METER ATMOS 14 User manual

ATMOS 14

i
TABLE OF CONTENTS
1. Introduction..............................................................................................1
2. Operation ...................................................................................................2
2.1 Installation ................................................................................................2
2.2 Connecting................................................................................................. 4
2.2.1 Connect to METER Logger................................................................4
2.2.2 Connect to Non-METER Logger........................................................5
2.3 Communication .........................................................................................6
3. System.........................................................................................................7
3.1 Specifications............................................................................................7
3.2 Components ............................................................................................ 12
3.2.1 Radiation Shield ............................................................................ 12
3.2.2 Relative Humidity and Temperature Sensor................................... 12
3.2.3 Barometric Pressure Sensor .......................................................... 13
3.3 Theory...................................................................................................... 13
3.3.1 Vapor Pressure............................................................................... 13
3.3.2 Relative Humidity .......................................................................... 14
3.3.3 Temperature .................................................................................. 14
4. Service....................................................................................................... 15
4.1 Calibration ............................................................................................... 15
4.2 Cleaning and Maintenance....................................................................... 15
4.3 Troubleshooting....................................................................................... 16
4.4 Customer Support.................................................................................... 17
4.5 Terms and Conditions .............................................................................. 18
References .................................................................................................... 19
Index ................................................................................................................. 20
18013-04
1.17.2020

1
ATMOS 14
1. INTRODUCTION
Thank you for choosing the ATMOS 14 temperature and relative humidity (RH) sensor from
METER Group.
The ATMOS 14 is designed to measure the following:
• Air temperature
• RH
• Barometric pressure
• Vapor pressure
A rugged design allows the ATMOS 14 to withstand long-term exposure to hostile conditions,
making it ideal for a wide range of applications including standard meteorological
monitoring, evapotranspiration measurement, greenhouse monitoring and control, concrete
moisture monitoring, and building humidity monitoring for mold prevention and remediation.
Verify that ATMOS 14 and radiation shield (if ordered) appear in good condition.

2
OPERATION
2. OPERATION
Please read all instructions before operating the ATMOS14 to ensure it performs to its full
potential.
PRECAUTIONS
METER sensors are built to the highest standards, but misuse, improper protection,
or improper installation may damage the sensor and possibly void the manufacturer’s
warranty. Before integrating ATMOS 14 into a system, follow the recommended installation
instructions and have the proper protections in place to safeguard sensors from damage.
2.1 INSTALLATION
In general, temperature and humidity measurements become more accurate as wind speed
increases. For most outdoor and greenhouse measurement scenarios, the ATMOS 14 must
be housed in a radiation shield with adequate air flow to allow the sensor to come into
equilibrium with air temperature. For nongreenhouse, indoor monitoring applications, a
radiation shield is not critical because the radiation loading is small.
Follow the steps listed in Table 1 to set up the ATMOS14 and start collecting data.
Table 1 Installation
Tools Needed
Wrench
Mounting pole
Preparation
Consider the Surroundings
Ensure that site selection is far from wind obstruction and objects that can
store heat.
Conduct System Check
Plug the sensor into the logger (Section2.2) to make sure the sensor is
functional.
Adjust Pole Height
Check Radiation Shield
Ensure the sensor is securely installed in the radiation shield.

3
ATMOS 14
Table 1 Installation (continued)
Mounting
Install on Mounting Pole
Use the radiation shield mounting bracket and V-bolt to mount the radiation
shield to the mounting pole at the desired height.
Secure the System
Use a wrench to tighten the bolts, securing the radiation shield to the
mountingpole.
Secure and Protect Cables
NOTE: Improperly protected cables can lead to severed cables or disconnected sensors.
Cabling issues can be caused by many factors such as rodent damage, driving over sensor
cables, tripping over cables, not leaving enough cable slack during installation, or poor
sensor wiring connections.
Install cables in conduit or plastic cladding when near the ground to avoid
rodent damage.
Gather and secure cables between the ATMOS 14 and the data logger to the
mounting mast in one or more places.
Connect to Data Logger
Plug the sensor into a data logger.
Use the data logger to make sure the sensor is reading properly.
Verify these readings are within expected ranges.
For more instructions on connecting to data loggers, refer to Section2.2.

