The Aquamatic 5200 is easy to use, but don't let its apparent simplicity deceive you. It is the most advanced grain moisture meter available, and utilizes advanced technology to provide rapid and accurate results.

How does a moisture meter work?

Just about all bench top moisture meters use what is often referred to as the capacitive method or RF dielectric method. With this method a radio signal at a specified frequency is sent through the sample. As water interacts with radio waves (that’s how your microwave oven works) it is possible to determine the moisture content by measuring how much the radio signal is changed by the sample.

The effect that the sample has on the radio signal is termed the dielectric constant, and it increases proportionally to the moisture content. There are a number of other factors that have an effect on the dielectric constant, perhaps most notably sample density and temperature. These two factors are measured and corrected for in advanced moisture meters.

150 MHz technology improves accuracy

Up until a few years ago moisture meters have used a radio signal with a frequency between 1-15 MHz. This is an area which is easy to work with as moisture has a strong signal there and electronic components have been available off the shelf for a long time. The problem is that there is a lot of noise, so the signal to noise ratio for moisture is poor, decreasing the accuracy of the moisture measurement and creating the need for frequent calibration updates, and
for specific calibrations for the different classes within a grain.

For example, older moisture meters often have to use several calibrations for wheat and barley, one per class. Another problem of older technology was the “rebound effect”, where the instrument would read too low when analyzing grain straight from the field. The reason was the lower radio frequencies would not penetrate the kernels, so the instrument would only see the surface moisture content.

In the USDA study quite some effort was spent on finding the optimal frequency. Measurements were done from 1 MHZ to over 200 MHz, and the results very clearly showed that the accuracy was much better at 150 MHz than the old 1-15 MHz range. At 150 MHz the noise is much lower and the signal is much more specific to moisture. The overall effect is that the shortcomings of the previous technologies are eliminated in a 150 MHz system. The sensitivity to kernel moisture distribution, grain variety, crop year and geographic location is much lower, and the performance will thus be significantly better.

UMA - one calibration for all products

Another important USDA development was the new UMA (Unified Moisture Algorithm) calibration technique. It further improves the accuracy and makes it possible to use one and the same calibration for all grains and oilseeds. There are three main components in the UMA – a new type of sample density correction, the use of a 4th order polynomial equation, and a new way to adjust for sample temperature effects.

A density correction is done in most advanced grain moisture meters. As written above, density has
an effect on the dielectric constant and in order to achieve good accuracy it is necessary to determine the density and adjust for it when calculating the moisture content. What is new in the UMA is the equation by which the density correction is calculated. The new density correction equation creates an almost perfect correlation between the dielectric constant of a sample and its moisture content. It is also an important factor behind the ability of the UMA to use one calibration for all grain types.

The 4th order polynomial equation, which is the actual calibration, is a more advanced mathematical technique than what is used in previous moisture meters. This is possible thanks to the higher processing power of the Aquamatic, which uses modern computing technology.

The effects of sample temperature has always been a difficulty for moisture meters, but with the introduction of UMA this is no longer a problem. The UMA uses a new algorithm for moisture correction which adapts the adjustment to the moisture content of the sample. The right adjustment for a cold wet sample is not the same as for a cold dry sample, and the UMA handles that with very good results.