Apogee Instruments SQ-610 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
EPAR SENSOR
Models SQ-610
Rev: 4-Jan-2022

TABLE OF CONTENTS
Owner’s Manual ............................................................................................................................................................................... 1
Certificate of Compliance......................................................................................................................................................... 3
Introduction ............................................................................................................................................................................. 4
Sensor Models ......................................................................................................................................................................... 6
Specifications ........................................................................................................................................................................... 7
Deployment and Installation.................................................................................................................................................. 10
Cable Connectors................................................................................................................................................................... 11
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: SQ-610
Type: ePAR 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 we rely on the information provided to us by our material suppliers.
Signed for and on behalf of:
Apogee Instruments, January 2022
Bruce Bugbee
President
Apogee Instruments, Inc.

INTRODUCTION
Radiation that drives photosynthesis is called photosynthetically active radiation (PAR) and, historically, is defined
as total radiation across a range of 400 to 700 nm. PAR is almost universally quantified as photosynthetic photon
flux density (PPFD) 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). However,
ultraviolet and far-red photons outside the defined PAR range of 400-700 nm can also contribute to
photosynthesis and influence plant responses (e.g., flowering).
Data from recent studies indicate that far-red photons synergistically interact with photons in the historically
defined PAR range of 400-700 nm to increase photochemical efficiency in leaves (Hogewoning et al., 2012;
Murakami et al., 2018; Zhen and van Iersel, 2017; Zhen et al., 2019). Measurements from whole plants and plant
canopies indicate adding far-red photons (using far-red LEDs with peaks near 735 nm and outputting photons
across a range of about 700-750 nm) to radiation sources outputting photons in the 400-700 nm range increases
canopy photosynthesis equal to the addition of the same number of photons in the 400-700 nm range for multiple
species, and C3 and C4 photosynthetic pathways, but far-red photons alone are photosynthetically inefficient and
result in minimal photosynthesis (Zhen and Bugbee, 2020a; Zhen and Bugbee, 2020b).
This research suggests that far-red photons drive canopy photosynthesis with similar efficiency as photons in the
traditional PAR range when they are acting synergistically with photons in the 400-700 nm range, meaning when
far-red photons are added to radiation sources outputting 400-700 nm photons. Thus, far-red photons need to be
included in the definition of PAR (Zhen et al., 2021).
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. Sensors that function like
traditional quantum sensors but measure a wider range of wavelengths can be thought of as an ‘extended range’
quantum sensor.
Typical applications of traditional 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. The extended photosynthetically active radiation (ePAR) sensor detailed
in this manual uses a detector that is sensitive to radiation from 383-757 nm ± 5 nm, which allows it to measure
photons from Far-red.
Apogee Instruments SQ-600 series ePAR sensors consist of a cast acrylic diffuser (filter), photodiode, and signal
processing circuitry mounted in an anodized aluminum housing. A cable to connect the sensor to a measurement
device is also included. SQ-600 series ePAR sensors are designed for continuous photon flux density measurements
in indoor or outdoor environments. SQ-610 models output an analog signal that is directly proportional to photon
flux density. The analog signal from the sensor is directly proportional to radiation incident on a planar surface
(does not have to be horizontal), where the radiation emanates from all angles of a hemisphere.
Hogewoning et al. 2012. Photosynthetic Quantum Yield Dynamics: From Photosystems to Leaves. The Plant Cell,
24: 1921–1935.

