Apogee Instruments PYRANOMETER SP-421 User manual

APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: [phone] | FAX: [phone] | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2018 Apogee Instruments, Inc.
OWNER’S MANUAL
PYRANOMETER
Models SP-421
(including SS model)

2
TABLE OF CONTENTS
Owner’s Manual ................................................................................................................................................................................................................ 1
Certificate of Compliance .................................................................................................................................................................................... 3
Introduction............................................................................................................................................................................................................. 4
Sensor Models ......................................................................................................................................................................................................... 5
Specifications........................................................................................................................................................................................................... 6
Deployment and Installation.............................................................................................................................................................................. 9
Operation and Measurement...........................................................................................................................................................................11
Maintenace and Recalibration .........................................................................................................................................................................17
Troubleshooting and Customer Support......................................................................................................................................................18

3
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: SP-421
Type: Pyranometer
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
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 cadmium, hexavalent chromium, lead,
mercury, polybrominated biphenyls (PBB), polybrominated diphenyls (PBDE).
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, May 2016
Bruce Bugbee
President
Apogee Instruments, Inc.

4
INTRODUCTION
Solar radiation at Earth’s surface is typically defined as total radiation across a wavelength range of 280 to 4000 nm
(shortwave radiation). Total solar radiation, direct beam and diffuse, incident on a horizontal surface is defined as global
shortwave radiation, or shortwave irradiance (incident radiant flux), and is expressed in Watts per square meter (W m-2, equal
to Joules per second per square meter).
Pyranometers are sensors that measure global shortwave radiation. Apogee SP series pyranometers are silicon-cell
pyranometers, and are only sensitive to a portion of the solar spectrum, approximately 350 to 1100 nm (approximately 80 %
of total shortwave radiation is within this range). However, silicon-cell pyranometers are calibrated to estimate total
shortwave radiation across the entire solar spectrum. Silicon-cell pyranometer specifications compare favorably to
specifications for World Meteorological Organization (WMO) moderate and good quality classifications and specifications for
International Organization of Standardization (ISO) second class and first class classifications, but because of limited spectral
sensitivity, they do not meet the spectral specification necessary for WMO or ISO certification.
Typical applications of silicon-cell pyranometers include incoming shortwave radiation measurement in agricultural,
ecological, and hydrological weather networks, and solar panel arrays.
Apogee Instruments SP series pyranometers consist of a cast acrylic diffuser (filter), photodiode, and signal processing
circuitry mounted in an anodized aluminum housing, and a cable to connect the sensor to a measurement device. Sensors
are potted solid with no internal air space and are designed for continuous total shortwave radiation measurement on a
planar surface in outdoor environments. SP series sensors output a digital signal using SDI-12 protocol.

5
SENSOR MODELS
This manual covers the SDI-12 protocol model SP-421 pyranometer sensor. Additional models are covered in their respective
manuals.
*Pyranometer model SP-230 is similar to model SP-110, but includes internal heaters designed to keep the diffuser free of precipitation
events such as dew or frost.
Model
Signal
SP-421
SDI-12
SP-110 Self-powered
SP-230* Self-powered
SP-212 0-2.5 V
SP-214 4-20 mA
SP-215 0-5 V
SP-420 USB
SP-422 Modbus
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.

6
SPECIFICATIONS
Calibration Traceability
Apogee Instruments SP series pyranometers are calibrated through side-by-side comparison to the mean of four Apogee
model SP-110 transfer standard pyranometers (shortwave radiation reference) under high intensity discharge metal halide
lamps. The transfer standard pyranometers are calibrated through side-by-side comparison to the mean of at least two ISO-
classified reference pyranometers under sunlight (clear sky conditions) in Logan, Utah. Each of four ISO-classified reference
pyranometers are recalibrated on an alternating year schedule (two instruments each year) at the National Renewable
Energy Laboratory (NREL) in Golden, Colorado. NREL reference standards are calibrated to the World Radiometric Reference
(WRR) in Davos, Switzerland.
SP-421
Input Voltage Requirement 5.5 to 24 V DC
Current Drain 0.6 mA (quiescent), 1.3 mA (active)
Output Range 0 to 1750 W m-2
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 1750 W m-2)
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 180º
Spectral Range
360 to 1120 nm (wavelengths where response is 10% of maximum;
see Spectral Response below)
Directional (Cosine) Response ± 5 % at 75º zenith angle (see Cosine Response below)
Temperature Response 0.04 ± 0.04 % 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 44.0 mm height, 23.5 mm diameter
Mass 177 g (with 5 m cable)
Cable
5 m of two conductor, shielded, twisted-pair wire, additional cable available in multiples of 5 m;
santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions); pigtail
lead wires