4
OPERATION
2.2 CONNECTING
The ATMOS 14 seamlessly with METER data loggers. The sensor can also be used with other
data loggers, such as those from Campbell Scientific, Inc. For extensive directions on how to
integrate the sensor into third-party loggers, refer to the ATMOS 14 Integrator Guide.
The ATMOS 14 sensor requires excitation voltages in the range of 3.6 to 15.0 VDC and
operates at a 2.8- to 5.5-VDC level for data communication. The ATMOS 14 can be integrated
using SDI-12 protocol. See the ATMOS 14 Integrator Guide for details on interfacing with data
acquisition systems.
The ATMOS 14 sensors come with a 3.5-mm stereo plug connector (Figure1) to facilitate
easy connection with METER loggers. ATMOS14 sensors may be ordered with stripped and
tinned wires to facilitate connecting to some third-party loggers (Section2.2.2).
Ground
Digital communication
Power
Figure1 Stereo plug connector
The ATMOS 14 comes standard with a 5-m cable. It may be purchased with custom cable
lengths for an additional fee (on a per-meter basis). In some instances, the cable can be
extended beyond 75 m by the user, but this is discouraged for a variety of reasons. Please
contact Customer Support for more details before extending or splicing cables.
2.2.1 CONNECT TO METER LOGGER
The ATMOS 14 works most efficiently with ZENTRA series data loggers. Check the METER
downloads webpage for the most recent data logger firmware. Logger configuration may
be done using either ZENTRA Utility (desktop and mobile application) or ZENTRA Cloud
(web-based application for cell-enabled data loggers).
1. Plug the stereo plug connector into one of the sensor ports on the logger.
2. Use the appropriate software application to configure the chosen logger port for the
ATMOS 14. METER data loggers will automatically recognize ATMOS 14 sensors.
3. Set the measurement interval.
METER data loggers measure the ATMOS 14 every minute and return the average of the
1-min data across the chosen measurement interval.
ATMOS 14 data can be downloaded from METER data loggers using either ZENTRA Utility or
ZENTRA Cloud. Refer to the logger user manual for more information about these programs.

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ATMOS 14
2.2.2 CONNECT TO NONMETER LOGGER
The ATMOS 14 can be purchased for use with non-METER (third party) data loggers. Refer
to the third-party logger manual for details on logger communications, power supply,
and ground ports. The ATMOS 14 Integrator Guide also provides detailed instructions on
connecting sensors to non-METER loggers.
ATMOS 14 sensors can be ordered with stripped and tinned (pigtail) wires for use with screw
terminals. Refer to the third-party logger manual for details on wiring.
Connect the ATMOS 14 wires to the data logger as illustrated in Figure2 and Figure3, with
the power supply wire (brown) connected to the excitation, the digital out wire (orange) to a
digital input, and the bare ground wire to ground.
Ground (bare)
Digital
communication (orange)
Power (brown)
Figure2 Pigtail wiring
NOTE: The VP-4 (predecessor to ATMOS 14) may have the older Decagon wiring scheme where the power supply is
white,the digital out is red, and the bare wire is ground.
Excitation Digital
in
Data Logger
Ground
Digital
communication
(orange)
Ground
(bare)
Power
(brown)
Figure3 Wiring diagram
NOTE: The acceptable range of excitation voltages is from 3.6 to 15.0 VDC.To read the ATMOS 14 with Campbell
Scientific data loggers,power the sensors off a switched 12-V port.
If the ATMOS 14 cable has a standard stereo plug connector and needs to be connected to
a non-METER data logger, use one of the following two option
Option 1
1. Clip off the stereo plug connector on the sensor cable.
2. Strip and tin the wires.
3. Wire it directly into the data logger.

