Environmental testing —Part 3: Background information —Section 1: Cold and dry heat tests
1. Introduction
1.1 Reference ambient conditions
1.2 Devices without heat-dissipation
1.3 Devices with heat-dissipation
1.4 Ambient temperature
1.5 Surface temperatures
2. Reasons for the differing test procedures
2.1 Mechanisms of heat transfer
3. Test chambers
3.1 General
3.2 Methods of achieving the required conditions in the test chamber
4. Measurements
4.1 Temperature
4.2 Air velocity
4.3 Emissivity coefficient
Appendix A —Effects of size of chamber on surface temperature of a specimen when no forced air circulation is used
FIGURE 1 Heat dissipation per unit surface area of the test specimen at which the deviation between the surface temperature of the specimen in a very large chamber and in a smaller chamber reaches 5 deg C
Appendix B —Effect of airflow on chamber conditions and on surface temperatures of test-specimens
FIGURE 2 Experimental data on the effect of airflow on surface temperature of a wirewound resistor —Radial airflow
FIGURE 3 Experimental data on the effect of airflow on surface temperature of a wirewound resistor —Axial airflow
FIGURE 4 Temperature distribution on a cylinder with homogeneous heat-generation in airflow of velocities 0.5, 1 and 2 m·s
APPENDIX C —Effect of specimen emissivity coefficient on temperature rise
FIGURE 5 Comparison of the temperature rise as a function of heat-dissipation for thermal white and thermal black specimens subjected to an ambient temperature of 70 ℃ in a chamber with thermal black walls. (Exper-imental values.)
APPENDIX D —Effect of wire termination dimensions and material on surface temperature of a component
FIGURE 6
APPENDIX E —Heat transfer calculations and nomograms
FIGURE 7 Relationship between the surface temperature Ts of the specimen and the heat dissipated P per unit time
at the ambient temperature Ts
FIGURE 8 Nomogram for evaluation of surface temperatures of the specimen Ts at different ambient temperatures Ts.
Average specimen dimension α=0.2 m, emissivity coefficient of the specimen ε2 = 0.7
FIGURE 9 Nomogram for evaluation of surface temperatures of the specimen Ts at different ambient temperatures Ts.
Average specimen dimensions α = 0.05 m, emissivity coefficient of the specimen ε2 = 0.7
FIGURE 10 Relation between overtemperature and emissivity coefficient ε2 of the specimen
APPENDIX F —Thermal conductivities of common materials
APPENDIX C —Measurement of temperature
APPENDIX H —Measurement of air velocity
APPENDIX J —Measurement of emissivity coefficient
FIGURE 11 Wien's displacement law
FIGURE 12 Relation between and λ·T
APPENDIX K —General block diagram, cold and dry heat tests
FIGURE 13
BS EN 60068-3-1:1999 history
2011BS EN 60068-3-1:2011 Environmental testing. Supporting documentation and guidance. Cold and dry heat tests
1999BS EN 60068-3-1:1999 Environmental testing - Guidance - Cold and dry heat tests - Cold and dry heat tests