Murakami et al. 2018. A Mathematical Model of Photosynthetic Electron Transport in Response to the Light
Spectrum Based on Excitation Energy Distributed to Photosystems. Plant Cell Physiology. 59(8): 1643–1651.
Zhen and Van Iersel. 2017. Far-red light is needed for efficient photochemistry and photosynthesis. Journal of Plant
Physiology. 209: 115–122.
Zhen et al. 2019. Far-red light enhances photochemical efficiency in a wavelength-dependent manner. Physiologia
Plantarum. 167(1):21-33.
Zhen and Bugbee. 2020a. Far-red photons have equivalent efficiency to traditional photosynthetic photons:
Implications for redefining photosynthetically active radiation. Plant Cell and Environment. 2020; 1–14.
Zhen and Bugbee. 2020b. Substituting Far-Red for Traditionally Defined Photosynthetic Photons Results in Equal
Canopy Quantum Yield for CO2Fixation and Increased Photon Capture During Long-Term Studies: Implications for
Re-Defining PAR. Frontiers in Plant Science. 11:1-14.
Zhen et al. 2021. Why Far-Red Photons Should Be Included in the Definition of Photosynthetic Photons and the
Measurement of Horticultural Fixture Efficacy. Frontiers in Plant Science. 12:1-4.

SENSOR MODELS
This manual covers the unamplified model SQ-610 ePAR Sensor (in bold below). Additional models are covered in
their respective manuals.
Model
Signal
SQ-610
Self-powered
SQ-612
0-2.5 V
SQ-614
4-20 mA
SQ-615
0-5 V
SQ-616
USB
SQ-617
SDI-12
SQ-618
Modbus
A sensor’s model number and serial number are
located on the bottom of the sensor. If the
manufacturing date of a specific sensor is
required, please contact Apogee Instruments
with the serial number of the sensor.

SPECIFICATIONS
Calibration Traceability
Apogee Instruments SQ-600 series ePAR sensors are calibrated through side-by-side comparison to the mean of
four transfer standard sensors under a reference lamp. The transfer standard sensors are recalibrated with a
quartz halogen lamp traceable to the National Institute of Standards and Technology (NIST).
SQ-610-SS
Power Supply
Self-powered
Sensitivity
0.01 mV per µmol m-2 s-1
Calibration Factor
100 µmol m-2 s-1 per mV
Calibration Uncertainty
± 5 % (see Calibration Traceability below)
Measurement Range
0 to 4000 µmol m-2 s-1
Measurement
Repeatability
Less than 0.5 %
Calibrated Output Range
0 to 40 mV
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
Less than 1 ms
Field of View
180°
Spectral Range
383 to 757 nm ± 5 nm (wavelengths where response is greater than 50 %; see Spectral
Response below)
Directional (Cosine)
Response
± 2 % at 45° zenith angle, ± 5 % at 75° zenith angle (see Directional Response below)
Azimuth Error
Less than 0.5 %
Tilt Error
Less than 0.5 %
Temperature Response
-0.11 ± 0.04 % per C
Uncertainty in Daily Total
Less than 5 %
Housing
Anodized aluminum body with acrylic diffuser
IP Rating
IP68
Operating Environment
-40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m
Dimensions
30.5 mm diameter, 37 mm height
Mass (with 5 m of cable)
140 g
Cable
5 m of two conductor, shielded, twisted-pair wire; TPR jacket; pigtail lead wires; stainless steel
(316), M8 connector located 25 cm from sensor head
Warranty
4 years against defects in materials and workmanship

Spectral Response
Mean spectral response measurements of
four replicate Apogee SQ-600 series ePAR
Sensors. Incremental spectral response
measurements were made at 10 nm
increments across a wavelength range of
370 to 800 nm in a monochromator with an
attached electric light source. Measured
spectral data from each quantum sensor
were refined and normalized by comparing
measured spectral response of the
monochromator/electric light combination
to measured spectral differences from a
quantum sensor reference.

Cosine Response
Directional, or cosine, response is defined as the
measurement error at a specific angle of radiation
incidence. Error for Apogee SQ-600 series ePAR Sensor is
approximately ± 2 % and ± 5 % at solar zenith angles of 45°
and 75°, respectively.
Mean directional (cosine) response
of seven Apogee 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 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.

