The Sweating Guarded Hotplate is suitable for a range of products such as fabrics, films, coatings, foams, and leathers, including mufti-layer assemblies used in clothing systems. Clothing is often made of materials that impede the flow of heat and moisture from the skin to the environment. Consequently, people may suffer from heat stress or cold stress when wearing clothing in different environmental conditions. Therefore, Sweating Hot Plate is important to quantify the thermal resistance and evaporative resistance of clothing materials and to consider these properties when selecting materials for different clothing applications.
In the standard testing environment, heat the fixed aluminum or copper to a specified temperature and maintain the specified temperature, then measure the power used for heating. Similarly, measure the power used for heating the copper or aluminum plate after placing the cloth specimen on it. According to the power difference of two measurements and area size of the tested plate, the thermal resistance and water vapor resistance of test samples can be indicated.
Hot Plate—The guarded flat plate shall be composed of a test plate, guard section, and bottom plate, each electrically maintained at a constant temperature in the range of human skin temperature (33 to 36°C). T
Temperature Control—Separate independent temperature control is required for the three sections of the hot plate (test plate, guard section, and bottom plate). Temperature control may be achieved by independent adjustments to the voltage or current, or both, supplied to the heaters using solid state power supplies, solid-state relays (proportional time on), adjustable transformers, variable impedance, or intermittent heating cycles. The three sections of the plate shall be controlled to the same temperature to within 60.1°C.
Power Measuring Instruments—Power to the hot plate test section shall be measured to provide an accurate average over the period of the test.
Temperature Sensors—Temperature sensors may be thermistors, thermocouples, resistance temperature devices (RTDs), or equivalent sensors.
Controlled Atmosphere Chamber—The hot plate shall be housed in an environmental chamber that can be maintained at selected temperatures between 20 and 35°C. T
Measuring Environmental Parameters—The air temperature, relative humidity, and air velocity shall be measured as follows:
Relative Humidity Measuring Equipment—Either a wet-and-dry bulb psychrometer or a dew point hygrometer shall be used to measure the relative humidity and calculate the dew point temperature inside the chamber.
Air Temperature Sensors—Shielded air temperature sensors shall be used. Any sensor with an overall accuracy of 60.1°C is acceptable. The sensor shall have a time constant not exceeding 1 min. The sensor(s) is suspended with the measuring point exposed to air inside the chamber at a point just prior to the air passing over the hot plate.
Air Velocity Indicator—Any calibrated means of measuring air velocity with an accuracy of 60.1 m/s is acceptable (for example, anemometer). Air flow speed is measured 15 mm above the plate surface.
Temporal Variations—Temporal variations shall not exceed the following air temperature 60.1°C, relative humidity 64 %, and air velocity 610 % of the mean value for data averaged over 5 min.
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