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Bluetooth or USB Field
Temp/RH Data Loggers:
Which is Right for You?
A decision-making guide to choosing the
most suitable temp/RH data logger for
monitoring outdoor environments
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Introduction
Common to most outdoor
eld research is the need to
systematically collect vital
temperature and relative
humidity (RH) data that
can be used to formulate
results and shape
conclusions.
Field research conducted in outdoor environments comprises a diversity of
methods and incorporates several disciplines and scientic areas. Typical
areas of study are agricultural research, forestry surveys, and ecological
investigations. Common to most outdoor eld research is the need to
systematically collect vital temperature and relative humidity (RH) data that
can be used to formulate results and shape conclusions.
In the eld of ecology, for example, data obtained from outdoor eld research
allows investigators to better understand how natural systems respond to
changing environmental conditions, providing insights for better protecting
valuable ecosystems. Likewise, data obtained from outdoor research can
provide environmental scientists with the means to analyze natural processes
and evaluate the impacts of human actions on the environment. Additionally,
data gathered from outdoor eld research can be used to help improve
agricultural practices, leading to more sustainable growing methods, higher
crop qualities, and greater productivity.
To ensure thorough and accurate results—and rigorous investigative
conclusions—emphasis in outdoor eld research needs to be placed on the
collection of quality data. For this reason, the use of robust and effective
monitoring instruments is a very important consideration.
Data loggers that measure eld temperature and RH are vital tools for
supporting efforts in this eld. Offering the capacity to automatically collect
data on a 24-hour basis, eld temp/RH data loggers are deployed in
outdoor locations to measure and record information over time, providing a
comprehensive and accurate picture of changing environmental conditions.
Generally, two categories of eld temp/RH data
loggers are available on the market: traditional USB
options and newer models that utilize Bluetooth
technology.
With USB eld temp/RH data loggers, users must
physically connect the data logger to the USB port
of a computer or handheld device (a shuttle) to
retrieve and download data—a task that is often
routine, but one that can also become burdensome
or challenging, depending on the environment or the
specic location where the data logger is deployed.
USB loggers can have either a USB connector built
into them, or some other form of communication
such as optical, in which case they use a base
station that plugs into a USB port in the computer. Because loggers with
optical communication don’t have electrical connections, which can be
unreliable in the eld, they can provide better reliability in eld applications
than loggers with USB connectors. If you are looking at loggers with optical
communication, look for ones that can work with an optical data shuttle to
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ofoad data, without having to take a laptop into the eld.
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Data loggers with Bluetooth communication allow
data to be transferred wirelessly to a mobile
device. When looking at Bluetooth data loggers,
keep in mind that there are different versions
of Bluetooth. Loggers that use older versions
of Bluetooth require “pairing” with the mobile
devices, which means having to push a button on
the logger to enable communications between it
and the mobile device. This may not be practical
for loggers in hard-to-access locations.
Data loggers with Bluetooth Low Energy (BLE)
technology, also known as Bluetooth Smart
or Bluetooth 4.0, allow data to be transferred
wirelessly without having to connect cables or
push a button on the logger. This means that you do not have to physically
access the logger to ofoad data. Instead, you simply use an app on your
mobile device to connect to any logger within range. The time savings when
deploying loggers or retrieving data can be dramatic.
BLE is particularly well-suited to data loggers, as it uses less battery power.
In addition, with a well-written app, Bluetooth loggers allow you to take
advantage of the power and connectivity of today’s smartphones and other
mobile devices.
The purpose of this white paper is to provide an unbiased comparison of
USB and BLE eld temp/RH data loggers for outdoor eld research. In doing
so, this analysis will seek to offer practical advice and objective guidance for
determining which option is best for your unique application.
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The HOBO U23 Temperature/RH
Data Logger offers convenient
user-replaceable battery.
Important features to consider in temp/RH data loggers
Before examining the primary considerations that will help drive a decision
between USB and BLE options, it’s important to think about the key features
and capabilities of eld temp/RH loggers in general, regardless of whether
they are USB or BLE.
User-replaceable battery
With eld temp/RH data loggers that have this option, the existing battery can
be swapped out with a new one. The ability to replace the battery eliminates
the need to purchase a new logger when the original battery dies.
Measurement accuracy
It’s critical to ensure that the logger will meet your accuracy requirements.
• Keep in mind that accuracy is typically specied as +/-X. This means
that for two loggers measuring the same temperature or RH, one could
be reading low by that amount, while the other reads high, so that
they could provide readings that are twice the accuracy spec apart.
For example, if the spec is +/- 0.5C, the readings from two loggers
measuring the same temp could be 1.0C apart. This is especially
important to keep in mind if you’re comparing data between loggers
deployed at different locations.
