apogee SQ-618 EPAR Sensor Owner’s Manual

SQ-618 EPAR Sensor
Owner’s Manual

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: 435-792-4700 | FAX: 435-787-8268 | WEB: APOGEEINSTRUMENTS.COM

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-614
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 rely on the  information provided to us by our material suppliers.

Signed for and on behalf of:
Apogee Instruments, March 2021

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).

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 380-760 nm, which allows it to measure photons from UV and 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-600 series ePAR sensors output an analog signal that is directly proportional to PFD. 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.

SENSOR MODELS

This manual covers the amplified voltage output model SQ-614 ePAR Sensor (in bold below). Additional models are covered in their respective manuals.

Sensor 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

| SQ-618-SS
---|---
Power Supply| 5.5-24 V DC
Current Draw| Maximum of 20 mA
Sensitivity| 0.004 mA per µmol m-2 s-1
Calibration Uncertainty| ± 5 % (see Calibration Traceability below)
Output Range| 4 to 20 mA
Measurement
Repeatability| 0 to 4000 µmol m-2 s-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| Less than 1 ms
Field of View| 180°
Spectral Range| 380 to 760 nm ± 5 nm (wavelengths where response is greater than 50 %; see Spectral
Response below)
Directional (CosineResponse| ± 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
Warranty| 4 years against defects in materials and workmanship

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).

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 LI190and  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 AL120 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.

CABLE CONNECTORS

Apogee offers 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.

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.

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 (yellow arrows).

OPERATION AND MEASUREMENT

Connect the sensor to a measurement device (meter, datalogger, controller) capable of measuring and displaying a 4-20 mA signal. To maximize measurement resolution and  signal-to-noise ratio, the input range of the measurement device should closely match the output range of the quantum sensor.
DO NOT connect the sensor to a power source greater than 24 V DC.

Wiring for SQ-614

Sensor Calibration
Apogee SQ-614 ePAR Sensors have standard calibration factors of exactly:

250 µmol m-2 s-1 per mA
Multiply the calibration factor by the measured mA signal to convert sensor output to photon flux density in units of µmol m-2 s-1:
Calibration Factor (250 µmol m-2 s-1per mA) Sensor Output Signal (mA) = Photon Flux Density (µmol m-2 s-1)
250 (12 – 4)= 2000

Modbus Interface
The following is a brief explanation of the Modbus protocol instructions used in Apogee SQ-618 ePAR 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.

Register Index
Each register in a sensor represents a value in the sensor, such as a measurement or a configuration parameter.
Some registers can only be read, some registers can only be written, and some can be both read and written. Each register exists at a specified index in the table for the sensor.  Often this index is called an address, which is a separate address than the sensor address, but can be easily confused with the sensor address.
However, there are two different indexing schemes used for Modbus sensors, though translating between them is simple. One indexing scheme is called one- based numbering,  where the first register is given the index of 1, and is thereby accessed by requesting access to regis er 1. The other indexing scheme is called zero-based numbering, where the  first register is given the index 0, and is thereby accessed by requesting access to register 0. Apogee Sensors use zero-based numbering. However, if using the sensor in a system  that uses one-based numbering, such as using a CR1000X logger, adding 1 to the zero- based address will produce the one-based address for the register.

Register Format:
According to the Modbus protocol specification, Holding Registers (the type registers Apogee sensors contain) are defined to be 16 bits wide. However, when making scientific  measurements, it is desirable to obtain a more precise value than 16 bits allows. Thus, several Modbus implementations will use two 16-bit registers to act as one 32-bit register.  Apogee Modbus sensors use this 32-bit implementation to provide measurement values as 32-bit IEEE 754 floating point numbers.
Apogee Modbus sensors also contain a redundant, duplicate set of registers that use 16-bit signed integers to represent values as decimal-shifted numbers. It is recommended to  use the 32-bit values, if possible, as they contain more precise values.

Communication Parameters:
Apogee Sensors communicate using the Modbus RTU variant of the Modbus protocol. The default communication parameters are as follows:
Slave address: 1
Baudrate: 19200
Data bits: 8
Stop bits: 1
Parity: Even
Byte Order: Big-Endian (most significant byte sent first)

The baudrate and slave address are user configurable. Valid slave addresses are 1 to 247. Since the address 0 is reserve as the broadcast address, setting the slave address to 0 will  actually set the slave address to 1. (This will also reset factory-calibrated values and should NOT be done by the user unless otherwise instructed.)

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 2000 µmol m-2 s-1. This yields an output signal of 12 mA.
This signal is converted to photon flux density by subtracting the 4.0 mA offset and then multiplying by the calibration factor of 250 μmol m-2 s-1s per mA.

Read only registers (function code 0x3).

