Using the Hobo U12 J,K,S,T Thermocouple Data Logger for wildland fire research: an example of its application
By Rex Hsieh
August 13, 2007
Introduction
Collecting temperature data is an integral part of fire research, but the wildland fire operating environment presents serious challenges for most data loggers. Finding suitable data loggers is an on-going process. An ideal temperature data logger for use in fire research should meet the following criteria:
· Small size
· Easy to activate
· Easy to download
· Able to record a temperature range up to 1100°C
The Hobo U12 J, K, S, T Thermocouple[1] Data Logger (Figure 1) meets the criteria. It was developed by Onset Computer Corporation in Massachusetts, USA and is available in Canada from Hoskin Scientific Limited in Vancouver.
FPInnovations – Feric’s Wildland Fire Operations Research Group used the Hobo data loggers to record thermal targets during an aerial infrared (IR) scanning evaluation project. We found the Hobo to be a useful tool in the IR scan evaluation; it was easy to use, affordable and reliable. The following description outlines this example of its use.
Figure 1. The Hobo U12 J, K, S, T Thermocouple Data Logger in a water tight case.
The IR scanning evaluation
The IR scanning project involved an aircraft with a sophisticated infrared camera that flew over a grid of simulated wildfire hotspots. The objective was to demonstrate an ability to locate thermal targets. In this project, the Hobo data loggers were used to record the time and temperature of each target. These data allowed the researcher to verify whether or not a target was “hot” when the IR scan was performed. If the IR scan did not detect the target and the temperature data from the data logger showed no heat, the researcher could then confirm that the absence of detection was due to a lack of a heat source. Conversely, if a heat source was not detected by the IR scan but the data logger showed heat, then the IR scan failed to detect the heat source.
Equipment and supplies
· Hobo U12 J, K, S, T Thermocouple Data Loggers
· K type thermocouple – to collect temperature from heat source
· USB cable – to connect a data logger and a PC
· Onset software – to activate the data loggers and download data
· Desktop/Laptop PC – to activate the data loggers and download data
· Zip lock bag – to keep data loggers dry
· Pens – to write the location on the label of data logger
· Masking tape – to label data logger
Equipment preparation and operation
For the IR project, we used 3 different heat sources for a total of 18 artificial hot spots:
1. Gas stove that heated cast iron fry pans
2. Gas stove that heated cast iron stove tops
3. Briquettes
Figure 2. The Hobo U12 J, K, S, T Thermocouple Data Logger with an artificial hot spot.
We activated the data loggers at 4:00 am. It required thirty minutes to activate all 18 Hobos using the Onset software on a laptop PC, and to place pieces of blank marking tape on each data logger. We set the recording interval to 1 second. The user interface was well designed and simple to use (Figure 3).
The data loggers were deployed at 4:30 am. Researchers set up hot spot heat sources at pre-determined locations and then attached the thermocouples to the heat source and to the data loggers. Each data logger was then labelled by writing its location and setup information on the marking tape. All equipment and data loggers were set up by 5:40 am.
IR testing started at 6:00 am and was completed by 7:00 am. All data loggers were retrieved. The PC and Onset software were then used to download temperature data.
Figure 3. User interface of the data logger software.
Results
The data loggers and software performed as described by the manufacturer. All data were successfully downloaded and analyzed (Figure 4). All datasets were valid.
Figure 4. An example of data output displayed on the interface.
Discussion and Conclusion
The Hobo U12 J, K, S, T Thermocouple Data Logger met our criteria for our wildland fire research data collection needs. It is compact, easy to carry, and simple to deploy. It is also affordable. Subsequent to this evaluation, we purchased a total 35 units for use on our research projects.
Software is required to activate the data logger and to download data. The license can be purchased through the Onset web site (http://www.onsetcomp.com). For remote locations, a laptop is highly recommended.
A PC will take up to a minute to connect to each data logger when connecting for the first time, because the computer must install a new driver for each data logger. Therefore, it is recommended that each data logger be connected to the PC, which will be used to later activate the data logger, at least once prior to deployment.
Some of our datasets contained false temperature records: for example, decreasing suddenly from 60oC to -5oC, and then immediately back to 70oC. We have no explanation of why this occurred, but these anomalies did not affect our overall dataset.
The USB connector on the data logger is a metal surface. Anything with an electric current, or static, that touches this exposed surface will interfere with the thermal current voltage and may affect the temperature record quality. Users need to take caution not to touch the connector with a bare finger.
Memory capacity of the data loggers is 64K. By recording every second, the maximum recording duration will be only 7 hours. There are some deployment techniques that can be used to extend this limitation (e.g. delay recording or manually press the activation button to begin recording).
Data logger operation is sensitive to external temperature. The operating temperature needs to be between 0°C and 50°C to make the connection function properly. During the spring, fall and winter in Alberta, ground temperatures are well below 0° C and the user may need to provide external heat sources.
The Hobo data logger is not waterproof. To prevent contamination from soil and moisture, we place the data loggers in a Pelican 1010 Micro Case (available at MEC http://www.mec.ca). We drill a small hole into the side of the case for the thermocouple wire and then seal the hole around the wire with plumber’s putty. We then place the Pelican Micro Case in a zip lock bag (Figure 1).
Acknowledgement
Thanks Colleen Mooney, Ray Ault, Ingrid Hedin and Greg Baxter for editing.
References
For further information, see the following websites:
http://www.onsetcomp.com/solutions/products/loggers/_loggerviewer.php5?pid=366