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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Sue Hedrick
Date posted: Mon Mar 5 16:01:08 US/Eastern 2007
Subject: Resistor Calculation
Message:
With regard to resistor calculations, how can I determine theta EC. I had thought that it was calculated using (storage temp - max operating temp) / resistor power rating. This gives me huge numbers, greater than 600 deg C / W. What should I be doing?

Thanks, Sue


Reply:

Subject: Theta-EC
Reply Posted by: David Dylis (ddylis@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Mar 5 17:47:22 US/Eastern 2007
Message:
PRISM provides five different methods for determining the part temperature of resistors:

Ambient Temperature + Default Temperature Rise Ambient Temperature + Actual Temperature Rise Ambient Temperature + Thermal Resistance (Theta-EA) * P Case Temperature + Thermal Resistance (Theta-EC) * P Ambient Temperature + Delta-T * Stress The thermal resistance, theta-EA (element-to-ambient) and theta-EC (element-to-case) are are typically not calculated by a user. Information for these values would need to be obtained from the device manufacturer. When information is not available, it is recommended that one of the alternative methods be used to determine resistor part temperature.


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