Apogee Instruments SU-321 User manual

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: [phone] | FAX: [phone] | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2023 Apogee Instruments, Inc.
OWNER’S MANUAL
ULTRAVIOLET INDEX &
ULTRAVIOLET-B SENSOR
Models SU-321
Rev: 5-Jan-2023

TABLE OF CONTENTS
Owner’s Manual ............................................................................................................................................................................... 1
Certificates of Compliance ....................................................................................................................................................... 3
Introduction ............................................................................................................................................................................. 5
Sensor Models ......................................................................................................................................................................... 6
Specifications ........................................................................................................................................................................... 7
Deployment and Installation.................................................................................................................................................. 10
Cable Connectors................................................................................................................................................................... 11
Operation and Measurement ................................................................................................................................................ 12
Maintenance and Recalibration............................................................................................................................................. 18
Troubleshooting and Customer Support................................................................................................................................ 19
Return and Warranty Policy................................................................................................................................................... 21

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: SU-321
Type: Ultraviolet Index and Ultraviolet-B 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 63000:2018 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 2023
Bruce Bugbee
President
Apogee Instruments, Inc.

CERTIFICATE OF COMPLIANCE
UK 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: SU-321
Type: Ultraviolet Index and Ultraviolet-B Sensor
The object of the declaration described above is in conformity with the relevant UK Statutory Instruments and
their amendments:
2016 No. 1091 The Electromagnetic Compatibility Regulations 2016
2012 No. 3032 The Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic
Equipment Regulations 2012
Standards referenced during compliance assessment:
BS EN 61326-1:2013 Electrical equipment for measurement, control, and laboratory use –EMC requirements
BS EN 63000:2018 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 2023
Bruce Bugbee
President
Apogee Instruments, Inc.

INTRODUCTION
Ultraviolet (UV) radiation constitutes a portion of the electromagnetic spectrum from 100 to 400 nm and is further
subdivided into three wavelength ranges: UV-A (315 to 400 nm), UV-B (280 to 315 nm), and UV-C (100 to 280 nm).
Much of the UV-B and all the UV-C wavelengths from the sun are absorbed by Earth’s atmosphere. There are also
multiple artificial UV light sources available.
Most UV sensors designed for sunlight measurements are sensitive to UV radiation in the UV-A or UV-B ranges.
Apogee Instruments SU-300 series UV-I/UV-B sensors detect UV radiation from 270 to 315 nm and are calibrated
to output UV Index measurements. UV Index is a relative metric that scales linearly with the intensity of UV
radiation that causes sunburn in humans. Measured UV Index can be converted to energy flux density units of
watts per square meter (W m-2, equal to Joules per second per square meter) or photon flux density units of
micromoles per square meter per second (µmol m-2 s-1).
Typical applications of UV-I/UV-B sensors include incoming UV radiation measurement in outdoor environments,
aimed at informing people of potential for UV exposure and sunburn, or in laboratory use with artificial light
sources (e.g., germicidal lamps).
Apogee Instruments SU-300 series UV-I/UV-B sensors consist of a sintered quartz diffuser, photodiode, and signal
processing circuitry mounted in an anodized aluminum housing and a cable to connect the sensor to a
measurement device. SU-300 sensors are designed for continuous UV-I/UV-B radiation measurement in indoor or
outdoor environments. The SU-300 series outputs an analog voltage that is directly proportional to UV-I/UV-B
radiation incident on a planar surface (does not have to be horizontal) where the radiation emanates from all
angles of a hemisphere.

