Nuclear Surface Moisture and Density Gauge Calibration

A new ASTM International standard provides guidance for the calibration of nuclear density gauges, which are used to measure the density, moisture content and inner structure of material. D7759, Guide for Nuclear Surface Moisture and Density Gauge Calibration, was developed by Subcommittee D18.08 on Special and Construction Control Tests, part of ASTM International Committee D18 on Soil and Rock.

Gauge calibration is performed to formulate two different mathematical equations:

  • A density calibration equation, which relates the gauge density system response to the soil-equivalent density of the standard on which this response is elicited, and
  • A water content calibration, which relates the gauge water content system response to the water mass per unit volume value of the standard on which this response is elicited.

Gauge calibration is also performed to ensure that the gauge has an in-place water mass-per-unit volume gauge precision level and a density precision level that are consistent with typical gauge response.

The verification of gauges is necessary to indicate when the mathematical relationship between the in-place density reading and the water mass-per-unit volumes indicated by the gauge must be adjusted so that the gauge calibration meets the required level of measurement uncertainty.

According to James Pratt, senior nuclear project physicist, Troxler Electronic Laboratories, and a D18 member, D7759 will provide users and calibrators with better guidance in comparative evaluations between existing calibration and verification methods and any methods to be developed in the future. Primary users of D7759 will be laboratories that calibrate gauges, with other potential users being customers who use and evaluate calibration services.

Subcommittee D18.08 welcomes interested parties to join in its standards developing efforts. "We are always looking for participation and feedback from nuclear gauge users in our ongoing effort to improve the use and understanding of these devices," says Pratt.

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CONTACT Technical Information: James D. Pratt, Troxler Electronic Laboratories Inc. • Research Triangle Park, N.C. • Phone: 919-314-2707 | O ASTM Staff: Robert Morgan • Phone: 610-832-9732 | Upcoming Meeting: Jan. 27-31 • January Committee Week • Jacksonville, Fla.

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