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United States Department of Agriculture

Agricultural Research Service

Research Project: Quality Based Inspection and Sorting of Specialty Crops Using Imaging and Physical Methods

Location: Healthy Processed Foods Research

Title: A Redesigned DFA Moisture Meter

Authors
item Haff, Ronald
item Young, Richard

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 1, 2012
Publication Date: April 11, 2012
Citation: Haff, R.P., Young, R. 2012. A Redesigned DFA Moisture Meter. Applied Engineering in Agriculture. 28(2):221-223.

Interpretive Summary: The DFA moisture meter has been internationally recognized as the standard for determining moisture content of dried fruit in general and is AOAC Official Method 972.2 for measuring moisture in prunes and raisins since 1972. The device has remained virtually unchanged since its inception. In recent times, obtaining appropriate parts for the device has become problematic, as maintaining the original Wheatstone bridge design requires a precision potentiometer with nearly identical non-linear characteristics to the original. The design of the moisture meter has now been updated to use modern electronic components to, among other things, mimic the original potentiometer so that calibration charts as well as AOAC certification remain valid. The redesigned meter was compared to the original in moisture readings of raisin, prunes and apricots. Scatter plot regression resulted in R2 of 0.9999 and slope of 0.9902, indicating high correlation and identity between the original and modified meters. Furthermore, the updated device consumes less power and does not require the reading of calibration tables or thermometers.

Technical Abstract: The DFA moisture meter has been internationally recognized as the standard for determining moisture content of dried fruit in general and is AOAC Official Method 972.2 for measuring moisture in prunes and raisins since 1972. The device has remained virtually unchanged since its inception, with its operation based on the Wheatstone bridge principal using a non-linear wire wound potentiometer to obtain a null reading when measuring the conductance of a sample across an electrode pair. In recent times, obtaining appropriate parts for the device has become problematic, as maintaining the original Wheatstone bridge design requires a precision potentiometer with nearly identical non-linear characteristics to the original. The design of the moisture meter has now been updated to use modern electronic components to, among other things, mimic the original potentiometer so that calibration charts as well as AOAC certification remain valid. The redesigned meter was compared to the original in moisture readings of raisin, prunes and apricots. Scatter plot regression resulted in R2 of 0.9999 and slope of 0.9902, indicating high correlation and identity between the original and modified meters. Furthermore, the updated device consumes less power and does not require the reading of calibration tables or thermometers.

Last Modified: 4/18/2014