Tips on Buying a Data Logger
No matter what you need to measure, understanding your measurement accuracy requirements is essential. For example, if you're monitoring air-conditioning temperature in an office space, you may only require a temperature measurement accuracy of +/- 2 degrees, while monitoring storage conditions for temperature-sensitive products or in a research lab may require far greater accuracy. Or when monitoring streams for suitability for certain fish species, for example, accuracy on the order of 0.2C is typically required.
Accuracy specifications vary widely among different types of data loggers, and a good understanding of specific accuracy requirements will help you avoid paying for accuracy you might not need. When looking at the accuracy specifications for a given data logger, be sure to look for charts that indicate accuracy over an entire measurement range, not just a single value. The accuracy a data logger can achieve at the high or low end of a given range may be far different from the accuracy at the middle of the range.
Another important factor is data logger resolution; that is, the number of increments of a value a data logger is capable of reporting. For example, a data logger with 12-bit resolution can report 4,096 values over a given temperature range. While a 12-bit data logger may offer more resolution than an 8-bit model, it's important to keep in mind that higher resolution does not necessarily mean better measurements.
If you're unsure about the data logger accuracy and resolution requirements of your application, an experienced data logger supplier should be able to help you determine which product will best meet your needs.
Data Access Options
When evaluating data loggers, it's a good idea to learn about the available options for accessing the collected data.
With USB stand-alone data loggers, data are directly offloaded to a computer via a USB interface. In many instances, however, it's not practical to bring a computer out to a site, nor is it always convenient to bring a data logger back to an office computer. In such cases, data retrieval from stand-alone loggers can instead be easily and quickly accomplished using a pocket-sized device called a data shuttle. With a shuttle, you can download and store the collected data without having to interrupt or move the logger, and later link the shuttle to a computer for downloading and analyzing the data.
Wireless sensor networks, such as Onset’s HOBO ZW data nodes, transmit highly accurate real-time energy and environmental monitoring data from dozens of points to a central location. With this arrangement, there’s no need to run wiring throughout a building to access critical data points, and the chore of manual retrieval and offloading of data from individual loggers is eliminated.
Web-based data logging systems, such as Onset HOBO RX3000 systems, can be used in both indoor and outdoor environments. They enable real-time remote access to data via GSM cellular, WI-FI, or Ethernet communications, and can be configured with a wide range of plug-and-play sensors for monitoring everything from weather conditions to building energy consumption. Data can be accessed easily through a secure web site or integrated into custom systems with a choice of automatic data delivery or web services.
Bluetooth Low Energy (BLE) data loggers, such as Onset's HOBO MX and InTemp CX series loggers, which measure and transmit data wirelessly to mobile devices over a 100-foot range, are particularly useful in applications such as refrigeration storage monitoring, or other applications where data loggers need to be deployed in hard-to-reach spaces or in limited-access areas within a facility.
Just as there are many different types of data loggers available, there are also many different types of data graphing and analysis software packages. In general, look for software that is Windows®- and MAC-based and highly intuitive so the learning curve is minimal. The software should enable you to quickly and easily perform tasks such as configuring parameters, launching the data logger, and offloading data, with point-and-click simplicity. Certain packages, such as Onset HOBOware® Pro software, allow you to batch-configure and readout hundreds of loggers very quickly.
The data logging software package should also offer powerful data plotting capabilities, with an ability to easily merge, append and crop data, and enable you to easily export data to other programs, such as Microsoft Excel, for analysis.
For BLE-enabled monitoring, configuring the loggers and managing data simply requires downloading a free app to your mobile device.
When buying a data logger, make sure the product's enclosure is designed to withstand the conditions of the environment where it will be located. For example, if you plan to conduct monitoring in an office hallway, a hard plastic enclosure should suffice. If the data logger needs to work in a non-condensing environment, however, you would want to choose a product with a moisture-protective enclosure. It's also a good idea to ask about the availability of protective cases and other enclosure accessories for situations where increased durability and/or protection may be necessary.
Overall, data loggers are extremely low-power devices. However, because they are used in a variety of environmental conditions and sample at different rates, battery life can vary widely. As a general rule of thumb, make sure the data logger you select has a battery life of at least one year.
You may also want to ask your supplier about whether or not the data logger battery is user-replaceable, as this can eliminate the time and expense of having to ship the logger back to the manufacturer for battery replacement. Finally, data loggers that run off standard household batteries offer greater convenience than those requiring specialized batteries.
Cost of ownership
The lower cost of microprocessors and sensors in recent years has helped push down the price of battery-powered data loggers. Although many data products available today are attractively priced, it’s important to look closely at the total cost of ownership before making your purchase. Here are some questions you may want to ask your potential supplier:
- Will the logger need to be calibrated by the manufacturer periodically, and if so, what are the cost implications over time?
- Will I need to invest in a pricey software package to analyze my results?
- Will I be able to use readily-available AA batteries, or will the logger require a proprietary or hard-to-find power source?
- Are cables included with the logger?
- Will I need to purchase a data plan for my web-based system, and if so, what types of plans are available?
Answers to these questions will help you understand the true cost of owning the data logger over the long term.
In general, data loggers should be easy to use, without requiring a great deal of technical assistance, even during the initial phases of use. Nevertheless, as with any high-tech product, there will always be questions. When evaluating data loggers, look for a supplier that offers a range of product support services. These services often start with a preliminary assessment of your application requirements, and should include both telephone support and Internet-based support resources.
It's also a good idea to find out if the supplier has the track record and financial stability to maintain the role of a long-term solutions provider. Then you can be assured that the company will be there to meet your future data logging requirements. Finally, you may want to ask the supplier for application notes and other references to gain a sense for how the data loggers performed in applications similar to yours.
Range of solutions
When buying a data logger, look for a supplier offering a full range of data loggers that can offer accurate, reliable performance in a range of monitoring environments: indoors, outdoors, or under water. In this way, you can be sure that you’re dealing with a supplier that has the spectrum of knowledge and expertise to best assess, understand, and meet your specific needs, now and in the future.
Also, if you want immediate notification when environmental conditions fall outside of set tolerances, be sure to ask your supplier about data loggers with alarm capabilities.
Knowing the right questions to ask in order to fully understand what’s available to best meet your needs should lead you directly to the best data logger for your particular application. Onset's wide-variety of available products, watch our products overview video.