Apogee Instruments PYRANOMETER SP-421 User manual

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA

TEL: (435) 792-4700 | FAX: (435) 787-8268 | WEB: APOGEEINSTRUMENTS.COM

OWNER’S MANUAL

PYRANOMETER

Models SP-421

(including SS model)

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

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.

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.

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.

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

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.

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.

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

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

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