Apogee Instruments S2-431 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
RED - FAR-RED SENSORS
Models S2-431
Rev: 31-Aug-2022

TABLE OF CONTENTS
Owner’s Manual ............................................................................................................................................................................... 1
Certificates of Compliance ....................................................................................................................................................... 3
Introduction ............................................................................................................................................................................. 5
Sensor Models ......................................................................................................................................................................... 6
Specifications ........................................................................................................................................................................... 7
Deployment and Installation.................................................................................................................................................... 9
Cable Connectors................................................................................................................................................................... 10
Operation and Measurement ................................................................................................................................................ 11
Maintenance and Recalibration............................................................................................................................................. 15
Troubleshooting and Customer Support................................................................................................................................ 16
Return and Warranty Policy................................................................................................................................................... 17

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: S2-431
Type: Red - Far-red Sensors
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, August 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: S2-431
Type: Red - Far-red Sensors
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, August 2022
Bruce Bugbee
President
Apogee Instruments, Inc.

INTRODUCTION
Specific wavelengths of radiation trigger distinct responses in plants. Red and far-red wavelengths are of particular
interest because they influence photosynthetic and morphogenic activity. Phytochrome pigments in plants are
sensitive to varying ratios of red and far-red radiation, providing information to the plant about the light
environment, and therefore, optimal growth patterns. Increasing the fraction of red radiation indicates less
shading and generally results in more conservative vertical growth patterns, while increasing the far-red radiation
fraction indicates more shading and results in more aggressive vertical growth patterns.
Red - far-red sensors are designed to have spectral sensitivities that approximate the phytochrome absorption
spectrum. Red - far-red sensors quantify properties of radiation sources, not plant responses. However, inferences
of plant responses can be made from measurements of the lighting/shading environment, so it is important that
red - far-red sensors have high sensitivity in the wavelength ranges where plants are most sensitive (i.e., the
wavelength ranges that drive the strongest responses in plants), hence red - far-red sensor spectral responses
should approximate the phytochrome absorption spectrum.
The primary application of red - far-red sensors is monitoring plant light environments, including calculation of the
red to far-red ratio (red photon flux density / far-red photon flux density) and far-red fraction (far-red photon flux
density / sum of red and far-red photon flux densities), in photobiology studies (e.g., researching plant
morphogenic activities).
Apogee Instruments S2 series red - far-red radiometers consist of a cast acrylic diffuser, pair of photodiodes that
measure specific wavelength ranges, and signal processing circuitry mounted in an anodized aluminum housing,
and a cable to connect the radiometer to a measurement device. Sensors are potted solid with no internal airspace
and are designed for continuous measurement in indoor and outdoor environments. S2-100 series sensors output
two analog voltages, one for each photodetector, that are directly proportional to red and far-red radiation
incident on a planar surface (does not have to be horizontal), where the radiation emanates from all angles of a
hemisphere.

SENSOR MODELS
This manual covers the SDI-12 model S2-431 (in bold below). Additional models are covered in their respective
manuals.
Model
Signal
S2-131
Self-powered
S2-431
SDI-12
S2-432
Modbus
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 S2 series Red - Far-red sensors are calibrated through side-by-side comparison to the mean of three
transfer standard sensors under a quartz halogen lamp. The transfer standard sensors are calibrated through side-
by-side comparison to red and far-red photon flux density calculated from solar spectra collected in Logan, Utah,
using an Apogee model PS-300 spectroradiometer. The PS-300 spectroradiometer is calibrated with a quartz
halogen lamp traceable to the National Institute of Standards and Technology (NIST).
S2-431
Power Supply
5.5 to 24 V DC
Current Draw
1.8 mA (quiescent), 1.9 mA (active)
Calibration Factor
(reciprocal of sensitivity)
Custom for each sensor and stored in firmware
Calibration Uncertainty
± 5 %
Output Range
SDI-12
Measurement Repeatability
Less than 1 %
Long-term Drift
Less than 2 % per year
Non-linearity
Less than 1 % (up to 400 µmol m⁻² s⁻¹)
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
180°
Wavelength Ranges
645 to 665 nm ± 5 nm (Red)
720 to 740 nm ± 5 nm (Far-red)
Directional (Cosine)
Response
± 2 % at 45°; ± 5 % at 75° zenith angle
Temperature Response
Less than 0.1 % per C
Housing
Anodized aluminum body with acrylic diffuser
IP Rating
IP68
Operating Environment
-40 to 70 C; 0 to 100 % relative humidity
Dimensions
30.5 mm diameter, 37 mm height
Mass (with 5 m of cable)
140 g
Cable
5 m of shielded, twisted-pair wire; TPR jacket (high water resistance, high UV stability, flexibility
in cold conditions); pigtail lead wires; stainless steel (316), M8 connector

Cosine Response
Spectral Response
Directional, or cosine, response is
defined as the measurement error at a
specific angle of radiation incidence.
Directional error for Apogee S2 series red
- far-red sensors is approximately ± 2 %
and ± 5 % at solar zenith angles of 45°
and 75°, respectively.
Mean spectral response
measurements of six replicate red -
far-red sensors (red sensor is centered
near 655 nm, far-red sensor is
centered near 730 nm). Spectral
response measurements were made
at 2 nm increments across a
wavelength range of 600 to 800 nm in
a monochromator with an attached
electric light source. Measured
spectral data from each sensor were
normalized by the measured spectral
response of the
monochromator/electric light
combination, which was measured
with a spectroradiometer.

DEPLOYMENT AND INSTALLATION
Mount the sensor to a solid surface with the nylon mounting screw provided to prevent galvanic corrosion. To
accurately measure red and far-red photon flux density 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
Nylon Screw: 10-32x3/8
Model AL-120
Model AL-100

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