• You should also consider sensor drift over time, and the response time
of the logger to changing conditions, as these factors can also affect the
accuracy of measurements.
• In addition, radiation heating from sunlight can cause articially high
readings. Please refer to the section on solar radiation shields later in
this document.
Above photo shows the MX2304 external
temperature data logger with an alarm status,
indicating a set temperature threshold has been
exceeded.
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Alarm notications
A visual alarm is a valuable feature in that it alerts users that out-of-range
conditions occurred. The user sets the temperature or humidity thresholds
when the logger is congured.
• Do you need to be notied of the alarm immediately? If so, you need
a logger that noties you, and this is usually accomplished through
the internet and a web-connected logger, which has cellular, Wi-Fi, or
Ethernet.
• Alternatively, if there will be people on site who can check for alarms, a
visual alarm on the logger or in the mobile app may work.
• In some cases you may just want to know that an alarm condition
happened during the deployment, so you know to take a closer look at
the data.
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Logging Modes
Besides the standard xed-rate logging, determine whether you need any
special logging modes such as: Wrap-when-full, Push-button start or stop,
Time-date stop, Burst logging, or Statistics logging.
Mounting mechanisms
Look for a logger that can be easily mounted in your eld sites.
Consider how you want to mount your loggers in place:
• Zip-ties are easy, fast, and secure, for speedy eld deployments.
• Screws take a little more time, but are a little more secure.
• Look for a logger that includes integrated mounting holes for your
preferred mounting method.
• Some loggers come with brackets that allow the logger to be removed
for data download.
Processing data from multiple loggers
If you are deploying several loggers at a time, look for loggers with these time-
saving features:
• Launch time-saving options: This is the ability to dene a deployment
conguration once (logging mode, logging rate, start time, etc.) and use
it to congure all the loggers for a deployment without having to re-enter
this information for each logger.
• Bulk-export or bulk-share option: This is the ability to select multiple les
and export or share them all at once.
• Automatic upload option: This is the ability for the software to
automatically merge data into a web database when the device or
computer is connected to the internet.
Phone screen capture above shows the
Congure settings in HOBOmobile for the
MX2301 temperature/relative humidity
data logger
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Key aspects to consider between BLE and USB eld
temp/RH data loggers
With BLE temp/RH loggers,
users can quickly and
seamlessly transmit
data wirelessly to mobile
devices from up to 100 feet
away, without coming into
physical contact with the
logger
For existing users currently employing USB eld temp/RH data loggers,
changing up equipment schemes to switch over to BLE can be a difcult
proposition. Many users may not necessarily feel a need to upgrade to newer
BLE technology. And continuing with the same technology means using the
base stations and software you already have, and not having to use two sets
of software and communication devices in the eld.
Nevertheless, given the potential to signicantly streamline both data logger
deployment and data retrieval in the eld, the convenience and advantages
offered by BLE can be signicant.
For users weighing both BLE and USB eld temp/RH data logger options,
a range of important factors should be considered. The following topics
represent key drivers to evaluate when deciding which option is more
appropriate.
Data access
For outdoor eld monitoring, data access can
be a critical issue—especially in applications
where data loggers need to be deployed in hard-
to-reach or limited-access locations. In these
situations, USB temp/RH data loggers—due to
the need to physically connect to a computer or
handheld device in order to download data—can
be more difcult to work with.
The above illustration depicts using a mobile
device to easily download data from a BLE
data logger in a hard-to-reach location.
With BLE temp/RH loggers, users can quickly
and seamlessly transmit data wirelessly to
mobile devices from up to 100 feet away, without
coming into physical contact with the logger, thus
overcoming many of the logistical challenges associated with downloading
data from limited-access areas. Some examples where BLE temp/RH loggers
can be benecial include:
• Critical or endangered habitats
• Bird nests
• Tree canopies
• Crop elds
• Human-conned spaces that might present a safety issue
• Bat caves (where bats could be disturbed)
• Environmental chambers that could be compromised if opened
• Rooftops and green roofs
• HVAC studies or energy-auditing applications that require site-specic
outdoor temperatures (data from a BLE logger placed on the outside
could be obtained from inside a building)
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Data sharing
Because of the power of today’s mobile devices, BLE data loggers that work
with them provide greater exibility and convenience in terms of where data
can be transmitted and how it can be shared. The logger app on a mobile
device can easily convert data into Excel or text les, and it lets you download
and send data in a few simple steps. The logger apps can work with other
apps on the mobile device to share these les via email, messaging, or Google
Drive, or automatically upload data to web databases, like Onset’s HOBOlink.
And all of this can be done while still in the eld, without having to return to
the ofce to share data. As such, for users who need to share data les or
measurement data, BLE temp/RH data loggers can be the most effective
option.