DEPLOYMENT AND INSTALLATION
Mount the sensor to a solid surface with the nylon mounting screw provided. To accurately measure photon flux
density incident on a horizontal surface, the sensor must be level. An Apogee Instruments model AL-100 leveling
plate is recommended for this purpose. To facilitate mounting on a cross arm, an Apogee Instruments model AM-
120 mounting bracket 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 0.5 %, 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 blue cap should be removed from the sensor. The blue 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
Model: AL-120
Nylon Screw: 10-32 x 3/8

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.
Inline cable connectors are installed 25 cm from 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, only twist the metal connector.
Finger-tighten firmly

OPERATION AND MEASUREMENT
Connect the sensor to a measurement device (meter, datalogger, controller) capable of measuring and displaying
or recording a millivolt signal (an input measurement range of approximately 0-40 mV is required to cover the
photon flux density range the sensor is capable of measuring). In order to maximize the measurement resolution
and signal-to-noise ratio, the signal input range of the measurement device should closely match the output range
of the ePAR sensor.
Wiring for SQ-610
White: Positive (signal from sensor)
Black: Negative (signal from sensor)
Clear: Shield/Ground

Sensor Calibration
Apogee unamplified SQ-610 ePAR Sensors have standard calibration factors of exactly:
100 µmol m-2 s-1 per mV
Multiply the calibration factor by the measured mV signal to convert sensor output to photon flux density in units
of µmol m-2 s-1:
Calibration Factor (100 µmol m-2 s-1 per mV) * Sensor Output Signal (mV) = Photon Flux Density (µmol m-2 s-1)
100 * 24 = 2400
Example of photon flux density measurement with an
Apogee model SQ-610 ePAR Sensor. Full sunlight yields a
photon flux density on a horizontal plane of approximately
2400 µmol m-2 s-1. This yields an output signal of 24 mV.
This signal is converted to photon flux density by
multiplying by the calibration factor of 100 mol m-2 s-1 /
mV.
Full Sunlight
(2400 µmol m-2s-1)
Sensor Output
24 mV

Spectral Error
Quantum sensors are the most common instrument for measuring PPFD, because they are about an order of
magnitude lower cost the spectroradiometers, but spectral errors must be considered. The spectral errors in the
table below can be used as correction factors for individual radiation sources.
Spectral Errors for PPFD Measurements with Apogee SQ-610 Series ePAR Sensors
Radiation Source (Error Calculated Relative to Sun, Clear Sky)
SQ-610 Series
PPFD Error [%]
Sun (Clear Sky)
2.5
Sun (Cloudy Sky)
2.6
Cool White Fluorescent (T5)
-0.5
Metal Halide
0.7
Ceramic Metal Halide
0.3
Mogul Base HPS
0.3
Dual-ended HPS
0.6
Cool White LED
-1.0
Warm White LED
-0.4
Blue LED (442 nm)
-2.7
Cyan LED (501 nm)
-0.7
Green LED (529 nm)
-0.7
Amber LED (598 nm)
-0.4
Red LED (666 nm)
-0.3
Far Red LED (737 nm)
4.5
Immersion Effect Correction Factor
When a radiation sensor is submerged in water, more of the incident radiation is backscattered out of the diffuser
than when the sensor is in air (Smith, 1969; Tyler and Smith, 1970). This phenomenon is caused by the difference
in the refractive index for air (1.00) and water (1.33) and is called the immersion effect. Without correction for the
immersion effect, radiation sensors calibrated in air can only provide relative values underwater (Smith, 1969;
Tyler and Smith, 1970). Immersion effect correction factors can be derived by making measurements in air and at
multiple water depths at a constant distance from a lamp in a controlled laboratory setting.
Apogee SQ-610 series ePAR sensors have an immersion effect correction factor of 1.25. This correction factor
should be multiplied by PPFD measurements made underwater to yield accurate PPFD.
Further information on underwater measurements and the immersion effect can be found on the Apogee
webpage (http://www.apogeeinstruments.com/underwater-par-measurements/).
Smith, R.C., 1969. An underwater spectral irradiance collector. Journal of Marine Research 27:341-351.
Tyler, J.E., and R.C. Smith, 1970. Measurements of Spectral Irradiance Underwater. Gordon and Breach, New York,
New York. 103 pages

