Study of Technology for Detecting Pre-Ignition Conditions of ... - NIST

2.4.1 Experimental Operation
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Each experiment began tith no heat applied to the food and ended soon after ignition of
the food. The duration of each test was detemined by the time to ignition which varied from
about 5 to 30 minutes, but was typically about 15 minutes. The steps involved in these
experiments are described in the following paragraphs.
All of the power cords and strips were plugged in or switched on. The test identification
and date labels were changed for photographic purposes. The pan-wall thermocouple was
attached, and the pan, tiemocouple, and lid were weighed together. After the food material
equilibrated to room temperature, the appropriate amount was weighed and placed in the pan.
Then the -pan, food, tiemocouple, and lid were reweighed to get an accurate mass of the food.
The pan was placed on the burner, and the pan handle was secured with a clamp to a heavy ring
stand to prevent spillage of the food during extin~ishment with the lid. As the pan was placed
on the burner, the burner-pan interface thermocouple was carefilly positioned. The lid was not
put on the pan, but the lowest thermocouples of the grid were checked for potential interference
when the lid would be used to extinguish the fire. The pan-wall thermocouple was plugged into
its data line, and the two food tiemocouples were positioned in the food. The plume
thermocouple grid was centered, and the He-Ne laser beams were turned on to check for
interference by the grid. Any range or range-hood thermocouples that had been previously
removed were repositioned.
The afterburner system and exhaust hood were turned on and allowed to equilibrate. If
the test protocol called for an active range hood, it was also turned on. The data acquisition
system was switched on, the program was initiated, and the required inputs were provided. The
pressure transducer was switched on, and tie height and centering of the hi-directional probe were
checked. The photodiode circuits were powered, and the horizontal alignment of the He-Ne
lasers was adjusted. For the electric range, the current meters and power meter were turned on
as was the digital vol~eter used to read the AC signals.
The FTIR and its computer were operated separately from the rest of the experimental
apparatus. The FTIR detector was filled with liquid nitrogen shortly before each test to cool the
sensing element. An iterative alignment procedure was performed on the FTB? receiver using
the spectrometer sofmare. Initially the apparatus was aligned to give 90 % of the signal, but
when some experiments experienced problems with flame radiation saturating the detector, it
became necessary to decrease the signal alignment to roughly 8(YX0.
The infrared camera also required liquid nitrogen. The camera was usually filled with
nitrogen about 10 minutes before a test and topped-off immediate y before the test to ~~arantee
sufficient cooling for a test of long duration. The infrared camera and optical video cmera were
both checked for need of cassette replacement. The optical video camera was focused and the
date and time labels were activated. The still photography camera was checked for slide film and
loaded if necessary. The initial cooking scene was usually photographed.
When all of the previous activities were completed, the test was nearly ready to begin.
Two zero scans were recorded with the data acquisition system and were checked for anomalies
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