Apogee Instruments PYRANOMETER SP-421 User manual

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: [phone] | FAX: [phone] | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2018 Apogee Instruments, Inc.
OWNER’S MANUAL
PYRANOMETER
Models SP-421
(including SS model)

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TABLE OF CONTENTS
Owner’s Manual ................................................................................................................................................................................................................ 1
Certificate of Compliance .................................................................................................................................................................................... 3
Introduction............................................................................................................................................................................................................. 4
Sensor Models ......................................................................................................................................................................................................... 5
Specifications........................................................................................................................................................................................................... 6
Deployment and Installation.............................................................................................................................................................................. 9
Operation and Measurement...........................................................................................................................................................................11
Maintenace and Recalibration .........................................................................................................................................................................17
Troubleshooting and Customer Support......................................................................................................................................................18

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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-421
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
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 cadmium, hexavalent chromium, lead,
mercury, polybrominated biphenyls (PBB), polybrominated diphenyls (PBDE).
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 rely on the information provided to us by our material suppliers.
Signed for and on behalf of:
Apogee Instruments, May 2016
Bruce Bugbee
President
Apogee Instruments, Inc.

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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, and 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. SP series sensors output a digital signal using SDI-12 protocol.

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SENSOR MODELS
This manual covers the SDI-12 protocol model SP-421 pyranometer sensor. 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-421
SDI-12
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-422 Modbus
Sensor model number and serial number are located near
the pigtail leads on the sensor cable. If you need the
manufacturing date of your sensor, please contact Apogee
Instruments with the serial number of your sensor.

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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-421
Input Voltage Requirement 5.5 to 24 V DC
Current Drain 0.6 mA (quiescent), 1.3 mA (active)
Output Range 0 to 1750 W m-2
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 1750 W m-2)
Response Time
0.6 s, time for detector signal to reach 95 % following a step change; fastest data transmission rate for
SDI-12 circuitry is 1 s
Field of View 180º
Spectral Range
360 to 1120 nm (wavelengths where response is 10% of maximum;
see Spectral Response below)
Directional (Cosine) Response ± 5 % at 75º 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 depths of 30 m
Dimensions 44.0 mm height, 23.5 mm diameter
Mass 177 g (with 5 m cable)
Cable
5 m of two conductor, shielded, twisted-pair wire, additional cable available in multiples of 5 m;
santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions); pigtail
lead wires

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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.

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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.

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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.
Nylon Screw: 10-32x3/8
Model AL-100
Nylon Screw: 10-32x3/8
Model AL-120

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Cable Connectors
Apogee started offering in-line cable connectors on some
bare-lead sensors in March 2018 to simplify the process of
removing sensors from weather stations for calibration by
not requiring the full cable to be uninstalled back to the data
logger.
The ruggedized M8 connectors are rated IP67, made of
corrosion-resistant marine-grade stainless-steel, and
designed for extended use in harsh environmental
conditions.
Inline cable connectors are installed 30 cm from the head
(pyranometer pictured)
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 data
logger connection, we remove the unused pigtail lead colors
at the data logger end of the cable.
If you ever need a replacement cable, please contact us
directly to ensure ordering the proper pigtail configuration.
Alignment: When reconnecting your 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 short
end of the cable and half the connector.
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.
Finger-tighten firmly