MAINTENANCE AND RECALIBRATION
Dust or organic deposits are best removed using water or window cleaner and a soft cloth or cotton swab. Salt
deposits should be dissolved with vinegar and removed with a soft cloth or cotton swab.
Blocking of the optical path between the target and detector can cause low readings. Occasionally, accumulated
materials on the diffuser of the upward-looking radiometer and in the apertures of the downward-looking
radiometer can block the optical path in three common ways:
1. Moisture or debris on the diffuser (upward-looking) or in the apertures (downward-looking).
2. Dust during periods of low rainfall.
3. Salt deposit accumulation from evaporation of sea spray or sprinkler irrigation water.
Apogee Instruments upward-looking sensors have a domed diffuser and housing for improved self-cleaning from
rainfall, but active cleaning may be necessary. Dust or organic deposits are best removed using water, or window
cleaner, and a soft cloth or cotton swab. Salt deposits should be dissolved with vinegar and removed with a cloth
or cotton swab. Salt deposits cannot be removed with solvents such as alcohol or acetone. Use only gentle
pressure when cleaning the diffuser with a cotton swab or soft cloth, to avoid scratching the outer surface. The
solvent should be allowed to do the cleaning, not mechanical force. Never use an abrasive material or cleaner on
the diffuser.
It is recommended that two-band radiometers be recalibrated every two years. See the Apogee webpage for
details regarding return of sensors for recalibration (http://www.apogeeinstruments.com/tech-support-
recalibration-repairs/).

TROUBLESHOOTING AND CUSTOMER SUPPORT
Independent Verification of Functionality
Apogee SQ-610 ePAR Sensors are self-powered devices and output an analog signal proportional to incident
photon flux density for the 383-757 nm ± 5 nm wavelength range. A quick and easy check of sensor functionality
can be determined using a voltmeter with millivolt resolution. Connect the positive lead wire from the voltmeter
to the white wire from the sensor and the negative (or common) lead wire from the voltmeter to the black wire
from the sensor. Direct the sensor head toward a light source and verify the sensor provides a signal. Increase and
decrease the distance from the sensor head to the light source to verify that the signal changes proportionally
(decreasing signal with increasing distance and increasing signal with decreasing distance). Blocking all radiation
from the sensor should force the sensor signal to zero.
Compatible Measurement Devices (Dataloggers/Controllers/Meters)
SQ-610 ePAR Sensors are calibrated with a standard calibration factor of 100.0 µmol m-2 s-1 per mV, yielding a
sensitivity of 0.01 mV per µmol m-2 s-1. Thus, a compatible measurement device (e.g., datalogger or controller)
should have resolution of at least 0.01 mV in order to provide photon flux density resolution of 1 µmol m-2 s-1 and
resolution of at least 0.001 mV in order provide photon flux density resolution of 0.1 µmol m-2 s-1.
An example datalogger program for Campbell Scientific dataloggers can be found on the Apogee webpage at
https://www.apogeeinstruments.com/downloads/#datalogger.
Cable Length
When the sensor is connected to a measurement device with high input impedance, sensor output signals are not
changed by shortening the cable or splicing on additional cable in the field. Tests have shown that if the input
impedance of the measurements device is greater than 1 mega-ohm there is negligible effect on the calibration,
even after adding up to 100 m of cable. All Apogee sensors use shielded, twisted pair cable to minimize
electromagnetic interference. For best measurements, the shield wire must be connected to an earth ground. This
is particularly important when using the sensor with long lead lengths in electromagnetically noisy environments.
Modifying Cable Length
See Apogee webpage for details on how to extend sensor cable length:
(http://www.apogeeinstruments.com/how-to-make-a-weatherproof-cable-splice/).