6
OPERATION
This option has the advantage of creating a direct connection and minimizes the chance of
the sensor becoming unplugged. However, it then cannot be easily used in the future with a
METER readout unit or data logger.
Option 2
Obtain an adapter cable from METER.
The adapter cable has a connector for the stereo plug connector on one end and three wires
(or pigtail adapter) for connection to a data logger on the other end. The stripped and tinned
adapter cable wires have the same termination as in Figure3: the brown wire is excitation,
the orange is output, and the bare wire is ground.
NOTE: Secure the stereo plug connector to the pigtail adapter connections using adhesive-lined heat shrink to ensure
the sensor does not become disconnected during use.
2.3 COMMUNICATION
The ATMOS 14 communicates using SDI-12 communication protocol. To obtain detailed
instructions, refer to the ATMOS 14 Integrator Guide.
The SDI-12 protocol requires that all sensors have a unique address. ATMOS 14 sensor
factory default is an SDI-12 address of 0. To add more than one SDI-12 sensor to a bus, the
sensor address must be changed as described below:
1. Using a PROCHECK connected to the sensor, press the MENU button to bring up the
Configuration tab.
NOTE: If the PROCHECK does not have this option, please upgrade its firmware to the latest version from the
METER Legacy Handheld Devices webpage.
2. Scroll down to SDI-12 Address. Press ENTER.
3. Press the UP or DOWN arrows until the desired address is highlighted.
Address options include 0...9, A…Z, and a…z.
4. Press ENTER.
Detailed information can also be found in the application note Setting SDI-12 addresses on
METER digital sensors using Campbell Scientific data loggers and LoggerNet.
When using the sensor as part of an SDI-12 bus, excite the sensors continuously to avoid
issues with initial sensor startup interfering with the SDI-12 communications.

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ATMOS 14
3. SYSTEM
This section describes the ATMOS 14 sensor.
3.1 SPECIFICATIONS
MEASUREMENT SPECIFICATIONS
Relative Humidity (RH)
Range 0–100% RH (0.00–1.00)
Resolution 0.1% RH
Accuracy Sensor measurement accuracy is variable across a range of RH.
Refer to the chart in Figure4.
Figure4 RH sensor accuracy
Equilibration
Time (τ, 63%)
<40 s (response time in 1 m/s air stream)
Hysteresis <1% RH, typical
Long-Term Drift <0.5% RH/year, typical
Temperature
Range –40 to 80 °C
Resolution 0.1 °C

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SYSTEM
Accuracy Sensor measurement accuracy is variable across a range of
temperatures. Refer to the chart in Figure5.
Figure5 Temperature sensor accuracy
Equilibration
Time (τ, 63%)
<400 s (response time in 1 m/s air stream
Long-Term Drift <0.04 °C/year, typical
Vapor Pressure
Range 0–47 kPa
Resolution 0.01 kPa
Accuracy Sensor measurement accuracy is variable across a range of
temperatures and RH. Refer to the chart in Figure6.
Figure6 Vapor pressure sensor accuracy

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ATMOS 14
Barometric Pressure
Range 50–110 kPa
Resolution 0.01 kPa
Accuracy ±0.4 kPa
COMMUNICATION SPECIFICATIONS
Output
DDI serial or SDI-12 communication
Data Logger Compatibility
Any data acquisition system capable of 3.6- to 15.0-VDC power and serial or SDI-12
communication.
PHYSICAL SPECIFICATIONS
Dimensions
Diameter 2.0 cm (0.8 in)
Height 5.4 cm (2.1 in)
Operating Temperature Range
Minimum –40 °C
Typical NA
Maximum +80 °C
NOTE: Sensors may be used at higher temperatures under certain conditions; contactCustomer
Supportfor assistance.
Cable Length
5 m (standard)
75 m (maximum custom cable length)
NOTE: Contact Customer Support if a nonstandard cable length is needed.
Connector Types
3.5-mm stereo plug connector or stripped and tinnedwires

