A DIY Thermocouple Datalogger is Suitably Comparable to a Commercial System for Wildland Fire Research

Abstract

Thermocouple probes have long been standard equipment for wildland fire scientists. But despite substantial advancements in the electronic datalogger technology necessary to read and store data from thermocouples, the effective cost per thermocouple sensor of commercial systems has not decreased such that most researchers can afford to deploy enough sensors to account for the high degree of variability in wildland fire behavior. Because the equipment must endure the extreme conditions of wildland fire, is unlikely that any thermocouple datalogger system will be considered “cheap.” However, the growing number of applications of open-source, do-it-yourself (DIY) microcontroller systems in scientific research suggests these products might be employed in thermocouple datalogging systems if (1) their performance can be shown to be comparable to commercial systems and (2) they can be protected from exposure in the wildland fire environment. In this paper, we compare the performance of an Arduino MEGA microcontroller board relative to a Campbell Scientific CR1000, reading standard K-type metal overbraided ceramic fiber insulated thermocouple probes, under the constant temperature of a drying oven and the variable flame of a Bunsen burner. In both comparisons, we found that the variability among individual thermocouples, which are known to have a $\pm\, 2\,^{\circ }\hbox {C}{-}6\,^{\circ }\hbox {C}$ margin of error, was greater than between the dataloggers. We also describe a compact and mobile Arduino-based system capable of recording wildland fire flame temperatures in agris. In considering these three systems, it is clear that Arduino-based open-source, DIY components can support a compact, low-cost datalogger that accommodates more sensors for lower cost than proprietary commercial systems with no sacrifice in data quality. The combination of low-cost, multi-sensor units can contribute to better understanding of variability in wildland fire behavior.

Appendices

Appendix A: Links to Online Materials

A list of links to code and other resources referred to in the text.

• The FireScienceDIY github repository (www.diyfirescience.info) aggregates material used in this paper:

  • FumeHoodFireScience contains sketch for Arduino MEGA eight-thermocouple datalogger system (https://github.com/devanmcg/FireScienceDIY/tree/master/FumeHoodFireScience).

  • FeatherFlame (https://github.com/devanmcg/FireScienceDIY/tree/master/FeatherFlame).

  • Links to specific components from Omega Engineering.

  • Sketches: Code for Adafruit Feather-based in agris six-thermocouple datalogger system.

  • PCB: CAD-type files for a printed circuit board that facilitates assembly of the in agris thermocouple datalogging system.

  • The PCB is also shared on OSH Park where orders can be placed directly (https://oshpark.com/shared_projects/cAXzsQJw).

• Components available from Adafruit Industries have been posted as public wishlists for each project described in this paper:

  • Fume Hood Fire Science: http://www.adafruit.com/wishlists/424024. Note that the Arduino MEGA is replaced here by an Adafruit Metro M0 Express, a more recently-available and less-expensive board.

  • FeatherFlame: http://www.adafruit.com/wishlists/459885.

Appendix B: Components and Prices for Thermocouple Datalogging Systems

See Table 1.

Table 1 Components for the Three Thermocouple Datalogger Systems Described in this Paper

Appendix C: FeatherFlame: A DIY Solution for Field Measurements

Our compact, mobile Arduino-based datalogger relies on the Feather system from Adafruit Industries (Brooklyn, NY), which also uses an ATmega microcontroller, is powered by a compact, rechargeable lithium-ion battery, and stores data on a removable $\upmu$SD card (Fig. 7). The unit fits into a small airtight box (we used the Pelican$^{\mathrm{tm}}$ 1020 case), which we shielded from flame and radiant heat with a galvanized steel cap (Fig. 7). The reliability of the datalogger system and the fire protection components were proven over the course of 243 individual datalogger deployments in 27 prescribed fires in North Dakota, USA [39]. While the specifics of the FeatherFlame system—including the spatial sampling scheme based on the low-cost/high-replication advantages of the DIY system and R scripts used for analysis—are described elsewhere [e.g., 39], links to online information about the construction of the FeatherFlame system are provided in “Appendix A”.

Figure 7

The Arduino-based Feather system from Adafruit Industries provides a compact solution for recording thermocouple responses in situ during wildland fires. a Three stackable Feather boards (Table 1 in “Appendix B”) replace the MEGA board, datalogging shield, and OLED display in the laboratory system (Fig. 2). The board has $\upmu$SD removable storage and an ATmega microcontroller. Battery not shown. b An example of how the FeatherFlame is deployed in agris. We affix three thermocouple probes to rods that form a 1 m equilateral triangle 15 cm from the ground, a fourth probe on the soil surface, and a fifth probe in the center of the triangle. c The dataloggers are protected from surface flame fronts by first scraping away vegetative matter so the box can be placed on mineral soil, then covering with a galvanized steel HVAC end cap. Dataloggers are placed away from the probe array to minimize disruption to fuels around the probes, which is made possible by leads protected by flexible metal conduit or high-temperature foil HVAC tape. d The steel junction box protects the connectors between the overbraided thermocouple probes and the leads from the datalogger