Apogee Instruments SP-422 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-422
Rev: 26-Sept-2022

TABLE OF CONTENTS
Owner’s Manual ............................................................................................................................................................................... 1
Certificates of Compliance ....................................................................................................................................................... 3
Introduction ............................................................................................................................................................................. 5
Sensor Models ......................................................................................................................................................................... 6
Specifications ........................................................................................................................................................................... 7
Deployment and Installation.................................................................................................................................................. 10
Cable Connectors................................................................................................................................................................... 11
Operation and Measurement .............................................................................................................................................. 111
Maintenace and Recalibration............................................................................................................................................. 168
Troubleshooting and Customer Support................................................................................................................................ 20
Return and Warranty Policy................................................................................................................................................. 221

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-422
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 63000:2018 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, September 2022
Bruce Bugbee
President
Apogee Instruments, Inc.

CERTIFICATE OF COMPLIANCE
UK 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-422
Type: Pyranometer
The object of the declaration described above is in conformity with the relevant UK Statutory Instruments and
their amendments:
2016 No. 1091 The Electromagnetic Compatibility Regulations 2016
2012 No. 3032 The Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic
Equipment Regulations 2012
Standards referenced during compliance assessment:
BS EN 61326-1:2013 Electrical equipment for measurement, control, and laboratory use –EMC requirements
BS EN 63000:2018 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, September 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 series pyranometers are silicon-cell
pyranometers that are only sensitive to a portion of the solar spectrum, approximately 350 to 1100 nm
(approximately 80 % of total shortwave radiation is within this range). However, silicon-cell pyranometers are
calibrated to estimate total shortwave radiation across the entire solar spectrum. Silicon-cell pyranometer
specifications compare favorably to specifications for World Meteorological Organization (WMO) moderate and
good quality classifications and specifications for International Organization of Standardization (ISO) second class
and first-class classifications, but because of limited spectral sensitivity, they do not meet the spectral specification
necessary for WMO or ISO certification.
Typical applications of silicon-cell pyranometers include incoming shortwave radiation measurement in
agricultural, ecological, and hydrological weather networks, and solar panel arrays.
Apogee Instruments SP series pyranometers consist of a cast acrylic diffuser (filter), photodiode, 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 total
shortwave radiation measurement on a planar surface in outdoor environments. The SP-422 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-422 pyranometer sensor (in bold below). Additional
models are covered in their respective manuals.
*Pyranometer model SP-230 is similar to model SP-110, but includes internal heaters designed to keep the diffuser
free of precipitation events such as dew or frost.
Model
Signal
SP-422
Modbus
SP-110
Self-powered
SP-230*
Self-powered
SP-212
0-2.5 V
SP-214
4-20 mA
SP-215
0-5 V
SP-420
USB
SP-421
SDI-12
A sensor’s model number and serial number are
located on the bottom of the sensor. If you need
the manufacturing date of your sensor, please
contact Apogee Instruments with the serial number
of your sensor.

SPECIFICATIONS
Calibration Traceability
Apogee Instruments SP series pyranometers are calibrated through side-by-side comparison to the mean of four
Apogee model SP-110 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-422
ISO 9060:2018
Class C (fast response)
Input Voltage Requirement
5.5 to 24 V
Average Max Current Draw
RS-232 37 mA;
RS-485 quiescent 37 mA, active 42 mA
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
360 to 1120 nm (wavelengths where response is 10% of maximum;
see Spectral Response below)
Directional (Cosine)
Response
± 5 % at 75° zenith angle (see Cosine Response below)
Temperature Response
0.04 ± 0.04 % per C (see Temperature Response below)
Operating Environment
-40 to 70 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

Spectral Response
Temperature Response
Mean temperature response of four
Apogee silicon-cell pyranometers.
Temperature response measurements
were made at approximately 10 C
intervals across a temperature range of
approximately -10 to 50 C under
sunlight. Each pyranometer had an
internal thermistor to measure
temperature. At each temperature set
point, a reference blackbody
pyranometer was used to measure solar
intensity.
Spectral response estimate of Apogee
silicon-cell pyranometers. Spectral
response was estimated by multiplying
the spectral response of the
photodiode, diffuser, and adhesive.
Spectral response measurements of
diffuser and adhesive were made with a
spectrometer, and spectral response
data for the photodiode were obtained
from the manufacturer.
Slope = 0.041 % per C

Cosine Response
Mean cosine response of eleven Apogee
silicon-cell pyranometers (error bars
represent two standard deviations
above and below mean). Cosine
response measurements were made
during broadband outdoor radiometer
calibrations (BORCAL) performed during
two different years at the National
Renewable Energy Laboratory (NREL) in
Golden, Colorado. Cosine response was
calculated as the relative difference of
pyranometer sensitivity at each solar
zenith angle to sensitivity at 45° solar
zenith angle. The blue symbols are AM
measurements, the red symbols are PM
measurements.
Directional, or cosine, response is
defined as the measurement error at a
specific angle of radiation incidence.
Error for Apogee silicon-cell
pyranometers is approximately ± 2 %
and ± 5 % at solar zenith angles of 45°
and 75°, respectively.