7
Spectral Response
Temperature Response
Mean temperature response of four Apogee
silicon-cell pyranometers. Temperature response
measurements were made at approximately 10 C
intervals across a temperature range of
approximately -10 to 50 C under sunlight. Each
pyranometer had an internal thermistor to
measure temperature. At each temperature set
point, a reference blackbody pyranometer was
used to measure solar intensity.
Spectral response estimate of Apogee silicon-cell
pyranometers. Spectral response was estimated
by multiplying the spectral response of the
photodiode, diffuser, and adhesive. Spectral
response measurements of diffuser and adhesive
were made with a spectrometer, and spectral
response data for the photodiode were obtained
from the manufacturer.

8
Cosine Response
Mean cosine response of eleven Apogee silicon-
cell pyranometers (error bars represent two
standard deviations above and below mean).
Cosine response measurements were made
during broadband outdoor radiometer
calibrations (BORCAL) performed during two
different years at the National Renewable Energy
Laboratory (NREL) in Golden, Colorado. Cosine
response was calculated as the relative difference
of pyranometer sensitivity at each solar zenith
angle to sensitivity at 45° solar zenith angle. The
blue symbols are AM measurements, the red
symbols are PM measurements.
Directional, or cosine, response is defined as
the measurement error at a specific angle of
radiation incidence. Error for Apogee silicon-
cell pyranometers is approximately ± 2 % and
± 5 % at solar zenith angles of 45° and 75°,
respectively.

9
DEPLOYMENT AND INSTALLATION
Mount the sensor to a solid surface with the nylon mounting screw provided. To accurately measure PPFD incident on a
horizontal surface, the sensor must be level. An Apogee Instruments model AL-100 Leveling Plate is recommended to level
the sensor when used on a flat surface or being mounted to surfaces such as wood. To facilitate mounting on a mast or pipe,
the Apogee Instruments model AL-120 Solar Mounting Bracket with Leveling Plate is recommended.
To minimize azimuth error, the sensor should be mounted with the cable pointing toward true north in the northern
hemisphere or true south in the southern hemisphere. Azimuth error is typically less than 1 %, but it is easy to minimize by
proper cable orientation.
In addition to orienting the cable to point toward the nearest pole, the sensor should also be mounted such that
obstructions (e.g., weather station tripod/tower or other instrumentation) do not shade the sensor. Once mounted, the
green cap should be removed from the sensor. The green cap can be used as a protective covering for the sensor when it
is not in use.
Nylon Screw: 10-32x3/8
Model AL-100
Nylon Screw: 10-32x3/8
Model AL-120

10
Cable Connectors
Apogee started offering in-line cable connectors on some
bare-lead sensors in March 2018 to simplify the process of
removing sensors from weather stations for calibration by
not requiring the full cable to be uninstalled back to the data
logger.
The ruggedized M8 connectors are rated IP67, made of
corrosion-resistant marine-grade stainless-steel, and
designed for extended use in harsh environmental
conditions.
Inline cable connectors are installed 30 cm from the head
(pyranometer pictured)
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 data
logger connection, we remove the unused pigtail lead colors
at the data logger end of the cable.
If you ever need a replacement cable, please contact us
directly to ensure ordering the proper pigtail configuration.
Alignment: When reconnecting your 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 short
end of the cable and half the connector.
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.
Finger-tighten firmly

11
Black: Ground
Red: Power In (5.5-24 V DC)
White: SDI-12 Data Line
Clear: Shield/Ground
Red: Power In (4.5-24 V DC)
Black: SDI-12 Data Line
Clear: Ground (shield wire)
OPERATION AND MEASUREMENT
The SP-421 pyranometer has a SDI-12 output, where shortwave radiation is returned in digital format. Measurement of SP-
421 pyranometer requires a measurement device with SDI-12 functionality that includes the M or C command.
VERY IMPORTANT: Apogee changed all wiring colors of 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 below.
Wiring for SP-421 Serial Numbers range 0-1173
Wiring for SP-421 Serial Numbers 1174 and above or with a cable connector

