Internal temperature measurements are made on both in-flight vehicles and on-ground test specimens; and, because of the importance of the temperature measurements to the design of various missile and spacecraft heat shields, it is essential that care be taken to minimize the sources of error in obtaining these measurements.

Over the past several years, the problems of using thermocouples to obtain accurate temperature measurements in low-conductivity specimens have been studied by various people to isolate the sources of error and to establish improved temperature measurement techniques. The major sources of error are listed in this document and recommended solutions to the problems are given.

1.1 This practice covers methods for instrumenting low-conductivity specimens for testing in an environment subject to rapid thermal changes such as produced by rocket motors, atmospheric re-entry, electric-arc plasma heaters, and so forth. Specifically, practices for bare-wire thermocouple instrumentation applicable to sheath-type thermocouples are discussed.

1.2 The values stated in inch-pound units are to be regarded as the standard. The metric equivalents of inch-pound units may be approximate.

1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.