New technology for grain moisture measurement

Bob Funk, Perten Instruments Inc., Springfield, IL, USA.

Fresh insights into the nature of the electrical properties of grain, an unprecedented data bank, and access to thousands of grain samples submitted for laboratory analysis each year to the US Federal Grain Inspection Service’s annual crop survey have yielded a new technology – the Unified Grain Moisture Algorithm (UGMA).

The UGMA was first presented to the grain trade by a United States Department of Agriculture (USDA) research team (led by David Funk) in 2001. This algorithm was far more than a suggestion for improving existing grain moisture meters – it was an extensively researched and exhaustively tested concept that would represent a major leap in attainable performance for rapid, objective measurement of grain moisture leading to three significant breakthroughs.

Year-to-year calibration stability

While it is well known that the dielectric properties of water are distinctive from those of the dry matter in grain, the measurement frequency for determining dielectric properties of grain are crucial. The UGMA research recommended a frequency of about 150 MHz for this determination, to minimize the surface conductivity effects that make lower frequency methods unstable. The result of this change is that year-to-year calibration stability is greatly enhanced, practically eliminating the need for annual calibration adjustments for new crops when varieties and conditions change.

Improved repeatability

The packing density of free-flowing grain is not consistent, which previously frustrated attempts to accurately measure moisture content in bulk. The UGMA introduces a new density correction technique that accurately adjusts for packing density over a wide range of conditions. This technique, along with the advantages of the higher frequency method, results in dramatically improved repeatability (precision) for most grain types.

Single calibration

A single calibration line accurately models the dielectric response of moisture in every grain type tested, with the application of simple linear adjustments. This unified calibration means that UGMA-based moisture meters are essentially one-calibration systems. The unifying parameters assigned to each grain type are easily derived with a relatively small number of reference points.

The UGMA was presented to industry as an opportunity for all stakeholders in the grain trade to benefit from breakthrough technology in a competitive environment. The first commercial grain moisture meter using the UGMA was introduced in 2006 (Perten Instruments model AM 5100), followed by Perten’s second-generation UGMA meter AM 5200 in 2011. The USDA is converting the US official grain grading system to UGMA as the official moisture method, beginning in the fall 2012.

At 150 MHz different grain types have very similar characteristics, although
there are some differences in dielectric constants.


After correcting for density most of the scatter disappears, and the different
grains fall into two groups.


When unifying parameters have been applied, all grains line up and there is
a perfect correlation between air oven moisture and moisture reported by
the AM 5200.