A sensor’s 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.
SENSOR MODELS
This manual covers the SDI-12 protocol UV-I/UV-B sensor model SU-321 (in bold below). Additional models are
covered in their respective manuals.
Model
Signal
SU-300
0-2 mV
SU-321
SDI-12

SPECIFICATIONS
Calibration Traceability
Apogee UV-I/UV-B series sensors are calibrated through side-by-side comparison to the mean of four transfer
standard UV-I/UV-B sensors under sunlight. The transfer standard UV-I/UV-B sensors are calibrated through side-
by-side comparison to an Apogee model PS-300 spectroradiometer under sunlight (clear sky conditions) in Logan,
Utah. The PS-300 is calibrated with a quartz halogen lamp traceable to the National Institute of Standards and
Technology (NIST).
SU-321-SS
Power Supply
5.5 to 24 V DC
Current Draw
1.4 mA (quiescent), 1.8 (active)
Calibration Factor
Custom for each sensor and stored in the firmware
Calibration Uncertainty
± 10 %
Measurement Range
0 to 20 UV Index
Measurement Repeatability
Less than 0.5 %
Long-term Drift
Less than 2 % per year
Non-linearity
Less than 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
270 to 315 nm (wavelengths where response is greater than 10 % of maximum; see
Spectral Response below)
Directional (Cosine) Response
± 2 % at 45°, ± 5 % at 75°
Temperature Response
Less than 0.1 % per C
Operating Environment
-30 to 85 C; 0 to 100 % relative humidity
Dimension
30.5 mm diameter, 37 mm height
Mass (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
Cosine Response Graph
-10
-8
-6
-4
-2
0
2
4
6
8
10
010 20 30 40 50 60 70 80 90
Difference [%]
Solar Zenith Angle [°]
Directional, or cosine, response is
defined as the measurement error at
a specific angle of radiation incidence.
Directional error for Apogee SU-300
series UV-I/UV-B sensors is
approximately ± 2 % and ± 5 % at solar
zenith angles of 45° and 75°,
respectively.
Mean cosine response of four Apogee
UV-I/UV-B sensors. Cosine response
was calculated as the relative
difference of UV-I/UV-B sensors from a
reference UV-I/UV-B sensor deployed
outdoors. These data are the average
of the AM and PM response.

Spectral Response
0.0001
0.0010
0.0100
0.1000
1.0000
10.0000
240 260 280 300 320 340 360 380 400
Relative Response
Wavelength [nm]
Spectral response estimate of
Apogee SU-300 UV-I/UV-B
sensors. Spectral response was
modeled from sensitivity of the
photodetector and
transmittance of the diffuser.
Gray line is the Erythemal Action
Spectrum and provides a relative
indication of skin damage
caused by UV radiation.

DEPLOYMENT AND INSTALLATION
Mount the sensor to a solid surface with the nylon mounting screw provided. To accurately measure UV-I/UV-B
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
Model AL-100
Nylon Screw: 10-32x3/8
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

OPERATION AND MEASUREMENT
The SU-321 UV-I/UV-B sensor has an SDI-12 output; UV radiation is returned in digital format. Measurement of SU-
321 UV-I/UV-B sensors require a measurement device with SDI-12 functionality that includes the M or C command.
Wiring for SU-321
White: Positive (signal from sensor)
Red: Input Power
Black: Ground (from sensor signal and output power)
Clear: Shield/Ground