12
Sensor Calibration
The SP-421 pyranometer has 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 SP-421
pyranometers. 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
SP-421 pyranometers 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 SP-421 Pyranometers
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
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 watts/m2
aM1!
a0011<cr><lf>
Returns millivolt output
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):

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Command
Sensor Response
Sensor Response when data is ready
0M0!
00011<cr><lf>
0<cr><lf>
0D0!
+1000.0<cr><lf>
0M1!
00011<cr><lf>
0<cr><lf>
0D0!
+200.0<cr><lf>
where 1000.0 is watts/m2and 200 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:
Command
Response
Response to 0D0!
aC! or aC0!
a00101<cr><lf>
Returns watts/m
2
aC1!
a00101<cr><lf>
Returns millivolt output
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!
+1000.0<cr><lf>
0C1!
000101<cr><lf>
0D0!
+200.0<cr><lf>
where 1000.0 is watts/m2and 200 is mV.
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!"
a13Apogee SP-421vvvxx…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 version number, and xx...xx is serial number.

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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:
<address>I<command>!
The format of the response is the same as if the sensor is making a measurement. For the Verification Command and
Measurement Commands, the response is atttn<CR><LF>. For the C Command, it is atttnn<CR><LF>. For the High Volume
Commands, it is atttnnn<CR><LF>. The address is indicated by a, the time in seconds to make the measurement is indicated
by ttt, and the number of measurements is indicated by n, nn, and nnn. The response is terminated with a Carriage Return
(<CR>) and Line Feed (<LF>).
Identify Measurement Command example:
3IMC2!
The Identify Measurement Command for sensor address 3, M2 command, requesting a CRC.
30032<CR><LF>
The response from sensor address three indicating that the measurement will take three
seconds and two data values will be returned.
Identify Measurement Parameter Commands
The Measurement Parameter Commands can be used to retrieve information about each data value that a command returns.
The first value returned is a Standard Hydrometeorological Exchange Format (SHEF) code. SHEF codes are published by the
National Oceanic and Atmospheric Administration (NOAA). The SHEF code manual can be found
at http://www.nws.noaa.gov/oh/hrl/shef/indexshef.htm. The second value is the units of the parameter. Additional fields
with more information are optional.
The Measurement Parameter Commands work 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 Parameter Command is the address, the capital letter I, the measurement command,
the underscore character (“_”), a three-digit decimal number, and the command terminator (“!”). The three-digit decimal
indicates which number of measurement that the command returns, starting with “001” and continuing to “002” and so on,
up to the number of measurements that the command returns.
<address>I<command>_<three-digit decimal>!
The format of the response is comma delimited and terminated with a semicolon. The first value is the address. The second
value is the SHEF code. The third value is the units. Other optional values may appear, such as a description of the data value.
The response is terminated with a Carriage Return (<CR>) and Line Feed (<LF>).
a,<SHEF Code>,<units>;<CR><LF>

15
Identify Measurement Parameter Command example:
1IC_001!
The Identify Measurement Parameter
Command for sensor address 1, C
command, data value 1.
1,RW,Watts/meter squared,incoming solar radiation;<CR><LF>
The response from sensor address 1, SHEF
code RW, units of Watts/meter squared,
and additional information of incoming
solar radiation.
Spectral Errors for Measurements with Silicon-cell Pyranometers
Apogee SP series pyranometers are calibrated under electric lamps in a calibration laboratory. The calibration procedure
simulates calibration under clear sky conditions at a solar zenith angle of approximately 45°. However, due to the limited
spectral sensitivity of silicon-cell pyranometers compared to the solar radiation spectrum (see graph below), spectral errors
occur when measurements are made in conditions that differ from conditions the sensor was calibrated under (e.g., the solar
spectrum differs in clear sky and cloudy conditions, thus, measurements in cloudy conditions result in spectral error because
sensors are calibrated in clear sky conditions).
Silicon-cell pyranometers can still be used to measure shortwave radiation in conditions other than clear sky or from
radiation sources other than incoming sunlight, but spectral errors occur when measuring radiation with silicon-cell
pyranometers in these conditions. The graphs below show spectral error estimates for Apogee silicon-cell pyranometers at
varying solar zenith angles and varying atmospheric air mass. The diffuser is optimized to minimize directional errors, thus
the cosine response graph in the Specifications section shows the actual directional errors in practice (which includes
contributions from the spectral shift that occurs as solar zenith angle and atmospheric air mass change with time of day and
time of year). The table below provides spectral error estimates for shortwave radiation measurements from shortwave
radiation sources other than clear sky solar radiation.
Spectral response of Apogee SP series
pyranometers compared to solar radiation
spectrum at Earth’s surface. Silicon-cell
pyranometers, such as Apogee SP series, are
only sensitive to the wavelength range of
approximately 350-1100 nm, and are not
equally sensitive to all wavelengths within this
range. As a result, when the spectral content of
solar radiation is significantly different than
the spectrum that silicon-cell pyranometers
were calibrated to, spectral errors result.

