Low-Cost Grain Bin Moisture Sensor Using Multiple Capacitive Elements

Date
2014-06
Authors
Knutson, Kevin Martin
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Faculty of Graduate Studies and Research, University of Regina
Abstract

The ability to know the condition of grain stored on the farm is very important. Grains grown in the prairie provinces of Canada are valuable commodities and the farm has become a primary storage location for more and more grain as farming operations have been getting larger and larger. With increased storage, the risk of spoilage is ever present. Both spoilage and the cost of drying grain reduce profit. These factors have created a need for better on farm management of stored grain, and therefore a need for a reasonable cost sensor to continuously monitor the moisture inside the bins. Historically, moderately expensive capacitance based instruments have been used to measure grain moisture samples to an accuracy of ±0.1% w.b. However, these moisture meters only work outside of the bin and therefore samples must be gathered every time a measurement is desired. Recently, some humidity and temperature based monitoring systems have been developed but they suffer from being plugged by dust. Timely information about the temperature and moisture content can prevent a disaster. To solve this problem an inexpensive capacitive sensor to measure grain moisture, temperature, and the level of grain stored inside a bin on the farm, was designed, constructed, and tested with a limited number of wheat samples in a six inch by five foot plastic pipe. Grain with different moisture levels from 9.7% wet basis (w.b) to 16% w.b. was used. The sensor accuracy was found to measure grain moisture content to ±0.5% w.b. for the majority of cases, and ±1.5% w.b. for all tested cases. A number of improvements to the current sensor are important. For one, the geometry should be improved by increasing the size of the anode and cathode plates. In addition, the electronics should be placed to limit parasitic and stray capacitances. Finally, only the high end frequency of 7 MHz was used in this implementation. Lower frequencies in the 500 kHz to 1 MHz range will likely improve the sensitivity and accuracy. These improvements could improve accuracy to ±0.2% w.b.

Description
A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Applied Science in Electronic Systems Engineering, University of Regina. xii, 77 p.
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