
Model AL-100
Nylon Screw: 10-32x3/8
Nylon Screw: 10-32x3/8
Model AL-120

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 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.
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 other method.
A reference notch inside the connector ensures
proper alignment before tightening.
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
The Green wire should be connected to 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 to.
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.
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

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 than 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 regis er 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 register.
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
reserve 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 device is busy, 0 otherwise)
8
9
firmware version
Integer Registers
40
calibrated output watts (shifted one decimal point to the right)
41
detector millivolts (shifted two decimal points to the right)
42
Reserved for Future Use
43
device status (1 means device is busy, 0 otherwise)
44
firmware version (shifted one decimal point to the right)

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 stopbits
54
multiplier (rounded to the nearest whole number)*
55
offset (rounded to the nearest whole number)*
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.

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.

MAINTENACE 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 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 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 need, 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 [e-mail]
to discuss test results and possible return of sensor(s).

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 middle of page and
an estimate of total shortwave
radiation is returned on right-hand
side of 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 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 an 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:
oBaud rate: 19200
oStop bits: 1
oParity: Even
oByte order: ABCD (Big-Endian/Most Significant Byte First)
oProtocol: 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, use, 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.

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: [phone] | FAX: [phone] | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2022 Apogee Instruments, Inc.
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 [phone] or email [e-mail] 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
5. 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 [e-mail] 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