Float Registers

0
1| calibrated output pmol m-2 s-1
2
3| detector millivolts
4
5| immersed output pmol m-2 s-1
6
7| solar output pmol m-2 s’
8
9| Reserved for Future Use
10
11| device status
(1 means device is busy, 0 otherwise)
12
13| firmware version
Integer Registers
40| calibrated output pmol m-2 s’ (shifted one decimal point to the left)
41| detector millivolts (shifted one decimal point to the left)
42| immersed output pmol m’ s’ (shifted one decimal point to the left)
43| solar output pmol m-2 s-1 (shifted one decimal point to the left)
44| Reserved for Future Use
45| device status (1 means device is busy, 0 otherwise)
46| firmware version (shifted one decimal point to the left)

Read/Write registers (function codes 0x3 and 0x10).

Float Registers

16
17| slave address
18
19| model number
20
21| serial number
22
23| baudrate (0 = 115200, 1 = 57600, 2 = 38400, 3 = 19200, 4 = 9600, any other number = 19200)
24
25| parity (0 = none, 1 = odd, 2 = even)
26
27| number of stopbits
28
29| multiplier
30
31| offset
32
33| immersion factor
34
35| solar multiplier
36
37| running average
38
39| heater status
Integer Registers
48| slave address
49| model number
50| serial number
51| baudrate (0 = 115200, 1 = 57600, 2 = 38400, 3 = 19200, 4 = 9600, any other number = 19200)
52| parity (0 = none, 1 = odd, 2 = even)
53| number of stopbits
54| multiplier (shifted two decimal points to the left)
55| offset (shifted two decimal points to the left)
56| immersion factor (shifted two decimal points to the left)
57| solar multiplier (shifted two decimal points to the left)
58| running average
59| heater status

Registers marked with an asterisk () cannot be written to unless a specific procedure is followed. Contact
Apogee Instruments to receive the procedure for writing these registers
Write only registers (function code 0x10).

Integer Registers

190| Writing to this register resets Coefficients to firmware defaults. (NOT factory  calibrated values!) Slave Address = 1, Model = 618, Serial = 1000, Baud = 3,  Parity = 2, Stopbits = 1, running average = 1

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-supportrecalibration- repairs/).

TROUBLESHOOTING AND CUSTOMER SUPPORT

Independent Verification of Functionality
Apogee SQ-614 ePAR Sensors provide a 4-20 mA output that is proportional to extended photosynthetically active radiation for the 380-760 nm wavelength range. A quick and  easy check of sensor functionality can be determined using a DC power supply and an ammeter. Power the sensor with a DC voltage by connecting the positive voltage signal to  the red wire from the sensor and the negative (or common) to the black wire from the sensor. Use the ammeter to measure across the white wire (signal output) and green  wire (signal ground). 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 4 mA.

Compatible Measurement Devices (Dataloggers/Controllers/Meters)
SQ-614 ePAR Sensors are calibrated with a standard calibration factor of 250 pimol m-251 per mA, yielding a sensitivity of 0.004 mA per pmol m-2 s-1. Thus, a compatible measurement device (e.g., datalogger or controller) should have resolution of at least 0.004 mA in order to provide photon flux density resolution of 1 limo! m-25-1.
The 4-20 mA circuit design allows the output to drive a resistive load (RL) to within 2 volts of the supply voltage to the sensor (VS), at 20 mA (0.02 A). The equation to calculate resistive load is RL = [VS — 2 V] / 0.02 A. For example, a sensor with a supply voltage of 12 V DC can drive a maximum load of 500 0 (RL = [12 V — 2 V] / 0.02 A = 500 0). The output voltage from the sensor is calculated by adding the wire resistance to the input resistance of the data collection system, and then multiplying by 0.02 A.
An example datalogger program for Campbell Scientific dataloggers can be found on the Apogee webpage at https://www.apogeeinstruments.com/downloads/#datalogger.

Cable Length
Shortening or splicing on additional cable in the field is generally not a problem for the current output of the SQ­614. However, adding cable will result in a greater resistive load, which should be taken into consideration when determining the maximum resistive load that the sensor will drive (see section above on Compatible Measurement Devices). 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.nogeeinstruments.com/how-to-make-a-weatherproof-cable-solice/).

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 other 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.

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 435-245-8012 or email techsupport@apogeeinstruments.com 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  arranty, 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 techsupport@apogeeinstruments.com 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
APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: 435-792-4700 | FAX: 435-787-8268 | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2021 Apogee Instruments, Inc.

References

• Recalibration and Repair | Apogee Instruments
• Underwater PAR Measurements | Apogee Instruments
• apogeeinstruments.com/content/Quantum-Modbus.CR1

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