ASTM STANDARD

ASTM 5334 was updated in 2008 to reflect the current state of the art of thermal properties measurements. Its last serious revision (not minor update or reaffirmation) took place a few decades ago, so it was time for a major overhaul.

INFINITE LINE HEAT SOURCE
We got involved with standards change not because we thought the KD2 didn’t conform to ASTM D5334. The KD2 has always conformed to the spirit of the ASTM standard—the idea of using the infinite line heat source method to determine thermal properties from a heated needle.

EXTRA WORK AND DEGRADED DATA
But D5334 still caused problems for some of our customers. The KD2 uses complex numerical methods to get an accurate resistivity, and that didn’t use to conform to the letter of the standard. In order to conform completely, our customers had to extract raw data and draw a graph. It created a lot of extra work and degraded the quality of their data.

OBSOLESCENCE
ASTM D5334-05 was obviously obsolete. It had survived most of the computer age intact. It called for heating a thermal needle for 1000 seconds, plotting log time vs. temperature, picking two points that looked good, eyeballing a straight line, and then getting resistivity from the slope of that line.

PENCIL AND PAPER NOT GOOD ENOUGH
Specified needle sizes were too big to give accurate data unless they were calibrated, but the standard didn’t call for calibration. And I’d be pretty surprised to find any professional engineer trying to get accurate resistivities from a crude pencil and paper graph.

TIME FOR AN UPDATE
I discovered that updating standards is a chore—even when everyone involved thinks it’s past time for an update. But the resulting standard, ASTM D5334-08, conforms to best practices in thermal properties measurements. Even if you don’t use our instrument, you should spec and use the new standard. It’s a leap forward for thermal properties measurements.