1.1 This practice covers the design of a circular line-heat-source guarded hot plate for use in accordance with Test Method C177.

1.2 The guarded hot plate with circular line-heat sources is a design in which the meter and guard plates are circular plates having a relatively small number of heaters, each embedded along a circular path at a fixed radius. In operation, the heat from each line-heat source flows radially into the plate and is transmitted axially through the test specimens.

1.3 The meter and guard plates are fabricated from a continuous piece of thermally conductive material. The plates are made sufficiently thick that, for typical specimen thermal conductances, the radial and axial temperature variations in the guarded hot plate are quite small. By proper location of the line-heat source(s), the temperature at the edge of the meter plate is made equal to the mean temperature of the meter plate, thus facilitating temperature measurements and thermal guarding.

1.4 The line-heat-source guarded hot plate has been used successfully over a mean temperature range from − 10 to + 65°C, with circular metal plates and a single line-heat source in the meter plate. The chronological development of the design for circular line-heat-source guarded hot plates having a single line-heat source in the meter plate is given in Refs (1-9).2

1.5 For high-temperature applications, the line-heat-source guarded hot plate has been used successfully over a mean temperature from 7 to 160°C, with circular metal plates and multiple line-heat sources in the meter plate. The chronological development for circular line-heat-source guarded hot plates having multiple line-heat sources in the meter plate is given in Refs (10-14).

1.6 This practice does not preclude (1) lower or higher temperatures; (2) plate geometries other than circular; (3) line-heat-source geometries other than circular; or (4) the use of plates fabricated from ceramics, composites, or other materials.

1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.