16
Spectral Errors for Shortwave Radiation Measurements with Apogee SP Series Pyranometers
Radiation Source (Error Calculated Relative to Sun, Clear Sky)
Error [%]
Sun (Clear Sky)
0.0
Sun (Cloudy Sky)
9.6
Reflected from Grass Canopy
14.6
Reflected from Deciduous Canopy
16.0
Reflected from Conifer Canopy
19.2
Reflected from Agricultural Soil
-12.1
Reflected from Forest Soil
-4.1
Reflected from Desert Soil
3.0
Reflected from Water
6.6
Reflected from Ice
0.3
Reflected from Snow
13.7
Spectral error for Apogee SP series
pyranometers as a function of atmospheric air
mass, assuming calibration at an air mass of
1.5.
Spectral error for Apogee SP series
pyranometers as a function of solar zenith
angle, assuming calibration at a zenith angle
of 45°.

17
MAINTENACE AND RECALIBRATION
Moisture or debris on the diffuser is a common cause of low readings. The sensor has a domed diffuser and housing for
improved self-cleaning from rainfall, but materials can accumulate on the diffuser (e.g., dust during periods of low rainfall,
salt deposits from evaporation of sea spray or sprinkler irrigation water) and partially block the optical path. 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. Never use an abrasive material or cleaner on the diffuser.
The Clear Sky Calculator (www.clearskycalculator.com) can be used to determine the need for pyranometer recalibration. It
determines total shortwave radiation incident on a horizontal surface at any time of day at any location in the world. It is
most accurate when used near solar noon in spring and summer months, where accuracy over multiple clear and unpolluted
days is estimated to be ± 4 % in all climates and locations around the world. For best accuracy, the sky must be completely
clear, as reflected radiation from clouds causes incoming radiation to increase above the value predicted by the clear sky
calculator. Measured values of total shortwave radiation can exceed values predicted by the Clear Sky Calculator due to
reflection from thin, high clouds and edges of clouds, which enhances incoming shortwave radiation. The influence of high
clouds typically shows up as spikes above clear sky values, not a constant offset greater than clear sky values.
To determine recalibration need, input site conditions into the calculator and compare total shortwave radiation
measurements to calculated values for a clear sky. If sensor shortwave radiation measurements over multiple days near solar
noon are consistently different than calculated values (by more than 6 %), the sensor should be cleaned and re-leveled. If
measurements are still different after a second test, email [e-mail] to discuss test results and
possible return of sensor(s).
Homepage of the Clear Sky Calculator. Two calculators are
available: One for pyranometers (total shortwave radiation) and
one for quantum sensors (photosynthetic photon flux density).
Clear Sky Calculator for pyranometers. Site data are input in
blue cells in middle of page and an estimate of total shortwave
radiation is returned on right-hand side of page.

18
TROUBLESHOOTING AND CUSTOMER SUPPORT
Independent Verification of Functionality
If the sensor does not communicate with the datalogger, use an ammeter to check the current drain. It should be near 0.6 mA
when the sensor is not communicating and spike to approximately 1.3 mA when the sensor is communicating. Any current
drain 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 http://www.apogeeinstruments.com/content/Pyranometer-Digital.CR1.
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/).
APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: [phone] | FAX: [phone] | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2018 Apogee Instruments, Inc.