RETURN AND WARRANTY POLICY
RETURN POLICY
Apogee Instruments will accept returns within 30 days of purchase as long as the product is in new condition (to be
determined by Apogee). Returns are subject to a 10 % restocking fee.
WARRANTY POLICY
What is Covered
All products manufactured by Apogee Instruments are warranted to be free from defects in materials and craftsmanship
for a period of four (4) years from the date of shipment from our factory. To be considered for warranty coverage an
item must be evaluated by Apogee.
Products not manufactured by Apogee (spectroradiometers, chlorophyll content meters, EE08-SS probes) are covered
for a period of one (1) year.
What is Not Covered
The customer is responsible for all costs associated with the removal, reinstallation, and shipping of suspected warranty
items to our factory.
The warranty does not cover equipment that has been damaged due to the following conditions:
1. Improper installation or abuse.
2. Operation of the instrument outside of its specified operating range.
3. Natural occurrences such as lightning, fire, etc.
4. Unauthorized modification.
5. Improper or unauthorized repair.
Please note that nominal accuracy drift is normal over time. Routine recalibration of sensors/meters is considered part of
proper maintenance and is not covered under warranty.
Who is Covered
This warranty covers the original purchaser of the product or another party who may own it during the warranty period.
What Apogee Will Do
At no charge Apogee will:
1. Either repair or replace (at our discretion) the item under warranty.
2. Ship the item back to the customer by the carrier of our choice.
Different or expedited shipping methods will be at the customer’s expense.

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: [phone] | FAX: [phone] | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2022 Apogee Instruments, Inc.
How to Return an Item
1. Please do not send any products back to Apogee Instruments until you have received a Return Merchandise
Authorization (RMA) number from our technical support department by submitting an online RMA form at
www.apogeeinstruments.com/tech-support-recalibration-repairs/. We will use your RMA number for tracking of the
service item. Call [phone] or email [e-mail] with questions.
2. For warranty evaluations, send all RMA sensors and meters back in the following condition: Clean the sensor’s exterior
and cord. Do not modify the sensors or wires, including splicing, cutting wire leads, etc. If a connector has been attached
to the cable end, please include the mating connector –otherwise the sensor connector will be removed in order to
complete the repair/recalibration. Note: When sending back sensors for routine calibration that have Apogee’s standard
stainless-steel connectors, you only need to send the sensor with the 30 cm section of cable and one-half of the
connector. We have mating connectors at our factory that can be used for calibrating the sensor.
3. Please write the RMA number on the outside of the shipping container.
4. Return the item with freight pre-paid and fully insured to our factory address shown below. We are not responsible for
any costs associated with the transportation of products across international borders.
Apogee Instruments, Inc.
721 West 1800 North Logan, UT
84321, USA
5. Upon receipt, Apogee Instruments will determine the cause of failure. If the product is found to be defective in terms
of operation to the published specifications due to a failure of product materials or craftsmanship, Apogee Instruments
will repair or replace the items free of charge. If it is determined that your product is not covered under warranty, you
will be informed and given an estimated repair/replacement cost.
PRODUCTS BEYOND THE WARRANTY PERIOD
For issues with sensors beyond the warranty period, please contact Apogee at [e-mail] to
discuss repair or replacement options.
OTHER TERMS
The available remedy of defects under this warranty is for the repair or replacement of the original product, and Apogee
Instruments is not responsible for any direct, indirect, incidental, or consequential damages, including but not limited to
loss of income, loss of revenue, loss of profit, loss of data, loss of wages, loss of time, loss of sales, accruement of debts
or expenses, injury to personal property, or injury to any person or any other type of damage or loss.
This limited warranty and any disputes arising out of or in connection with this limited warranty ("Disputes") shall be
governed by the laws of the State of Utah, USA, excluding conflicts of law principles and excluding the Convention for the
International Sale of Goods. The courts located in the State of Utah, USA, shall have exclusive jurisdiction over any
Disputes.
This limited warranty gives you specific legal rights, and you may also have other rights, which vary from state to state
and jurisdiction to jurisdiction, and which shall not be affected by this limited warranty. This warranty extends only to
you and cannot by transferred or assigned. If any provision of this limited warranty is unlawful, void or unenforceable,
that provision shall be deemed severable and shall not affect any remaining provisions. In case of any inconsistency
between the English and other versions of this limited warranty, the English version shall prevail.
This warranty cannot be changed, assumed, or amended by any other person or agreement