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 green 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-422 pyranometer has a Modbus output, where shortwave radiation is returned in digital format.
Measurement of SP-422 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 pyranometers (model SP-422) 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-422 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.
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 5.5 to 24 V

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
Baudrate: 19200
Data bits: 8
Stop bits: 1
Parity: Even
Byte Order: Big-Endian (most significant byte sent first)
The baudrate and slave address are user configurable. Valid slave addresses are 1 to 247. Setting the slave
address to 255 will trigger a reset event, and all settings will revert back to the original default, which is slave
address 1 (i.e. if a sensor with a slave address of 5 is changed to 0, it will revert to slave address 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 (multiplied by 10)
41
detector millivolts (multiplied by 100)
42
Reserved for Future Use
43
device status (1 means device is busy, 0 otherwise)
44
firmware version (multiplied by 10)

Read/Write registers (function codes 0x3 and 0x10).
Writing to these registers has no effect on sensor settings until the user has written to the register 100. For
example, to update the Slave Address, the user must first write the desired address to register 20. Then the user
must also write to register 100 to save/store the new values.
Float Registers
16
17
slave address
18
19
model number*
20
21
serial number*
22
23
baudrate (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
baudrate (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 down to nearest integer)*
55
offset (rounded down to nearest integer)*
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.
Spectral Errors for Measurements with Silicon-cell Pyranometers
Apogee SP series pyranometers are calibrated under electric lamps in a calibration laboratory. The calibration
procedure simulates calibration under clear sky conditions at a solar zenith angle of approximately 45°. However,
due to the limited spectral sensitivity of silicon-cell pyranometers compared to the solar radiation spectrum (see
graph below), spectral errors occur when measurements are made in conditions that differ from conditions the
sensor was calibrated under (e.g., the solar spectrum differs in clear sky and cloudy conditions, thus,
measurements in cloudy conditions result in spectral error because sensors are calibrated in clear sky conditions).

Silicon-cell pyranometers can still be used to measure shortwave radiation in conditions other than clear sky or
from radiation sources other than incoming sunlight, but spectral errors occur when measuring radiation with
silicon-cell pyranometers in these conditions. The graphs below show spectral error estimates for Apogee silicon-
cell pyranometers at varying solar zenith angles and varying atmospheric air mass. The diffuser is optimized to
minimize directional errors, thus the cosine response graph in the Specifications section shows the actual
directional errors in practice (which includes contributions from the spectral shift that occurs as solar zenith angle
and atmospheric air mass change with time of day and time of year). The table below provides spectral error
estimates for shortwave radiation measurements from shortwave radiation sources other than clear sky solar
radiation.
Spectral response of Apogee SP series
pyranometers compared to solar radiation
spectrum at Earth’s surface. Silicon-cell
pyranometers, such as Apogee SP series, are
only sensitive to the wavelength range of
approximately 350-1100 nm and are not
equally sensitive to all wavelengths within
this range. As a result, when the spectral
content of solar radiation is significantly
different than the spectrum that silicon-cell
pyranometers were calibrated to, spectral
errors result.
Spectral error for Apogee SP series
pyranometers as a function of solar zenith
angle, assuming calibration at a zenith
angle of 45°.

Spectral Errors for Shortwave Radiation Measurements with Apogee SP Series Pyranometers
Radiation Source (Error Calculated Relative to Sun, Clear Sky)
Error [%]
Sun (Clear Sky)
0.0
Sun (Cloudy Sky)
9.6
Reflected from Grass Canopy
14.6
Reflected from Deciduous Canopy
16.0
Reflected from Conifer Canopy
19.2
Reflected from Agricultural Soil
-12.1
Reflected from Forest Soil
-4.1
Reflected from Desert Soil
3.0
Reflected from Water
6.6
Reflected from Ice
0.3
Reflected from Snow
13.7
Spectral error for Apogee SP series
pyranometers as a function of atmospheric
air mass, assuming calibration at an air
mass of 1.5.

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.