Data Logger Basics

Introduction

In today’s data-driven world of satellite uplinks, wireless networks, and the Internet, it is common to hear the terms “data logging” and “data loggers” and not really have a firm grasp of what they are.

Most people have a vague idea that data logging involves electronically collecting information about the status of something in the environment, such as temperature, relative humidity, or energy use. They’re right, but that’s just a small view of what data logging is.

In the fields of building performance and environmental research, everyone seems to be using data loggers. But what are they, and why are they useful?

This guide will introduce you to the wide world of electronic data loggers and data logging, and will help to clarify your understanding, whether you:

• are a new hire embarking on a project or career where data loggers are required
• have been asked by a supervisor or team member to purchase data loggers
• must persuade a decision-maker that data loggers will be useful for your work (for starters, they can save labor costs and increase efficiency by reducing travel time)
• have heard about data loggers and are just curious about their applications, or,
• are a longtime user of the devices and want to refresh your understanding and stay up-to-date with the technology and capabilities offered

In the following pages, we’ll cover data logger basics (the what, where, and why); explain the steps involved in using a data logger; outline important considerations to keep in mind when selecting data loggers; and finish with real-world examples of data loggers being used by professionals in fields ranging from building energy efficiency to water quality management to basic scientific research.

Throughout you’ll find examples, resources, and helpful information for you to use in evaluating data loggers for your work, and you’ll have a solid sense of why professionals worldwide rely on electronic data loggers more than ever as part of their toolkit.

Data logger basics

What is a data logger?

A data logger is an electronic instrument that records measurements at set intervals over a period of time. Depending on the particular data logger, such measurements can include:

• Air temperature
• Relative humidity
• AC/DC current and voltage
• Differential pressure
• Time-of-use (lights, motors, )
• Light intensity
• Water temperature
• Dissolved oxygen
• Soil moisture
• Rainfall
• Wind speed and direction
• Leaf wetness
• Pulse signals
• Room occupancy
• Plug load

…and many more

Data loggers are typically compact, battery-powered devices equipped with an internal microprocessor, data storage, and one or more sensors. They can be deployed indoors, outdoors, and underwater, and can record data for up to months at a time, unattended. A data logger may be a single-unit, stand-alone device with internal sensors, which fits in the palm of a hand, or it may be a multi-channel data collection instrument equipped with one or more external sensors.

Why use data loggers?

Data loggers are valuable tools for anyone who wants to continuously monitor conditions without having to be on site. Environmental consultants, building managers, energy auditors, research scientists, and many more professionals all rely on data loggers because of their:

Low cost

The price of data loggers has come down with advances in microprocessors in recent years, and a single, one-sensor logger can cost less than $100.

Users save time and money by launching and leaving a logger unattended to take time-stamped measurements, rather than having to be on-site themselves. The low cost of data loggers also allows for the deployment of multiple loggers at a time, in some cases reducing project length and enhancing the volume of data available for analysis.

Because of the long battery life characteristic of many portable data loggers, they can be deployed for long periods of time, meaning less time spent travelling to and from the logger to download data. For remotely-placed loggers, or in situations where many loggers are used, that can be a huge saving in time and money.

Ease of use

Data loggers are certainly used by engineers and research technicians, but they’re also used by elementary school children in science projects. It can be a mere 15 minutes from opening the box to the deployment of a data logger; for some models, simply connect the logger to a computer, use the data logger’s software to configure the sampling frequency and start/stop times, and you’re ready to go. Bluetooth Low Energy (BLE) enabled loggers don’t even require a computer, only a mobile device and app.

Downloading data is simple as well, and it can be easily analyzed, graphed, and formatted for presentation or export to other applications. We’ll cover this in more detail in another section.

Reliability

Once configured and deployed, you can rely on a battery-powered data logger to gather the information you need, for as long as you need. No human error, schedule conflict, inclement weather, bad handwriting, or data entry errors will affect your data collection. And whether indoors or out, data loggers are rugged instruments designed to withstand a wide range of environmental conditions, including saltwater, refrigeration, strong winds, and constant sunlight.

Time-stamped data

Collection of data is, of course, at the core of these devices, and their purpose is to provide objective, time-stamped proof of conditions over time, which can be used to test theories, confirm operations, provide a record

for supervisors or regulatory agencies, and supply information to decision-makers. The data they collect allows for better interpretations and choices and can save time and money in the long run.

