- Establish the scientific and technical basis for Australian Standards on drying of Australian hardwoods, in particular AS/NZS 1080.1 (1996) and AS 2796 (1999);
- Establish accuracy limits for both resistance and capacitance moisture meters based on the procedure prescribed under AS/NZS 1080.1 (1996);
- Benchmark the accuracy limits against the Oven Dry method under AS/NZS 1080.1 (1996);
- Develop protocols to enable moisture meters to be calibrated to meet the requirements of the Australian Standards; and
- Develop appropriate correction factors for the main commercial hardwood species.
The major results of the study were:
The selection of species and sample material covered a wide range of basic densities ranging from a mean of 414 kgm-3 for plantation grown Shining Gum (Eucalyptus nitens) up to 865 kgm-3 for mature Lemon Scented Gum (Corymbia citriodora).
- The expected accuracy (95% confidence intervals for predicted OD MC%) for most of the species corrections on boards within the MC% range of between 7-22% were:
- mostly between ±1.5% MC and ±3% MC for resistance type meters. The species corrections for the low density species were generally more accurate than for the higher density species.
- Due to the characteristics of the meters, the expected accuracy locally around the critical 10-12% MC range could possibly be improved to around ±0.5-1.0% MC for most species.
- mostly between ±3% MC and ±6% for dielectric (capacitance) type meters. The accuracy limits depend on thickness as well for dielectric meters.
- The main reason that the accuracy of the resistance meters was about twice that for the dielectric meters was the effect of sample density on meter readings. For most meters and species, when boards were equilibrated under the same conditions, density explained as much or more of the variation in meter readings as oven dry MC% and thickness.
- When using moisture meters to assess drying quality, the approach taken in AS/NZS 4787 (2001) of defining allowable ranges for meter readings is much more practical and achievable than the absolute OD MC% limits set in AS 2796.
|