Apogee SQ-421 QUANTUM SENSOR Owner’s Manual

Apogee SQ-421 QUANTUM SENSOR

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-204X
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 biphenyls (PBDE), bis(2-Ethylhexyl) phthalate (DEHP), butyl benzyl phthalate (BBP), dibutyl phthalate (DBP), and di isobutyl 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, June 2021
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 variable. 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-100X series quantum sensors consist of a cast acrylic diffuser (filter), interference 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-100X series sensors output an analog voltage that is directly proportional to PPFD. The voltage 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 SDI-12 communication protocol, original quantum sensor model SQ-421. Additional models are covered in their respective manuals.

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.

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.

SPECIFICATIONS

| 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

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).

Spectral Response

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.

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.

Cosine Response

Directional, or cosine, response is defined as the measurement error at a specific angle of radiation incidence. Error for Apogee SQ-100X series quantum sensors is approximately ± 2 % and ± 5 % at solar zenith angles of 45° and 75°, respectively.

Mean cosine response of five SQ-100 series quantum sensors. Cosine response measurements were made by direct side-by-side comparison to the mean of seven reference 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.

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 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 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.

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 methods.

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).

OPERATION AND MEASUREMENT

The SQ-421 quantum sensor has a SDI-12 output, where shortwave radiation is returned in digital format. Measurement of SQ-421 quantum sensors requires a measurement device with SDI-12 functionality that includes the M or C command.
VERY IMPORTANT: Apogee changed the wiring colors of all our bare-lead sensors in March 2018 in conjunction with the release of inline cable connectors on some sensors. To ensure proper connection to your data device, please note your serial number or if your sensor has a stainless-steel connector 30 cm from the sensor head then use the appropriate wiring configuration listed below. With the switch to connectors, we also changed to using cables that only have 4 or 7 internal wires. To make our various sensors easier to connect to your device, we clip off any unused wire colors at the end of the cable depending on the sensor. If you cut the cable or modify the original pigtail, you may find wires inside that are not used with your particular sensor. In this case, please disregard the extra wires and follow the color-coded wiring guide provided.

Wiring for SQ-421 Serial Numbers 2053 and above or with a cable connector

Wiring for SQ-421 Serial Numbers within the range 0-2052

Sensor Calibration

All Apogee SDI-12 SQ-400 series quantum sensors have sensor-specific calibration coefficients determined during the custom calibration process. Coefficients are programmed into the microcontrollers at the factory.

SDI-12 Interface
The following is a brief explanation of the serial digital interface SDI-12 protocol instructions used in Apogee SQ-421 quantum sensors. For questions on the implementation of this protocol, please refer to the official version of the SDI-12 protocol: http://www.sdi-12.org/specification.php (version 1.4, August 10, 2016).

Overview
During normal communication, the data recorder sends a packet of data to the sensor that consists of an address and a command. Then, the sensor sends a response. In the following descriptions, SDI-12 commands and responses are enclosed in quotes. The SDI-12 address and the command/response terminators are defined as follows:
Sensors come from the factory with the address of “0” for use in single sensor systems. Addresses “1 to 9” and “A to Z”, or “a to z”, can be used for additional sensors connected to the same SDI-12 bus. “!” is the last character of a command instruction. In order to be compliant with SDI-12 protocol, all commands must be terminated with a “!”. SDI-12 language supports a variety of commands. Supported commands for the Apogee Instruments SQ-421 quantum sensors are listed in the following table (“a” is the sensor address. The following ASCII Characters are valid addresses: “0-9” or “A-Z”).

Supported Commands for Apogee Instruments SQ-421 Quantum Sensors

the line
Send Identification Command| aI!| Responds with sensor information
Measurement Command| aM!| Tells the sensor to take a measurement
Measurement Command w/ Check

Character

| aMC!| Tells the sensor to take a measurement and return it

with a check character

Change Address Command| aAb!| Changes the sensor address from a to b
Concurrent Measurement Command| aC!| Used to take a measurement when more than one

sensor is used on the same data line

Concurrent Measurement Command w/ Check Character| ****

aCC!

| Used to take a measurement when more than one sensor is used on the same data line. Data is returned

with a check character.

Address Query Command| ?!| Used when the address is unknown to have the sensor

identify its address, all sensors on data line respond

Get Data Command| aD0!| Retrieves the data from a sensor
Running Average Command| aXAVG!| Returns or sets the running average for sensor

measurements.

Make Measurement Command: M!