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SYSTEM
ELECTRICAL AND TIMING CHARACTERISTICS
Supply Voltage (VCC to GND)
Minimum 3.6 VDC
Typical NA
Maximum 15.0 VDC
Digital Input Voltage (logic high)
Minimum 2.8 V
Typical 3.0 V
Maximum 5.5 V
Digital Input Voltage (logic low)
Minimum –0.3 V
Typical 0.0 V
Maximum 0.8 V
Digital Output Voltage (logic high)
Minimum NA
Typical 3.6 V
Maximum NA
Power Line Slew Rate
Minimum 1.0 V/ms
Typical NA
Maximum NA
Current Drain (during measurement)
Minimum 4.50 mA
Typical 4.75 mA
Maximum 5.00 mA
Current Drain (while asleep)
Minimum NA
Typical 0.03 mA
Maximum NA

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ATMOS 14
Power Up Time (DDI serial)
Minimum NA
Typical NA
Maximum 100 ms
Power Up Time (SDI-12)
Minimum 100 ms
Typical 1,100 ms
Maximum 1,100 ms
Measurement Duration
Minimum NA
Typical 550 ms
Maximum 600 ms
COMPLIANCE
Manufactured under ISO 9001:2015
2004/108/EC and 2011/65/EU
EN61326-1:2013
EN50581:2012

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SYSTEM
3.2 COMPONENTS
The ATMOS 14 sensor consists of electronics potted in marine-grade polyurethane
encapsulant (Figure7). The sensor can then be inserted into a radiation shield
(Section3.2.1).
Mesh screen covering
filter and sensors
Connection cord
Sensor body
Figure7 ATMOS 14 components
The ATMOS 14 uses a primary sensor chip to measure RH and air temperature (Section3.2.2)
and a secondary chip to measure barometric pressure (Section3.2.3). A microprocessor
within the ATMOS 14 calculates vapor pressure from the RH and temperature
measurements. Calibration coefficients are applied before data are output. Air temperature,
RH, vapor pressure, and barometric pressure are output from the sensor.
The sensor chips are protected by a hydrophobic porous TeflonTM filter that is water- and
dustproof but has an extremely high vapor conductance, allowing fast sensor equilibration
with the surrounding atmosphere. A stainless steel screen protects the filter and sensors
from impact and abrasion.
3.2.1 RADIATION SHIELD
The radiation shield comprises a mounting bracket and seven discs. The shield prevents
direct sunlight from coming into contact with the sensor. This isolation from solar radiation
prevents false readings of elevated temperatures, allowing for accurate measurement of
ambient air temperature.
3.2.2 RELATIVE HUMIDITY AND TEMPERATURE SENSOR
The ATMOS 14 utilizes a capacitance-type RH sensor chip to measure the RH and
temperature of the surrounding air. For RH to be an accurate representation of the
atmospheric humidity, it is critical that the humidity sensor be at air temperature. For
most measurement scenarios, the ATMOS 14 should be housed in the radiation shield with
adequate airflow to allow the sensor to come into equilibrium with air temperature.

13
ATMOS 14
Each sensor chip is verified as accurate before prior to shipment. However, all capacitance
RH sensors drift over long periods of exposure to environmental conditions. The sensor chip
typically drifts less than 0.5% RH per year. METER recommends that ATMOS 14 sensors be
calibrated every 1 to 2 years under normal use conditions (Section4.1).
3.2.3 BAROMETRIC PRESSURE SENSOR
The barometric pressure sensor measures the atmospheric pressure of the environment
in which the ATMOS 14 is deployed. With a range from 49 to 109 kPa, it is suitable for
measurement across a wide range of elevations, but the magnitude of sensor output will
depend chiefly on the installation altitude with subtle changes caused by weather.
3.3 THEORY
This section explains how the ATMOS 14 sensor measures vapor pressure, RH, and
temperature.
3.3.1 VAPOR PRESSURE
Vapor pressure is calculated from the primary measurements of RH and temperature.
First, the saturation vapor pressure (es ) is calculated from the sensor temperature using
the Magnus-Tetens equation for calculating saturation vapor pressure over liquid water
formulated by Murray (1967):
Equation 1
es=aexp bT
T+c
⎛
⎝
⎜⎞
⎠
⎟
with coefficients defined by Buck (1981):
a = 0.611 kPa
b = 17.502,
c = 240.97 °C, and
T= temperature in degrees Celsius.
Then vapor pressure is calculated as the product of saturation vapor pressure and RH, with
RH expressed as a unitless ratio ranging from 0 to 1.
Equation 2
eRHVapor pressure s =×
Vapor pressure is conservative across temperature differences and small spatial scales.
This means that the vapor pressure of the atmosphere near the ATMOS 14 is the same
as the vapor pressure at the ATMOS 14 sensor, even if the ATMOS 14 is not at the same
temperature as the atmosphere. Additionally, it is the vapor pressure of the atmosphere (not
RH) that controls the rate of vapor phase water transport (e.g., evaporation, transpiration,
and distribution of water vapor). As discussed, RH measurements below a temperature

