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What Is a Temperature Data Logger and How Is It Used in Environmental Monitoring?

There are many industries in which controlling the temperature of spaces like warehouses, freezers, and shipping containers is a critical part of doing business. In these industries, data loggers are commonly used to measure and record temperature.

Modern digital data loggers (DDLs) have a number of features that make them a powerful component of an overall environmental control strategy. For example, integrating a network of remote DDLs that upload environmental data continuously to a cloud-based software tool allows environmental data to be accessed from anywhere. This type of system can improve the reliability of a distribution network by quickly alerting response personnel when a problem is detected, or even proactively identifying possible temperature excursions before they happen.

In this article, we’ll cover the key features and options available in data loggers today, and talk about some of the places where they are used.

What Is a Temperature Data Logger?

A temperature data logger is a compact, self-contained unit that integrates a sensor, data storage, and data transmission in a single package. They’re highly adaptable, convenient to use, and can be deployed in a wide range of different environments.

One example of a simple use for a DDL is in a temperature-controlled space, like a refrigerated warehouse used for frozen food. It is set up to record the temperature at regular intervals, store the temperature readings, and transmit them to a central monitoring station. Temperature data is then periodically reviewed to confirm that the warehouse is held within the specified temperature, and that the food was held under safe conditions during the monitoring time period.

Close analysis of the temperature data might also indicate issues with the refrigeration equipment, or how much the temperature of the warehouse fluctuates when doors are opened. The logger could also trigger alarms if the temperature of the space goes outside of a pre-set range.

What Types of Temperature Data Loggers Are There?

DDLs can be thought of as the modern replacements for paper chart recorders. They take advantage of microprocessor technology to enhance data storage, precision, and communication, and significantly reduce operating cost.

There are many styles of temperature DDLs on the market today, but they all have a few components in common: a temperature sensor, communication hardware, a power source, and electronics for processing the sensor signal and storing it in memory.

There are two primary aspects to consider when selecting a temperature DDL: the type of sensor it uses, and the way it transmits data. There are three common choices for the temperature sensor: thermistors, thermocouples, and resistance thermometer detectors (RTDs). All three types generate an electronic signal that changes with temperature. The choice of sensor depends on a balance of considerations including cost, temperature range, accuracy, sensitivity, response time, and sensor drift over time.

The sensor itself can either be integrated into the body of the logger, or external and attached by a wire. The latter type is useful if the sensor is in a harsh environment, or buffered in liquid or beads. (Buffering is recommended by the CDC for temperature sensors in vaccine refrigerators, so that the sensor temperature more accurately reflects the temperature of the vaccine vials.)

Another important consideration is how the temperature sensor is calibrated. Temperature sensors require periodic calibration, due to natural drift, contamination, or other malfunctions. Replaceable sensors simplify this, since the sensor can simply be swapped with a calibrated replacement, with little to no downtime.

There are many applications that require the measurement of both temperature and humidity, so for this reason it is not uncommon for both temperature and humidity sensors to be incorporated into a single unit.

The second major feature of temperature data loggers is data retrieval or transmission. Here, the distinction is mainly whether access to monitoring data is local or remote. Local access makes sense when monitoring data isn’t needed continuously in real time, and the logger can be accessed easily. In this setup, data is stored in the logger for later retrieval via USB. Storage in the logger is always limited, so key specifications include the number of data points that can be stored, and the data sampling frequency.

Another option is to transmit data from the logger via bluetooth or NFC (near-field communication). This can be useful when the logger is difficult to access, or when more continuous access to the data is needed. For example, temperature monitors in refrigerated shipping containers.

The third option, which is the state of the art for DDLs, is to have monitoring data continuously uploaded to a cloud-based software tool. This makes it possible to access the data from anywhere, and react to it in real time. This approach is particularly powerful with a distributed network of many sensors, and is well suited for businesses with dynamic monitoring needs, or that plan to scale up operations. These loggers transmit data via WiFi or ethernet, with additional local data backup in case connectivity is lost.

Other options to consider when selecting a temperature data logger are the power source (battery versus hard wired), and the level of protection provided by the housing against water and other contamination. The level of protection can be quantified by the IP (ingress protection) code.  

blue-capsule-medicine-pill-production-line

What Industries Use Temperature Data Loggers?

Temperature control is important across a wide variety of industries. In healthcare settings, temperature control is important for maintaining the integrity of medicines. Vaccines are a critical example of this, since they can degrade in ways that are not visually apparent when they aren’t held in a narrow temperature window. The risks involved with this are reflected in thorough guidance provided by the CDCWHO, and VFC (Vaccines for Children) program.

The temperature and humidity of critical care areas, like operating rooms and pathology labs, are also designed to be held within certain temperature ranges.

In pharmaceutical and medical device manufacturing, there are two classes of temperature monitors. One is for ambient environments, like spaces where in-process materials and products are held. The other is for monitoring the temperature in processing units like ovens or reactors. These are both considered to be highly regulated industries, with environmental monitoring and other good manufacturing processes (GMP) set out in federal laws and enforced by the FDA.

Temperature monitoring and control is also complicated for perishable food storage and transport, since frozen foods, produce, meats, prepared foods, dairy, and dietary supplements all require different storage conditions. Regulations in this area were redefined by the Food Safety Modernization Act (FSMA) in 2011, which effectively shifted risk management from a reactive to a proactive model.

Pharmaceuticals and foods are examples of materials that are shipped via temperature-controlled supply chains or cold chains, where temperature data loggers are used to confirm that products are held within a specified temperature window throughout transportation.

Since product quality can affect consumer safety, aerospace manufacturing is another area where data loggers are used for temperature monitoring. Here, temperature can affect things like the curing of composite materials and advanced coatings. Environmental monitoring for aerospace is included in the AS9100 standard.

Two themes across all of these industries are (1) it is unfeasible or impossible to directly test the quality of the final product, and (2) quality of the final product has a direct impact on human health and safety. For example, it is impossible to check that every dose of a vaccine is effective, or to cross-section all the parts of an advanced composite in an aerospace part. Instead, ensuring product quality relies on consistently using a well-characterized, thoroughly monitored, and controlled process (also known as a validated process) every time. Reliable temperature monitoring is a key part of this.

Outside of these regulated industries, temperature DDLs are also used for monitoring areas where valuable artifacts are stored, in climate and agricultural research, and to characterize the performance of building HVAC systems.

How Are Temperature Data Loggers Used?

Data loggers are customizable and scalable, and can be used in different ways to meet a variety of business needs.

In some cases, stand-alone data loggers with local data access are sufficient. Here, employees would extract data periodically to review trends, and be alerted to temperature excursions via audible or visual alarms. The main weaknesses of this type of setup are that it is not easy to scale, and does not allow for real-time data access.

On the other end of the spectrum is a network of remotely connected loggers, integrated through a cloud-based software tool. This approach is used in areas where real-time access to data is needed, or where there are too many monitoring points, or where monitoring points are too widely distributed to allow for employees to manually collect data. In this system, monitoring data can be quickly combined, summarized, and analyzed, using a web-based dashboard.

This also simplifies the environmental monitoring process, and helps to ensure regulatory compliance, since all of the data collected is organized and time-stamped. (The FDA recommends an ALCOA rule for data integrity- attributable, legible, contemporaneously recorded, original, and accurate.) An enterprise-level approach can also include preventative maintenance scheduling and calibration tracking for the network of loggers.

An additional feature of remote monitoring systems is that custom alarms and notifications can be set up, so that targeted, specific messages can be sent to response personnel via phone call, email, or SMS text when a problem is detected.

Conclusions

Temperature data loggers are customizable and adaptable pieces of monitoring equipment that can be deployed in a variety of settings, and are used in many different industries. A major consideration when selecting and configuring a data logger is how the monitoring data will be transmitted and used.

Data loggers are a key component to a robust environmental monitoring strategy. Anyone with questions about these topics is encouraged to contact the experts at Dickson.