It is, however, also easy to export data from a desktop program to Excel or
other programs, often with more powerful formatting options available, such
that the les can be directly opened in the other programs. Desktop software
like HOBOware, for example, provides the ability to customize exported data
in terms of international date and decimal formats. If you will be looking at data
on your own laptop computer, using USB loggers that can be directly ofoaded
to your laptop can save you the step of having to transfer les later.
Durability
When determining the durability of a logger, look for its IP or NEMA rating,
and conrm that it’s made from all UV-resistant materials. For outdoor
deployments, you should use loggers that are rated IP64 or higher, or NEMA
4 or higher. For use in corrosive environments, look for RH sensors that are
user-replaceable.
Also keep in mind that loggers requiring electrical connections can be less
reliable in eld deployments. Ideally you’d want a logger that can remain
sealed during deployments and data ofoad. Having to open the logger in the
eld can expose electronic circuits to moisture, which can lead to failures.
Generally speaking, the ability for both BLE and USB temp/RH data loggers
to withstand harsh environmental conditions will vary from manufacturer to
manufacturer. (See sidebar for a comparison of Onset temp/RH loggers.)
Comparing Durability
Onset’s BLE options—the HOBO MX
series temperature/RH loggers —are
IP67-rated and have housing made of
100% UV-resistant materials.
Onset’s Optic USB options, which
include the HOBO U23 Pro v2 series
temperature/RH loggers, use optical
communications in the logger for
reliable data download with a base
station or data shuttle.
While both are durable, the BLE
option is generally more robust and
could represent a better choice for
monitoring in extreme climates such
as arctic regions, deserts, and coastal
areas.
On the other hand, if you are
monitoring in an environment that’s
corrosive to RH sensors—with
high levels of ammonia in the air,
for example—you may want to use
HOBO U23s, as they are equipped
with user-replaceable RH sensors.
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Cost of ownership
Product costs can vary among manufacturers. In general, however, for temp/
RH data loggers the BLE option is less expensive for users who need only one
or two data loggers. Cost savings are realized because BLE users don’t need
to buy computer software or a base station—all they need is the free app to
run on their mobile devices.
For larger studies that involve the purchase of dozens of loggers, however, the
extra cost associated with peripheral equipment required for USB temp/RH
data loggers becomes less of a factor.
Alarm notications
Both USB and BLE loggers can provide alarm notications. With BLE loggers,
however, the app can highlight which (if any) loggers in the area have
exceeded limits, letting the user ofoad and review data from those loggers
rst.
Radiation shield integration
With many outdoor applications, the need to protect data
loggers from direct sunlight is essential in order to prevent
false high readings from heating caused by solar radiation.
Both USB and BLE temp/RH data loggers have cables/
probes that can easily be placed inside a radiation shield.
The HOBO MX2301 Temperature/Relative
Humidity data logger shown mounted inside
the RS1 Solar Radiation Shield
BLE options, however, allow users to mount loggers inside
a shield, eliminating the inconvenience of having to remove
the sensor from the radiation shield to download data and
then reinstall it...and eliminating the risk of exposed cables
that can be chewed by insects or rodents.
Conclusion
When choosing temp/RH loggers it’s critical to select loggers that meet your
measurement needs and that hold up well in harsh eld conditions. Once
these basic requirements are met, you should consider the advantage of BLE
loggers for deploying in hard-to-access locations, where wireless data ofoad
can save a lot of time and prevent disruption to the environment. And because
they work with an app on your phone or tablet, BLE loggers give you access to
all the convenience and power that today’s mobile devices provide.
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About Onset
Onset is a leading supplier of data logger and monitoring solutions used to measure, record and manage data
for improving the environment and preserving the quality of temperature-sensitive products. Based on Cape Cod,
Massachusetts, Onset has been designing and manufacturing its products on site since the company’s founding in 1981.
Visit Onset on the web at www.onsetcomp.com.
Sales (8am to 5pm ET, Monday through Friday)
Email sales@onsetcomp.com
Call 508-759-9500
In US call toll free 800-564-4377
Fax 508-759-9100
Technical Support (8am to 8pm ET, Monday through Friday)
Email loggerhelp@onsetcomp.com
Call 508-759-9500
In US call toll free 877-564-4377
Access our full resources library at:
www.onsetcomp.com/resources
Onset Computer Corporation
470 MacArthur Blvd.
Bourne, MA 02532
Copyright© 2018, Onset Computer Corporation. All information in this document is subject to change without notice. Onset and HOBO are registered trademarks of Onset Computer
Corporation. All other trademarks are the property of their respective owners. All rights reserved. Printed in the USA. Lit. No. MKT1203-
1218
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Onset Computer
Corporation
470 MacArthur Blvd.
Bourne, MA 02532
Fax: 508-759-9100
1-800-LOGGERS
(1-800-564-4377)
www.onsetcomp.com
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