**** The make measurement command signals a measurement sequence to be performed. Data values generated in response to this command are stored in the sensor’s buffer for subsequent collection using “D” commands. Data will be retained in sensor storage until another “M”, “C”, or “V” command is executed. M commands are shown in the following examples:

calibration
aM1!| a0011| Returns millivolt output
aM2!| a0011| Returns µmol m-2 s-1 using sunlight calibration
aM3!| a0011| Returns immersed µmol m-2 s-1 for underwater measurements with electric light calibration
aM4!| a0011| Returns angle offset from vertical in degrees. (0 degrees if pointed up, 180 degrees if pointed

down.) Available in sensors with serial number 2401 or greater.

aMC0!| a0011| Returns µmol m-2 s-1 using electric light calibration w/CRC
aMC1!| a0011| Returns millivolt output w/ CRC
aMC2!| a0011| Returns µmol m-2 s-1 using sunlight calibration w/ CRC
aMC3!| a0011| Returns immersed µmol m-2 s-1 for underwater measurements with electric light calibration w/

CRC

aMC4!| a0011| Returns angle offset from vertical in degrees w/CRC. (0 degrees if pointed up, 180 degrees if pointed down.) Available in sensors with serial numbers 2401 or greater.

where a is the sensor address (“0-9”, “A-Z”, “a-z”) and M is an upper-case ASCII character.
The data values are separated by the sign “+”, as in the following example (0 is the address):

where 2000.0 is µmol m-2 s-1 and 400.0 is mV.

Concurrent Measurement Command: aC!

A concurrent measurement is one which occurs while other SDI-12 sensors on the bus are also making measurements. This command is similar to the “aM!” command, however, the nn field has an extra digit and the sensor does not issue a service request when it has completed the measurement. Communicating with other sensors will NOT abort a concurrent measurement. Data values generated in response to this command are stored in the sensor’s buffer for subsequent collection using “D” commands. The data will be retained in the sensor until another “M”, “C”, or “V” command is executed:

calibration
aC1!| a00101| Returns millivolt output
aC2!| a00101| Returns µmol m-2 s-1 using sunlight calibration
aC3!| a00101| Returns immersed µmol m-2 s-1 for underwater measurements with electric light calibration
aC4!| a00101| Returns angle offset from vertical in degrees. (0 degrees if pointed up, 180 degrees if

pointed down.) Available in sensors with serial number 2401 or greater.

aCC! or aCC0!| a00101| Returns µmol m-2 s-1 using electric light calibration w/CRC
aCC1!| a00101| Returns millivolt output w/CRC
aCC2!| a00101| Returns µmol m-2 s-1 using sunlight calibration w/CRC
aCC3!| a00101| Returns immersed µmol m-2 s-1 for underwater measurements with electric light calibration

w/CRC

aCC4!| a00101| Returns angle offset from vertical in degrees w/CRC. (0 degrees if pointed up, 180 degrees

if pointed down.) Available in sensors with serial numbers 2401 or greater.

where a is the sensor address (“0-9”, “A-Z”, “a-z”, “*”, “?”) and C is an upper-case ASCII character.
For example (0 is the address):

where 2000.0 is μmol m-2 s-1 and 400.0 is mV.

Change Sensor Address: aAb!
The change sensor address command allows the sensor address to be changed. If multiple SDI-12 devices are on the same bus, each device will require a unique SDI-12 address. For example, two SDI-12 sensors with the factory address of 0 requires changing the address on one of the sensors to a non-zero value in order for both sensors to communicate properly on the same channel:

where a is the current (old) sensor address (“0-9”, “A-Z”), A is an upper-case ASCII character denoting the instruction for changing the address, b is the new sensor address to be programmed (“0-9”, “A-Z”), and ! is the standard character to execute the command. If the address change is successful, the datalogger will respond with the new address and a .

Send Identification Command: aI!

The send identification command responds with sensor vendor, model, and version data. Any measurement data in the sensor’s buffer is not disturbed:

identifying values are returned

where a is the sensor address (“0-9”, “A-Z”, “a-z”, “*”, “?”), 421 is the sensor model number, vvv is a three character field specifying the sensor version number, and xx…xx is serial number.

Running Average Command
The running average command can be used to set or query the number of measurements that are averaged together before returning a value from a M! or MC! command. For example, if a user sends the command “0XAVG10!” to sensor with address 0, that sensor will average 10 measurements before sending the averaged value to the logger. To turn off averaging, the user should send the command “aXAVG1” to the sensor. To query the sensor to see how many measurements are being averaged, send the command “aXAVG!” and the sensor will return the number of measurements being averaged (see table below). The default for sensors is to have averaging turned off.

Query running

Average

| a XAVG!| an| a = sensor address, n = number of measurements used in

average calculation. Note: n may be multiple digits.

Set running

Average

| a XAVG n!| a| a = sensor address, n = number of measurements to be used in

average calculation. Note: n may be any value from 1 to 100.

Metadata Commands

Identify Measurement Commands

The Identify Measurement Commands can be used to view the command response without making a measurement. The command response indicates the time it takes to make the measurement and the number of data values that it returns. It works with the Verification Command (aV!), Measurement Commands (aM!, aM1! … aM9!, aMC!, aMC1! … aMC9!), and Concurrent Measurement Commands (aC!, aC1! … aC9! , aCC!, aCC1! … aCC9!).
The format of the Identify Measurement Command is the address, the capital letter I, the measurement command, and the command terminator (“!”), as follows: