It’s easy to feel nostalgic for the chart recorder. They have a certain “steam-punk” appeal, like monocles and bomber goggles. They were the height of technology in a bygone era, innovated by no less than locomotive inventors to do a specific job—track data to create a paper record of conditions like temperature.
Of course, technology marches forward—out with the old and in with the new. But now that digital data loggers have almost completely replaced chart recorders, why not take a stroll down memory lane? They may mostly occupy life-sized dioramas in the Smithsonian, but chart recorders occupy an important place in the history of quality assurance—an early attempt to automate accurate data recording in a pre-microchip era.
Let’s take a walk down memory lane and fondly remember chart recorders, but also address why digital data loggers replaced them for important tasks like temperature monitoring for quality assurance in food production, pharmaceutical manufacture, and other regulated industries.
Chrales Babbage invented the first chart recorder as a component of his 1838 invention the dynamometer car. The first railroad car capable of recording data about the locomotive, the car relied on twelve pens connected to sensors, which oscillated based on conditions of the locomotive, including spread, pulling force, and horsepower.
A long strip of paper was pulled along under the pens. The pens oscillated based on the input from the sensors, creating a graph-like record of the conditions measured by the sensors. This system was repurposed by another 19th-century innovation, Samuel Morse’s telegraph.
This is the essence of a chart recorder—a sensor that controls the oscillation of a pen on the end of a pendulum. The pen marks a strip of paper or tape, which is pulled through the chart recorder at a regular pace. The wavy line produced by the pen tells you what input it was receiving from the sensor.
Chart recorders adapted to record ambient temperature did so by connecting the oscillating pen to a thermometer. They were instrumental in the safety practices of industries that depended on a cold chain—for example, food production and pharmaceuticals.
With the advent of the microprocessor, digital temperature data loggers began to take the place of chart recorders. Compared to the computers to come, digital data loggers were basic, but ingenious. They consisted of three simple components:
● A sensor. In the case of temperature data loggers, the sensor was a thermometer capable of recording the surrounding temperature.
● A microprocessor. This small computer was capable of interpreting the readings of the sensor, i.e. the thermometer, and rendering it into digital data.
● A data drive. This small storage drive was capable of recording and time-stamping the data interpreted by the microprocessor.
Digital data loggers helped regulated industries meet the “ALCOA” standard of data integrity used by the US Food and Drug Administration (FDA). Under the ALCOA standard, data was presumed to have “integrity” if it meets the following five conditions:
● Attributable. Data is “attributable” when you can trace it back to the person or thing that recorded the data. Both chart recorders and digital data loggers are equally attributable.
● Legible. Data is “legible” when a human observer can readily interpret it. By recording digital data instead of lines on a graph, digital data loggers had an advantage over chart recorders in terms of legibility.
● Contemporaneous. Data is considered more “contemporaneous” the sooner it is recorded relative to the creation of the data. Since chart recorders and digital data loggers both record data in real time, the data they produce are equally contemporaneous.
● Original. Data is considered “original” when it is the first record of the data. For a chart recorder, only the paper tape was the original record. If the data were copied onto another document, that data lacked integrity because it was not original. By contrast, digital data, when copied and pasted, is still considered “original.” Therefore, digital data loggers made it much easier to preserve the originality of the record.
● Accurate. Data is considered “accurate” when the method of recording is sensitive enough to produce a true record. The increasing resolution of data processors and improved sensor technology made digital data loggers a better solution for accurate data.
Digital data loggers thus improved on at least three of the metrics the FDA uses to assess data integrity. This Dickson article on temperature data loggers has more on how they factor into environmental monitoring.
Modern digital temperature data loggers work in much the same way as their predecessors. While the thermometers, microprocessors, and data drives have improved in sophistication and sensitivity, the three main components still work together in roughly the same way.
What has changed significantly is the sophistication with which users interact with the data logger. Data from the drive previously required manual retrieval from the device, often by USB connection.
Complicating this fact was that most facilities don’t just have one digital data logger. Temperatures vary throughout large facilities, so multiple data loggers must be monitored, often far apart from each other. Retrieving the data manually could be time-consuming and inconvenient.
Today’s most sophisticated digital data loggers are full-fledged components of the Internet of Things (IoT). They communicate by WiFi and other remote digital technologies to push data directly to the cloud, where it can be retrieved without having to manually interact with a whole network of data loggers.
Rather than having to manually compile that data into compliance reports, Cloud-based software can often auto-generate those reports, saving organizations that use them time and resources.
Compared to the chart recorder, the digital data logger lacks a certain drama. Small, quiet, and innocuous, it doesn’t draw much attention. It doesn’t produce a long strip of paper with an exciting squiggly line that represents the incoming data.
There’s no question—digital data loggers are better at doing the job that chart recorders were designed to do. More affordable, efficient, and reliable, they produce more accurate data with greater integrity.
Like so many obsolete technologies, the chart recorder pointed in a direction that more sophisticated technologies could then follow. It represents an early experiment in automation. Automation is commonplace today. In a pre-digital world, the chart recorder’s ability to automate data recording brushes against the miraculous