A data logger is a compact, self-contained electronic unit that measures, records, and transmits a stream of data. In other articles, we’ve covered the types of data they’re used to collect, which include temperature, humidity, pressure, and many others.
We’ve also previously discussed the industries they’re commonly used in, including pharmaceuticals, perishable food distribution, aerospace, water treatment, and others. Data loggers are especially valuable in applications where product quality is sensitive to environmental conditions, or to the operating parameters of a manufacturing process.
In this article, we’ll turn our focus to how modern data loggers are powered, and how they transmit the data they collect. When selecting a data logger, there isn’t a universal best option for either. The optimal configuration will depend on the size and needs of your operation, so it’s important to know what options are available.
How are data loggers powered?
The small amount of power that a data logger requires can come from a number of different sources:Wired AC Connection
When the main building power is accessible, data loggers can use an AC adapter plugged into a normal wall outlet. A variety of options exist, usually for 100-240 VAC supplies, with fittings available for non-US standard outlets. The AC adapters for data loggers typically step down the mains AC voltage to the lower DC voltage required by the logger. These units can include a rechargeable battery backup in case of a power outage.
Data loggers that rely on battery power alone are designed to minimize power use and maximize battery life. Typical battery change intervals are greater than 1 year, depending on how the logger is operated. If battery change intervals are a concern, models that use Li-ion batteries instead of standard alkaline batteries can be used. When looking at the specs for a battery powered data logger, you may see that battery life depends on the measurement interval. For example, recording a data point every 1 hour will give longer battery life compared to every 30 seconds. For this reason, battery life is sometimes specified at a particular measurement interval.
Power over ethernet (PoE)
This is a convenient option if the data logger is connected by an ethernet cable. In PoE, electrical power is delivered through the same cable used for communication, eliminating the need for a separate power supply line.
These cover the most common options. For specialized, remote applications, renewable sources like solar panels combined with a rechargeable battery can be used. This type of setup is typical for weather monitoring stations and other off-grid locations where battery replacement would be difficult.
Data Logger Connectivity Options
Modern data loggers have several options for how they can export or transmit the data they collect, including:
For data loggers without access to a wireless or wired network connection, data can be temporarily stored in the logger, then downloaded manually to a laptop or satellite collection device using a USB connection. Storage space in the logger is limited, so an important specification is how much data can be stored, usually given in terms of data points. To figure out how much time the logger can run without exceeding its storage capacity, you’ll need to do a calculation that also takes into account the measurement interval:
- Maximum storage time = (data point capacity) ✕ (measurement interval)
For example, a logger with a capacity of 400,000 points, collecting data every 10 seconds, can run for about 46 days without exceeding its memory.
This approach is growing in popularity, since it uses largely existing infrastructure to significantly enhance the capabilities of the logger. Wi-Fi enabled data loggers are able to continuously transmit data to cloud-based monitoring tools, eliminating the need for periodic download and providing real-time access to monitoring data from anywhere.
Another major advantage of Wi-Fi is that it is inherently scalable. New monitoring points can be added to an existing network easily, and the data from these loggers is visualized, organized, and archived automatically with online monitoring tools (we’ll talk more about that in the next section).
These advantages are also available with data loggers that communicate via wired ethernet or cellular connections, where those are more convenient.
This is a low-power, long-range wireless communication protocol that’s well suited for data loggers. In a LoRa network, individual data loggers are set up to transmit to a central gateway device, which can then upload data to a local network, or to the cloud.
For data loggers, LoRa has the advantage of long range communication relative to Wi-Fi, but requires the use of a gateway device to connect to cloud based monitoring.
A Bluetooth-enabled data logger can operate in a couple of different modes. One mode is similar to a USB logger, where the data is stored locally, then periodically transferred via Bluetooth. An example is a temperature data logger that is embedded in a refrigerated package during shipment. When it arrives at the customer site, the temperature history in the logger is downloaded via Bluetooth, giving the customer a full record of temperature during the trip. (A data logger enabled with NFC, near field communication, also works this way.)
Another way to use a Bluetooth logger is to have it continuously transmit data to a nearby handheld device or computer. From there, data can be monitored in real time, or uploaded to the cloud for remote access.
In terms of accessing the data collected by a logger, there are two general strategies: (1) data is stored in the logger for later download (USB and NFC), or (2) data is continuously transmitted to a cloud server or local network (Wi-Fi, ethernet, cellular, LoRa).
There are also a number of options for the format of the data itself. For example, a simple system can export a table of time-stamped data points, which can then be plotted and organized in data analysis software.
More sophisticated monitoring systems use online software tools that integrate seamlessly with data logger hardware. This is a powerful approach that can be used to collect and visualize data that is continuously transmitted by any number of Wi-Fi or ethernet enabled loggers in the field, organizing it by time, location, data type, or other user-selected parameters. Data logger software can also provide dashboards that quickly summarize the most critical data for large monitoring networks, including the status of any custom alarm limits.
Beyond collecting and visualizing data, specialized data logger monitoring software also allows the user to adjust measurement settings, and track sensor calibration status.
One final note on data collection- for FDA-regulated industries, it’s important to confirm that your data collection hardware and software is compliant with 21 CFR Part 11, which is the federal regulation covering electronic records.
When selecting a data logger, the way that it’s powered and how it transmits data are two of the most important options. Modern data loggers have several capabilities for data collection and transmission that make them powerful tools for monitoring sensitive processes.
Anyone with questions about data loggers or environmental monitoring is encouraged to contact the experts at Dickson.