14
SYSTEM
of 0 °C introduce errors due to the use of liquid water as the reference. However, because
the Buck (1981) formulation for liquid water is used to calculate vapor pressure over the
full temperature range, ATMOS 14 vapor pressure output values are correct over the full
temperature range.
The METER ZENTRA system calculates and outputs vapor pressure deficit (VPD) in the
standard data stream. VPD is simply es(Tair ) – eaand gives a good indication of evaporative
demand.
3.3.2 RELATIVE HUMIDITY
The ATMOS 14 sensor provides an RH measurement that is referenced to saturation vapor
pressure over liquid water, even at temperatures below freezing, where ice is likely to be
present (WMO, 2008). Although this is the standard way to define RH, it has the disadvantage
of providing incorrect RH values below freezing when referenced to ice.
Figure8 shows the maximum RH the ATMOS 14 measures at saturation over ice. RH values
over ice can be corrected by dividing reported vapor pressure values by saturation vapor
pressure calculated with the Magnus-Tetens equation (Equation 1) using the ice phase
coefficients of b= 21.87 and c= 265.5 °C. Note that supercooled liquid water is often still
present at temperatures well below 0 °C, and the liquid water coefficients should be used in
those cases.
Figure8 RH value corrections
3.3.3 TEMPERATURE
The ATMOS 14 has a band gap temperature sensor integrated into the sensor electronics.
The temperature sensor accurately measures the sensor temperature. Sensor temperature
should remain close to air temperature if the ATMOS 14 radiation shield is adequately
shielded and aspirated.

15
ATMOS 14
4. SERVICE
This section describes the calibration and maintenance of ATMOS 14. Troubleshooting
solutions and customer service information are also provided.
4.1 CALIBRATION
Prior to shipping, the RH sensors are verified over salt solutions at 25%, 50%, and 76% RH
to ensure that they are properly functioning. METER recommends that ATMOS 14 sensors be
recalibrated every 1 to 2 years under normal use conditions to ensure best possible accuracy.
For safety-critical or high-accuracy applications, more frequent calibration is recommended.
Contact Customer Support for more information.
If sensors have been exposed to chemicals and conditioning fails to restore accurate
measurements, the sensors should be sent back to METER for evaluation and possible
calibration (Section4.2).
4.2 CLEANING AND MAINTENANCE
The ATMOS 14 sensor does not require any regular cleaning or maintenance. The radiation
shield should be cleaned with a damp cloth to remove dirt, debris, and nesting insects
or webs as these will reduce the airflow through the radiation shields and may reduce
itseffectiveness.
However, the polymer RH sensing element in the ATMOS 14 can be poisoned by exposure
to volatile organic compounds, solvents, and other chemicals. The effects of exposure
to these chemicals can range from subtle loss of accuracy to catastrophic failure.
If the ATMOS14 may have suffered chemical exposure (evident in questionable RH
measurements), check the sensor accuracy using known RH conditions.
A convenient method for generating known RH conditions is through the use of salt
solutions. For an initial check, prepare a saturated NaCl solution, which has an equilibrium
RH of 0.75 (75%):
1. Pour laboratory-grade NaCl into a sealable container that is large enough to
accommodate a salt solution and the ATMOS 14.
2. Mix in enough water that there is a thin layer of liquid water present over a thick slurry of
NaCl crystals.
3. Seal the ATMOS 14 sensor into the container, making sure that the ATMOS 14 is held or
suspended above the salt solution .
NOTE: Ensure the ATMOS 14 sensor is at the same temperature as the salt solution or large errors in the
measured RH occur.