Sensor Calibration
The SU-321 UV-A sensor has sensor-specific calibration coefficients determined during the custom calibration
process. Coefficients are programmed into the microcontrollers at the factory.
Sensor Noise Reduction
To reduce noise in the signal, Apogee recommends enabling averaging of 10 measurements in the sensor. For
more information on how to enable measurement averaging, see the Running Average Command section.
SDI-12 Interface
The following is a brief explanation of the serial digital interface SDI-12 protocol instructions used in Apogee SU-
321 UV-I/UV-B 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 SU-221 UV-A 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 SU-321 UV-I/UV-B Sensor
Instruction Name
Instruction Syntax
Description
Send Identification Command
aI!
Send identification 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 address of the sensor 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
Get Data Command
aD0!
Retrieves the data from a sensor
Running Average Command
aXAVG!
Returns or sets the running average for 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:
Command
Response
Response to 0D0!
aM! or aM0!
a0011<cr><lf>
Returns UV Index
aM1!
a0011<cr><lf>
Returns watts
aM2!
a0011<cr><lf>
Returns detector millivolts
aM3!
a0011<cr><lf>
Returns µmol
aM4!
a0011<cr><lf>
Returns angle offset from vertical in degrees. (0 degrees if pointed up, 180
degrees if pointed down.)
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):
Command
Sensor Response
Sensor Response when data is ready
0M0!
00011<cr><lf>
0<cr><lf>
0D0!
+3.0<cr><lf>
0M1!
00011<cr><lf>
0<cr><lf>
0D0!
+30.0<cr><lf>
0M2!
00011<cr><lf>
0<cr><lf>
0D0!
+6.0<cr><lf>
0M3!
00011<cr><lf>
0<cr><lf>
0D0!
+12.0<cr><lf>
0M4!
00011<cr><lf>
0<cr><lf>
0D0!
0+90.2<cr><lf>
where 3.0 is the UV Index, 30.0 is watts, 1.0 is mV, and 20.0 is µmol.
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:
Command
Response
Response to 0D0!
aC! or aC0!
a00101<cr><lf>
Returns UV Index
aC1!
a00101<cr><lf>
Returns watts
aC2!
a00101<cr><lf>
Returns detector millivolts
aC3!
a00101<cr><lf>
Returns µmol
aC4!
a00101<cr><lf>
Returns angle offset from vertical in degrees. (0 degrees if pointed up, 180
degrees if pointed down.)
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):
Command
Sensor Response
0C0!
000101<cr><lf>
0D0!
+3.0<cr><lf>
0C1!
000101<cr><lf>
0D0!
+30.0<cr><lf>
0C2!
000101<cr><lf>
0D0!
+6.0
0C3!
000101<cr><lf>
0D0!
+12.0<cr><lf>
0C4!
000101<cr><lf>
0D0!
0+90.2<cr><lf>
where 3.0 is the UV Index, 30.0 is watts, 1.0 is mV, and 20.0 is µmol.
Change Sensor Address: aAn!
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:
Command
Response
Description
aAb!
b<cr><lf>
Change the address of the sensor
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 <cr><lf>.
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:
Command
Response
Description
"aI!"
a14Apogee SU-221vvvByyxx…xx<cr><lf>
The sensor serial number and other 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 firmware version, Byy is the hardware version, 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.

Command Name
Characters Sent
Response
Explanation
Query running
Average
aXAVG!
An
a= sensor address, n= number of measurements used
in average calculation. Note: nmay be multiple digits
Set running Average
aXAVGnn!
A
a= sensor address, n = number of measurements to be
used in average calculation. Note: nmay be any value
from 1 to 100.
UV-I/UV-B Measurements and Spectral Errors
Apogee Instruments model SU-300 UV-I/UV-B sensors are calibrated to measure ultraviolet radiation from the sun
between 300 and 400 nm in Watts per square meter. In addition to naturally occurring UV-I/UV-B radiation from
the sun, there are many electric light sources that emit UV-I/UV-B radiation (e.g., cool white fluorescent, metal
halide, mercury arc, and germicidal lamps). Although the relative wavelengths of UV-I/UV-B radiation differ among
sunlight and electric lights, the error estimates shown in the table below indicate the SU-200 provides reasonable
estimates of UV-I/UV-B radiation coming from electric lamps (table provides spectral error estimates for UV-I/UV-B
radiation measurements from radiation sources other than clear sky solar radiation). For most common lamps, the
error is less than 10 %. The SU-300 is particularly useful for determining the UV-I/UV-B filtering capacity of the
transparent plastic and glass barriers that are commonly used below electric lamps.
Radiation Source (Error Calculated Relative to Sun, Clear Sky)
Expected EFD Error [%]
Expected PFD Error [%]
Clear Sky
0.0
0.0
Overcast
-4.0
-5.0
Direct Normal
-2.8
-3.6
Diffuse Blue
3.6
4.7
CWF T5
18.0
19.0
Metal Halide
-5.3
-7.6
Quartz Halogen
-4.1
-5.6
Mercury Arc
18.8
19.2
T12 Fluorescent UV-A Enhanced
17.6
20.0
UV-A LED (365 nm Peak)
19.0
16.9
UV-A LED (386 nm Peak)
-26.4
-30.6
UV-A LED (395 nm Peak)
-53.7
-57.0

