Apogee Instruments S2-432 User manual

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: [phone] | FAX: [phone] | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2021 Apogee Instruments, Inc.
OWNER’S MANUAL
RED - FAR-RED SENSORS
Models S2-432
Rev: 2-Aug-2021

TABLE OF CONTENTS
Owner’s Manual ............................................................................................................................................................................... 1
Certificate of Compliance......................................................................................................................................................... 3
Introduction ............................................................................................................................................................................. 4
Sensor Models ......................................................................................................................................................................... 5
Specifications ........................................................................................................................................................................... 6
Deployment and Installation.................................................................................................................................................... 8
Cable Connectors..................................................................................................................................................................... 9
Operation and Measurement ................................................................................................................................................ 10
Maintenance and Recalibration............................................................................................................................................. 10
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: S2-432
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 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, August 2021
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 sensors 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. The S2-432 model outputs a digital signal using Modbus RTU communication protocol over RS-232 or
RS-485.

SENSOR MODELS
This manual covers the Modbus RTU communication protocol, Red - Far-red model S2-432 (in bold below).
Additional models are covered in their respective manuals.
Model
Signal
S2-131
Self-powered
S2-431
SDI-12
S2-432
Modbus
Sensor 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).
S2-432
Power Supply
5.5 to 24 V DC
Average Max Current Draw
RS-232 37 mA;
RS-485 quiescent 37 mA, active 42 mA
Calibration Factor
(reciprocal of sensitivity)
Custom for each sensor and stored in firmware
Calibration Uncertainty
± 5 %
Output Range
Modbus
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)
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 black cap should be removed from the sensor. The black 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

OPERATION AND MEASUREMENT
The S2-432 Red - Far-red sensor has a Modbus output, where red and far-red photon flux density are returned in
digital format. Measurement of S2-432 Red - Far-red sensors 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 Red - Far-red sensors (model S2-432) have 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 S2-432 Red - Far-red
sensors. 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 +12 V