16
SERVICE
Salt solutions in a wide range of RH can be carefully prepared with pure, dry salts using the
ratios in Table 2 or are available from METER. METER salt solutions are specified accurate to
within ±0.3% RH.
Table 2 Salt solutions
Equilibrium RH
(% saturation) Salt Molality (mol salt/kg water)
25 LiCl 13.41
50 LiCl 8.57
76 NaCl 6.00
If the ATMOS 14 sensor has lost accuracy due to exposure to solvents or other chemicals, the
following conditioning procedure may bring the sensor back to the original calibration state:
1. Bake the sensor in dry heat at 100 to 105 °C for 10 h.
2. Rehydrate the sensors by exposing them to a ~75% RH environment at 20 to 30 °C
for12 h.
A 75% RH environment can be conveniently established by sealing the sensor in a
headspace over prepared saturated NaCl.
4.3 TROUBLESHOOTING
Table 3 lists common problems and their solutions. Most issues with the ATMOS 14 sensor
may manifest themselves in the form of no reading from communication problems,
catastrophic sensor failure, or highly inaccurate measurements due to sensor poisoning
by volatile chemicals. If the problem is not listed or these solutions do not solve the issue,
contact Customer Support.
Table 3 Troubleshooting the ATMOS 14
Problem Possible Solutions
Data logger not
receiving readings
Check that the connections to the data logger are correct and secure.
Ensure that data logger batteries are not dead or weakened.
Check sensor cables for nicks or cuts that could prevent communication.
Check the configuration of the data logger in ZENTRA Utility to make sure
the ATMOS 14 is selected.
Sensor not reading
RHaccurately
Check the screen and filter for contamination or obstructions. Airflow
must not be restricted through the filter. Breathe heavily on sensor and
check for a corresponding change in measured RH to see if adequate
airflow ispresent.
Recondition the sensor as described in Section4.2.

17
ATMOS 14
Table 3 Troubleshooting the ATMOS 14 (continued)
Problem Possible Solutions
Sensor not reading
barometric pressure
accurately
Check the screen and filter for contamination or obstructions. Airflow
must not be restricted through the filter. Seal and pressurize the sensor
(e.g., with mouth or hand) and check for a corresponding change in
measured barometric pressure to see if adequate airflow is present.
Sensor not reading
air temperature
accurately
Ensure that ATMOS 14 sensor body is not exposed to solar radiation
(make sure it is fully shaded). This includes direct, diffuse, incident, and
reflected solar radiation.
Ensure that the ATMOS 14 radiation shield is mounted in a location with
adequate ventilation/wind speed to bring the sensor to air temperature.
Ensure that the ATMOS 14 sensor body is not exposed to high levels
of thermal radiation. This is could be important in some industrial
applications.
Test to see if the sensor responds to changes in temperature by holding
sensor body in hand (or at different temperature from ambient) for 2 min
and check for corresponding change in temperature measurement.
4.4 CUSTOMER SUPPORT
NORTH AMERICA
Customer service representatives are available for questions, problems, or feedback Monday
through Friday, 7:00 am to 5:00 pm Pacific time.
Email: [e-mail]
[e-mail]
Phone: [phone]
Fax: [phone]
Website: metergroup.com
EUROPE
Customer service representatives are available for questions, problems, or feedback Monday
through Friday, 8:00 to 17:00 Central European time.
Email: [e-mail]
[e-mail]
Phone: [phone]
Fax: [phone]
Website: metergroup.de