Apogee Instruments SQ-421 User manual

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: [phone] | FAX: [phone] | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2020 Apogee Instruments, Inc.
OWNER’S MANUAL
QUANTUM SENSOR
Model SQ-421
Rev: 28-Oct-2020

TABLE OF CONTENTS
Owner’s Manual ............................................................................................................................................................................... 1
Certificate of Compliance......................................................................................................................................................... 3
Introduction ............................................................................................................................................................................. 4
Sensor Models ......................................................................................................................................................................... 5
Specifications ........................................................................................................................................................................... 6
Deployment and Installation.................................................................................................................................................... 9
Cable Connectors................................................................................................................................................................... 10
Operation and Measurement ................................................................................................................................................ 11
Maintenance and Recalibration............................................................................................................................................. 21
Troubleshooting and Customer Support................................................................................................................................ 23
Return and Warranty Policy................................................................................................................................................... 24

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: SQ-421
Type: Quantum Sensor
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 rely on the information provided to us by our material suppliers.
Signed for and on behalf of:
Apogee Instruments, October 2020
Bruce Bugbee
President
Apogee Instruments, Inc.

INTRODUCTION
Radiation that drives photosynthesis is called photosynthetically active radiation (PAR) and is typically defined as
total radiation across a range of 400 to 700 nm. PAR is often expressed as photosynthetic photon flux density
(PPFD): photon flux in units of micromoles per square meter per second (µmol m-2 s-1, equal to microEinsteins per
square meter per second) summed from 400 to 700 nm (total number of photons from 400 to 700 nm). While
Einsteins and micromoles are equal (one Einstein = one mole of photons), the Einstein is not an SI unit, so
expressing PPFD as µmol m-2 s-1 is preferred.
The acronym PPF is also widely used and refers to the photosynthetic photon flux. The acronyms PPF and PPFD
refer to the same parameter. The two terms have co-evolved because there is not a universal definition of the
term “flux”. Some physicists define flux as per unit area per unit time. Others define flux only as per unit time.
We have used PPFD in this manual because we feel that it is better to be more complete and possibly redundant.
Sensors that measure PPFD are often called quantum sensors due to the quantized nature of radiation. A quantum
refers to the minimum quantity of radiation, one photon, involved in physical interactions (e.g., absorption by
photosynthetic pigments). In other words, one photon is a single quantum of radiation.
Typical applications of quantum sensors include incoming PPFD measurement over plant canopies in outdoor
environments or in greenhouses and growth chambers, and reflected or under-canopy (transmitted) PPFD
measurement in the same environments.
Apogee Instruments SQ series quantum sensors 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 PPFD
measurement in indoor or outdoor environments. SQ-421 model sensors output a digital signal using SDI-12
communication protocol.

SENSOR MODELS
This manual covers the SDI-12 communication protocol, original quantum sensor model SQ-421. Additional models
are covered in their respective manuals.
Model
Signal
Calibration
SQ-421
SDI-12
Sunlight and Electric light
SQ-110
Self-powered
Sunlight
SQ-120
Self-powered
Electric light
SQ-311
Self-powered
Sunlight
SQ-321
Self-powered
Electric light
SQ-313
Self-powered
Sunlight
SQ-323
Self-powered
Electric light
SQ-316
Self-powered
Sunlight
SQ-326
Self-powered
Electric light
SQ-212
0-2.5 V
Sunlight
SQ-222
0-2.5 V
Electric light
SQ-214
4-20 mA
Sunlight
SQ-224
4-20 mA
Electric light
SQ-215
0-5 V
Sunlight
SQ-225
0-5 V
Electric light
SQ-420
USB
Sunlight and Electric light
SQ-422
ModBus
Sunlight and Electric light
Serial Number 0-2400: 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.
Serial Numbers 2401 and above: 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 SQ series quantum sensors are calibrated through side-by-side comparison to the mean of transfer
standard quantum sensors under a reference lamp. The reference quantum sensors are recalibrated with a 200 W
quartz halogen lamp traceable to the National Institute of Standards and Technology (NIST).
SQ--421
Input Voltage
Requirement
5.5 to 24 V DC
Current Drain
1.4 mA (quiescent), 1.8 mA (active)
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 4000 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°
Spectral Range
410 to 655 nm (wavelengths where response is greater than 50% of maximum; see Spectral
Response below)
Directional (Cosine)
Response
± 5 % at 75° zenith angle (see Cosine Response below)
Temperature Response
0.06 ± 0.06 % 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
Serial # 2401 and above
30.5 mm diameter, 37 mm height
Dimensions
Serial # 0-2400
44.0 mm height, 23.5 mm diameter
Mass (with 5 m cable)
Serial # 2401 and above
140 g
Mass (with 5 m cable)
Serial # 0-2400
117 g
Cable
5 m of two conductor, shielded, twisted-pair wire; TPR jacket (high water resistance, high UV
stability, flexibility in cold conditions); pigtail lead wires; stainless steel (316), M8 connector

Spectral Response
Temperature Response
Mean temperature response of eight
SQ-100 series quantum sensors (errors
bars represent two standard deviations
above and below mean). Temperature
response measurements were made at 10
C intervals across a temperature range of
approximately -10 to 40 C in a
temperature controlled chamber under a
fixed, broad spectrum, electric lamp. At
each temperature set point, a
spectroradiometer was used to measure
light intensity from the lamp and all
quantum sensors were compared to the
spectroradiometer. The
spectroradiometer was mounted external
to the temperature control chamber and
remained at room temperature during the
experiment.
Mean spectral response of six SQ-100
series quantum sensors (error bars
represent two standard deviations
above and below mean) compared to
defined plant response to photons.
Spectral response measurements were
made at 10 nm increments across a
wavelength range of 300 to 800 nm with a
monochromator and an attached electric
light source. Measured spectral data from
each quantum sensor were normalized by
the measured spectral response of the
monochromator/electric light
combination, which was measured with a
spectroradiometer.

Cosine Response
Mean directional (cosine) response of
six apogee SQ-100 series quantum
sensors. Directional response
measurements were made on the
rooftop of the Apogee building in
Logan, Utah. Directional response was
calculated as the relative difference of
SQ-500 quantum sensors from the
mean of replicate reference quantum
sensors (LI-COR models LI-190 and LI-
190R, Kipp & Zonen model PQS 1).
Data were also collected in the
laboratory using a reference lamp and
positioning the sensor at varying
angles.
Directional (cosine) response is defined as the
measurement error at a specific angle of
radiation incidence. Error for Apogee SQ-100
series quantum sensors 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: 10-32 x 3/8
Model AL-100
Nylon Screw: 10-32 x 3/8
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