Photo courtesy of Onset Computer Corp.
Battery-powered data loggers are fast becoming the tool of choice among contractors, service technicians and engineers responsible for monitoring indoor air quality, evaluating HVACR systems and monitoring energy efficiency and usage.

Data loggers, in most cases, are easy to set up, and can be used as stand-alone devices without having to be attached to a computer. More importantly, the measurement accuracy offered by today's most advanced data loggers rivals the performance of many higher priced, PC-based data acquisition systems.

However, not all data loggers are created equal, and with so many choices available today, it can be challenging to know which one is right for your application. Do you need to measure a range of conditions, or just a single parameter? Does your application require alarm notification when conditions go beyond a certain threshold? Will the data logger withstand harsh environments? How often will you need to retrieve data?

Whether you are an experienced data logger user, or just getting started, this article can help you during your data logger selection process. It points out some of the most important considerations to make, and offers tips on specific features to look for.

Measurement accuracy

No matter what you need to measure, the most important thing is understanding your measurement-accuracy requirements. For example, if you're monitoring air conditioning temperature in an office space, you may only require a temperature measurement accuracy of plus/minus 2 degrees, while monitoring conditions in a research lab may require accuracy that is far greater.

Accuracy specifications vary widely among different types of data loggers. A good understanding of specific accuracy requirements will help you avoid paying for accuracy that you may not need. When looking at the accuracy specifications for a given data logger, be sure to look for charts that indicate performance 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 in the middle range.

Another important factor is resolution, which basically refers to 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 note that higher resolution does not necessarily mean better measurements.

Data-extraction options

When evaluating data loggers, it's a good idea to ask about the available options for off-loading data at field sites. In many instances, it's not practical to bring a PC out to the site to pull collected data, nor is it convenient to bring a data logger back to the office. For that reason, some data loggers can be off-loaded using a "data shuttle."

A data shuttle is a pocket-sized device that enables technicians to quickly and easily off-load and store the data from a logger without interrupting or having to move the logger. The shuttle can then be linked to a PC for downloading and analyzing the data.

It's also a good idea to ask the data logger supplier about compatibility with Palm and other hand-held PC products, as these can also be a convenient means for retrieving data.

Data-extraction options

When evaluating data loggers, it's a good idea to ask about the available options for off-loading data at field sites. In many instances, it's not practical to bring a PC out to the site to pull collected data, nor is it convenient to bring a data logger back to the office. For that reason, some data loggers can be off-loaded using a "data shuttle."

A data shuttle is a pocket-sized device that enables technicians to quickly and easily off-load and store the data from a logger without interrupting or having to move the logger. The shuttle can then be linked to a PC for downloading and analyzing the data.

It's also a good idea to ask the data logger supplier about compatibility with Palm and other hand-held PC products, as these can also be a convenient means for retrieving data.

Software capabilities

Just as there are many different types of data loggers available, there are also many different types of data graphing and analysis software packages to choose from. In general, look for software that is Windows-based and highly intuitive so any learning curve is minimal. The software should enable you to quickly and easily perform tasks such as configuring parameters, launching the logger and off-loading data, with point-and-click simplicity. At the same time, it should offer powerful data plotting capabilities, and enable you to easily export data to other programs, such as Microsoft Excel, for analysis.

When buying a data logger, make sure the product's enclosure is designed to withstand the conditions it will be subject to. For example, if you need to monitor conditions in an office hallway, a hard-plastic enclosure should suffice. On the other hand, if the data logger needs to work in a damp environment, you will 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.

Battery life

In general, 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's battery can be replaced by a user. 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 cost of battery-powered data loggers. However, while many low-priced data products available today, it is important to look closely at the total cost of ownership when shopping around. Here are some questions you may want to ask your supplier:

  • Will the logger need to be calibrated by the manufacturer periodically? What will it cost?

  • Will you need to invest in a software package to analyze your results? What's the cost of the package?

  • Will you be able to use standard batteries, or will the logger require a proprietary or hard-to-find power source?

    Answers to these questions will help you understand the true cost of owning the data logger over the long term.

    When evaluating data loggers, look for a supplier that offers a range of product-support services. These services often start with an assessment of your application requirements and should include telephone as well as Internet-based support resources.

    Photo courtesy of Onset Computer Corp.

    Range of solutions

    While stand-alone data loggers are suitable for a broad range of applications, there may be situations where you need more of a centralized data-gathering mechanism for measuring parameters. For this reason, it's a good idea to ask your supplier if they offer systems-based data-logging solutions.

    Today's most advanced systems-based data loggers are based on "smart sensor" technology, which means that you can simply plug in individual sensors to measure various parameters and the system recognizes each one without complicated wiring, programming or calibration. Most are also battery powered and allow you to configure the system with any combination of available sensors.

    Finally, if you require immediate notification when environmental conditions fall outside of set tolerances, be sure to ask your supplier about data loggers with alarm capabilities.

    (This article was supplied by Onset Computer Corp.)