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USB or Bluetooth Temperature Loggers in the Field – Which Are Right for You?

Accurate outdoor data is critical to field research aimed at understanding and protecting the environment, from how natural ecosystems are responding to changing conditions to the impacts of human interactions. Today, there are a range of solutions on the market for systematically collecting vital temperature and relative humidity (RH) data. These include options for how the data loggers communicate for setup and data offload using technologies such as Universal Serial Bus (USB) and Bluetooth Low Energy (BLE). However, with more options, it can be difficult to determine the best approach for a given project. Following are factors researchers should consider when choosing between BLE and USB data loggers.

How USB and BLE Data Loggers Work
Field temp/RH data loggers are vital tools for monitoring environments, offering the capacity to automatically collect data on a continuous 24/7 basis and provide a comprehensive picture of changing conditions. The two primary types of field temp/RH data loggers available are traditional USB options and newer models utilizing Bluetooth technology. 

With USB, users physically connect the data logger to the USB port of a computer or handheld device (shuttle) to retrieve and download data. USB loggers may have a built-in USB connection or use optical communication via a base station or data shuttle, which then plugs into a computer’s USB port. Because loggers with optical communication don't have electrical connections, they can provide better reliability outdoors, but they need an optical data shuttle to offload data if users want to avoid taking a laptop into the field.

By contrast, data loggers with Bluetooth communication can wirelessly transfer data to a mobile device. Combined with a well-written application, Bluetooth loggers harness the power and connectivity offered by today’s smartphones, tablets, and other mobile devices.

Loggers using older Bluetooth versions require "pairing" with the mobile devices, which may not be practical for some locations. Data loggers with newer Bluetooth Low Energy (BLE) technology, also known as Bluetooth Smart or Bluetooth 4.0, can transfer data wirelessly without pairing. Instead, researchers simply use an app on their mobile devices to connect to any logger within range. BLE technology is well-suited to field data loggers, as it uses less battery power and can enable significant time savings when deploying loggers or retrieving data.

Important Features for any Temp/RH Data Logger
Before comparing USB and BLE options, it's important to review the key features and capabilities of field temp/RH loggers in general.

Measurement Accuracy: Researchers need to ensure that loggers meet their accuracy requirements. Accuracy is typically specified as +/-X, meaning that the recorded data is within that range of the true value.

Alarm notifications: An alarm is valuable for alerting users when out-of-range conditions occur, based on temperature or humidity thresholds set by users when a logger is configured. Researchers who require immediate alerts will need loggers connected to the internet through cellular, Wi-Fi, or Ethernet technology. Alternatively, people working onsite may simply need a visual alarm on the logger or in the mobile app.

Processing data from multiple loggers: Researchers using several loggers may want launch time-saving options for defining a deployment configuration once and using it to configure all the loggers. Also, a bulk-export or bulk-share option lets users export or share multiple files at once. And an automatic upload option enables software to automatically merge data into a web database when the device or computer is connected to the internet.

Durability: BLE and USB temp/RH data loggers built to withstand harsh environmental conditions are available. When determining durability, it's best to look for loggers rated International Protection (IP) 64 or higher, or National Electrical Manufacturers Association (NEMA) 4 or higher, and confirm that they are made from all ultra violet (UV) resistant materials. Moreover, outdoor loggers that can remain sealed during deployments and data offload are more reliable.

Logging modes: Besides standard fixed-rate logging, researchers should determine whether they need any special logging modes, such as wrap-when-full, push-button start or stop, time-date stop, event-triggered burst logging, or statistics logging.

User-replaceable battery: The ability to replace the battery in a field temp/RH data logger eliminates the need to purchase a new logger when the original battery dies.

Mounting mechanisms: Researchers should look for loggers that can be easily mounted in field sites using their preferred method, typically zip-ties or screws. This may include integrated mounting holes or brackets, the latter enabling a logger to be removed for data download.

BLE Versus USB Loggers
Researchers weighing BLE and USB field temp/RH data logger options should consider a range of important factors.

Cost of ownership: Even if BLE temp/RH data loggers carry slightly higher price tags, they can cost less to own if researchers only require a couple data loggers; since users don’t need to buy computer software or a base station, all they need is the free app running on their mobile devices. However, for larger studies involving dozens of loggers, the extra cost of peripheral equipment required for USB temp/RH data loggers becomes less of a factor. Additionally, users already employing USB loggers can continue using their existing base stations and software. Nevertheless, the convenience and potential to significantly streamline both data logger deployment and data retrieval in the field using BLE may justify the cost of migrating to this newer technology.

Data access: For outdoor field monitoring, data access can be a critical issue—especially in hard-to-reach or limited-access locations, such as bird nests, tree canopies, bat caves, or fragile habitats. USB temp/RH data loggers, which need to physically connect to a computer or device to download data, can be more difficult to use. By contrast, BLE temp/RH loggers let users transmit data wirelessly to mobile devices up to 100 feet away, eliminating the need for physical contact.

Data sharing: Researchers using programs such as Excel on their laptop computers may find that USB loggers, which directly offload data to the laptop, save them time. For users that want to share data files via the internet, BLE temp/RH data loggers may serve as a more effective option, since they work with mobile devices. The logger app on a mobile device can easily convert data into Excel or text files, and work with other mobile apps to share these files via email, messaging, or Google Drive.

Alarm notifications: Both USB and BLE logger models provide alarm notifications. With BLE loggers, however, the app can highlight which (if any) loggers in the area have exceeded limits, so users can offload and review data from those loggers first.

Radiation shield integration: Many applications require data loggers to be protected from direct sunlight 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. BLE options, however, let users mount loggers inside a shield and not have to remove them for download data.

Summary
There is no one right answer in choosing USB or BLE temp/RH data loggers for field monitoring. Instead, by evaluating the factors outlined here, researchers can determine the best approach for their projects.

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