Where are data loggers used?

Data loggers are used in a broad range of indoor, outdoor, and underwater environments, from high-rise buildings to the Arctic – essentially anywhere data is needed and the convenience of battery power is preferred.

Building Performance

• Track building electricity usage to understand energy profiles and manage peak demand
• Verify energy cost savings to determine ROI of new equipment
• Monitor equipment runtimes to ensure efficient operation
• Monitor equipment for leaks to cut wasteful energy consumption
• Diagnose causes of occupant comfort complaints
• Ensure healthy indoor air quality
• Track room occupancy and light use patterns
• Optimize HVAC system performance
• Better manage peak energy demand

Environmental Research

• Perform ecological studies that provide a detailed picture of the habitat
• Conduct agricultural research that reveals opportunities for improving yields
• Set up animal studies that verify the impact of climate on species
• Perform soil studies to understand the effects of climate on soil quality
• Gather essential data for more effective stormwater management
• Perform detailed water quality studies
• Conduct rigorous oceanographic research
• Run long-term climate change studies
• Study and measure the environmental impact
• Do in-depth hydrology research that reveals the movement, distribution, and quality of water – even across a broad area

Anatomy of a data logger

Let’s dig a bit deeper into what the device actually is and does. A data logger, at its most basic, is a small device with an internal microprocessor, data storage, and one or more sensors, all housed in a hard plastic casing that is weatherproof and/or tamper-resistant, depending on the model.

When most people use the term “data logger,” they’re usually referring to the whole device, which is comprised of a data logger that does the logging, and sensors that measure the parameters. The sensor or sensors may be housed inside the data logger’s case, or they may be attached to the logger’s sensor ports via a cable. Data loggers also have either a cable port or an optical sensor, through which data can be transmitted to the user. Finally, some models have LCD screens that provide operating information, while others have simple light indicators.

All data loggers share these basic parts and characteristics; where they diverge is in exactly how data can be downloaded to the user. To this end, there are

3 main types of data loggers: stand-alone USB data loggers, web-based data logging systems, and Bluetooth Low Energy data loggers.

Stand-alone USB data loggers are compact, reusable, and portable, and offer low cost and easy setup and deployment. Internal-sensor models are used for monitoring at the logger location, while external-sensor models (with flexible input channels for a range of external sensors) can be used for monitoring at some distance from the logger. Most stand-alone loggers communicate with a computer via a USB interface. For greater convenience, a data shuttle device can be used to offload data from the logger for transport back to a computer.

Web-based data logging systems enable remote, around-the-clock

internet-based access to data via GSM cellular, Wi-Fi, or Ethernet common enunciations. These systems can be configured with a variety of external plug-in sensors and transmit collected data to a secure web server for accessing the data.

Data loggers that utilize Bluetooth Low Energy (BLE) technology measure and transmit temperature and relative humidity data wirelessly to mobile devices over a 100-foot range.

Depending on the scope of your data logging needs, your budget, the distances involved, and the time you have to access sites, you can choose among these four types of data logging systems for your application.

Using a data logger

Today’s data loggers are easy to use and require only a computer with a USB port for configuration and launch, or a mobile device and app, as well as a few simple hand tools for securing the units in place.

1. Configure and launch – First, connect the data logger to a computer via a USB interface. Next, use the accompanying data logger software to select logging parameters (sampling intervals, start time, etc.) and activate the logger. Some software allows for configuring large numbers of data loggers at the same time, which can be a huge time saver. (BLE data loggers can be configured and launched wirelessly, after deployment.
2. Secure in place – Next, deploy the data logger in the desired location. Securing it in place can be as simple as using a magnet, screw, or lanyard to fasten it to a wall. In other instances, installation can be more complex, particularly when dealing with multi-channel data logging systems such as a weather station, where the user needs to assemble and secure a weather station tripod, arrange and protect sensors from elements and animals, plug everything in, and weatherproof all connections.
3. Download or access data – After the desired monitoring period, reconnect the data logger to the computer, and launch the software to read out the data. In the case of web-based data logging systems, data are pushed to the Internet for access; and with BLE loggers, data are downloaded directly to your mobile device.
4. Process/analyze/present data – The data logger’s software allows you to combine and compare data, and display the measurements in graphs that show profiles over time. Alternatively, tabular data can be viewed as well, or exported to a spreadsheet for further manipulation.