Converting from UV Index to UV-B in Units of W m-2 and mol m-2 s-1
There is a relatively linear relationship between UV Index and UV-B irradiance for sunlight (see graph below),
suggesting UV-B irradiance can be approximated from UV Index measurements from the SU-300 UV-I/UV-B sensor.
To convert from UV Index to UV irradiance in units of W m-2, divide UV Index by 5.7 (slope of the line in the graph
below).
UV-B irradiance (in units of W m-2) can be converted to UV-B photon flux density by dividing UV-B irradiance (in
units of W m-2) by the average energy content of solar UV-B photons, 0.384 J per mol. To convert UV Index to UV-
B photon flux density, divide the UV Index measurement by 2.2 (slope of the line in the graph below multiplied by
0.384 J per mol).
0
1
2
3
4
5
6
7
8
9
10
11
12
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
UV Index
UV-B Irradiance [W m-2]
Relationship between UV Index and UV-B irradiance (in units of W m-2). Data are from multiple solar
spectra representing a wide range of atmospheric conditions. Slope of the line is 5.7, with an r2= 0.99.

MAINTENANCE AND RECALIBRATION
Blocking of the optical path between the target and detector can cause low readings. Occasionally, accumulated
materials on the diffuser of the SU-300 series UV-I/UV-B sensors can block the optical path in three common ways:
1. Moisture or debris build-up on the diffuser.
2. Dust during periods of low rainfall.
3. Salt deposit accumulation from evaporation of sea spray or sprinkler irrigation water.
SU-300 series 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.
Never use solvents such as alcohol or acetone to clean the sensor. Use only gentle pressure when cleaning the
diffuser with a cotton swab or soft cloth, to avoid scratching the outer surface. The vinegar should be allowed to
do the cleaning, not mechanical force. Never use an abrasive material or cleaner on the diffuser.
It is recommended that UV-A sensors 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
If the sensor does not communicate with the datalogger, use an ammeter to check the current draw. It should be
near 1.4 mA when the sensor is not communicating and spike to approximately 1.8 mA when the sensor is
communicating. Any current draw greater than approximately 6 mA indicates a problem with power supply to the
sensors, wiring of the sensor, or sensor electronics.
Compatible Measurement Devices (Dataloggers/Controllers/Meters)
Any datalogger or meter with SDI-12 functionality that includes the M or C command.
An example datalogger program for Campbell Scientific dataloggers can be found on the Apogee webpage at
https://www.apogeeinstruments.com/downloads/#datalogger.
Zero Offset Error
With the use of certain dataloggers it is possible to measure a non-zero voltage (zero offset) when the sensor
output should be zero (no UV irradiance incident on diffuser). This offset can be corrected by adding or subtracting
the measured offset from the sensor output. However, if the offset is substantial, and your sensor is outputting
unrealistic values then it may need to be recalibrated. In this case, contact Apogee customer support to recalibrate
the sensor.
Modifying Cable Length
SDI-12 protocol limits cable length to 60 meters. For multiple sensors connected to the same data line, the
maximum is 600 meters of total cable (e.g., ten sensors with 60 meters of cable per sensor). See Apogee webpage
for details on how to extend sensor cable length (http://www.apogeeinstruments.com/how-to-make-a-
weatherproof-cable-splice/).
Unit Conversion
SU-300 series UV-I/UV-B sensors are calibrated in energy flux units of W m-2. It is possible to convert the energy
flux value to photon flux units of µmol m-2 s-1 using a conversion factor. Below is an example of how to convert
energy flux units to photon flux.
1) Calculate the sensor output in units of J m-2 s-1.
 
     
2) Multiply the energy flux units by the conversion factor. It’s important to note that each light source needs
a specific conversion factor. The conversion factor used in the example equation is the sunlight
conversion factors.
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
 
 


NOTE: Remove protective cap before using any sensor.