Abstract
The measured fire resistance of a structure tested in different furnaces in accordance with ISO 834 may differ considerably. Similarly, the fire resistance of that same structure may be 25% longer when tested in accordance with ISO than it is when tested in accordance with ASTM. These anomalies complicate the evaluation of test results and must be eliminated to reach harmonized international testing.
The heat transfer to a test specimen in a test furnace at high temperature depends primarily on radiant flux rather than convection. Temperature measurement devices used to control furnaces should therefore respond to this type of heating in a way similar to that in which test specimens respond. They should have a large area so that the radiant heat transfer dominates, and they must, at the same time, have a quick thermal response.
The plate thermometer is designed to have these properties. It consists of a thin steel plate, 100 mm by 100 mm and 0.7 mm thick, with an insulating fiber board on one side. A thermocouple is welded to the center of the plate. It should be placed in front of the specimen, with the insulated side facing the specimen. The exposed side will then receive the same radiant heat flux as the specimen.
This paper describes the plate thermometer and gives a basic theoretical analysis of the heat transfer conditions in furnaces. Measurements with the plate thermometer in several furnaces are also reported.
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Wickström, U. The plate thermometer - a simple instrument for reaching harmonized fire resistance tests. Fire Technol 30, 195–208 (1994). https://doi.org/10.1007/BF01040002
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DOI: https://doi.org/10.1007/BF01040002